Geology and Mineral Resources of Paraguay A Reconnaissance

Geology and MineralResources of ParaguayA ReconnaissanceGEOLOGICAL SURVEY PROFESSIONAL PAPER 327Prepared in cooperation with the Departamentode Geologia, Ministerio de Obras Publicas yComunicacioneSj Republica del Paraguay,under the auspices of the Institute ofInter-American Affairs

Geology and MineralResources of ParaguayA ReconnaissanceBy EDWIN B. ECKELWith sections onIGNEOUS AND METAMORPHIC ROCKSBy CHARLES MILTON and EDWIN B. ECKELSOILSBy PEDRO TIRADO SULSONAGEOLOGICAL SURVEY PROFESSIONAL PAPER 327Prepared in cooperation with the Departamentode Geologia^ Ministerio de Obras Publicas yComunicaciones, Republica del Paraguay,under the auspices of the Institute ofIn ter- Am er ica n Affa irsUNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1959

UNITED STATES DEPARTMENT OF THE INTERIORFRED A. S EATON, SecretaryGEOLOGICAL SURVEYThomas B. Nolan, DirectorThe U. S. Geological Survey Library has cataloged this publication as follows:Eckel, Edwin Butt, 1906-Geology and mineral resources of Paraguay, a reconnaissance.With a section on igneous and metamorphic rocksby Charles Milton and Edwin B. Eckel and a section on soilsby Pedro Tirado Sulsona. Prepared in cooperation with theDepartamento de Geologia, Ministerio de Obras Publicas yComunicaciones Republica del Paraguay, under the auspicesof the Institute of Inter-American Affairs. Washington,U. S. Govt. Print. Off., 1958.v, 110 p. illus., maps (part fold, col.) diagrs., tables. 29 cm.(cU. S.] Geological Survey. Professional paper 327)Bibliography: p. 101-105.(Continued on next card)G S 59-154tEckel, Edwin Butt, 1906-Geology and mineral resourcesof Paraguay . . . 1958. (Card 2)1. Geology Paraguay. 2. Mines and mineral resources Paraguay.3. Petrology Paraguay. 4. Soils Paraguay. (Series)QEY5.P9 no. 327 558.92 G S 59-154Copy 2.QE245.E3tFor sale by the Superintendent of Documents, U. S. Government Printing OfficeWashington 25, D. C.

CONTENTSPageAbstract-__________________________________________ 1Introduction _______________________________________ 1Present investigation.___________________________ 1Previous geologic investigations_________________ 2Maps of Paraguay______________________________ 3Acknowledgments. ______________________________ 4Geography-________________________________________ 4Location and area_______________________________ 4Topography and drainage______________________- 6Climate. _______________________________________ 7Vegetation,____________________________________ 8Transportation __--__-----______________________ 9Population._ ___________________________________ 10Industries. _____________________________________ 10Fuel and power_________________________________ 11Geology-__________________________________________ 11General features________________________________ 11Igneous and metamorphic rocks, by Charles Miltonand Edwin B. Eckel_________________________ 12Precambrian metamorphic and granitic rocks. _ 12Southern area __________________________ 13Older metamorphic rocks____________ 13Younger igneous rocks____________ 15Central area____________________________ 19Northern area._________________________ 19Rio Apa region_____________________ 19Amambay region.__________________ 21Tres Hermanos hills near PuertoGuarani-________________________ 21Fuerte Olimpo__________________ 22Analyses of Precambrian igneous rocks___ 22Upper Triassic or Jurassic lavas and relatedrocks_ ___________________________________ 26Serra Geral basaltic lavas-_______________ 26General features.___________________ 26Petrography of the basalt at Foz deIguagu, Brazil.__________________ 29Carmen del Parana-_____--_--______ 30Diabase _______________________________ 31Cordillera de los Altos_______________ 31Other occurrences of diabase _________ 32Olivine basalt near Asunci6n_____________ 33"Pseudotrachyte" near Aregua and Luque_ 34Analyses of Serra Geral lava and relatedrocks_ _ ______________________________ 34Alkalic rocks of unknown age_______________ 36Northern area__________________________ 36Phonolite at Centurion ______________ 36Syenitic rock of Paode Agucar, Brazil- 36Central area____________________________ 37Nepheline basalt at Ybytymi_________ 37Phonolite from SapucaL_____________ 37Geology ContinuedIgneous and metamorphic rocks, by Charles Miltonand Edwin B. Eckel ContinuedAlkalic rocks of unknown age ContinuedCentral area ContinuedMica porphyry from east of Villarrica-Basalt, rhyolite, and scoria of Acahaycaldera __________________________Porphyry and agglomerate from Ypacaraihighway quarry._____________Basalt flow between Paraguari and Carapegua._________________________Nepheline syenite and shonkinite atMbocayaty__ ____________________Analyses of alkalic rocks.________________Sedimentary rocks.________--_-_____-------__-_-Eastern Paraguay_________________________Cambrian and Ordovician systems(?)_____-Itapucumi series-___________________Silurian system ____________-________-__Caacupe series._________--_---___--_Paraguari conglomerate-_. ______Arkosic sandstone.____________White saccharoidal sandstone.____Upper shale and sandstone unit__Paleontology ___________________Devonian system_______________________Itacurubi series.____________________Gondwana (Santa Catarina) beds---_--_---Pennsylvanian or Permian systems.Tubarao series-_____---_-__-----Permian system_________-__-____---Independencia series-___________Triassic system.____________________Misiones sandstone____________Tertiary and Quaternary systems. _ _ _ _Gran Chaco.__________________---___---_--_General features.____________--__-___--_Outcrops of consolidated rocks___________Subsurface rocks___--_____-___-____--_Well records______________________Fossils. ____-_-____-_-_--------_----Interpretation of well records___-----_Chaco sediments-_______-______-----__--Structural geology_____________-_-_______-___---General relations__________-__________-_-_-_-Anticline between Rio Apa and San JuanBautista_ _ _______________________________Gran Chaco basin_________________________Geologic history________________________________Generalized account-________________________Gran Chaco plains-_________________________mPage3738404344475050505052525353555658595961626263636565666767676969737474757576767677

IVCONTENTSMineral resources.__________________________________Summary. _____________________________________Barite_ ____-_____--_---__-___-_________________Bauxite_ _______________________________________Beryl________________________________________Cement._____________________________________Clay__________________________________________Refractory clay___________________________Alluvial clay_______________________________Weathered shale____________________________Copper-__________-----__---___________________Fuel resources,_________________________________Solid fuels_________________________________Petroleum and natural gas___________________Gem stones-___________________________________Glass sand_____________________________________Gold and silver.________________________________Gypsum _______________________________________Iron _ _________________________________________Early iron industry_________________________Apichapa mine _____________________________Del Puerto deposit__________________________Deposit south of Caapucu-__________________Deposit near Paso Pind6____ _________________Yta-cue mine_______-_----____-___________Aguirr6-cue mine.__________________________Deposit near Roque Gonzalez de Santa Cruz___Deposit in Amambay region__________________Yuty deposit-______________________________Lead_ _________________________________________Lime and limestone _____________________________Manganese. ____________________________________Emboscada deposit-. _______________________787879797979808081818282828283838484848485858686868686868687878787Mineral resources ContinuedManganese ContinuedYaguaron deposit.._________________Mercury_______________________---_---Mica_ _______________________---------Pigments ______________-_-_---__--__--Pyrophyliite ____________--___- ----Quartz crystals._______________________SaltSand and gravel - - ---_-- ------_Stone- __________________-___- _ -Sulfur______________________ ___Talc-TinTungsten ____ _Miscellaneous minerals, locality unknown-Future of the mineral industry ______________General statement.____________-_---__-Suggestions for prospecting _____________Development of local industries________Iron _____________-------------__--Building and ornamental stones_____Glassware_ _ ________-__-_-_----____Mineral paints. ___________________Portland cement _ ____ - _Pottery an d clay products __________Talc and pyrophyllite_______---____Water resources____________-_-____--_--__-Eastern Paraguay____________________Gran Chaco___________________________Page_____ 89_____ 89_____ 90_____ 91_____ 91_____ 92_____ 92_____ 93_____ 93_____ 94___ 94_____ 94_____ 95_____ 95. 95--___ 96_____ 96_____ 96_____ 97_____ 97_____ 98_____ 98_____ 98______ 98______ 99______ 99Soils of Paraguay, by Pedro Tirado Sulsona____________ 101References and annotated bibliography._______________ 101Index_ 107ILLUSTRATIONS[Plates 1 and 3 in pocket]PagePLATE 1. Geologic map of Paraguay.2. Sketch of an extinct volcano________________________________________--__-__---_---_-------------facing 343. Soil map of Paraguay.FIGURE 1. Index map of South America____-_-_________________-_____-_--__-_- -__-_--_-----_ _------_ 52. Typical terrain and vegetation in the Gran Chaco__________________-___-_-____ -- -_--_--------- -- 63. Average annual rainfall and temperatures, 1940-50____--_-_--_-_---__--_----_--_-----_-------_------- - 84. Map showing density of population, 1950_________-----_--_------_--__--------------- ---------------- 105. View of Precambrian rocks north of San MigueL_ ___-_____________-_---___----__--_------_-- _.---- 136. Sheared Precambrian granite near Villa Florida.-______________-___-_----.-___--_--------_---_----------- 147. Arkosic sandstone in Precambrian rocks near Villa Florida, ______________________ _ ______________________ 158. Coarse Precambrian granite near Barrerito__--_-__--------__-----_--__---_-__-------------------------- 179. Coarse porphyritic aplite near Barrerito_ ____-_________-_______-______-_-_____---_-_-----_------------- 1810. Aplite, road between Villa Florida and Caapucu- _____--_______--__-_--_--_-_---_--_-_---_------------_- 1911. Typical weathering profile on Precambrian quartz porphyry__-_--___-_____-_______________-___----_-__--- 2012. Partly weathered Precambrian quartz porphyry- ___________________________-__----__-_---_--____--_---- 2013. Hand specimen of Precambrian quartz porphyry, brown phase, north of CaapucvL__________________________ 2014. Precambrian quartz porphyry, red-brown phase, north of CaapucvL__________________-______--___-_-_--__- 2115. Precambrian porphyry, gray phase_________________-__________-____-_-_-_____--_--_------_---.--_--_-_- 2216. Pyritic porphyry, Del Puerto deposit__________-_____-_________-________-_-____----_-_-----_--_--_-___- 2317. Black porphyry dike near Del Puerto vein_ _ __________________________-_______---___----__- -_ _- 2418. Precambrian rhyolite, south of CaapucvL _____________-______----_-_-------_---_---_--------------- 2519. Typical terrain on Serra Geral lavas___________________________-_____---___-----_----_-_-----------_-__ 2720. Exposures of Serra Geral basalt along Rio Alto Parana--____-__-_______-_-_____----------------_---- 27

CONTENTSVPageFIGURE 21. Vuggy basalt of Serra Geral lavas, Foz de IguaciL_____________________________________----______------- 2922. Basalt, Foz de Iguacu-________________^_____________________________________________________________ 3023. Basalt from Foz de Iguacu__ _________________________________________________________________________ 3124. Basalt from Foz de Iguacu-_______________________________________________________----_---__--------- 3225. Basalt from Foz de Iguacu, with vein materials___--__------_______-___--_------_--------------_----_--- 3326. Serra Geral basalt from Carmen del Parana.___________^-^__________________^______------_----_-----~--- 3427. Diabase near Piribebuy______________________________________________________________________________ 3528. Mica porphyry east of Villarrica______________________________________________________________________ 3829. Basalt from flow east of the Acahay caldera_____________________________________________________________ 3930. Rhyolite agglomerate from the Acahay caldera_ ________-__________________________--_------.---_-------- 4031. Highway quarry in rhyolite agglomerate at YpacaraL___________________________-____-------___--------- 4132. Rhyolitic-breccia tuff from the highway quarry at YpacaraL________________________-_-----_-___--_------ 4233. Porphyry from the highway quarry at YpacaraL _________________________^_____^___--_--_______________ 4334. Porphyry, dark phase, from the highway quarry at YpacaraL_______________________-_____---_____-_-_--- 4435. Quarry in alkaline rocks on the outskirts of Mbocayaty_____________________-_____--_-----__--__--------- 4536. Shonkinite from Mbocayaty___________________________^-_____________-_________-----__---------_----- 4637. Nepheline syenite from Mbocayaty_________________________________-_______________-_--_--_-----_-_--- 4738. Shonkinite from Mbocayaty____________________________________________________^_---_----_-__--_----- 4839. Shonkinite from Mbocayaty______________________________________________________--_--_-.-___--------- 4840. Analcite-shonkinite from Mbocayaty__________________________________________________________________ 4941. Shonkinite from Mbocayaty_____^_____________________________________^_-_____-_--^-_^-----__--_--_-- 4942. Shonkinite from Mbocayaty___________-_______________________-___-_____-_____-----------__-_-----_-- 5043. Outcrops of limestone of Itapucumi series along Rio Paraguay,___________________.,____-_-----___-_-.----_- 5244. Sandstone hills of Caacupe series near ParaguarL__________________________-_________-_-----____-_--_-__ 5445. Typical weathering pattern on case-hardened sandstone of Caacupe series__________________________________ 5546. Joint pattern and pitted surfaces of white sandstone of Caacupe series_____________________________________ 5647. Ocher quarry in white sandstone of the Caacupe series, at TobatL_____________________-_--_--_____-_----- 5748. Minor thrust fault in shale of Itacurubi series-____________________________-_________-_--__-_____------- 6049. Arkosic sandstone of Independencia series_____________________________________-_-_-------___----_-___ 6350. Unusually good outcrop of sandstone of Independencia series showing typical vegetation___-___-________-_-__ 6451. Typical flagstone quarry in Misiones series______________________________-_-_____-_-_---________________ 6652. White pottery clay, with red beds of the Misiones sandstone, near Yhu____________________________________ 6753. Major rock units in exploratory wells drilled in the Gran Chaco_ ____________-_________---_----______-_-_- 6854. Manganiferous arkose, probably Misiones, near Yaguaron_____________________-__-----__--_-.-_-__-----_-- 8855. Quarry and paint factory near TobatL ___________________________________-_________--__---_--__-----_- 8956. Test pit in deposit of pyrophyllite_____________________________________________________________________ 9057. Pyrophyllite with diaspore, northwest of Caapucu________________________-__________---_-----__---_-_--- 9158. Test pit on outcrop of talc deposit. ___________________________________________________________________ 94TABLESTABLE 1. Chemical analyses of Precambrian rocks___________________-______________-_-_____-^-_------.__--_--_-_--_ 232. Spectrographic analyses of Precambrian rocks_________-_-_---_____-_---_-_---_--------_-__--_-_---------- 243. Chemical analyses of Serra Geral lava and related rocks of Paraguay.______________________________________ 354. Spectrographic analyses of Serra Geral lava and related rocks__________-______-____________---------__---- 355. Chemical analyses of alkaline rocks_-___--__________^___________________----____--_------_-_-----__---_- 476. Spectrographic analyses of alkalic rocks_________________________________________________________________ 50

GEOLOGY AND MINERAL RESOURCES OF PARAGUAY A RECONNAISSANCEBy EDWIN B. ECKELABSTRACTAlthough this report includes the results of a 6-month reconnaissanceinvestigation of the geology and mineral resources ofParaguay, it is essentially a compilation and interpretation ofexisting published and unpublished information on the subject.The rocks can be divided into five major classes, depending onage and mode of origin. The oldest are of Precambrian age,here subdivided into an older group of metamorphic rocks anda younger group of granitic rocks. They are a part of the Brazilianshield and underlie the entire country but are exposed atthe surface in only a few places. The second group consists ofmarine sedimentary rocks and ranges in age from Cambrian orOrdovician through Early Devonian. It comprises three mappableunits, here called the Itapucumi series, the Caacup6 seriesand the Itacurubi series. The third group, which ranges fromPennsylvanian through Triassic in age, constitutes the Gondwanaor Santa Catarina continental clastic sedimentary rocksknown in a large part of South America. This group is divisibleinto three map units the Tubarao series of glacial deposits, theIndependencia series, and the Misiones sandstone, and, like themarine beds of Paleozoic age, is much thinner in eastern Paraguaythan it is in parts of the Gran Chaco in the western half of thecountry. The fourth group is Tertiary to Recent in age andconsists in large part of un consolidated clay and sand of conti­nental origin. These materials are very thin in most of easternParaguay, but they cover nearly all of the Gran Chaco to depthsas great as 2,000 feet.The fifth large group of rocks consists of igneous extrusive andintrusive rocks, mostly of basic composition. The most importantsingle member is the Serra Geral basaltic lava, of LateTriassic or Jurassic age, which covers the eastern edge of thecountry and extends far into Brazil. Associated with the SerraGeral lavas are many smaller bodies of intrusive diabase, extrusivebasalt, and possibly other rocks. There are also manyintrusive and extrusive igneous rocks whose age is unknown.Some are strongly alkalic and of considerable interest petrographically;some may be related in age and origin to the SerraGeral lavas, but for others there is strong evidence that they areno older than late Tertiary. Chemical and spectrographicanalyses of a number of samples of the igneous rocks are includedin the report.The geologic structure of Paraguay appears to be relativelysimple in its grosser aspects, but little is known of even the largerfeatures. In the eastern half of the country the beds dip gentlyeastward toward the great Parana1 basin of southeastern Brazil.This easterly dip appears to reverse along the axis of a low anticlinethat trends north-south only a few kilometers east of theRio Paraguay and exposes the older sediments and the Precambrianbasement rocks at the surface in many places. West ofthis axis the beds either dip steeply westward, or are downfaultedto the west, into the depths of the Gran Chaco basin. The rocksin this basin are, in places, at least 10,000 feet deeper than theyare in eastern Paraguay; west of the basin, in eastern Bolivia,they rise to the surface in a series of anticlines and synclines thatform the foothills of the Andes.Paraguay possesses large quantities of certain nonmetallicmineral resources, notably clays for brick, tile, and pottery,limestone and other raw materials for portland cement and forlime; common and ornamental building stones; glass sand; talc;and mineral pigments. Except for iron ore, of which there aremany small but rich deposits, Paraguay appears to be poorlyendowed in most other mineral resources. It has a little manganese,copper, mica, and beryl and there are good geologicreasons for hoping that worthwhile deposits of salt, gypsum, andbauxite may yet be discovered.Aside from wood, and water power that is both remote andundeveloped, the only known source of fuel or energy lies insome little-known peat deposits near Pilar. Petroleum mayexist in the Gran Chaco basin, but proof of its presence mustawait a willingness on the part of Paraguayan or other investorsto risk much more money than has already been spent in oneexploratory campaign.Besides the available facts on all of the country's known andreported mineral resources, a number of suggestions are givenfor establishing local industries that could provide mineralproducts for local use and conserve some of Paraguay's foreignexchange. By all odds the most valuable and promising ofParaguay's mineral resources are the water resources, bothsurface and underground, and the soils.INTRODUCTIONPRESENT INVESTIGATIONThe investigation recorded here was a part of theUnited States' Point Four program of giving technicalaid to underdeveloped countries. The author wasassigned by the U. S. Geological Survey to act asgeologic technical advisor to the Government of Paraguayunder the auspices of the Institute of Inter-American Affairs. He was in Paraguay from February25 through August 6, 1952. In addition to the workwhose results are recorded here, his duties includedadvice on the establishment and maintenance of aDepartment of Geology arid Mines, as well as therelated problems of staffing and training geologists andengineers for such a Department. These latter dutieswere discharged by means of official written and oralcommunications to the Government of Paraguay.This report contains a base map and a geologic mapthat are as complete as can be expected from the factsnow available. The chief contributions of this report

GEOLOGY AND MINERAL RESOURCES OF PARAGUAYare that it assembles in one place most of the hithertowidely scattered published information on the geologyof Paraguay; it contains a considerable amount ofhitherto unpublished information collected from varioussources; it presents new facts, based on modernpetrographic and chemical methods, on a few of theigneous rocks; and it contains an objective summaryof the country's mineral resources and its potentialitiesas a mineral producer. This summary is not as optimisticas many would hope, but it does point out afew real possibilities and narrows the areas that mostdeserve further study.The report is, then, a compilation and interpretationof existing information on the geology and mineralresources of Paraguay based on a 6-month reconnaissancestudy, but if it were confined to recording personalobservations during that period it would be a"thin" report indeed. Travel conditions in Paraguayare difficult at best, and were made somewhat more soby greater than average rainfall during the winter of1952. These and other tangible and intangible factorspermitted field work for considerably less than halfthe total time available for the project. The author'spersonal observations were limited to a comparativelysmall part of central Paraguay, plus spot studies atthe termini of a few airplane trips; these flights permittedexcellent aerial views of representative crosssections of the country. These personal observationswere greatly supplemented by the use of aerial photographs,by the study of specimens in various museumsand private collections, and by data supplied by severalgeologists and others who had observed and recordedthe geology at particular spots.The facts gathered would, by themselves, have beenbeen utterly insufficient as a basis for a report of thescope attempted here. Personal observations, supportedby studies of the small collections of rocks andfossils have, however, given a clearer understandingof the existing literature en the subject. They havealso given a modicum of confidence in this attempt togather published information on the geology of Paraguayand to integrate it with facts observed by workersin neighboring countries, where geologic knowledge ismore advanced than in Paraguay.Throughout this report an effort has been made todistinguish between fact and fancy as well as betweenthe author's own contributions and those of others.Since facts that are absorbed by the mind, regardlessof their source, have a tendency to emerge as newdiscoveries, these efforts have doubtless been onlypartially successful. The reader would, therefore, dowell to remember that the present author is a compilerof scattered information, rather than a recorder ofhis own observations. Naturally, he must bear responsibilityfor all the interpretations, good or bad, thathave been drawn from the basic data.PREVIOUS GEOLOGIC INVESTIGATIONSA considerable body of knowledge on the geology andmineral resources of Paraguay has been accumulatedthrough the years. Most of this information, however,is widely scattered through the world literature ofgeology, where it appears in several languages, orexists only in unpublished files or in the memories ofindividuals who have made observations of particularspots or restricted areas. It should be remembered,too, that until 1938 more than half of the Gran Chacobelonged to Bolivia, hence descriptions of this areain the older literature are referenced under the nameof that country. The pertinent literature that hasbeen found is listed in the annotated bibliography,which contains a number of items that are not referredto specifically in the text. Such items haveserved a purpose by providing needed background forother facts and all will be of interest to future seriousstudents of the subject.The most complete descriptions of the geology ofParaguay that have appeared in print are the recentpapers by Harrington (1950, 1956). Unfortunately,his work is limited to the eastern part of the countryand is based on only a few weeks fieldwork. Even withthese limitations, he was able to present a clear andaccurate picture of the stratigraphy and geologic history,one on which the present author has leaned veryheavily in preparing this compilation. The only othercomprehensive study of the geology known to theauthor is that made by the Union Oil Company duringits exploration for petroleum in 1944-49. In additionto the drilling of five deep wells, this company is understoodto have done reconnaissance geologic mapping ofthe entire country, plus a very large amount of geophysicalexplorations in the Gran Chaco. Of theinformation accumulated, only the records of the deepwells and fossil identifications made by Dr. Horacio J.Harrington are available for publication.Among the older descriptions of the geology of easternParaguay, those of Carnier (1911, 1913), supplementedby Goldschlag's (1913) chemical and petrographicdescriptions of Carnier's rocks, are by far the mostuseful; much dependence has been placed on themhere and in the compilation of plate 1. Kanter (1936)gives the most complete description extant of the geologyof the Gran Chaco region. DeMersay (1860) andDuGraty (1865) give far more complete accounts ofthe country's mineral resources than any more modernworkers and both give, in addition, many notes on thegeology. M. S. Bertoni (1921), A. deW. Bertoni (1939),G. T. Bertoni (1940), Conradi (1935), and Boettne

INTRODUCTION(1947, 1952) are the only Paraguayan writers who havecontributed materially to the literature; each of theirpapers supplies data on areas or on phases of the geologythat are not to be found elsewhere.Information gleaned from the literature on Paraguayhas been supplemented in part by unpublished factsgenerously furnished by various individuals who havevisited parts of Paraguay. Another valuable source ofinformation is, of course, the literature on the geologyof the neighboring countries. The summary works ofAhlfeld (1946) on Bolivia, of Oliveira and Leonardos(1943) on Brazil, and of Stappeiibeck (1926) on Argentinaare particularly helpful in understanding andcollating the relatively few scattered bits of knowledgeon Paraguay itself.MAPS OF PARAGUAYBase maps on a scale sufficiently large to use fordetailed geologic mapping are not available for any partof Paraguay. There are, however, several sets of mapsthat are adequate for reconnaissance investigations.The Mapa Provisional de la Republica del Paraguay,published in 1945 by the Institute Geogrdfico Militar,is the best base map produced in Paraguay. Publishedon a scale of 1:1,000,000 (1 cm=10 km) as well as onseveral smaller scales, it can be purchased from theInstitute and from several book stores in Asunci6n.Though very generalized in many places, it is particularlyuseful for its delineation of all roads and trails inthe country and for location of towns and settlementsand official spelling of their names. It contains noinformation as to altitudes, but the main topographicfeatures are shown by shading.Various sheets of the Carta Aeronautica de la RepriblicaArgentina, published by the Institute GeograficoMilitar of Argentina in 1945 and succeedingyears, cover the entire Republic of Paraguay. Onscales of both 1:500,000 and 1:1,000,000, they are noteasily available in Paraguay but can be purchased"over the counter" from the Institute GeograficoMilitar offices in Buenos Aires. Like the Paraguayanmap described above, their portrayal of many naturaland cultural features is much generalized, but theyhave great usefulness because of then* detailed data onaerial navigation. Perhaps even more important to thegeologist, they show the elevations of many points andportray the shape of the land by means of reasonablyaccurate contours at intervals of 100, 200, 500, and 1,000meters.The Asimcidn, Corumba, Rio Apa, Rio Pilcomayo,Sucre, and Tucuman sheets of the World Map, of theAmerican Geographical Society published in 1940 andsucceeding years on a scale of 1:1,000,000, with topog-465871 59 2raphy shown in colors by 100-meter intervals, wereused extensively for checking place names and topographicrelationships.A set of preliminary base maps published in 1949and succeeding years by the U. S. Aeronautical ChartService cover all of Paraguay except two small areasone along the Cordillera de Amambay in the northeasterncorner, and the other along the upper reachesof the Rio Paraguay, near the common junction ofParaguay with Bolivia and Brazil. These maps, ona scale of 1:500,000 (1 cm=5 km), are not readilyavailable to the public, but can be obtained for officialuse from the Headquarters, Aeronautical Chart Service,Washington 25, D. C. Prepared from trimetrogonaerial photographs with little or no ground control orfield checking, they are inadequate as to identificationof towns and other human features. Their portrayalof roads is even more inaccurate, particularly as totheir classification and usability. On the other hand,the natural features such as streams and swamps areshown far more accurately than they are on anyother maps known to the author. Land elevationsare shown by 1,000-foot (300 meters) contours andby many point elevations. The detailed portrayal onmost of the sheets of forested and cultivated lands aswell as of swamps and other features is of incalculablevalue to the reconnaissance geologist, not only becausethey help to solve problems of location but becauseall these features have geologic meaning when properlyinterpreted.In addition to the base maps mentioned ajaove, thereare aerial photographs for most of the country. Thoseknown to the author are the trimetrogon photographs,taken by the U. S. Air Force in 1943 through 1945,which were used in compilation of the preliminarybase maps described above. The pictures were takenat altitudes of 20,000 feet, and cover virtually all thecountry except the northeastern corner. The stripsof vertical pictures were extremely useful in both fieldand office for studying and mapping geology. Theoblique pictures were also useful in studying generalrelations, but they are not easily adapted to fieldmapping without special trimetrogon stereoscopicequipment that was not available in Paraguay at thetime of this investigation. Complete sets of printsof the trimetrogon pictures are available for officialuse in Washington, D. C., in the offices of the AeronauticalChart Service and in Asuncion in the InstituteGeografico Militar. In 1952, an exasperatingly incompleteset of prints was also available in the Asuncionoffice of the Institute of Inter-American Affairs.All the maps and pictures described above and muchmaterial from other sources were used in compiling the

GEOLOGY AND MINERAL RESOURCES OF PARAGUAYbase for plate 1. The compilation was done under theauthor's direction by Mrs. Gladys Benedict of theGeological Survey. This base, originally compiledon a scale of 1:1,000,000 for reduction to the presentscale of 1:1,500,000, is as accurate as the source datawould permit and is far more accurate in most placesthan the geologic map for which it was primarilyprepared. It admittedly lacks completeness in atleast two important respects its portrayal of townsand roads. To have shown all of the towns, forts(fortin), ports (puerto), and ranches (estancia) that areshown on other base maps of the country would havecluttered this map unnecessarily; instead it was decidedto show only the more important places, plus smallerones whose names or locations were needed in describingthe geology. Similar decisions were made with regardto roads. A great majority of the innumerable roadsshown on other base maps are only cart tracks; manyof them are difficult to find on the ground, and evenmore difficult to travel during large parts of everyyear. Only the more important roads ones that arebelieved to be usually the best means of access to thetowns shown on the map are shown on plate 1. Themap user who is interested in other places will findtheir approximate locations, and possible routes oftravel thereto, on some of the other base maps describedabove. The traveler will also do well to make inquiryof local inhabitants.Most of the names of places or of natural features aretaken from the Guarani language or from a mixture ofGuarani and Spanish. Because many of these namesare descriptive of the local scene, some knowledge oftheir meaning is helpful to any reconnaissance naturalscientist. The dictionaries of Bottignoli (1926) andRuiz de Montoya (1876) are helpful, as is a brief glossarygiven by DuGraty (1865).ACKNOWLEDGMENTSThe author is indebted to many officials of the Ministeriode Obras Piiblicas y Communicaciones, Republicof Paraguay, of the Institute of Inter-American Affairs,in both Asuncion and Washington, and of the U. S.Geological Survey for the many facilities and the constantadvice and encouragement that made his workpossible. In particular, the help of Ing. Ricardo Maz6Ugarriza, Jefe, Departamento de Geologia, Ministe'riode Obras Piiblicas y Communicaciones warrants specialacknowledgment for his direct and indirect contributionsto the work. Except for that part of his time that hadto be devoted to administrative and related duties ofhis own Department, he worked with the author for theentire period of the latter's visit, acting as co-observer,interpreter, and friend. In addition, he contributed themany data on the subject that had been accumulatedin the past by his Department.Messrs. Charles Milton of the Geological Survey andPedro Tirado Sulsona of the Institute of Inter-AmericanAffairs deserve special thanks for contributing the chapterson igneous rocks, and on soils, respectively, as doesMrs. Gladys Benedict who compiled the base map usedfor plate 1. Messrs. A. J. Boucot, A. R. Palmer, andR. J. Ross, all of the Geological Survey, studied thepaleontologic evidence that is available for the Paleozoicrocks.Dr. Horacio J. Harrington, then of the Universidadde Buenos Aires but later a visiting lecturer on geologyat the University of Kansas, was kind enough to advisethe author of many of his unpublished geologic observationsand also helped immeasurably by reviewing thisreport in manuscript form. His critical but friendlyeye, backed by vast knowledge of South American geology,caught many errors that would otherwise havefound their way into print here.Mr. Robert Miller of Asunci6n gave largely and generouslyof his time and special knowledge of many ofthe mineral deposits as did Mr. Albert Morris with regardto his records of water wells and his geologic ob­servations in many parts of the country. Unpublishedreports for the Institute of Inter-American Affairs byElvin A. Duerst and Bertram H. Lindman on economicresources and on the transportation problem were ofmuch help, as were the many additional facts suppliedinformally by Mr. Duerst.Finally, a great many other people, both public officialsand private citizens, gave freely of their time,knowledge, and hospitality; sincere thanks are herebyextended to all of them.GEOGRAPHYMuch of the material in this section is derived fromthe report by Duerst (1952) and from other unpublishedreports on file in the Asuncion and Washington officesof the Institute of Inter-American Affairs.LOCATION AND AREAParaguay, one of the two land-locked countries in theAmericas, lies south of the center of South America,between latitudes 19° and 28° S. and longitudes 54°and 63° W. (fig. 1). The Tropic of Capricorn passesthrough its center at the latitude of Conception. Thetotal area of the country is about 407,000 square kilometers,or 40.7 million hectares (157,000 square miles),almost exactly that of California. Its extreme dimensions,both from north to south and east to west, areapproximately 900 kilometers (570 miles). It isbounded by Bolivia, Brazil, and Argentina. Approxi-

GEOGRAPHYFIGURE 1. Index map showing the location of Paraguay.

6 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYmate airline distances from Asuncion, the capital city,to capitals of neighboring countries are as follows:Miles KilometersBuenos Aires, Argentina ___________________ 650 L, 050La Paz, Bolivia___________________________ 610 980Lima, Peru_ _______________________________ 1,000 1, 610Montevideo, Uruguay_______ ________________ 650 1, 050Rio de Janeiro, Brazil-______________________ 920 1,480Santiago, Chile_____________________________ 1, 100 1,770TOPOGRAPHY AND DRAINAGEThe entire country is one of low relief (pi. 1), withaltitudes ranging from 55 meters above sea level at thejunction of the Rio Paraguay and Rio Alto Parana toan extreme of 700 meters on one peak just east ofVillarrica.There is, however, a marked difference in the topographyon the two sides of the Rio Paraguay, whichbisects the country along a north-south line. Thatportion east of the river, called Paraguay Oriental, isgently rolling to hilly, with nearly level valleys. Someof the relatively low hills and mountains occur in ratherdistinct chains. Made up in large part of soft sedimentaryrocks or of deeply weathered basalt, the hillsare being degraded by erosion processes and presentlow rounded outline in most places. Here and there,however, where there are outcrops of harder sedimentaryor igneous rocks, they have more rugged shapesand present bits of spectacular scenery, albeit on arather small scale.The Chaco Boreal on the western side of the RioParaguay, the Paraguayan part of the Gran Chaco, isa vast aggrading alluvial plain that rises almost imperceptiblywestward from the river toward the foothillsof the Andes not far within the Bolivian border. Themonotony of this nearly level, poorly drained plain(see fig. 2) is broken only in its most northern part,where there are a few good-sized hills, both in Paraguayand in Bolivia, that mark places where islands of bedrockprotrude above the thick alluvium.Virtually all of Paraguay lies within the great drainagebasin of the Rio Parana, which also drains appreciableparts of Bolivia, Brazil, Argentina, and Uruguayand empties into the estuarine Rio de la Plata, aboveBuenos Aires. A few maps show a small area in theextreme northwest corner of Paraguay as drained bythe Amazon, but the weight of existing evidence isthat the entire country lies within the Parana basinand it is so shown on plate 1.The true Rio Parana heads at the southern tip ofParaguay at the junction of its two main branches, theParaguay and the Alto Parana. The Rio Paraguay isthe larger of these two and is the main avenue of drainageand of river commerce in the country. It heads inMato Grosso, Brazil, and trends nearly due south. ItFIGUKE 2. Typical terrain and vegetation in the Gran Chaco. View about 30 kilometers west of Puerto Casado.

GEOGRAPHYbisects the Republic of Paraguay in its lower reaches,and marks striking differences in topography, vegetation,and cultural development between the two partsof the country. It has a total fall of only 250 meters inits 2,500 kilometer course, and a speed through itsParaguayan portion of 5 to 7 kilometers per hour. Itis several hundred meters wide in most places and isgenerally navigable as far as Corumbd, Brazil, by shipswith 3-meter draft and even farther by smaller craft.Its course is characterized by innumerable meandersand by frequent channel shifts. From the Rio Apasouthward almost to Conception the east bank ismarked by discontinuous cliffs of limestone and marble,nearly vertical, and several tens of meters high inplaces. Elsewhere the sandy to muddy banks slopegently into the river or form steep cutbanks, carvedfrom flood-plain alluvium and only a few meters highat most.The Rio Paraguay, with its tributaries, drains all butthe southeastern portion of the country. The RioPilcomayo, heading 2,000 kilometers westward in theAndes in Bolivia, and forming much of the internationalboundary with Argentina, is the largest tributary 011the western or Gran Chaco side of the river. It isnavigable in places by small boats. Except for itslength and relative continuity, it is similar to any ofthe other streams that drain the Gran Chaco. Normally,they are all sluggish, intermittent, and discontinuousstreams that wind their way slowly across thenearly level plains between banks that are seldom morethan a couple of meters high. During rainy seasonsthey overflow their banks and spread over most of theland. Working together, first in one part of the GranChaco and then in another, they are still building upthe plains. Their loads of mud, silt, and fine sanddebris, earned down from the Andes, are redistributedover the plains during periods of overflow or by changesof course that take place on most streams, if not fromyear to year, at least from decade to decade.Most of the eastern part of Paraguay drains into theRio Paraguay through seven main tributaries andseveral smaller ones. Five are 180 to 275 kilometerslong and are navigable in part by small boats and barges,but all the tributaries are slow and shallow in mostplaces and subject to frequent shifts in channel.The Rio Alto Parana, about 3,000 kilometers long,heads deep in southeastern Brazil; in its lower reachesit forms the southeastern boundary of Paraguay for adistance of 850 kilometers. On its way toward Paraguayit meanders slowly across high basalt plains, butwhere it first touches Paraguay it plunges abruptlyover a series of jagged basalt escarpments to form theawe-inspiring cataracts of Salto del Guaira. Fromthese falls to Encarnaci6n it is incised in basalt andfollows a relatively straight, narrow and swift courseas compared with its upstream or downstream portions.From Encarnaci6n to its junction with the Paraguaythe stream is broad and shallow, characterized byshifting, braided channels. It is navigable by moderatesizedcraft as far upstream as Guaira. The southeasternpart of the country drains to the Alto Parandby means of 11 major tributaries, only 2 of which aremore than 150 kilometers long. These, too, are slowmeandering streams and resemble the tributaries ofthe Rio Paraguay in all but two important respects.First, though their meanders superficially resemble theaimless wanderings of the rivers farther west, on closerstudy they are seen to be related to fracture patternsin the basalt flows that underlie most of the area.Second, most of the tributaries make their final descentinto the Alto Parana gorge by a series of low steplikefalls or rapids where they cross the edges of the basaltflows. Recognition of these two features is of greathelp to the reconnaissance geologist. Moreover, thefalls seem to represent the only potential source ofhydroelectric energy that is not subject to internationalcomplications.There are two fairly large permanent but shallowlakes in the country Lago Ypoa and Lago Ypacaraiand countless intermittent ponds, lagoons, and swamps,some of them enormous.CLIMATEThe climate, comparable in some respects to that ofsouthern Florida or south-central Texas, ranges fromsubtropical to tropical. Paraguay is an interior countryof hot summers and mild winters, with the dominantcharacteristic of the weather extreme unpredictabilityfrom month to month and from year to year.The winter months, especially July through Septemberare generally somewhat drier and considerably colderthan the summer months, December through February,with rainfall ranging between one-fifth and two-thirdsthe average of all months.The summer months and shorter periods throughoutthe year are hot and humid, though moderated fromtime to time by heavy rains that may last only a fewminutes or may continue almost steadily for severaldays. Virtually all living habits, from housing arrangementsto business hours, are adjusted to the predominantlywarm parts of the year. This is particularlynoticeable during the comparatively few cooler days ofwinter, when tile floors, high ceilings and the generallack of heating arrangements tend to make temperaturesof 5° to 10°C (41° to 50°F) somewhatuncomfortable.Figure 3 shows the geographic distribution of meanaverage temperatures by isotherms ranging from 22° to

8 GEOLOGY AND MINERAL RESOURCES OF PARAGUAY24° C (72° to 75° F). The average maximum summertemperature measured during the same period, 1940-50, shown on figure 3 was 36°C (97°F) in the northernGran Chaco and the average minimum wintertemperature at Encarnacidn was 10°C (50°F).During this period, an extreme maximum of 43°C(110°F) was recorded in the Gran Chaco in July1942, and extreme minimums of 4° and 5°C (21°and 23°F) were measured at Encarnacion in July1945 and in the Gran Chaco in July 1942. Five ofthe country's eight weather stations reported freezingtemperatures or below in at least 1 month during theperiod 1940-50, and Encarnacidn had freezing weatherin one or more months in each of the 11 years.Figure 3 shows also that the average annual rainfallduring the period 1940-50 inclusive ranged uniformlyfrom 600 millimeters (23 inches) in the western GranChaco to 1,800 millimeters (71 inches) along the easternborder of the country. This uniform, and ratherabrupt, increase in rainfall from west to east bears noapparent relationship to the local topography, hence isobviously controlled by more regional factors. Of23Average annual temperature,in degrees centigradeFIGURE 3. Average annual rainfall and temperatures in Paraguay, 1940-50, inclusive.Compiled from various sources, 1953, by Dorothy A. Oassel for the Instituteof Inter-American Affairs.these, the high Andes on one side and the much lowerhighlands of southern Brazil on the other, together withthe prevailing north winds, appear to be dominant incontrolling rainfall.The periods of highest relative humidity are generallyin March, June, July, and August; the lowest occurduring December in eastern Paraguay and in Augustand September in the Gran Chaco. Evaporation generallyexceeds precipitation from June through Augustin the east and during nearly all of the year in theGran Chaco.VEGETATIONMore than half of Paraguay is heavily forested withvirgin stands of tropical and subtropical trees andshrubs. More than 3,000 species of these have beenrecorded. Many of the trees are deciduous hardwoods,but new leaf growth follows so quickly on the fall ofolder leaves, or even accompanies it, that bare trees arerare at any season. Many species bloom profusely inthe spring and a few bloom at other seasons, lendinggreat masses of white, yellow, pink, purple, and bluecolors to the landscape. The undergrowth of shrubsand vines is commonly thick, and virtually impenetrablein places, especially around the fringes of theforested areas. There is no true rain forest, but hereand there many individual trees tower far above theforest blanket.In eastern Paraguay, the forests once covered nearlyall of the hills and rolling uplands. In the more heavilypopulated central region, the hills, called "islas" or"islands," have been partly or entirely cleared andnow support the bulk of the country's farm lands.Farther from centers of population the forests are stillvirtually untouched, though here and there they arestrikingly marked by angular farm clearings, most ofthem small in comparison to the forests around them.The forestry industry itself, large though it is, does notgenerally result in denudation of the land or in clearingsthat can be converted to agriculture. This is becausethe trees most sought by lumbermen are widely scatteredand their cutting results in little or no visiblethinning of the forest.The lower and flatter portions of eastern Paraguay,called "campos" or "camplands," are grass covered inlarge part, with trees and brush in thick borders alongthe water courses. Parts of these plains, which areused principally for grazing, are swampy, but somecould be easily drained by ditching.On the Gran Chaco side of the Rio Paraguay, vastareas of nearly level grasslands drain into sluggishmeandering rivers that are bordered by thick stands ofdeciduous trees. The grasslands are interspersed withpeculiar brush forests of mesquite and many other

GEOGRAPHY 9thorny semidesert plants that are adapted to alternationsof severe droughts and prolonged wet seasonswhen almost all of the surface of the Gran Chaco isswampy or actually covered by water. Scatteredthrough the brush forests are various hardwoods; alongtheir edges are groves of black palm (carandai), somemany square kilometers in extent (fig. 2).TRANSPORTATIONParaguay is severely handicapped in its developmentand in international commerce by its inland location,which necessitates travel through neighboring countriesfor access to ocean transport. Its international commercedepends largely on facilities that are owned andcontrolled by foreign governments or corporations.Even so, the international transportation situation isbetter than the domestic one.Within the country, all the usual forms of transportationwater, rail, air, and road are represented butall are inadequate for the present needs of the countryand will, unless improved greatly, hinder its developmentin future.By far the greater part of the country's internationaltrade, and a considerable part of its internal trade, iscarried by water. Between 1941 and 1950, more than87 percent of total exports were moved by river, nearlyall of the remainder going on the one international railroadthat links Paraguay with Buenos Aires. Truckshipments to and from Brazil and Argentina are negligible,but substantial contraband movements of cattleon the hoof are generally believed to take place regularly.The Paraguay-Parana river system, comparable inmost respects to the Mississippi, is the main avenue ofcommerce. Its channel accommodates ships with9-foot draft during periods of normal flow, but this isdecreased to 7-foot draft during low water. The AltoParana, the only other stream that can be used forregular navigation, is shallower than the Paraguay andrequires smaller craft. Asuncion, Conception, Villeta,Pilar, and Encarnacion are the main ports. Of these,only Asuncion has modern port facilities; even here logsmust be floated out to waiting ships and lifted from thewater by cranes or made up into rafts.More than 200 vessels, most of them old wood-firedships and barges originally designed for ocean travel,and of Argentine registry, serve the country's inter­national transport needs. Most of them connectAsuncion with Buenos Aires, 1,600 river kilometers tothe south, but a few move 1,100 kilometers up-river toCorumba, Brazil.Shipping rates for the trip from Asuncion to BuenosAires range from 4 percent of the f. o. b. value of somemeat products to 86 percent of that for some timberproducts. A surcharge of 50 percent is commonlyadded during periods of low water, which sometimeslast more than 6 months.In addition to the international commerce describedabove, there is a large internal water traffic. Most ofthis is limited to the many ports along the Paraguayand Alto Parana rivers, but there is some movementof goods on the smaller tributary rivers.A British-owned standard-gage railroad connectsAsuncion, Villarrica, Encarnacion, and many smallertowns along its route with Buenos Aires. It providesregular freight and passenger service but outwornwood-burning equipment and poorly maintained trackagecause delays at times. A number of other railroadsare shown on plate 1. All are privately owned narrowgagelines, used principally for moving of forestproducts.Several foreign airlines provide regular passenger,mail, and freight service between Asuncion and Riode Janeiro, Montevideo, Buenos Aires, Santiago, LaPaz, and Lima. All but Lima are only 4 to 5 hours'flight time from Asuncion. One Argentine company useshydroplanes that operate from the Asuncion harbor;all the other companies use the national airport, whichhas a single, asphalt-paved runway on the outskirts ofAsuncion. Aside from, a few privately owned planes,all internal air transportation is by a governmentcontrolledcompany, which uses small 1 to 3 passengeraircraft and Paraguayan Air Force pilots. Most of thetowns, as well as many private ranches, have earth orgrass landing strips. Any of these can be reachedwithin about 3 hours' flying time from Asuncion,though there are likely to be many delays, due toweather and other factors, in obtaining passage.Moreover, many of the landing strips are likely to beunserviceable during parts of every year because ofrain, mud, or overflow from nearby streams.Within the country, most travel and transport ofgoods are by roads and cart tracks. At the end of1951 there were about 5,000 automotive vehicles inthe country; nearly four-fifths of them were registeredin the capital city. Of the total, about half werepassenger automobiles and half were trucks or buses.Horses with light wagons are used extensively in afew of the colonies settled by Europeans, but the greatbulk of overland transportation throughout the countryis done by oxen. In 1943 there were 27,000 carretastwo-wheeled heavy carts drawn by one to six oxen inuse by farmers alone, plus an unknown but largeadditional number in the forest industries.The principal road net is shown on plate 1. Asidefrom some of the streets in Asuncion and a few blocksin Encarnacion and Villarrica, the only paved, allweatherhighway in the country extends eastward from

10 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYAsuncion to Eusebio Ayala, a distance of 73 kilometers(45 miles). In addition to this two-lane, asphaltsurfacedhighway there are nearly 965 kilometers (600miles) of graded and maintained highways, abouttwo-thirds of them gravel surfaced. Except for thelack of bridges in places, most of these roads areexcellent during fine weather; it is both illegal andvirtually impossible to traverse any of them for a periodof 24 hours after each rain.There are also many thousand miles of unimprovedroads and cart tracks throughout the country. Onlya few are shown on plate 1, and fewer yet can be easilytraveled by other than oxen or specially sturdy automotivevehicles, even in dry weather.POPULATIONAccording to the 1950 census, the total population ofParaguay was 1,405,627, or an average of 3.5 personsper square kilometer (0.7 per square mile). This is thelowest population density in South America and amongthe lowest in the world. As indicated by figure 4, thepopulation is very unevenly distributed. In fact,96 percent of the people live east of the Rio Paraguayand more than half occupy only 4 percent of the landin Asuncion and nearby departments.The Paraguayan people are predominantly a homogeneousmixture of Spanish and Guarani Indian.Spanish is the official language but outside Asunci6nand even within it to considerable extent, Guarani isfar more widely used than Spanish.There are a total of about 40,000 indigenous Indiansbelonging to about 30 different family and linguisticgroups. Nearly all of them lead nomadic lives in theGran Chaco; a few work for timber companies or forfarmers.The 1950 census showed that there were 38,000foreign nationals in Paraguay, representing a score ofcountries, but largely from central Europe. Nearlyall are religious, political, or economic refugees who havecome to Paraguay since 1900. Offered asylum, aswell as lands, by Paraguay, they are largely settled inisolated colonies, particularly in the central GranChaco, in the area southeast of Conception, and in theMisiones region along the Rio de Alto Parand nearEncarnacion. To date there has been little tendencytoward social or economic mixing between the immigrantand Paraguayan populations.INDUSTRIESParaguay depends almost entirely on agriculture,livestock, and forest products for its economic existence.Local industries are largely limited to partial processingof these products for export; nearly all manufacturedgoods are imported. One indirect result of the heavy(URUGUAY \ ~"FIGURE 4. Density of population, Paraguay, 1950, compiled from data in the fliesof the Institute of Inter-American Affairs, Asuncion.dependence on food growing is that the people are wellfed, with a calorie intake per capita of 2,813 per dayas compared with 3,098 calories in the United States.On the other hand, the money income per capita isone of the lowest in the world, amounting to less than$40 in United States money per year in 1950.Four percent of the total land is in farms, but lessthan one percent is actually under cultivation. Allbut about 10 percent of the farmers have less than20 hectares (50 acres) per farm. Of the remainingland, 40 percent is devoted to grazing, 54 percent isforested, and 2 percent is classed as wasteland.Exports in 1950, which were approximately balancedby imports, were valued at 167.4 million guaranies, or18.6 million United States dollars at the then averageofficial rate of exchange for exports. Forest products,

GEOLOGY 11chiefly logs, rough lumber, quebracho extract for tanning,and oil of petit grain for perfume, made up 43.3percent of the total value. Agricultural products,chiefly cotton, vegetable oils, tobacco, and mate accountedfor 28.4 percent; animal products, largely beef,meat extract, and hides yielded 22.2 percent. Nopacking plants were in operation in 1952. Largequantities of meat, grain, fruit, root crops, and canesugar are, of course, produced for local consumption.The mineral industries are limited to production ofmaterials for local use. Clay products, chiefly brickand tile but including some pottery, lead the list.Stone, sand, and lime are produced in quantities sufficientto meet local needs but the several small bottlefactories fall far short of meeting the local demand forglass. A portland cement plant, with an ultimaterated capacity considerably larger than Paraguay'sprobable consumption, went into operation in a smallway early in 1952.FUEL AND POWERExcept for wood, charcoal, and alcohol, Paraguayhas no fuels whatever and no other developed sourcesof electric or other power. This is one of the chieffactors that has retarded the development of manufacturingindustries. Electricity is available in onlynine towns; in all of them the generating equipment iswood fired, as are all locomotives, and virtually allships and barges. All gasoline and other petroleumproducts are imported, but some alcohol for domesticheating is produced as a byproduct of the sugar industry.The demand for wood fuel is so great that the suppliesnear the heavily populated centers, particularly nearAsunci6n, are being rapidly depleted with consequentincreases in cost due to longer hauls. The high costof wood and charcoal is in part also due to the expenseof chopping by hand the extremely hard woods thatmake up so much of the forest growth and to the primitiveand wasteful methods used in making charcoal.It is not known whether wind-operated electricgenerators, which are used in many parts of the westernUnited States, would be successful in Paraguay, noiwhether they have been tried there. They might wellbe adapted for domestic use, however, particularlyat the ranches and colonies in the Gran Chaco, wherethe winds are stronger and more constant than ineastern Paraguay.The only promising sources of hydroelectric powerknown are along some of the tributaries to the Rio AltoParana and at the falls of Guaira on the Rio Paranaitself. The latter falls could be used to develop verylarge amounts of power, but very valuable power sitescould be developed at the places where low falls andrapids form on the Monday, the Acaray, and severalother tributaries of the Alto Parana in their finaldescent to the level of the Parana. Unfortunately,all these potential sources of power are remote from thecenter of population; moreover, the most promisingone, Guaira, is partly owned by Brazil, so that anypower development would require international efforts.GEOLOGYGENERAL FEATURESThe rocks of Paraguay can be divided into five majorclasses, depending on age and mode of origin as shownin the table below and on the geologic map (pi. 1).The oldest ones are the granitic and metamorphicrocks of the Precambrian complex; they underlie theentire country at varying depths but are exposed atthe surface in only relatively small areas near the RioApa and in the south-central part of eastern Paraguay.The second group consists of marine sedimentary rocks,mostly shale and sandstone, and ranges in age fromCambrian or Ordovician through Early Devonian.This group is relatively thin in eastern Paraguay butmuch thicker in the Gran Chaco basin west of theRio Paraguay. The third group of rocks, which rangefrom Pennsylvanian or Permian through Triassic inage, constitute the Gondwana or Santa Catarina continentalclastic sediments known in a large part ofSouth America. Like the older marine beds of Paleozoicage of the second group, they are thicker in atleast part of the Gran Chaco basin than they are ineastern Paraguay. The fourth group is Tertiary toRecent in age. It consists, at least in large part, ofunconsolidated clay and sand of continental origin butmay contain some marine beds in places. It coversall but a tiny fraction of the western half of the country,where it appears to be as much as 2,000 feet thick inplaces. In eastern Paraguay these younger unconsolidatedmaterials are very thin in most places andconsist of swampy alluvium.The fifth large group of rocks consist of igneous extrusiveand intrusive rocks, mostly of basic composition,and some of uncertain age. The most important singlemember of the group is a thick series of basaltic lavaflows that cover the eastern edge of the country andextend far eastward into Brazil where they reach theirmaximum thickness in the Parana basin. Associatedgenetically with these lavas, which are of Triassic orpossibly Jurassic age, are a number of smaller bodies ofintrusive diabase, extrusive basalt, and possibly otherrocks. Besides the igneous rocks whose age is fairlycertain, there are many bodies of igneous rock whoseage is unknown. Some are intrusive and others areextrusive; all are small as compared with the extensivebasalt flows. Some are strongly alkalic and of considerableinterest to the petrographer. Some of the bodies

12 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYgroup here may be related to the basaltic lava flows,hence of Triassic or Jurassic age; for some, however,there is strong geomorphic and other evidence that theyare no older than late Tertiary.The geologic structure of Paraguay appears to berelatively simple in its grosser aspects, but there ismuch to learn of even the larger features. In theeastern half of the country the beds dip gently eastwardtoward the great Parana basin of southeasternBrazil. This easterly dip appears to reverse along theaxis of a low anticline that trends north-south only afew kilometers east of the Rio Paraguay and exposesthe older sediments and the Precambrian basementrocks at the surface in many places. West of this axisthe beds either dip steeply westward, or are downfaultedto the west, into the depths of the Gran Chacobasin. The rocks in this basin are, in places, at least10,000 feet deeper than they are in eastern Paraguay;west of the basin, in eastern Bolivia they rise to thesurface in a series of anticlines and syncliiies that formthe foothills of the Andes.IGNEOUS AND METAMOBPHIC BOCKSBy CHARLES MILTON and EDWIN B. ECKELIn the course of a 6-month field study of the geologyof Paraguay, Eckel collected about a hundred specimensof rocks in 1952. Earlier, geologists had made suchcollections, notably Pohlmaim (1886), Lindner (Milch,1895), and Cariiier (1911c, 1913); these collections havebeen described respectively by Pohlmann (1886), Milch(1895 and 1905), and Goldschlag (1913a). Harringtonmade extensive collections in 1946 which, unfortunately,were lost, so that his otherwise excellent memoir onthe geology of Paraguay (1950) contains only field noteson the petrology. Milton has studied the collectionmade by Eckel and to a considerable extent compiledthe notes here presented.The igneous and metamorphic rocks may be classifiedin three main groups metamorphic and granitic, basalticand diabasic, and alkalic. Geographically, thereare a southern and a central area, both examined byEckel, and a northern area, examined by Carnier andothers. The sedimentary rocks collected by Eckel arebriefly described in connection with the stratigraphy;one peculiar sedimentary rock that has columnar jointingis described here in the section on diabase as' 'pseudotrachy te.''PRECAMBRIAN METAMORPHIC AND GRANITIC ROCKSIn eastern Paraguay there are two extensive areas,and several smaller ones, of Precambrian granitic andmetamorphic rocks. One of the larger areas is theregion around Centurion near the Rio Apa; it extendsnorthward into Brazil. The other is in southern Paraguay.This report discusses only briefly rocks of theRio Apa region, which have been investigated byCarnier (1911c), Goldschlag (1913a), and Boettner(1947); it deals more especially with the rocks fromthe southern and central region.The basal complex, a southern extension of the Brazilianshield, is overlain unconformably by Paleozoicand Mesozoic sedimentary rocks as in many other partsof the world. It underlies, at no great depth, all easternParaguay and the northern part of the Gran Chacowest of the Rio Paraguay, where there are a few smalloutcrops of these rocks. In the southern and westernparts of the Gran Chaco, however, the basement rocksare deeply buried beneath sedimentary rocks.The surface of the exposed Precambrian rocks in theRio Apa region is comparatively rugged, with relief ofmore than 200 meters, whereas in the southern regionthe surface is smoother, with relief of less than 100meters. Reasons for this difference in topographicexpression are not apparent.The metamorphic rocks, which are undoubtedly olderthan the igneous rocks, are made up largely of schistand gneiss. A great variety of other rocks, whose distributionis not known precisely, is associated with theserocks. They include ultrabasic igneous rocks as wellas argillite, quartzite, marble, and other kinds.Most of the igneous rocks are of intrusive origin, butsome are probably extrusive. Medium- to coarsegrainedgranite and quartz porphyry predominate, butthere are many bodies of aplite and pegmatite associatedwith them. In at least one place, near Caapucii, fragmentalpyrophyllitized volcanic rocks are associatedwith porphyritic rocks that show flow structure, indicatingthat they probably originated as surface flows.Probably the earliest rocks were gneisses and schiststhat were overlain by shale and sandstone beds, andthis whole sequence was then intruded by the graniticrocks, accompanied by extensive metamorphism and aconsiderable amount of folding and faulting. The Precambrianrocks were later eroded to a relatively smoothsurface before the deposition of the limestone andargillite of the Itapucumi series, of possible Cambrianand Ordovician age. This interpretation agrees withthat of Carnier (1913) and of Harrington (1950).Without more knowledge than is available at presentit is impossible to assign definite ages to any of theserocks. Harrington (1950) suggests correlation of themetamorphic rocks with the Cuiba series of MatoGrosso which has been assigned to the AJgonkian byOliveira and Leonardos (1943, p. 217), Evans (1894),and others. Possibly both Archean and Algonkian erasare represented, just as they are believed to be innortheastern Bolivia (Ahlfeld, 1946, p. 19-25). Forconvenience, the metamorphic rocks are grouped here

IGNEOUS AND METAMORPHIC ROCKS 13and shown on plate 1 as "older Precambrian metamorpliicrocks" whereas the granitic and porphyritic rocksare grouped as "younger Precambrian igneous rocks."SOUTHERN AREAOne of the two large bodies of Precambrian rocks isin the southern part of the country between the latitudesof Carapegua and San Juan Bautista. The mappingof this area (pi. 1) is based in large part on EckePs fieldobservations, supplemented by Harrington's map (1950)and by interpretation of aerial photographs.OLDER METAMORPHIC ROCKSThe eastward-trending belt of older Precambrianrocks between San Juan Bautista (pi. 1) arid VillaFlorida is very poorly exposed in most places, and itscharacter is known only in a general way. The northerncontact of this belt with the younger granitic rocks iscovered in all places examined, but is thought to besomewhere near the Eio Tebicuary at Villa Florida, asshown on the map. Along the ridge west of San JuanBautista the Triassic sedimentary rocks south of thebelt rest uri conformably on the metamorphic rocks,with a thick basal conglomerate. This same relationshippossibly exists along the entire contact, but theapparent absence of basal conglomerate just north ofSan Juan Bautista and strong shearing within themetamorphic rocks near San Miguel indicate that partof the contact between Triassic and Precambrian rocksmay be a fault.The best exposures are along the highway from SanMiguel to a point about 6 kilometers north of that town.At and near San Miguel most of the rocks consist ofwhite to gray glassy quartzite with a little feldspar,most of which has been intensely crushed and containsmuch bright-green muscovite along fracture surfaces.The lineation of this crushed material strikes N. 80° E.and dips 45° N. There are also two sets of prominentjoints that strike due north and N. 45° E. and dip 30°E. and 60° NW., respectively. The quartzite is conspicuousbecause of its bright-green mica. Small flakesof graphite are fairly abundant in the specimens athand, and numerous grains of rutile are seen under themicroscope.From San Miguel northward toward Villa Floridathe rocks are fairly well exoosed in roadside ditches(fig. 5). They consist of a wide variety of rocks inparallel bands that trend N. 40° E. and dip northwestat angles of 30° to 60°. Nearly all the rocks arecrushed and their constituent minerals are strung outalong the direction of the bands so that they resembleflow banding in glassy volcanic rocks. The rocksrange from granite, aplite, and pegmatitic quartzFIGURE 5. Precambrian rocks exposed in a gully along the highway just north of San Miguel. The weathering profile is distinct. The rocksare mostly granite and aplite, but also contain some gneiss, schist, and talc, the latter probably derived from basic rocks.

14 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYthrough mica schist, gneiss, and ultrabasic rocks.Harrington (1950) says that in the Sierra de Itayuru, alittle north of San Juan Bautista, this same series ofgneiss and schist contains intercalations of marble.At kilometer 176,' about 3 kilometers north of SanMiguel, there are several bands, 30 to 50 meters apartand each 2 to 3 meters wide, that are largely altered totalc. The original rock, as exposed in the road ditchesand in a shallow prospect pit (see fig. 58), was apparentlyan ultrabasic rock. The talc, which containsa few specks of chromite locally, ranges from whitethrough dull green to gray and from very smooth togritty texture. It contains a few narrow and irregularveinlets of white quartz and a cross-fiber mineral thathas the appearance of asbestos but which is shown byX-ray-diffraction methods to be fibrous talc.In addition to the talc, the belt of metamorphic rocksis known to contain deposits of magnetite and hematite(p. 85), some of them rich near San Miguel.On a hill 1 kilometer east of the main road, andabout 5 kilometers north of San Miguel there is a comparativelylarge body of white quartz in country rock1 As used in this chapter, kilometer numbers refer to markers along the main highways(Rutas). They measure distances from Asuncion.that has a rhyolitic appearance. The quartz outcropsover a roughly circular area about 50 meters in diameter.It is milk white and glassy, with a few faceted crystals,2 to 3 centimeters in diameter, in vugs. One smallbleb of coarse-grained galena was found on the dumpof a shallow prospect pit; a few specks of free gold arereported by former prospectors. This deposit ofquartz, obviously of hydrothermal origin, containing alittle galena and possibly some gold, lends some basisto reports that the early Jesuits found gold and mercuryore near San Miguel.In a strong shear zone near Villa Florida is whatappears to be a sheared granite (specimen P-70).(Throughout this chapter, field numbers assigned tospecimens collected by Eckel are retained so as toavoid confusion and repetition.) It is a thinly bandedrock, with layers of dark-gray glassy quartz andgreenish-brown epidote with feldspar. Microscopically,it shows sheared aggregates of highly alteredmicrocline, diopsidic pyroxene, and zoisite (garnet?)interlayered with quartz. The photomicrograph (fig. 6)shows the elongate lenses of feldspar in the coarselycrystallized quartz. The diopsidic pyroxene is associatedwith these feldspar pods. A more siliceous phaseFIGURE 6. Sheared Precambrian granite (specimen P-70), from shear zone near Villa Florida, g, quartz; /, feldspar (microcline) with mafic minerals. X 15.Crossed nicols.

15FIGURE 7. Arkosic sandstone (specimen P-6) from near Villa Florida. X 15.of this granitic rock (specimen P-71), from a shear zonenear the talc deposit just north of San Miguel, consistslargely of massive bluish-gray quartz, with minorfeldspathic lenses.On a cart track between the main highway and thePaso Pindo copper deposit, about 6 kilometers northnortheastof Villa Florida there is a body of arkosicsandstone with intercalated shale 50 to 100 meters indiameter, that appears to be enclosed by granite andaplite. The shale is hard and fissile and apparentlymetamorphosed by baking, with a little fine epidotealong seams. It is interlayerecl with the arkose, andshows very thinly layered even bedding, with layersranging from a centimeter to a hairline in thickness.The arkose is made up of moderately calcic plagioclasewith some quartz. Some of the arkose forms crosscuttingclastic veinlets in the shale and closely resemblesintrusive aplite. Figure 7 (specimen P-6)shows the microstructure of the arkosic sandstone.The relations of this sequence of shale and arkose toother rocks in the area are not known, but it probablyrepresents an inclusion of older rocks in the granitemass.YOUNGER IGNEOUS ROCKSThe 3Tounger igneous rocks comprise granite and avariety of porphyries, most of them quartz-bearing,with many smaller bodies of aplite and pegmatite.They do not show the intense shearing of the presumablyolder granitic rocks mentioned above as part ofthe older series of metamorphic rocks. Only aboutone-third of the comparatively large area of Precambrianrocks in southern Paraguay is exposed; theremainder, largely in the lowlands that border the RioParaguay, is obscured in most places by swamps withonly a few "islas" or hills, that stand above the plain.How much of this area is underlain by granitic andporphyritic rocks and how much by metamorphicrocks is open to question, but the distribution shownon plate 1 is partly substantiated by Hibsch (1891),who describes quartz porphyry collected by Jordan(1893) from near Lago Ypoa that appears to be identicalwith the quartz porphyry exposed farther east inthe vicinity of Caapucu.Even in the area where the rocks are comparativelywell exposed, the granite and porphyries are notmapped separately because of lack of information. It

16 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYis known that the northern part of the mapped area,in the vicinity of Quiindy, is made up mostly of graniteand also that granite makes up most of the area betweenCaapucu and Quyquyo. Most of the remainder appearsto be porphyry. The contacts between the two kindsof rock are very irregular but are comparatively easyto trace on the ground and even on aerial photographs,because the porphyries almost invariably have astreaky appearance in photographs that the granites donot. The age relations of granite and porphyry arenot known.The surface of the granite ranges from nearly levelto gently rolling, with even less relief, in general, thanthe surface of the porphyry, which here and thereforms small steep-sided hills, that rise 50 to 100 ormore meters above the surrounding plains. The extensiveareas of swamp that characterize these rocks,particularly the granite, suggest that they are relativelyunfractured and unjointed, and therefore, unusuallyimpermeable.Similar lateritic soil profiles are formed on the graniteand porphyry; both are very different from profilesformed on the sedimentary rocks. There is no evidenceas to the age of the laterization but by analogywith similar laterites in other parts of the world, itmay well be an ancient laterite and represent a quitedifferent climatic environment than the present one.The surface material consists of a few centimetersof loesslike fine sandy loam that supports lush grasses,but very few trees. This material changes abruptly to1 to 2 meters of white to buff sandy clay that gradesdownward to fresh granitic rock. The clay containsrounded grains and small euhedral crystals of freshquartz. Most of the quartz grains and crystals arecoated with 1 to 3 millimeters of limonite; nodules oflimonite % to 2 centimeters in diameter are scatteredthroughout the clay. The limonite and quartz materialstend to concentrate at the top of the clay,beneath the loam, and are cemented in places to ahardpan that forms an excellent and widely usedmaterial for road surfacing. In places there are largeresidual boulders of fresh granitic or porphyritic rocksin the soil; locally the lateritic soil is missing and thereare fairly large smooth outcrops of unaltered rock.So far as known, the granite itself contains nomineral deposits, though it offers distinct promise asan attractive building stone. The porphyries, on theother hand, not only have potential use as building stonebut contain nearly all the iron and copper deposits,as well as the one known deposit of pyrophyllite, insouthern Paraguay (p. 90).Granite and related rocks. In general, the granite ismade up of interlocking grains of pink and white feldsparsin approximately equal amounts, 1 to 2 centimetersin diameter, with smaller, nearly sphericalgrains and euhedral crystals of clear-gray quartz.The only dark mineral is biotite, largely altered in mostplaces to a soft brown or green material, which formsvery small clusters interstitial to the quartz and feld­spars. In most exposures the near-surface rock ispartly weathered and crumbly, but in a few places, ason the road 8 kilometers southwest of Quyquyo", thegranite is brilliantly fresh and would form an attractivepolished building stone.A typical specimen of the granite (P-62), collecteda short distance east of Barrerito consists of glassyquartz, pink alkalic feldspar, and dark biotite, withporphyritic crystals of white feldspar a centimeterlong. The rock is apparently much the same as abiotite-gneiss studied by Goldschlag (1913a, p. 54)from Estancia Machuca-cue near the Rio Apa; andis also similar to granite from many other parts of theworld. Figure 8 shows partly chloritized biotite anda few opaque (black) ore grains. The feldspars aresodic plagioclase and orthoclase, both somewhat sericitized.There are a few euhedral deep-brown grainsof allanite(?) and also some sphene. A chemicalanalysis of this rock is given in table 1.Comparatively small dikes and irregular masses ofaplite and, to lesser extent, pegmatite are widely distributedin both the granitic and porphyritic rocks andin some of the older metamorphic ones. Some arestrongly sheared and fractured and contain considerableamounts of epidote on fracture faces. At kilometer156 on the Caapucu-Villa Florida highway, streaks ofcomparatively coarse-grained dull-green hornblenditewere noted in the aplite. Similar small hornblendicbodies are found in many localities.Good examples of typical aplites (specimen P 74, 75)are shown in figures 9 and 10; chemical analyses ofthese two rocks are reported in table 1. The rockshown in figure 9, taken from along the road betweenBarrerito and Quyquyo, is particularly interestingbecause it is porphyritic and closely resembles some ofthe quartz porplryries (see fig. 14) in external appear­ance. It is a red felsic rock, with large glassy quartzphenocrysts. Unlike the porphyries, however, it has adistinctly granular texture throughout.Porphyry. The predominant porphyritic rock is aquartz porphyry, close to rhyolite in composition;most of it is reddish brown but some is dark gray. It ischaracterized by the presence of irregular grains andeuhedral crystals of clear glassy quartz 3 millimetersto 1 centimeter in diameter, together with irregulargrains of dull-pink feldspar that are usually smaller inany given specimen than the quartz grains. Theseare set in a dense dull-brown to gray stony groundmass.The rock varies widely in the relative proportions of

IGNEOUS AND METAMORPHIC ROCKS 17FIGURE 8. Coarse-grained granite (specimen P-62) from east of Barrerito on the road to Quyquyo; partly chloritized biotite, 6, with feldspar, / (orthoclase andoligoclase), partly sericitized, and quartz, g, and a few ore grains, o. X 20.groundmass and phenocrysts, so that some exposurestend to resemble granite or aplite.Good examples of the freshest rock, that wouldserve as beautiful polished building stone, can be seenon the Caapucu road at kilometer 134.On the road from Quiindy, north of Caapucu, porphyriticrocks are well exposed (figs. 11, 12). In placeswhere the clay formed by weathering processes hasbeen removed, the rock surfaces are studded with resistantquartz phenocrysts, as shown in figures 12 and 13.The microstructure of this rock (specimen P-67) isshown in figure 14. The rock is reddish brown, becauseof the abundance of reddish plagioclase phenocrysts.Where the reddish phenocrysts are not abundant, theporphyry is gray; quartz phenocrysts are few and whitefeldspars are present.The gray phase of the porphyry appears to be lessabundant than the reddish brown. Figure 15 shows atypical specimen of the gray phase taken from anexposure close to the rock shown in figure 14. Thethin section shows no quartz phenocrysts at all, butother specimens of outwardly similar rock contain afew euhedral crystals of quartz. The texture of thefelsic groundmass is obviously quite different from thatof the rock shown in figure 14. A chemical analysis ofthis rock (specimen P-60) is given in table 1.About 12 kilometers northwest of Caapucu, and somedistance west of ttie main highway, there is a largedeposit of pyrophyllite. The country rocks in thisvicinity are normal brown quartz porphyry, but thepyrophyllite (see p. 90) appears to be an alterationproduct, of a volcanic tuff that is probably interlayeredwith the porphyry.Associated with the quartz porphyries just described,notably just north of Caapucu, are many other varietiesof porphyry that, in the field, appear to range fromglassy rhyolite to dense gray quartz-free monzonite.Microscopic examination shows, however, that theyare probably textural variants of the quartz porphyriesalready described.One of these rocks (specimen P-31) forms the wallrock of the Del Puerto pyritic hematite deposit northof Caapucu. It is a brick-red fine-grained rock, withglassy quartz, red feldspar, and dark mafic phenocrysts.Pyrite is also disseminated through the rock, visiblewith a hand lens. Its microscopic character is shownin figure 16. At the lower left is a large quartz crystal,embayed by potassic feldspar, which, with quartz,

18 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGT'RE 9. Coarse-grained porphyritic aplite (specimen P-75) from the road between Barrerito and Quyquyo, cuts granite shown in figure 8. Aplite is madeup of sodic plagioclase in a groundmass (g) of quartz (q) and turbid orthoclase with a little altered brown biotite. This rock resembles, externally, theporphyry in figure 14. Crossed nicols.comprises the groundmass. In the upper middle, is alarge feldspar phenocryst in the center of which is anaggregate of green chlorite, zoisite, and apatite. Thereis more chlorite along the edges, apparently afterbiotite. One such mass of chlorite is seen in the lowerleft corner. Several other large feldspar crystals areseen in the illustration. An analysis of this rock isgiven in table 1; the pyrite content is about 0.5 percent.The quartz porphyry from Cerro Yahape, southeastof Lago Ypoa, as described by Hibsch (1891) appearsto be similar in most respects to the rocks describedabove. He describes the Yahape rock as reddishlight brown, with dihexahedral crystals of quartz andcrystals of red feldspar interspersed through a microcrystallinegroundmass that is rich in quartz.A few meters east of the Del Puerto pyritic-hematitevein, and parallel with it, is a black porphyry dike(specimen P-32). It is very similar to the dark rockdescribed above (specimen P-60, fig. 15) from theQuiindy road north of Caapucu and to the dark porphyriticrock (specimen P-34) quarried for highwayuse near Ypacarai in the central region (see p. 40). Allare fine-grained, almost aphanitic dark-gray rocks,with conspicuous dull-white feldspar phenocrysts, amillimeter or two in diameter. Microscopically thethree rocks are very similar. The photomicrograph ofthe black porphyry at the Del Puerto locality (fig. 17)shows the sodic plagioclase phenocrysts in a felsicmatrix, strewn with black iron oxide, some epidoticchloriticdebris, and very minor amounts of quartz(a few small grains can be seen in thin section).Another of these porphyritic rocks from near thetalc deposit just north of San Miguel is brick-red,finely granular, with conspicuous anhedral whitishfeldspar phenocrysts, and numerous rounded darkglassy quartz grains, both as much as a centimeter indiameter.Microscopically, this rock shows a feldspathic matrixin which isolated quartz grains are abundant. Someof the larger quartz grains enclose feldspar. Thefeldspar is turbid, strongly alkalic, and is mostlyorthoclase with less sodic feldspar that shows albitetwinning and is also slightly clearer. Myrmeldte isabundant, in places showing an "hour-glass" structure.Strongly pleochroic brown biotite, apparently disintegrating,arid a little black opaque iron oxide are the

IGNEOUS AND METAMOKPHIC ROCKS 19accessory minerals. This rock is almost identical witha rock (specimen P-30, fig. 18) 9 kilometers south ofCaapucu and also resembles superficially but notmicroscopically that shown in figure 16 (specimen P-31),north of Caapucu.CENTRAL AREAAn exposure of granite at San Bernardino is smallbut nevertheless significant. The northern part of thetown is underlain by this rock; the freshest material isalong the eastern shore of Lago Ypacarai, where thereare nearly continuous exposures for a distance of about1 kilometer.The exposure, whose size is somewhat exaggeratedon the map, (pi. 1) is scarcely more than 1 squarekilometer in extent, as the rock is covered in mostplaces by sediments in the lake or by the basal beds ofthe Caacupe" group. Harrington (1950, p. 16) mentionshaving seen specimens of similar but coarsergrainedgranite said to have come from a small hill afew kilometers west of Yaguaron and a little south ofIta. This indicates that the granitic basement may berelatively close to the surface along both sides of theYpacarai depression.At San Bernardino the granite is pinkish brown andcoarse to medium grained in texture, with some suggestionof schlieren. It contains pink and white feldspar,a little interstitial biotite, and numerous glassyquartz "phenocrysts" thai are subspherical and uniformlyabout twice the size of the feldspar grains thatform the matrix.On the upper slopes of the hill at the north edge oftown the granite is very weathered and crumbly. It iscapped unconformably by the basal beds of the Caacupeseries.NORTHERN AREARIO APA REGIONA complex of Precambrian rocks occupies most ofthe area from the Rio Apa southward to the RioAquibadan, and between the latitudes of Centurionand Santa Luisa. Other outcrops of some of thesesame rocks, though not described in the literature, mustexist near Bella Vista and just north of Conception, forthere are authenticated reports of mica-bearing pegmatitesnear both places. Their probable positionsare sketched in plate 1. This area was not visited byEckel, but it was possible to draw a rough approxima-FIGURE 10. Fine, even-grained aplite (specimen P-74), a brick-red aggregate of flesh-colored orthoclase CO, somewhat perthitic, and glassy quartz (g), fromthe road between Villa Florida and Caapucu. X 20.

20 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 11. Typical weathering profile on Precambrian quartz porphyry on thehighway between Caapucu and Quyquyo.FIGUEE 12. Partly weathered Precambrian quartz porphyry at same locationfigure 11. showing characteristic weathering out of quartz phenocrysts.tion of the distribution of rocks by interpretation ofaerial photographs, by use of sketch cross sections publishedby Carnier (1913c), and by Boettner (1947),and by piecing together scattered observations recordedin the literature.The western part of the main area of Precambrianrocks is a relatively high and rugged chain of hills thattrends northward to and beyond the Rio Apa. Tt iscalled the "Apa Bergland" by Carnier (1913c) andother authors. The Paraguayan part, marked by theeminences of Cerro Paiba and Loma Pora, is alsoknown as the Cordillera de las Quince Puntas. Eastof this chain is a rolling upland, known as the Satyplateau or Potrero Saty.Biotite and hornblende gneiss, mica schist, andgranite make up most of the area. Associated withthese rocks are aplite, pegmatite, argillite, quartzite,hematitic schist, and other rocks. Lineations in themetamorphic rocks trend northeastward in general anddip steeply either northwest or southeast. Many ofFIGUEE 13. Brown variety of quartz porphyry (specimen P-67) from Quiindyroadside north of Caapucu. Shows weathered aspect of hand specimen. The projectionsare quartz grains.the rocks are much fractured, principally along N. 30°-50° W. trending zones. The northward-trending faultshown on plate 1 is based on interpretation of photographsand may well be in error.

IGNEOUS AND METAMORPHIC ROCKS 21FIGURE 14. Typical Precambrian quartz-porphyry (specimen P-67) reddish-brown phase, from the road between Quiindy and Caapucu. Phenocrysts areeuhedral quartz, q, and reddish sericitized sodic plagioclase, /, each as much as 2 millimeters in diameter, with a little chloritized biotite, b. The fine-grainedgroundmass, g, contains some ore grains, o, and shows striking flow structure. X 15.Petrographic descriptions of the granites, aplites, andgranite porphyries that are available indicate that theserocks are similar to those in southern Paraguay.The "biotite-gneiss" studied by Goldschlag (1913a,p. 54) from Estancia Machuca-cue is similar in mineralogyand chemical composition to the granite fromsouthern Paraguay, for example, specimen P-62 fromnear Barrerito. This suggests that much of the gneissdescribed by Carnier (IQllc), Goldschlag (1913a), andBoettner (1947), from the Rio Apa region is closelyrelated genetically and petrologically to the rocks ofsouthern Paraguay that are here called "granites."Goldschlag's "biotite-gneiss" is said to extend over alarge area from the Rio Pitonoaga to the Rio Apa. AtZanja Moroti it strikes N. 55°-60° E. and is cut bymany small veins of "quartzite," aplite, and pegmatite.It does not extend beyond the Rio Termentino. Goldschlag'sspecimens from Estancia Machuca-cue werefound by him to consist of microcline, albite-oligoclase,and quartz, with biotite, green hornblende, sphene,magnetite, and epidote.AMAMBAY REGIONEckel saw in Asuncion a rather large collection ofspecimens of metamorphic and igneous rocks that werereliably reported by their owner to have come from the"Amambay region, near Pedro Juan Caballero." Thereare no published geologic maps that show Precambrianrocks in the region cited and the locality descriptionavailable is so vague that no attempt has been made toportray them on plate 1.The specimens seen include crenulated mica schist,gneiss, and granite and quartz porphyry similar to therocks exposed near Caapucu in southern Paraguay.Coarsely bladed specular hematite and sheets of muscovitemica, streaked with brown and black materialand as much as 7 by 10 centimeters in size, were seenin the same collection.TRES HERMAN OS HILLS NEAR PUERTO GTJARANfCarnier (1913) mentions the Tres Hermanos hills,near Puerto Guarani, as probably related in origin androcks to the Pao de Acucar. They are in the Gran

22 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 15. Precambrian porphyry (specimen P-60), gray phase, associated with quartz porphyry of figure 14. Megascopically a gray stony rock with conspicuousgrayish-white feldspar phenocrysts, the section shows sodic plagioclase phenocrysts, /, and a few small chloritized and epidotized mafic mineralsin a felsic groundmass. Other specimens of similar appearance contain considerable quantities of quartz as phenocrysts. X 20.Chaco, 20-30 kilometers northwest of the river, and areonly 30 to 40 meters high. Quarried rock from thesehills that was seen by Eckel at Puerto Guarani resembledthe Precambrian quartz porphyry more closelythan the younger alkaline volcanic rocks and it is somapped on plate 1.FUERTE OL1MPOAccording to DuGraty (1865), grayish-brown denseporphyry, with grains of quartz and plates of oligoclase,makes up the small hill on which Fuerte Olimpo issituated on the upper Rio Paraguay. Several laterwriters have quoted him, but no further descriptionsare known to the author. The body is shown in figure 2as of younger Precambrian age. This assignment issupported only by the fact that most writers on Paraguaytend to characterize the Triassic or Tertiaryigneous rocks as something other than porphyry,whereas this is the term used by most of them in describingthe Precambrian quartz porphyries of the RioApa and Caapucu regions. The porphyry is reportedto contain barite deposits.ANALYSES OF PRECAMBRIAN IGNEOUS ROCKSTable 1 shows the results of chemical analysis of sixof the Precambrian rocks collected by Eckel from centraland southern Paraguay. To these are added threeof Goldschlag's anah'ses of rocks from the RJ'O Aparegion.An analysis of a specimen of rhyolite agglomerate(P-58b), collected by Eckel near the much youngercaldera at Acahay, is also included, though discussionof its geologic setting and meaning is reserved for thesection on alkalic rocks.Also, because of the close similarity of the chemicalanalysis and other features, the analysis of a rhyoliteporphyry from the highway quarry near Ypacarai isgiven here. However, a Precambrian age for this rockis doubtful; the matter is discussed further on pages42-43.Spectographic analyses of Eckel's analyzed rocks, aswell as of two pebbles of quartz porphyry collectedby him from the Tubarao tillite, of Pennsylvanian orPermian age, are shown in table 2.

IGNEOUS AND METAMOEPHIC ROCKS 23TABLE 1. Chemical analyses of Precambrian rocks of Paraguay[Analysts: For specimens P-31 to P-75, Lois D. TrumbuU, U. S. Geological Survey; densities by L. N. Tarrant, U. S. Geological Survey; for specimens A, B, and C, MauriceGoldschlag. Spectrographic analyses for trace elements made for samples, except P-31, P-58b, A, B, and C, see table 2. Tr.=trace]SiO2 ~ --------A12O3__________________Fe2O3 _ _____________FeO _ ________________MgO____--_-__________CaO___________________NaaO__ -__ ______K2O___________________H2O-_________________H20 + _________________TiO2 _ _________________CO* -P2O5S08___-_-__s_____________________MnO ___________ _____BaO __ _________ ___ _LessDensityNormP-3174 2013. 58. 63.72. 26.793. 804. 49. 17. 47. 25.01.06.04.23.07. 1199. 88. 1299. 762. 621-4-1-3P-3474. 2613. 12. 471 Q8. 221. 533. 803. 34. 06.43.23. 16.05. 07.0599. 772. 66I-4-2-3P-58b77. 361 1. 371. 22QO. 16. 513.034. 74.05.08. 16.00.03.05. 1599. 812. 621-3-8-3P-5976. 7212. 36. 65. 63. 16. 623. 504. 71.03. 15. 14.04.03. U4.0799. 852. 611-4-1-3P-6066. 4616.082. 301. 851. 112. 744. 712. 79.09.78.47.02. 20, 13.2099. 932. 651-4-2-4NOTE. See following table for description of specimens and locality of collection numbers.P-6274. 5313.00.89. 94.461. 393.474. 47.06. 16. 27.01.07.06.0799. 852. 621-4-2-3P-7477. 8312. 29.47. 17.02. 283. 424. 96.07. 26. 10.00.01.01.0099 892. 551-3-1-3P-7577. 1712. 46. 62.48.01. 194. 144.45.03. 18.07.00.01.03.0099. 842. 56I.4-1-3A75. 8713.091. 80.35.874. 212. 83. 19. 41Tr.Tr.99. 621-3-1-3B77. 7211. 532. 182. 42. 534. 372. 57.48Tr.. 19Tr.101. 991-3-1-4C68.3517. 613.44. 651.031.223. 122.221. 12Tr.. 1798. 931-3-2-3Field No.P-31 -.__P-34.____P-58b_____P-59 _____P-60- _____P-62__ ._P-74______RockRhyolite porphyry, darkphase.Rhyolite agglomerate. _ _Rhyolite porphyry ___ ___Porphyry (fine-grained) _Aplite __ ____ _ ._Localitynear Caapucu.Highway quarry near Ypacarai.Acahay caldera.North of Caapucu on Quiindy road.Near Caapucu.Near Villa Florida-Caanucu road.Field NoP 7^B__.______C________-RockAplite__-____ ____________Apllte- ________ _Quartz porphyry __ ___Locationnortheast of Conception.Pitonoaga near Estancia Machucacufi,northern Paraguay.Northeast of Estancia La Paz, Cordillerade las Quince Puntas.FIGUEE 16. Pyritic porphyry, wall rock of the Del Puerto pyritic hematite deposit north of Caapucu. This rock (specimen P-31) contains about half percentpyrite, p; quartz, g; feldspar, /; and chloritized biotite, 6. X 15.

24 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 17. Black porphyry (specimen P-32) from dike parallel to the Del Puerto vein near Caapucu shows andesinic phenocrysts, /, in finely crystallinematrix, a rather coarsely crystalline cognate xenolitli, c-x, not discernible in the hand specimen, and quartz (q). X 20. Crossed nicols.In the norm symbols (Washington (1917)), thefollowing significance attaches to the four parts ofthe symbol.The initial Roman numerals termed the "class" indicatesthe relation of salic to femic minerals, that is,TABLE 2. Spectrographic analyses of Precambrian rocks ofParaguay[Analyst: Paul R. Barnett, TJ. S. Geological Survey. Tr.=trace; concentrationuncertain. Looked for but not found, As, B, Bi, Cd, Ge, In, Pt, Sb, Ta, Th, Tl,U, and W]Ag_____Ba_ _Be..___Co._.__Cr_____Cu____.Ga_ _La...__Mo_.__Nb__._Ni._ -.Pb_.___Sc_-._Sn__Sr . ._V......Y.____.Yb____.Zn_____Zr ...P-310. 0001.1.0006.0002.0003.003.002.006.0002.0010 .009.00050.02.002.005.0004.2.02P-34 P-58b P-59 P-600 0 0 0 .05 .1 .07 .2.0007 .0004 .0003 0. 0002i Tr. Tr. .0008. 0004 . 0002 .0001 .0003.0007 .0003 .0002 .0007.002 .002 .001 .001.006 .006 .006 0.0002 .0001 .0003 .0003.001 .001 .001 .0020 . 0004 0 0 .002 .004 .003 .004.001 .0003 .0003 .0010 0 0 0.02 .009 .009 .05.0009 .002 .0004 .004.007 .006 .005 .007.0007 .0004 .0004 .00030 0 0 .03 .01 .040 .01P-62P-75 P-lOla P-lOlb0 0. 00004 0 .004 .02 .1.0007 .0006 .00050 .0005 .0005Tr. .002 .001.0002 .002 .001.003 .004 .00100 00 .002 .0002.003 .01 00 .001 .0008.005 .002 .0030 0 .00040 .0006 0 .0006 .002 .01Tr. .007 .005.007 .02 .004.0008 .002 .00040 0 0 0.01 .03 .08 .01P-740 0 .07 .0020 .0004.0003 0.0001 .0001.0003 .0002.001 .002.005 0.0002 .0003.001 .0020 0 .003 .003.0004 00 0.03 .002.002 Tr..004 .004.0002 .00040 .02NOTE. See following table for description of specimen and locality of collectionnumbers.Field No.P-31 .....P-34___P-58b..._-P-59 __ _P-60__P-62_____.P-74 _____P-75- -P-lOlb. _.RockPorphyry, dark phase ...Rhyolite agglomerate. _ _Rhyolite porphyry ......Porphyry (fine grained) _LocalityCountry rock of Del Puerto vein outcropnear Caapucu.Highway quarry near Ypacarai.Acahay caldera.North of Caapucu on Quiindy road.Near Caapucu.quartz-|-f el dspars+feldspathoids versus ferromagnesiansilicates-)-oxides + carbonates-]-phosphates, and others.There are five classes.The second numeral indicates the order, based ondifferences in the chief subgroup of the preponderantsalic or femic group, and serves to distinguish thosechemical characters that are dependent on the dominantacid-forming components of the magma, silicon, titanium,and ferric iron. For rocks not definitely femicin character, there are nine orders.The third numeral indicates the rang, based on theproportions of alkalies to lime in the preponderant salicage.age.

25FIGURE 18. Ehyolite (specimen P-30) from 9 kilometers south of Caapucu, with abundant myrmekite, m. g, quartz;/, feldspar (oligoclase and orthoclase).X20.minerals of rocks such as these under consideration, inwhich there are five rangs.The fourth numeral, signifying the subrang, distinguishesbetween .five divisions of the K^O/NaaO enteringthe feldspars or feldspathoids.Inspection of the norm symbol for each analysisrecorded in table 1 shows that for every one of theserocks, the class I, is that in which there is more thanseven times as much salic minerals as femic; the order,either 3 or 4, showing a ratio of quartz to feldspar notover 5/3, but not les^ than 1/7; the rang, 1 or 2, showingK2O+Na2O/CaO in excess of 7/3; finally, the subrang is3 or 4, indicative of K2O/Na2O less than 5/3 but greaterthan 1/7.In view of this chemical constancy, as well as thesimilarities in petrography and in geologic settings describedabove there is a strong suggestion that theserocks are genetically related, or comagmatic.The eight rocks of this suite collected by Eckel alloccur within a radius of 50 kilometers east and southof Asuncion. Similarly the three collected by Carnierand analyzed by Goldschlag occur within a similarlyrestricted area near the Rio Apa in the north.The consistency noted with respect to the majorchemical constituents of these rocks appears to persistwith respect to the so-called trace elements, as shown intable 2. It is difficult to assess this consistency quantitatively,yet it is evident, especially when comparison ismade with data from the other rock t^^pes basaltic,diabasic, and alkalic which are discussed further on.The only marked enrichment, with respect to gold,copper, lead, and zinc, is in a pyritic rock from amineralized zone, near Caapucu (specimen P-31). Certainelements, namely barium and strontium, departwidely from the mean, but these are the only two thatdo." As with the chemical analyses, the inference fromthe consistency that does exist in trace elements, isthat these rocks are comagmatic, and presumably moreor less contemporaneous. Unless positive stratigraphicor other evidence can be adduced to the contrary,mapping these rocks as related in age appears tobe justified.The last two spectographic analyses of specimensP-lOla and P-lOlb are of interest in their obviousconformity to the others. They are of quartz porphyrypebbles or cobbles from the glacial till of the Tubaraoseries, of Penns\lvanian or Permian age. Their conformity,in respect to content of trace elements, with

26 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYthe other rocks shown in the table, suggests that theglaciers of Pennsylvanian or Permian time derived theirpebbles, or some of them, from outcrops of Precambrianrocks similar to those that are now exposed in southernParaguay and in the Apa region.GENEKAL FEATUKESThe entire eastern and southeastern side of Paraguayis blanketed by basaltic lavas. The name Serra Geralis adopted by Harrington (1950) and for this reportfrom current usage in Brazil (Oliveira and Leonardos,1943, p. 499). Of Late Triassic or Jurassic age, theserocks constitute the westerly fringe of the great basaltfield of the Parana basin, which, as Baker (1923) pointsout, covers an area of 800,000 square kilometers inBrazil, Paraguay, Argentina, and Uruguay, and isnearly as large as the Deccan and Columbia Plateaulava fields combined. Oliveira and Leonardos (1943)ascribe an even larger area to the Serra Geral lavas1.2 million square kilometers, of which 900,000 squarekilometers are in Brazil.The Serra Geral lavas are typical plateau-type basalts,with no known pyroclastic features or other evidenceof explosive activity; the consensus seems to be thatthe magma rose quietly along fissures in various partsof the basin. They may possibly be related to thedikes, flows, and other bodies of basic alkalic igneousrocks that occur in other parts of Paraguay. Evenmore probably, they may be closely related to theintrusive diabasic rocks that are known in a number ofplaces.The only exposures of the Serra Geral lavas thatwere actually examined by Eckel are in the valley ofthe Rio Parana, near the town of Foz de Iguagu (spelledIguassu on Paraguayan maps and either Iguassii orIguazii on Argentine maps) on the Brazilian side ofthe Parana. This small port town is the gateway tothe Brazilian Parque Nacional de Iguagu that surroundsthe spectacular cataracts on the Rio Iguaguand which are also called Foz de Iguagu on some maps.To avoid confusion, the falls are here called the "Iguagufalls" whereas the name "Foz de Iguagu" refers to thetown, which is about 20 kilometers west of the fallsand, as its name implies, is near the mouth of the RioIguagu.The specimens collected by Eckel at Foz de Iguagushow an alkalic character that may possibly be anexceptional feature of the Serra Geral lavas. Oneother specimen of the Serra Geral rocks, specimen P-14,from about 200 kilometers southwest of Foz de Iguaguwas also obtained and is described on p. 30.A good idea of the extent and geomorphologic characterof the basaltic terrain in the uplands was gainedby air views along several flight lines. The distributionof the lavas shown on plate 1 is probably moreaccurate than that of most other map units becausethe streams that drain the lava-covered areas followangular courses that are almost certainly controlled bytwo or more intersecting joint systems in the underlyingbasalt. By interpreting stream forms as shownon air photographs and on large scale base maps it waspossible to add appreciably to the detail of the map byHarrington (1950) without direct field observation.Although the characteristic stream drainage pattern islargely lost on a map at the scale of plate 1, it is clearlyshown on the 1:500,000 scale U. S. Air Force chartsfrom which plate 1 was compiled; on these charts thereis an abrupt change in the pattern of virtually everystream as it leaves the sedimentary rocks farther eastand enters the lava-covered area. The westerly contactof the lavas, therefore, is drawn to connect thesechanges in stream pattern.The Serra Geral lavas once extended fai west andsouth of their present outcrops in the northern pampasof Argentina. This is shown by their discovery inseveral deep borings in Santiago del Estero andSanta Fe provinces. Within Paraguay, however,it seems probable that the lavas never extended muchfarther west than is indicated by their present distribution,taking account of the few outliers that lie west ofthe main body. That they never reached the GranChaco region is clearly indicated by the absence ofbasalt or basaltic debris in any of the five exploratoryholes that were drilled there. Moreover, even thoughthe lavas are rather deeply weathered on the uplandswest of the Rio Parana, they are far more resistant toerosion than most of the sedimentary rocks. It seemsreasonable to suppose, then, that if they ever coveredthose rocks west of their present outcrop they wouldhave protected the latter from erosion to the presentday.The lavas, called trap, dolerite, basalt, diabase,melaphyr, and other terms by various authors, rangefrom andesite and augite porphyrite to typical limburgitewith abundant olivine (Baker, 1923); in Paraguay,judging from published accounts, basalt with little orno olivine (tholeitic basalt) appears to be the predominantkind.As seen in the vicinity of Foz de Iguagu (figs. 19 and20), individual flows range from less than 1 to 4 metersthick; at Iguagu falls, a few kilometers east of the town,some flows are 10 or more meters thick. The rocks inthe different flows vary widely in appearance, but thisis due more to differences in structure and porosity thanto composition. Many, if not most, flows are stronglyamygdaloidal, others are massive, and a few show

IGNEOUS AND METAMORPHIC ROCKS 27FIGURE 19. Typical terrain, exposures, vegetation, and culture of Serra Qeral basalt region in extreme eastern Paraguay. View westward across RioParana from point near Fez de Iguacu, Brazil.FIGUBE 20. Serra Geral465871 59 3between high and low water levels of Rio Parana. View down river from Fez de Iguacu, Brazil. Paraguay ison the right bank.

28 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYswirled flow structures that resemble pillow-structures.All the flows seen are dark brown to black and aredense glass with sparse small dark phenocrysts. Amygdaloidalfillings and irregular discontinuous veinletsconsist of dull- to bright-green chlorite and variouskinds of silica chalcedony, agate, carnelian, opal, andclear to pale amethystine quartz crystals. Otherauthors have also recorded calcite, zeolites, native copper,and copper carbonate minerals in the amygdules.There is little doubt that copper minerals do occur inthe basalts in places, but it also seems probable thatmost of the recurrent reports of discoveries of richcopper deposits in the lava-covered parts of southeasternParaguay are based on misidentification of the greenchlorite that characterizes many flows.Structure sections drawn across the lava-coveredarea, such as sections A-B and C-D, plate 1, suggestthat the total thickness of lava in southeastern Paraguayis not much more than 200 meters. This figure is basedon assumptions that the lava dips very gently towardthe southeast and that comparatively little lava hasbeen removed by erosion. In the valley of the Paranaat Foz de Iguacu, where neither top nor bottom isexposed, there is a little less than 100 meters of lava.Farther east, in Brazil, the entire series is generally atleast 400 meters thick and locally as much as 800 meters(Gordon, 1947, p. 15).The lavas rest on red beds of the Misiones sandstone.Conradi (1935) gives an excellent description of theirregularity of the contact between lava and sandstonein the vicinity of Pedro Juan Caballero and of themetamorphism of the sandstone there. Several authorsincluding Washburne (1930) and Gordon (1947) mentionthe fact that beds of sandstone are interlayeredwith the lava flows, and are more numerous towardthe base of the lava series than near its top. Such interlayeringwas not observed by Eckel, nor by Baker(1923), who examined the lavas along the entire lengthof the Parana valley; Baker believes that interlayeringmay be confined to the edges of the Parana basin butWashburne describes and pictures some of the red bedsat Salto del Guaira. Whether the interlayering is dueto intrusion of sills among the red beds, or to alternatingdeposition of red beds and surface flows is not known.Unless the small body of sedimentary rock along theParana valley and northeast of Encarnacion is ofCretaceous age, an unlikely possibility that is discussedin the section on the Misiones sandstone, the SerraGeral lavas are not covered by younger rocks anywherein Paraguay. They are, however, overlain by continentalsediments of the Caina formation age in adjacentparts of Brazil. The Caina, which is very similar tothe underlying Botucatu (Misiones) sandstone, hasbeen shown by Scorza (1952) to be of latest Triassicor earliest Jurassic age. It is possible that similarsediments once overlay the lavas in Paraguay, thoughBaker (1923) presents fairly convincing evidence thatover most of the Parana basin the lavas have beenexposed to erosion ever since their deposition.Since the Serra Geral lavas rest on beds of Triassicage, and are overlain in Brazil by Late Triassic orEarly Jurassic age, the lavas themselves are quiteprobably also Triassic. Washburne (1939), Oliveiraand Leonardos (1943, p. 500), and Harrington (1950)incline toward this view, but Baker (1923), Gordon(1947) and others consider them to be possibly or probablyJurassic. Even though the work of all these writersantedated that of Scorza (1952), who determined theage of the overlying Caina, it seems safest here to assignthe lavas to the Upper Triassic or Jurassic.The only good exposures of the Serra Geral lavasin Paraguay, known to the author, are along the RioAlto Parana and the lower reaches of some of its tributaries.Elsewhere the lava is weathered to depths of3 to 8 or more meters to a chocolate-red clayey butcrumbly soil; close to the surface even the chloriticand chalcedonic amygdule fillings have disappeared.The resultant deep soils support luxuriant vegetationeverywhere and form, incidentally, the best coffeegrowinglands in both Paraguay and southern Brazil.The valleys of the Parana and its tributaries tend todevelop steplike profiles, both in longitudinal and transversedirection, due to differences in erodability of theflows. Except at major waterfalls, however, such asGuaira, Iguacu, and the smaller ones on the Nacundayand Monday rivers, the steplike pattern is not generallydiscernible on casual inspection.The 30-meter zone between high and low water onthe Parana is a good field for study of erosion of resistantvolcanic rock by slow-moving, relatively clearwater. The Parana carries remarkably few tools forerosion (silt, sand, or larger size pebbles), no doubtbecause the dense vegetation prevents active erosionof the deep soils. Yet the river has, since Jurassictime, carved a gorge several kilometers wide and 100to 200 meters deep into the lavas. The dominantmeans of downcutting appear to be constant removalof chemically weathered rock by running water andabrasion by the little sand and silt carried by the stream.There are pot holes and undercut notches in someplaces (fig. 20), but they are rare. Angular blocks ofrock tend to remain on the river bed close to theirsource, and there are almost no boulders, cobbles, orother large cutting tools. In many places the rocksurfaces are beautifully etched, as if by a wire brush,and are evidently abraded by fine sand.

IGNEOUS AND METAMORPHIC ROCKS 29PETEOGEAPHY OF THE BASALT AT FOZ DE IGUA£TJ, BEAZILThe basalt from near the town of Foz de Iguacuappears to be somewhat variable lithologically, asindicated by the several specimens collected by Eckel.Conditions during crystallization, that resulted invariations in color of the rock from gray to brown andthe action of hydrothermal solutions during the laterstages of crystallization of the magma are reflected invariations that resulted in formation of vugs andreplacement of rock by quartz-chlorite aggregates.Whether this variation is a special feature of the Foz deIguacu locality, revealed by the abundance of unweatheredexposures, or whether the Serra Geral lavas lesswell exposed elsewhere would show comparable diversity,is not known.A vuggy type of rather coarsely crystallized basalt(specimen P-92a) is shown in figure 21. There is anoteworthy amount of pseudobrookite as a result ofthe action of hydrothermal solutions acting on theilmenite of the basalt (specimen P-92, figs. 22 and 23).The pyroxene of this rock is almost completelyreplaced by opaque black oxide, perhaps ilmenite,FeO-TiO2 . However, immediately adjacent to the vugswithin the chlorite-chalcedonic quartz lining, thisblack oxide is mantled and in some places completelyreplaced by bright-golden-yellow prismatic pseudobrookiteFe2O3-TiO2. This mineral characteristicallyhas slight, hardly perceptible pleochroism and brilliantlow-order (0.030±) interference colors, is biaxial andoptically positive, and has negative elongation.The conversion of ilmenite to pseudobrookit e is thus:2FeO.TiO2+Fe2O3+O^2Fe2O3-TiO2 or 3FeO-TiO2+Fe3O4+20-^3Fe2O3 -TiO 2, and ilmenite is commonlyassociated with magnetite or hematite in basaltic rocks.Ramdohr (1950, p. 735-736) observesSo far, pseudobrookite is known almost without exception as agaseous alteration product in titanium-rich magmas, in opencavities, intergrown therein with hematite; and, very rarely,as a constituent mineral of foyaite-pegmatite. In the first case,it is formed indirectly or directly from titanomagnetite, throughoxidation at the temperature of hot fumaroles (e. g. AranyerBerg, Thomas Range, and Katzenbuckel), thus: 3FesO4+FeTiO3+20-»4Fe2O3-!-Fe2TiOs . Apparently, the hematite thusformed may often be removed.He also notes that pseudobrookite is easily producedby heating ilmenite and hematite in air.Fries, Schaller, and Glass (1942) list 15 occurrencesFIGURE 21. Brown moderately fine grained vuggy basalt (specimen P-92a) from Foz de Iguagu, Brazil. Well-formed calcic plagioclase phenocrysts,/, in amatrix of apparently similar but rather turbid feldspar. The black areas are pyroxene almost completely replaced by black iron oxide. Two large vugsare shown in the upper half of the illustration, with a lining, 1, of chalcedonic quartz and pale-green chlorite. Pseudobrookite is formed around thesevugs. X 15. Crossed nicols.

30 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 22. Basalt (specimen P-92) from Foz de Iguacu, Brazil, showing a core of ilmenite, i, with a hull of pseudobrookite, ps. X 300.of pseudobrookite: all but two of them are in extrusivevolcanic rocks in cavities and on fissure walls.Other vugs are lined or filled: some with a darkgreenmicaceous mineral, others with a brown micaceousmineral accompanied by microscopic "dogtooth"calcite crystals. Both of these platy mineralswere studied by their X-ray diffraction pattern byJ. M. Axelrod. He found the pattern of" the darkmineral to resemble that of nontronite or saponiteFe2 (OH) 2SiO4O10-nH2O or 9MgO-Al2O3-10SiO2.16H2O(approximately) and that of the brown substanceto be mainly similar but also with a 7A spacing that may bechlorite, a kaolinite group mineral, or serpentine.A fine-grained phase of the basalt (specimen P-92b),which presumably chilled early and thus was imperviousto hydro thermal solutions, is shown in figure 24.The relations of the basalt to the replacing quartzchloriteaggregate are shown in specimen P-92, figure25. Basalt is shown at the bottom of the photograph,with a bordering phase of incompletely absorbedbasalt. Several partly assimilated basalt fragmentsare seen in the quartz-chlorite area. The basalt awayfrom, the contact appears to be normal olivine basalt,the brown olivine often being completely altered toiddingsite, although the pyroxene and calcic-plagioclaseis unaltered. The light-gray turbid areas of the illustrationconsist essentially of almost isotropic finegrainedchalcedonic quartz and light-green chlorite,with scattered pyrite and bright-red hematite. Theclear areas are quartz and radial chalcedony, containingabundant extremely minute long fibers, which may berutile or, possibly, pseudobrookite. A small group ofsuch, much larger than usual, are seen in the upperright center of the photomicrograph.CARMEN DEL PARANACarmen del Parana is 200 kilometers southwest ofFoz de Iguagu. It was not visited, but a representativespecimen (P-14) from, this locality was studied. Therock is quartz basalt, with amygdaloidal cavities, somelined with bright-green chlorite and filled with calcite,others with chlorite and quartz. The rock, believedby its owner to be copper ore, contains little if anycopper; the conspicuous green "copper staining" isceladonite or a related chloritic mineral. Microscopically,the spherical cavity shown in figure 26 consistsof chlorite with quartz. Irregularly shaped quartzparticles, usually with chlorite, are strewn about. Thedarker areas are green chlorite, the white are quartz.

IGNEOUS AND METAMORPHIC ROCKS 31DIABASEThroughout central Paraguay there are smallerbodies of diabase and similar rocks, mostly in the formof dikes, but including some flows and sills. Theknown bodies are shown on plate 1, but it seems probablethat there are still many others that have not beenreported. Because of their petrologic and chemicalresemblance to the Serra Geral basaltic lavas, as wellas of their suggestive geographic distribution, they arebelieved to be genetically related to the Serra Geralrocks and of approximately the same age.CORDILLERA DE LOS ALTOSSeveral dikes of diabase are known in the southernpart of the Cordillera de los Altos, the eminence, madeup principally of sandstone of the Caacupe series, thatforms the east edge of the Ypacarai depression.Two dikes, each trending eastward, are exposed alongthe road that connects Paraguari and Piribebuy withthe main paved highway east of Caacupe. Severalother northward-trending dikes are indicated in thisarea on plate 1. Mapping of the dikes is based entirelyon lineations seen on aerial photographs; these lineationsmay represent faults or dike& of some other kindof rock than diabase.Of the two dikes exposed along the road, one (specimenP-18) is about midway between Paraguari andPiribebuy. It strikes N. 45° W. and dips 75°-80° NE.It is about 4 meters thick, and it cuts massive, crossbeddedsandstone that dips 15° SE. It can be tracedseveral tens of meters toward the northwest, but apparentlyends abruptly at the road, for it cannot betraced to the southeast, even though rock exposuresthere are relatively good.The second dike (specimen P-37) is about 3 kilometersnorth of Piribebuy and is exposed in a smallroadside quarry. The country rock is the white saccharoidalsandstone unit of the Caacupe series that herestrikes due east and dips 10° S. The dike also strikesdue east and is vertical. It is 12 meters wide and ofunknown length; the sandstone wall rocks are sheared,slickensided, and strongly impregnated with iron oxidesfor about 4 meters on each side of the dike.The fresh rock (specimen P-37) is extremely toughand hard and contains numerous brown glassy subhedraland euhedral crystals of augite or olivine asFIGUEE 23. Basalt (specimen P-92) from Fez de Iguacu, Brazil, showing core of augite, a, incompletely replaced by ilmenite, i, withabundant pseudobrookite, ps. X 300.

32 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 24. Basalt (specimen P-92b) from Foz de Iguacu, Brazil. A fine-grained dark-gray dense rock, similar to that in figure 21, but not vuggy andmuch finer grained. The pyroxene (olivine?) appears to be orthorhombic (parallel extinction), and occurs as sparse porphyroblasts, p. The groundmassconsists of calcic plagioclase with abundant minute yellowish prisms of monoclinic pyroxene (strongly inclined extinction), and opaque blackore grains. The pyroxene (olivine?) is largely replaced by brown biotitic material. X 20.much as 1 centimeter in diameter, in a relatively finegrained groundmass. Alteration, due to weathering orother processes, has proceeded deeply along all jointsseen, so that the fresh rock is confined to nearly perfectspheres, 5 to 30 or more centimeters in diameter, surroundedby brown fibrous iron oxides and silicates andby red and brown clay minerals.As shown in the illustration (fig. 27) the rock is adiabase showing the characteristic texture; mineralogicallyit consists essentially of calcic plagioclase andaugite. No olivine or quartz was observed in thethin section.The effects of layering in a large diabase body mayproduce striking differences in composition; thus theabsence of olivine or quartz in the specimen studied byno means precludes their presence in lower or higherhorizons, respectively.OTHER OCCURRENCES OF DIABASEGoldschlag (1913a, p. 28) describes a coarse-graineddiabase from Arroyo Bolas-cue, a small stream 12 kilometerssouthwest of Caaguazu, on the road to Villarrica.It is a green to black rock that weathers to brown andconsists principally of macroscopic crystals of andesinelabradoritefeldspar and augite, with minor amounts ofmagnetite, apatite, and serpentine. No analysis isgiven.Olivine diabase caps the sandstone beds that make upCerro Domingo and Cerro Alberto, two of the peaks ofSierra Ybyturuzu, a part of the Cordillera de Caaguazuthat is also known as Sierra Villarrica, east of Villarrica;there is also an anrygdaloidal diabase on Cerro Domingo.Goldschlag (1913a), whose analyses are givenin table 3, describes the olivine diabase at the latterlocality as made up of visible crystals of albite-twinnedandesine-labradorite, with augite and olivine; accessoryminerals are apatite, zircon, and magnetite. Theamygdaloidal rock, whose cavities are filled with quartz,chalcedony, and zeolite (chabazite), contains crystalsof oligoclase-andesine feldspar, augite, and olivine in aglassy groundmass.With the Cerro Domingo diabase Goldschlag describesan amygdaloidal phase with chabazite. Thediabase overlies sandstone, which is found as xenolithsin the diabase.Carnier (19 lie) and Goldschlag (1913a) also describe

IGNEOUS AND METAMOEPHIC ROCKS 33a diabase porphyrite from Cerro Howyi. This hill isnot shown by name on recent maps, but from Carnier'sdescription it appears to be a prominent conical hillabout half way between Yataity and Coronel Martinez,west of Villarrica. It contains phenocrysts of augite,olivine, and feldspar as much as 0.5 centimeters long ina glassy groundm.ass that contains smaller crystals offeldspar, brown hornblende, magnetite, and apatite.The chemical analysis of this rock is given in table 4.OLIVINE BASAIT NEAR ASUNCIONThick layers of columnar basalt characterized byprominent phenocrysts of olivine cap Cerro Tacumbu,on the south edge of Asuncion; Cerro Lambare, a fewkilometers south; and several other hills both northeastand southeast of the city. Most of these deposits arequarried extensively for building and paving stone.They appear to be remnants of a once-extensive lavaflow, but the fact that similar basalt has been found inseveral deep water wells in Asuncion indicates that thebasalt may be, at least in part, intrusive and sill-like inform, rather than wholly extrusive.Milch (1895) described the rock on Tacumbu as afeldspar-free olivine basalt or limburgite. The rock isdense dark brown to black, with many large phenocrystsof olivine and some of augite and magnetite.The olivine phenocrysts, some showing rapid growth inone direction, are colorless to light green and very fresh,with only a little iron hydroxide on some fracture planes.Some crystals are homogeneous olivine, but others containgreater or smaller amounts of magnetite and glassas inclusions. The augite phenocrysts are generallylarger than those of olivine. They are light in color,hence, only slightly pleochroic; zonal structure is clearlyrecognizable. The groundmass consists of augite crystalsvery irregularly distributed through glass. Theaugite forms stubby prisms as well as angular androunded grains; with magnetite it tends to rim thephenocrysts. Some of the glass is entirely free of inclusionsbut elsewhere it is filled with thin small greenor colorless prisms and needles. Some of these crystalsare believed b}T Milch to be feldspar, but they are sofew that the rock is designated as essentially feldsparfree.Harrington (1950) also briefly describes the basaltson Cerro Tacumbu and Cerro Lambare, in particularemphasizing the amygdular character and absence ofolivine (at least macroscopic) in the latter place.__,FIGURE 25. Basalt (specimen P-92) from Foz de Iguacu, Brazil. Shows basalt dissolved in chalcedony-chlorite vein material. X 20.

34 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 26. Serra Geral basalt (specimen P-14) from near Carmen del Parana is quartz basalt with bright-green chlorite, c. Light areas are quartz, g.Other vesicles (not shown) are filled with calcite. X 20."PSEUDOTBACHYTE" NEAR ABEGUA AND LUQUEOn the hills south and west of Aregua there are severalsmall bodies of arkosic sandstone that, in both externalappearance and in geologic relations, closely resembletrachytic igneous rock. At least one similar body isreported near Luque. The deposits are so unusual thatthey deserve mention here, even though their origincannot be explained.The body that crops out on a small hill just south ofthe main road to Aregua, and about 2 kilometers southof the town is representative. There, several smallquarries have been opened to remove "pseudotrachyte"for use as building stone material in walls, walks andthe like. The country rock is red Misiones sandstone ofTriassic age that strikes N. 60° W. and dips 36° SW.The pseudotrachyte is interbedded with the sandstonein a layer about 2 meters thick. This layer is strikinglycharacterized by perfect columnar jointing similar tothat in columnar-jointed basalt flows except that thecolumns are parallel to the bedding rather than normalto it. The individual columns, some as much as 3meters long, range from 4 to 15 centimeters in diameterand have from 5 to 8 smooth, sharply denned sides.On and near their surfaces they appear to be made upof small quartz grains set in a matrix of finer quartzgrains and white clay. The interior parts of the columns,however, are fresher and have the megascopicappearance of dense light-colored igneous rock in whichquartz, pink and white feldspar, and a little biotite canbe distinguished. Under the microscope, however, therock is seen to be unquestionably arkose, consisting ofsubrounded to angular grains of quartz and feldsparembedded in a turbid feldspathic matrix. Undercrossed nicols the quartz grains are seen to have growninto the matrix, each grain being surrounded by a turbidouter zone in parallel optical orientation.More study is needed to determine the characterand origin of this rock. It may represent a clasticintrusive sill or it may merely represent local metamorphismof the sedimentary rocks by some of thenearby basaltic or diabasic rocks.ANALYSES OF SERE A GEEAL LAVA AND EELATED EOCKSChemical analyses of a specimen of the Serra Geralbasalt from Foz de Iguacti, as well as of four chemicallysimilar rocks, are shown on table 3. Spectrographicanalyses of the Foz de Iguacu rock and of two of thealkalic rocks from Mbocayaty (p. 44), are given in

GEOLOGICAL SURVEY PROFESSIONAL PAPER 327 PLATE 2SKETCH OF AN EXTINCT VOLCANO NEAR ACAHAY, SOUTHERN PARAGUAYDrawn from air photographs.

IGNEOUS AND METAMORPHIC ROCKS 35FIGURE 27. Diabase (specimen P-37) on the road north of Piribebuy showing characteristic holocrystalline aggregate of calcic plagioclase,/, and augite,py, with magnetite-ilmenite, m-i. X 15. Crossed nicols.TABLE 3. Chemical analyses of Serra Geral lava and related rocksof ParaguaySiO 2____A1.03Fe2O3____. _ _ ...FeO _____________MgO_ ...........CaO ____ ... _Na2O_ ....... .K20 _____________H20+ ... ..Ti0 2 __. ............CO 2_. _____________P 2OS .... ...MnO_... ___________Cr2O 3 _ __ .Density, _ _ .NormP-58a i51.2715.728.611.533.725.983.714.15.871.821.64.01.43.17.1899.812.73II-5-2-3P-92150.0512.955.798.204.258.382.50J.501.18.803.56.00.53.2599.942.81III-4-3-41 Spectrographic ai nalyses for trace elements made. Densities by L. N. Tarrant,U. S. Geological Survey.NOTE. See following table for explanation of field numbers.Field No.RockP-58a_____ Basalt, Acahay calderaA48.6312.4911.729.082.378.752.46.64.79.802.20.77100. 70II1.4-3-4B48.3810.4212.114.993.537.984.741.50.961.972.581.04Tr.100. 20m-5-1-4C49.659.2615.254.123.218.824.391.75.332.431.42.43101. 06III-5-1-4AnalystD40.9515.376.364.3810.4611.673.971.26.863.93.25.09Tr..10.1999.842.932III-6-3-4III-7-3-4Lois D. Trumbull, U. S. Geol.Survey.Lois D. Trumbull.Maurice Goldschlag.P-92 __... . B asalt, Foz de Iguacu, Brazil __A_. _______ 0livine diabase, Ce rro Domingo,Sierra Ybytu ruzu.B_________ 0livine diabase, Cerro Alberto, Maurice Goldschlag.Sierra Ybyturuzu.C.. . E iabase porphyrite, Cerro Maurice Goldschlag.Howyf.D_ __ Limburgite, Cerro Tacumbu_ ... Lindner (Milch 1905).465871 5£TABLE 4. Spectrographic analyses of Serra Geral lava and relatedrocks of Paraguay[Analyst: Paul R. Barnett, U. S. Geological Survey. Looked for but not found: As,Ag, Au, B, Bi, Cd, Ge, In, Pb, Pt, Sb, Sn, Ta, Th, Tl, U, W, Zn]BaBeCoCr. ... ...CuLaMo...Nb_PbSc_ -Sr_ ._____ _V ____________-ynZr_ -NOTE.P-58a0.20 .004.0005.005.002.01.0004.004.002.002.002.2.04.009.0002.03P-920.060 .004.003.03.0020.0005.005.005.002.004.09.05.008.0002.02See table below for explanation of field numbers.Field No.P-58a__ __P-92__ .P 54dp-54g;::::Basalt (TertiarBasalt (Serra CNepheline syerShonkinite (an riteRockP-54d0.20 .002.002.005.002.020 .008.001.003.001.3.02.006.0002.07LocalityP-54g0.20 .004.04.005.002.010.005.03.003.002.2.03.005.0001.04Acahay caldera.Foz de Iguacu, Brazil.Mbocayaty.Do.table 4. Analyses of basalt from the Acahay calderaare included in both tables.Five of the six analyses of basalt and related rocksshown in table 3 are obviouslv similar, indicating; that

36 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYdespite the variation in names, the rocks are essentiallysimilar. The diabase porphyrite (proterobase) fromTagaruassu in Mato Grosso, Brazil, described by Goldschlag(1913a, p. 25) is also similar. The Acahay basalt(specimen P-58a), however, is chemically more relatedto the group of alkalic rocks discussed below. Further,both the shonkinite from Mbocayaty, and the phonolitefrom Centurion, are chemically similar to the fivebasaltic rocks. The spectrographic analysis (table 4)appears to confirm this relationship.All these rocks (and the alkalic types describedbelow) differ both in major and minor chemical relationshipsfrom the granitic-porphyritic Precambrianrocks. Whether any valid conclusions as to relation ofchemical similarities to age of the rocks are possiblecannot be said from the data at hand.ALKALIC ROCKS OF UNKNOWN AGEAlkalic rocks have been reported from many localitiesin Paraguay and nearby Brazil. One body of theserocks at Mbocayaty, was studied by Eckel and anumber of specimens from it have been analyzed(specimens P 54). A second locality of possibly alkalicrock that was visited is a mica-porphyry dike 10 mileseast of Villarrica (specimen P-50).The Acahay volcanic mass and a group of porphyriesand agglomerates from near Ypacarai are also describedhere, though from the scanty evidence at hand thesebodies appear to be complex and not all of the rocksassociated with them are alkalic.From the available data (Pohlmann, 1886; Carnier,1911, 1913; Goldschlag, 1913), it appears that atCenturion in the northern Rio Apa region and atMbocayaty, in the central region, there are verysimilar occurrences of alkalic rocks. Likewise, similarrocks occur at Cerro Ybytymi, part of the CerroApitagua (Hibsch, 1891), near Sapucai (Milch, 1895),and the Pao de Agucar region in Brazil, and adjacentParaguay (Lisboa, 1909; Carnier, 1913; Gerth, 1935;Oliveira and Leonardos, 1943).Data are not at hand for any satisfactory discussionof the alkalic rocks of Paraguay. The few analysesavailable leave uncertain what relationship may existbetween the undoubted alkalic rock types and thebasaltic rocks of Paraguay.The age of the alkalic rocks is not known. Someseem to be closely related geographically and petrographicallyto the Serra Geral lavas of Triassic orJurassic age and some of particularly youthful appearance,as parts of the Acahay body and the one atPao de Agucar, Brazil, are no older than Late Tertiary.All the alkalic rocks are shown on plate 1 as "ageunknown, possibly Triassic through Tertiary."NORTHERN AREAPHONOLITE AT CENTURIONGoldschlag (1913a) describes phonolite from theRio Apa region, 2-3 kilometers west-southwest ofCenturion. This probably is the "felsite porphyry"mentioned by Carnier (19lie) as occurring in thisgeneral vicinity. According to Carnier, dikes ofsyenite and felsite cut muscovite schist, metamorphicsandstone, and quartzite. This is the only reportedoccurrence of alkalic rocks in the Rio Apa region exceptfor the nepheline basalt and olivine kersantite describedby Pohlmann (1886).Goldschlag says that the phonolite near Centurionis bluish green, characterized in hand specimen byphenocrysts of pyroxene (as much as 1 centimeter long)and secondary zeolites. Under the microscope phenocrystsof aegirine augite, orthoclase and andesinelabradoritein poorly defined crystals, olivine partlyaltered to serpentine, and biotite are seen. Very smallcrystals of noselite, magnetite, and apatite are dispersedthrough a groundmass composed largely of feldspar.The groundmass is zeolitized; there is also secondarycalcite and part of it appears as well-formed crystals.Goldschlag's analysis of the rock is given in table 5(analysis C). It is evident from comparison withMbocayaty shonkinite (P-54g, table 5, analysis B)that the rock analyzed by Goldschlag is similar andthat the phonolite described by Milch from Sapucai(table 5, analysis D) is also a similar rock. Olivinekersantitefrom the limestone of Colonia Santa Mariadel Apa, was described by Pohlmann (1886); it isassociated with nepheline-basalt. Pohlmann does notdescribe the field relations, and no analysis is available.SYENITIC KOCK OF PAO de AgUCAR, BRAZILThe prominent Pao de Agucar is on the Brazilianside of the Rio Paraguay, just north of P6rto Murtinho,Brazil, and about 35 kilometers north of Puerto PalmaChica, Paraguay. It is included here because smallbodies of rock that appear to be related to it appearin Paraguay. The Pao de Agucar rises nearly 400meters abruptly from the river's edge; it is about5 kilometers in diameter. With steep sides and ajagged top, from the air it appears to be a relativelyyoung complex volcanic cone, not unlike the calderaat Acahay (p. 38), but considerably modified byerosion.Several much smaller and lower hills form theParaguayan bank of the river just southwest of thePao de Agucar. From the air they appear to belong tothe same rock mass, separated from it only by the riveralluvium. This mass of rocks is dated as post-Permianby Lisboa (1909, p. 51-53), as of probable Tertiary

IGNEOUS AND METAMORPHIC ROCKS' 37age by Carnier (191 Ic) as part of the Serra Geraleruptive rocks of Triassic age by Gerth (1935, pt. 2,p. 244) and as Triassic (Rhaetic) by Oliveira andLeonardos (1943, p. 99). The apparent youthfulnessof the cone strongly suggests a late Tertiary age.Carnier (1913) describes the Pao de Acucar asaugite syenite. Lisboa (1909, p. 51-53), however,says that it is made up principally of nepheline syenite(foyaite) with lesser amounts of augite syenite, bostonite,and phonolite. He characterized the mass as arelatively young volcano, but dates it only as post-Permian. He says that the nepheline syenite, whichforms the major part of the body, has a granitoidtexture and is made up mainly of orthoclase, nepheline,and acmite, which is nearly opaque and without crystalform. The augite syenite, which Lisboa says formsthe north part of the mass and extends into Paraguay,is coarse-grained, with anorthoclase the only feldspar.Biotite, with some acmite and magnetite, is abundant,and sphene is a very abundant accessory. Blackpyroxenes give the rock a porphyroid appearance. Henotes that this differs materially from the rock describedby Evans (1894) from the same locality. That rockcontained both orthoclase and plagioclase, as well ashornblende, augite, apatite, and sphene. Lisboa'sphonolite is a nearly black rock with fluidal texture.It contains large phenocrysts of orthoclase and rareones of nepheline and acmite in a fine-grained tospherulitic groundmass of the same minerals. Thebostonite is very fine grained, with trachytic texture.It consists of a microcrystalline aggregate of orthoclaseand prisms of pyroxene that are partly altered tomagnetite. Treatment with hydrochloric acid producesthe gelatinization characteristic of nepheline.There is confusion in some bibliographies betweenthis Pao de Agucar and a mountain of the same namein Departamento de Maldonado of southeasternUruguay; the latter is remarkably similar in compositionto the Brazilian Pao de Acucar on the banks ofthe Rio Paraguay (Willmann, 1915).CENTRAL AREAMilch (1895) describes limburgite from Cerro Tacumbu;an abstract of his description with analysis(Milch 1905) is given in the section of this report onthe Serra Geral lavas (p. 33) but the rock may possiblybelong with the alkalic rocks.NEPHELINE BASALT AT YBYTYMfAccording to Hibsch (1891), the top of Cerro Ybytymi,south of the town of that name, is made up of nephelinebasalt. The exact location of this hill is not known,but the rock is doubtless a part of, or closely related to,the elongate body of alkalic volcanic rocks shown onplate 1 as Cerro Apitagua. The mapping of thisrelatively large body, incidentally, is based on interpretationof aerial photographs and on the twodescriptions by Hibsch and Milch. The igneous rocksmay cover less of the area than shown on the map,but the entire area appears to be nearly homogeneouson the photographs. The rock described by Hibsch isdark gray to black, with brown weathered surfaces;it is porphyritic, with phenocrysts of augite and cavitiesfilled with zeolites with radial structure. Microscopically,it is seen to be made up of phenocrysts ofaugite and olivine in a groundmass that containsgrains of magnetite, small crystals of augite andmagnesian mica, nepheline, and sanidine.PHONOLITE FROM SAPTJCAIA sample of phonolite described by Milch (1895) camefrom a railroad cut through a ridge at or near the townof Sapucai. The size or character of the rock bodyfrom which it came is not known, but it is almostcertainly related to the large body of alkalic rocksthat make up Cerro Apitagua and vicinity. Milchdescribes the rock as yellow brown, compact, andmarked by phenocrysts of a dark mineral in thickprisms. Biotite, hornblende, and aegirine-augite alloccur as phenocrysts, but they are much less abundantthan sanidine, a member of the hauyne-nosean family,and nepheline. All the phenocrysts are obscured byalteration weathering, resorption, and zeolitization.The groundmass consists of aegirine-augite, with someaegirine, small prisms of feldspar, small grains of ore;and an aggregate of decomposition products that includezeolites, carbonate, and iron ore. The alkalifeldspar sanidine is the chief constituent of the groundmass.It appears as long prisms which ramify astrichites. This structure, together with the almostcomplete zeolitization of the nepheline, gives a trachytoidappearance to the rock.In 1905 Milch published an analysis of this rock,(see p. 47, table 5, D). Washington (1917, p. 905)lists the rock as altered by weathering, a reasonableinference from the nearly 4 percent H2O, and 1 % percentCO2 . Milch likewise mentions the weathering ofthis rock. Nevertheless, a norm has been computed,which (1-6-2-4) places the rock with other nephelinesyenites and phonolites in Washington's tables.MICA PORPHYRY FROM EAST OF VILLARRICAThe mica porphyry (specimen P- 50) occurs as a dike,4 meters thick, trending N. 25° E. in sandstone nearthe base of the Independencia series; locally it spreadsout as a thin sill along a bedding plane in the sandstone.It does not resemble any of the other specimens fromParaguay, but because of the highly alkalic composition

38 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYof the rock it is grouped with the alkalic rocks. Super­ 'ficially it resembles the "weathered peridotites" thatare known from Ithaca and Syracuse, N. Y., Pennsylvania,Kentucky, Illinois, and elsewhere, but microscopicallyit is seen to contain no mafic mineral otherthan biotite.This specimen is a dull-reddish-gray rock, withabundant large conspicuous plates of golden-yellowmica. The plates have almost a metallic lustre, andare as much as a centimeter across, with hexagonaloutline. The matrix is fine grained, and has an earthyaspect.Despite the seemingly advanced decomposition ofthe rock, a thin section shows a fairly recognizablemineralogy. The alteration observed seems more of ahydrothermal nature than simple weathering. However,mechanical effects crumpling of biotite platesare evident too. The rock consists essentially ofpotassic feldspar (sanidine?), some of it radiallycrystallized, with what appears to be nepheline (verylow birefringence, negative uniaxial), brown biotite inboth large ragged grains and fresh-looking sharplyeuhedral small plates (some showing zoning) and blackore grains. No chloritization of the biotite is seen.The photomicrograph (fig. 28) shows an area ofsanidinic(?) feldspar with nepheline (?) in the rightcenter of the field. Upper center is a large biotitegrain, peripherally replaced by a black oxide aggregate.The dark gray is largely altered mica; the black representsore particles.BASALT, RHYOLITE, AND SCORIA OF ACAHAY CALDERAThe Acahay volcanic cone or caldera, 7 kilometersnorthwest of the town of Acahay (pi. 1), is a prominentfeature of the landscape in southern Paraguay. It isrudely oval in plan, with a maximum diameter of 5 to6 kilometers. Its base is about 200 meters above sealevel and the highest point on its southwest rim is 500meters in elevation. A sketch, (pi. 2) drawn fromphotographs, shows the shape of the body. Thisbody was not visited by Eckel, but it was observedfrom the air, and the rocks are doubtless related to, ifnot identical with, the flow rocks seen on the roadbetween Carapegua and Acahay, and also those betweenParaguari and Carapegua.The mass has the tj^pical form of a volcanic caldera,with a large central crater, steep sides, an irregular rim,and several flows and dikes that radiate from the vol-FIGUEE 28. "Mica porphyry" (specimen P-50) found 16 kilometers east of Villarrica. Photograph shows rather obscurely crystallized aggregate of alkalicfeldspar, /, and biotite, 6, with abundant opaque grains of iron oxide, o. X 20.

IGNEOUS AND METAMORPHIC ROCKS 39came pile itself. The shape may be due to erosion ofa single volcanic cone, but it seems more likely to havebeen formed as a series of more or less coalesced cones,since dimly seen flow structures along the rim appearto be related to individual cones. No ash or cinderswere seen, but in at least two places along the Acahayroad there are exposures of red to black scoria.The plains east and northeast of the volcano aredotted with smaller cones and a number of dikes canbe seen on aerial photographs.The age of the Acahay volcanism is not known, but itmust be relatively young. The Acahay volcanic pileitself, as well as the smaller nearby cones, are so typicalin shape that they could not have been greatly eroded.Moreover, except for a little soil that supports smallfarms in the crater of the volcano and along its outerslopes, all the volcanic rocks seen in this area are veryfresh, even at the surface.Another bit of evidence that strongly indicates theyouthfulness of the volcanism is that the flows andcones are related to the present topography in valleysor on broad plains that could hardly have survivedsince Triassic time.Harrington (1950, p. 43) refers briefly to this occurrencein his description of the "necks and small plutonsin the Carapegua-Ybycui-Quiindy district," and notesthe presence of "granular phanerocrystalline faciesgabbros, syenites, or basic diorites" besides the dominantdark olivinc basalt.Three specimens collected from the outer fringes ofthe volcanic cone, along the road between Carapeguaand Acahay, represent three different rock types. All,however, are such as have been observed in manyplaces in connection with basaltic eruptions: basalticrock proper (P-58a), rhyolitic agglomerate (P-58b) andscoriaceous material. The first two may be flows, thethird ejected material.The basalt is illustrated in figure 29. It is a finegrainedbrown rock, with few if any phenocrysts. Microscopically,it is an even textured aggregate of minutepale-green pyroxene and opaque iron oxide in a groundmassof sodic plagioclase, with a few porphyritic iddingsitizedbrown olivine crystals. Some of the groundmassmay be glass. It resembles the Serra Geral basalt fromthe Foz de Iguacii, Brazil, referred to Triassic or Jurassicage.A rhyolitic agglomerate (specimen P-58b) that occursin the vicinity of the Acahay caldera, along the roadFIOUBE 29. !(specimen P-58) from flow just east of the Acahay caldera. Photomicrograph shows uniform fine-grained texture, with sparse alteredolivine (?) hi upper left corner. X 20.

40 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYnorth of Acahay, is a fine-grained dark-gray rock, withminute quartz veinlets, reddish spots and a little pyritevisible with a hand lens. The weathered surface isbleached white to a depth of 1 centimeter. Close to thenorth edge of the town there are exposures of redbasaltic scoria also.Microscopically, the agglomerate is seen to be a siliceousrhyolite agglomerate. Anhedral quartz and sodicplagioclase phenocrysts are enclosed in a micro crystallinefelsic aggregate (fig. 30).The chemical analysis of this rock, specimen P-58b,table 1, resembles those of the Precambrian granite, porphyry,and aplite. The question naturally arises as towhether this is another instance of the commonly observedassociation of basalt and rhyolite or merely aspatial association of two unrelated rocks. If theformer is true, then the rhyolite would be contemporary,broadly speaking, with the Acahay basalt, and thereforefar younger than the Precambrian age attributedto the other granitic and rhyolitic rocks of Paraguaydiscussed in this report. Field studies should decidethis.PORPHYRY AND AGGLOMERATE FROM THE YPACARAI HIGHWAYQUARRYThe quarry that yielded most of the rock for thepaved highway between Asuncion and Eusebio Ayalais just east of the railroad and about midway betweenYpacarai and Pirayu. Though mapped as a singlebody of igneous rock on plate 1, there are actuallyfive small rounded knolls, each appearing to be geologicallycomplex. The knolls are rudely circular in planand range from 200 to 1,000 meters in diameter. Theyrise only 10 to 50 meters above the swampy plain of theYpacarai depression.Only the easternmost knoll of the cluster (the one onwhich the quarry was opened), was examined by Eckel,but, from nearby ground and aerial observation theother four appear to be similar in shape and geologicmakeup.The quarry, part of which is shown in figure 31, isnearly circular, with an irregular floor. It is about 100meters in diameter and 10 meters deep along its western,or highest, edge.The dome-shaped hill consists of black to brownshale, siltstone, and sandstone all intruded and brec-FIGUEE 30. Rhyolite agglomerate (specimen P-58b) from the Acahay caldera has a microprotoclastic texture with quartz, q, filling microscopic fractures.The dark patch, x, to the left is a xenolith. X 20.

FJGUEE 31. Panorama of highway quarry at Ypacaral. The rocks are largely rhyolite agglomerate, with muua ^ oreccia made up of altered sedimentary rocks in igneous matrix.

42dated by two kinds of porphyry. One kind, whichappears to be the older, is brown and contains muchglass, scattered small phenocrysts of pink feldspar, andmany small phenocrysts of dark-gray smoky quartz.The other porphyry is gray to black, with white feldsparsin a nearly black groundmass and with only afew phenocrysts of quartz. In thin section, however(figs. 33 and 34) the igneous rock (apart from xenolithicinclusions) appears to be essentially the same inboth the brown and the gray varieties.The sedimentary rocks are all very metamorphosedand very hard; even those that retain evidence of originalbedding contain veinlets and scattered crystals offeldspar. All the rocks, both igneous and sedimentary,are dense, tough and hard, and break with hacklyjagged fractures. Both kinds of porphyry containangular inclusions of metamorphosed sediments. Theseinclusions range in quantity from one to each cubicmeter of rock to intrusive breccia with only a little igneousmatrix cementing the fragments.These hills appear to represent the top of a smallcomplex stock, or possibly a group of small laccoliths,that broke through older sedimentary rocks, crushedsome of them, and converted others to igneous rockby partial replacement. The age of the igneous activityis unknown; the body is shown on plate 2 as belongingto the alkalic rocks of Triassic(?) to Tertiary(?) age.This age assignment is based in part on certain similaritiesof these rocks with the agglomerate near theAcahay caldera (specimen P-58b) but in greater parton the fact that so far as can be determined now thehost rocks must belong to the Tubarao series hencethe intrusive rocks must be at least post-Permian inThe single sample of the Ypacaral igneous rocks thathas been analysed (specimen P-34, table 1) is muchcloser in chemical composition to the younger Precambriangranitic rocks than it is to any of the muchyounger alkalic rocks (see table 5). That the Ypacaralrocks may themselves be of Precambrian age seemsunlikely, however, because although the intruded sedimentsshow evidence of baking and other contact metamorphiceffects, there is no evidence whatever thatthis contact metamorphism has been superimposed onregional metamorphism such as would be expected ifthe sediments were of Precambrian age. The YpacaraiFIGURE 32. Rhyolitic-breccia tuff (specimen P-35) from the highway quarry at Ypacaral contains a conspicuous elongated cognate xenolith, x, andmany less conspicuous xenoliths: irregular chloritized hornblende areas, c, and partly resorted quartz crystals, q. Flow structures in the rock arearent. X 15.

IGNEOUS AND METAMORPHIC ROCKS 43agglomerate contains inclusions of sedimentary rocksand shows considerable evidence of replacement of sedimentsby igneous material; one would therefore expectgreat variability in chemical composition from onesample to another.The brown phase of the porphyry (specimen P-35)is a dark-brown dense rock, with red (not whitishgray)feldspathic and glassy quartz areas. It is fragmental,as seen microscopically, though this is not obviousin hand specimens. The photomicrograph (fig.32) shows an elongated fragment of very fine-grainedrock. The irregular dark areas are chloritized hornblende.Several embayed quartz phenocrysts may beseen, as well as flow structure in the rhyolite. Nearthe center are several strongly sericitized plagioclasephenocrysts (gray).The brown, relatively fine grained rock, such asshown in figure 32, grades into much coarser volcanicbreccia, with strongly contrasting fragments of finegrained,light- to dark-gray sandstone or siltstone,cemented by quartz rhyolite porphyry (specimen P-36,fig. 33).The dark phase (specimen P-34) of the porphyry isfine grained dark gray with whitish-gray feldspar andglassy quartz. Microscopically, it is seen to consistof andesine and quartz, with some chloritized biotitein a felsic groundmass. The feldspars are only slightlysericitized. The analysis of this rock is given in table 1.It is illustrated in figure 34.BASALT FLOW BETWEEN PARAGTJARI AND CAEAPEGuAThe broad grassy flat plains drained by ArroyoCaanabe, which heads not far from Ybytymi and flowswestward to the swampy land north of Lago Ypoa, isshown on figure 2 as underlain by basaltic flow rocks.This designation is based on observation of only oneexposure, supported to some extent by an interpretationof physiographic forms as seen in the field and inaerial photographs.Near a bridge on the main road between Paraguariand Carapegua, and about 4 kilometers northeast ofthe latter town, there is an extensive shallow quarryin basalt. In that vicinity the loamy cover of the plainis underlain at depths of 60 to 130 centimeters by alayer of basalt that is at least 5 meters thick. Locallythe top of this flow rock is dull red and scoriaceous, butmost of the rock is dense, dark gray to black, andcryptocrystalline.FIGUEE 33. Porphyry (specimen P-36) from highway quarry at Ypacaral. Photomicrograph shows rounded resorbed shate fragments, sh, and quartz, q,in rhyolite porphyry. X 20.

44FJGTJEE 34. Porphyry (specimen P-34), dark phase, from the highway quarry at Ypacarai. Photomicrograph shows partly resorbed quartz crystals, g,and slightly sericitized andesinic plagioclase, /, in rhyolitic groundmass. X 25.No other exposures of this rock are known in theextensive plain along the Arroyo Caanabe, but theuniformity of its virtually flat surface and of the vegetationgrowing on the plain suggests that the entirearea is, as mapped, underlain by basalt that is coveredby a thin mask of silty loam. This conclusion isstrengthened by the fact that several volcanic conesrise from the plain not far east of the Paraguari-Carapegua road; these and the nearby volcanic pilesof Acahay and Cerro Apitagua would seem to be likelysources for lava flows that moved westward down thebroad valley of Arroyo Caanabe to or beyond thelongitude of Yaguaron. No specimens were collectedso that it is impossible to state whether this basalt issimilar to the alkalic basalt (specimen P-58b) (p. 39),that came from closer to the Acahay caldera.NEPHELINE SYENITE AND SHONKINITE AT MBOCAYATYAn interesting assemblage of alkalic shonkinites, verysimilar to those in the Highwood Mountains of Montana,are exposed in a quarry at the northwest edge ofMbocayaty. The quarry is on a small rounded hill,about 25 meters high and 75 meters in diameter, thatstands above the nearly level plain cut on tillites andother sediments of the Tubarao series of Pennsylvania!!age. A fairly large quantity of rock has been quarriedfor road surfacing and rough building stone; most ofthe quarried rock apparently consisted of loose blocksthat had been separated from the main mass by weathering,but some shallow drilling and blasting was alsodone. Figure 35 shows one of the larger quarryopenings.The hill is made up of rocks that differ widely intexture, though all of them are shown by microscopicexamination to be alkalic rocks, such as nephelinesyenite, shonkinite, and closely related types. Themost abundant type is a dark-gray coarse-grained rock,containing clear green crystals of olivine that resemblesgabbro in the hand specimen. There is also muchmaterial that appears to be an intrusive breccia andcontains angular fragments of most of the textural typesfound on the hill. Smaller quantities of a spheruliticphase, and of an exceedingly tough rock made up ofcoarse interlocking crystals of sanidine in a dense blackgroundmass, are also to be seen. The relations of the

IGNEOUS AND METAMORPHIC ROCKS 45FIGURE 35. Quarry in alkaline rocks (mostly shonkinite) on the outskirts of Mbocayaty.different textures could not be deciphered on hastyexamination.Different parts of the rock body differ widely in theirdegree of weathering, but there is no apparent relationshipbetween weathering and the different texturaltypes. Some parts are almost completely disintegratedwhereas other parts are extremely fresh. Weatheringtends to proceed along the strong vertical and nearlyhorizontal joints that characterize the body; there issome tendency toward spheroidal weathering in places.There are no indications of the shape of the Mbocayatybody, but it appears most likely to be a plug orsmall stock, intruded into the surrounding beds of theTubarao series, that has suffered multiple injectionsof alkalic magma. No similar rocks were found elsewhereby Eckel, but several of the other small massesof igneous rock shown on plate 1 in the general vicinityof Mbocayaty are reported by highway engineers andothers to be similar in appearance to this material.Seven specimens, respectively P-54, a-g, were studiedand are described in order below. All except specimenP-54b are dark rocks; this one is light colored and resemblesa coarse porphyritic syenite. The others havea gabbroic aspect.P-54a, shonkinite. Specimen P-54a (fig. 36) is a coarsely crystallizedgabbroic-textured rock, with dark mafic patches strewnin feldspathic groundmass. The abundant mafic minerals, moreor less subhedral, are strewn in a groundmass consisting largelyof sanidinic orthoclase. It has replaced nepheline, which is convertedto the hydronephelite aggregates shown in figures 36 to42, inclusive. The replacement appears to be progressive, thefinal stage being the graphic structures shown in figures 36 and38. Apatite and ore grains are in the feldspar. The maficminerals include colorless (in section) olivine, brown biotite,pale-green titanaugite, and titaniferous amphibole related tokataforite. The latter is described in detail (p. 46), in connectionwith specimen P 54g, where it also was noted."Hydronephelite" is a rather ill-defined replacement of nephe­line. It is listed as a species by Dana (6th edition p. 609) andmore recently by Troger (1952). Dana lists it with ranite andspreusteiri. In Maine it replaces sodalite, in Norway, nepheline(Dana). Apparently it consists of natrolite, epiriatrolite, hydrargillite,and diaspore (Thugutt, 1932).P-54b, nepheline syenite. Specimen P-54b (fig. 37) is a rathercoarsely crystallized feldspathic rock, with dark sodic(?) augiteas the chief visible mafic. The feldspar laths are several millimeterslong, well shown on the weathered surface of the rock.The dark constituents are interstitial to the feldspar.Microscopically the rock has the features shown in figure 37 asfollows: coarsely crystallized orthoclase (sanidine?) comprisesthe bulk of the rock. Near the lower right corner a large blackgrain of iron oxide has hydronephelite (on the left of it) withrectangular outlines; it is uniaxial positive, with indices lowerthan feldspar and birefringence slightly higher; hexagonal crosssections show irregular triangular fields under crossed nicols.With it is green aegirine(?) augite (the smaller dark grains).Another large augite is seen at the middle right edge. Small

46 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 36. Shonkinite (specimen P-54a) from Mbocayaty. Note the large rounded hydronephelite, h, crystals at left. At the center right are "graphic"remnants of nepheline or hydronepheline, g, that have been partly replaced by sanidine. Light-green monoelinic pyroxene, p, showing good cleavage,and dark-brown biotite, b, are abundant; olivine, o, in the lower right edge, is enclosed in biotite. Pale-bluish apatite and black iron oxide are accessoryminerals. X 15.strongly pleochroic brown biotite grains, sphene, and apatiteare also present.P 54c, shonkinite. Specimen P 54c is similar to specimenP-54a, described above. Numerous olivine crystals are seenin figure 38 (just upper left of center, just left of middle loweredge, and elsewhere). Large pyroxene crystals, showing goodcleavage, are also abundant. In the middle of the left half ofthe field is a large crystal of hydronephelite. The white areasare sanidinic feldspar.P-54d and P-S4e, shonkinite. Specimens P-54d and P-54eare similar. Both are rather coarse-grained medium-dark rockswith prominent tabular feldspars. They are variants of specimensP-54a and P-54c and differ essentially in having no olivine,and very little titaniferous amphibole. Titaniferous amphiboleshows normal absorption in deep brown parallel to c, unlike thekataphorite amphibole found in the other rocks from thislocality. Specimen P-54d has been analyzed (table 5).Figure 39 (specimen P-54d) shows the abundant tabular(laths in cross section) feldspar, and titaniferous augite. Undercrossed nicols, many of the clear feldspars show turbid cores,indicating perhaps replacement of an earlier generation offeldspar.Specimen P-54e contains some analcite, with clear feldsparapparently replacing nepheline. Many of the feldspar crystalshave turbid inner zones.P-64f and P-S4g, shonkinite. Specimens P-54f and P-54gare similar, and differ from the others somewhat. No definitelath-shaped feldspars are seen; instead there are abundant roundedwhitish areas, as much as 0.5 centimeter across, which arereplacements of nepheline. Figure 40 shows specimen P-54f, inwhich two such replacements (with more or less hexagonal outline)are seen in the upper half of the field. The smaller and clearerone is isotropic, and may be analcite; the other appears to behydrouephelite. In the center of the field, to the right of alarge augite, is more of the hydronephelite aggregate enclosingclear feldspar. There is an abundance of mafic minerals,including olivine, in this rock. Hornblende, though, is absent.Specimen P 54g, shown in figure 41, contains abundantwell-formed crystals of colorless fresh olivine, augite colorlessinside but usually with a thick outer green zone (aegirineaugite)fresh red-brown biotite, and some kataphorite amphi­bole. This mineral shows a strong and unusual pleochroism:X, pale yellow, Y, wine-red brown, Z, yellow; a small opticangle; strong dispersion, v>p; and the amphibole type ofcleavage, against which an extinction of about 15° can bemeasured.This amphibole resembles a kataphoritic amphibole namedmagnophorite by R. T. Prider (1939) from a leucite-bearing

IGNEOUS AND METAMOEPHIC ROCKS 47, ',* , * - *^ S . Jf , ? ^..1^-filFIGTJEE 37. Nepheline syenite (specimen P-54b) from Mbocayaty. Coarsely crystallized orthoclase, /, with hydronephelite, ft, after nepheline, which isslightly darker, and sphene, s. The darker small areas are green pyroxene, a, and black ore grains, o, of magnetite-ilmenite. Much of the hydronepheliteretains the characteristic stubby hexagonal prism shape of the original nepheline; however, it is uniaxial positive with appreciably higher birefringencethan nepheline. X 15.TABLE 5.Chemical analyses of alkalic rocks[Analyses of A, B, and E by Trumbull with densities by L. N. Tarrant; analysis ofC, by Goldschlag; D, by Lindner]SiO 2 - - -Al2OsFeO.. . ......MgO ... ...Cao...-_ ______Na2O -. ... _.K20 .__....H.O- -H20+.. .... _.TiOs .....-.-.CO.. .........PsOs. -SOs.S....MnO ...BaO. ___ ____Less O . ..Norm...NOTE.AP-54d53.2916.104.502.982.323.783.459.42.201.231.11.02.71.50.03.13.1999.96.0299.942.68II-5-1-2BP-54g50.4111. 173.505.059.237.732.317.10.12.761.61.00.41.12.03.14.2099 89!0299.872.87III-6-1-2C48.5511. 975.734.414. 7710.064.864.30} 2.623.04Tr.100. 31III-6-1-3See explanation of specimen designations below.52.2020. 673.261.38.484.436.614.90f .36\ 3.56.141.54.12.04D. 09(Mn2O 3).0999. 872.463I-6-2-3EP-58a51. 2715. 728.611.533.725.983.714.15.871.821.64.01.43.17.1899.812.731I-5-2-3SpecimenNo.A (P-54d)_._T! CP-'Hfr}D ____ .E (P-58a) ........doRockLocalityDo.2.3 km west-southwest of Centurion.Sapucai, Ibytymi district.rock from Western Australia. Prider gives an analysis. Asecond paper by Wade and Prider (1941) gives a further description,with illustration of a peculiar "herringbone" structurewhich is also present in the Mbocayaty mineral. Figure 42shows this amphibole, with "herringbone" structure.The amphibole also resembles an amphibole from Wyoming,described by Cross (1897), which Cross states is almost uniaxial,and with a color scheme X, a pale yellow, b, red similar tohypersthene, Z, a bright yellow.ANALYSES OF AIKAIIC ROCKSFive chemical analyses of the alkalic rocks of Paraguayare available, three new ones (of nepheline syenite

48 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGUEE 38. Shonkinite (specimen P-54c) from Mbocayaty is similar to sample P-54a (fig. 36) but shows abundant hydronephelite, ft. The large grainswith good cleavage are pyroxene, p; another large grain, o, showing a few fractures but no cleavage is olivine; k, is kataforite amphibole: and orthoclase,/, is myrmekitic replacement of hydronephelite. The black areas are brown biotite, ft, and opaque ore grains. X 15.FIGURE 39. Shonkinite (specimen P-54d) from Mbocayaty. Aggregate of orthoclase, /,- pyroxene, p; hydronephelite, ft; magnetite-ilmenite ore, o.biotite and brown hornblende are sparse. X 15.Brown

IGNEOUS AND METAMOEPHIC ROCKS 49FIGURE 40. Shonkinite (specimen P-54f) from Mbocayaty. Near the upper edge are two large hydronephelite replacements, h, of nepheline. The replacementnear the middle appears to be isotropic analcite. Feldspar, /, is inconspicuous, forming the groundmass of the crowded pyroxene, p, olivine, o, biotite,and other crystals. X 15.FIGURE 41. Shonkinite (specimen P-54g) from Mbocayaty. Diopsidic pyroxene, p, augite; olivine, o; brown biotite, b; iron oxide; and euhedral hydronephelite,ft all in clear matrix of sanidine. X 15.

50 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 42. Shonkinite (specimen P-54a) from Mbocayaty, showing katoforite amphibole, with "herringbone structure" fc; biotite, 6; magnetite-ilmeniteore, o; olivine, ol, and pyroxene, p, X 300.TABLE 6. Spectrographic analyses of aikalic rocks[Analyst: Paul R. Barnett, U. S. Geological Survey. Looked for but not found:Ag, As, Au, B, Be, Bi, Cd, Oe, In, Pt, Sb, Sn, Ta, Th, Tl, V, W, Zn]Ba _. ____________OrCu ... ... .Ga .LaMoNbNi ... ... ... .....Pb._ ..............ScSr ................V .............YbZr_NOTE.See explanation of field numbers below.Field No.P-54d ....P-58a._- ...RockP-54d0.2.002.002.005.002.020 .008.001.003.001.3.02.006.0002.07Basalt- .. __ .. . .Specimen No.P-54g0.2.004.04.005.002.010 .005.03.003.002.2.03.005.0001.04LocalityP-58a0.2.004.0005.005.002.01.0004.004.002.002.002.2.04.009.0002.03Mbocayaty.Do.Acahay volcanic cone.and shonkinite from Mbocayaty and of basalt fromAcahay), one of the Sapucal phonolite by Lindner,and one made by Goldschlag of the phonolite fromCenturion (table 5). The basalt from the Acahayvolcanic cone is included here because of its similarityto that of the Mbocayaty nepheline syenite (specimenP-54d). The analyses are shown in tables 5 and 6.Specimen P-92, "Triassic or Jurassic basalt" fromFoz de Iguagu (see tables 3, 4) resembles chemicallyboth Mbocayaty analcite shonkinite and the Centurionphonolite (norms respectively IIL4-3-4, IIL5-1-2,III-6-1-3). Also there is a chemical resemblance betweenthe nepheline syenite at Mbocayaty and the basaltof the Acahay volcanic cone (norms respectively IL5-1-2andII-5-2-3).SEDIMENTARY BOCKSEASTERN PARAGUAYCAMBRIAN AND OEDOVICIAN SYSTEMS(?)ITAPUCUMI SERIESA series of calcareous and dolomitic limestonedeposits, which contain a few beds of shale or argillite,almost surround the body of Precambrian rocks southof the Rio Apa and east of the Rio Paraguay. It isnamed the Itapucumi series by Harrington (1950) forthe good exposures at the village of Itapucumi and isthought to be the equivalent of the Corumba series ofBrazil. No fossils have yet been found in these rocks

SEDIMENTARY ROCKS 51and, in view of differences and fairly frequent changesin the opinions of geologists as to the ages of theserocks and of their supposed equivalents in Brazil andBolivia, no closer age assignment than that ofCambrian (?) and Ordovician(?) seems justified.The distribution of the series and the attitudesymbols, as shown on plate 1, are based on groundand air observations by the author along the RioParaguay, particularly in the vicinity of the Vallemicement plant, on his interpretations of aerial photographs,and on various published observations byCarnier (1911c), Kanter (1936), Boettner (1947) andHarrington (1950). Several relatively small outliersof the Itapucumi series rise from the alluvium alongand near the Gran Chaco side of the Rio Paraguay.Most of them form low rounded hills scarcely morethan 5 to 10 meters high, but the largest one, CerroGalban, just southwest of Puerto Casado, rises 140meters above the swampy plain and is about onekilometer long. It is sketched and described by Krieg(1931) as made up almost entirely of limestone, witha small hillock of red sandstone near its eastern end.The limestone from the main hill, which is quarried forvarious uses at Puerto Casado, is dark blue gray andcrystalline.The series is almost continuously exposed along theeast bank of the Rio Paraguay from near San Salvadorto the mouth of the Rio Apa (pi. 1). Over much ofthis distance there are conspicuous cliffs 15 to 20meters high (figs. 21 and 23), backed by rounded andheavily forested hills that are 100 to 200 meters high.Eastward from the river the limestone is more or lesscontinuously exposed as far as the Apa highland, in thevicinities of Cerro Paiba and Loma Pora. There theywere seen by Carnier (191 Ic) to rest on or against olderPrecambrian rocks, unconformably in some places andin fault contact in others. The belt trends southwardaround the end of the Precambrian body but is apparentlynot well exposed there for it is not describedby any investigators. It reappears along the eastside of the Precambrian rocks, where it is describedand sketched by Boettner (1947) between ArroyoYtaguy and Arroyo Hermosa.The Itapucumi series is thought by Harrington(1950) to be about 300 to 400 meters thick. This isonly an approximation, however, since no detailedmapping has been done and the general pattern offolding, indicated on plate 1 by scattered observationsof attitude, has yet to be worked out.Figure 43 shows the character of the limestone anda description of the rocks exposed in the Vallemiquarry is given in the section on cement. In general,the series is made up of light- to dark-gray limestonein well-defined, relatively thin beds. Locally the bedsare thick and massive, alternating with shaly limestoneand marly shale. All the rocks are hard and dense andmost of them are fine grained, but some are partly orentirely recrystallized and cut by veins of calcite ordolomite. Oolitic and lithographic limestone, as wellas various kinds of green- and pink-toned marble havebeen reported from a number of places.The rocks range from nearly pure limestone with 95percent or more calcium carbonate to nearly puredolomite. The analyses below are believed to befairly representative. As noted on page 80, the purerlimestone at Vallemi contains approximately 95percent calcium carbonate, whereas the varieties thatare streaked green by chloritic material contain 80 to85 percent calcium carbonate.Analyses of typical limestones of Itapucumi seriesCaO ___ ____ __ _____ ______MgO_-_ - _- _-(Fe, A1) 2O3_-- _ __ _______H 2O___ __ _____ ___ ___ ___ _CO2_______ ___ ____ __ ________[M. Goldschlag (1913c), analyst]13.3450.900.932.971.7540.98100. 9523.9052.691.9741.300.69100.5531.1252.853.030.3642.2099.6643.3830.9117.942.541.8543.79100.41NOTE. Explanation of localities of samples:1. Limestone, Cordillera de las Quince Puntas, 10 kilometers west-northwest ofCenturion.2. Oolitic limestone, 35 kilometers north-northwest of Puerto Max on RioParaguay (near Puerto Fonciere).3. Limestone, Cerro Paiba, 10 kilometers southwest of San Carlos.4. Dolomitic limestone, left bank of Rio La Paz, east of San Luis de la Sierra.The limestone series rests uncomformably on the Precambrianbasement rocks that make up the PotreroSaty. They are shown on plate 1 as everywhere overlaindirectly by the Tubarao series of Pennsylvanian orPermian age but only in the extreme northeastern partof their belt of outcrop, near Santa Luisa, is this contactactually known. Not far from the town of Santa Luisa,and along Arroyo Hermosa, Boettner (1947) found tilliteof the Tubarao beds, with striated pebbles, resting onthe Itapucumi limestone.It appears certain that the Itapucumi beds do not extendfar into southern Paraguay, because Silurian andyounger beds rest directly on the Precambrian basementin many places farther south. According to availableknowledge, none of the wells drilled by the Union OilCompany were deep enough to have reached these beds,so it is not known whether the Itapucumi rocks extendbeneath the Gran Chaco. Quite possibly they do not,for no rocks of similar character seem to be known in theeastern Andes, where the deeper beds of the Gran Chacobasin reappear at the surface (Ahlfeld, 1946, geologicmap).Boettner (1947) notes that marble was once quarriedat Puerto Max for ornamental stone and DuGraty

52 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 43. Outcrops of limestone of Itapucumi series, Cambrian and Ordovician age, on the east bank of the Rio Paraguay just south of Valleml.Joints in the rock are characterisically enlarged close to river level; some evidence of horizontal niching by the river can also be seen. Patcheson the distant water surface are floating islands (camalotes) of flowering water plants.(1865) describes two dolomitic marbles from Itapuguazu.This locality is not shown on modern maps,but the name clearly refers to one of the more prominentcliffs along the east bank of the river. One marble describedby DuGraty is rosy white and contains a littlemore than 93 percent calcium and magnesium carbonate;the other is nearly white but lightly veined withrose, and contains 99 percent combined carbonates.A report on "Concurrencia del Banco Agricola delParaguay" (Anon., 1911) reports that President MariscalLopez (circa 1860) had a table made of all classesand colors of Paraguayan marble, and sent it to NapoleonIII of France, who had it prominently displayedin the Tuilleries for a long time.The rocks of the Itapucumi series appear to be unfossiliferousand their age is unknown. The series isthought by Almeida (1945) and Harrington (1950) tobe probably equivalent to the Corumba series of MatoGrosso, Brazil. Both authors trace the history ofattempts to date this series and conclude that it, andhence the Itapucumi series is probably of OrdovicianThe cliffs along the river are deeply notched at andnear the present water level, but not above it. Moreover,joints in the limestone, though tight in the higherparts of the cliffs, are enlarged by solution to tentshapedcaves at river level. (See p. 78.)Except along the cliffs just mentioned, the Itapucumilimestone beds are weathered to a dark-gray to blackclayey soil that is commonly less than 2 meters thickand is characterized by many outcrops of limestone andby poor drainage. On the uplands the soils supportluxuriant vegetation, but in the poorly drained lowlandsthe principal tree is the black or carandai palm.Were it not for the clayey texture and poor drainagethe soils would doubtless be among the best agriculturalsoils of Paraguay, despite their thinness, for they arethe only ones that contain lime in any quantity.The limestone forms the basis of a considerable limeindustry, as well as providing raw material for thecountry's cement plant. In addition to these uses,there is a strong possibility that many of the rockscould be used for attractive ornamental stone. Manysmall kilns, which supply nearly all the lime used in thecountry, are scattered along the limestone cliffs on theeast bank of the Rio Paraguay. This industry is saidby Boettner (1947) to have been begun between 1825and 1840, under the regime of President Francia, whoeffectively closed the country to all foreign commerce.

SEDIMENTARY ROCKS 53SILURIAN SYSTEMCAACUPE SERIESThe Caacupe series, at least 700 meters (2,300 feet)thick, consists largely of arkosic sandstone with a basalconglomerate and with some beds of clay and shale.Fossil evidence shows it to be of Early Silurian age.The probable correlatives of these beds in the GranChaco basin, as determined by deep exploratory wellsand as described in another section in this report, arelargely black marine shale with comparatively littlesandstone.As shown on plate 1, the Caacupe series occupiesmuch of the heavily populated west central part of thecountry extending southward from the banks of theRio Paraguay above Asuncion to Quiindy and Mbuyapeyand from Ypacarai eastward to the longitude ofEusebio Ayala.The Caacupe series can be divided into four lithologicunits, as follows:ApproximatethicknessTop.1. Sandstone, red to brown, massive, fossiliferous; highlymicaceous in part; underlain by soft light-coloredshale or clay with thin beds of sandstone. _________ 2002. Sandstone, white, saccharoidaL _ __________________ 1003. Sandstone, brown to red-brown, fine- to coarse-grained,arkosic; several f ossilif erous clayey horizons nearbase._________________________________________ 4004. Basal Paraguari conglomerate. _____________________ 1-50These units, which are described below, cannot beshown separately on plate 1, but more detailed geologicstudies will almost certainly prove them to be easilymappable units that may ultimately deserve the statusof formations or members. It is also possible that theupper unit may be subdivisible into a lower shaly unitand an upper one of sandstone.Paraguari conglomerate. The lowest unit of theseries is a basal conglomerate that grades both laterallyand upward to conglomeratic sandstone. It wasnamed the Paraguari conglomerate by Harrington(1950) for the excellent exposures just northeast of thattown. There it is 40 to 50 meters thick, but elsewhereit appears to be thinner and is probably no more than2 or 3 meters thick in most places. The conglomeraterests unconformably on the weathered surfaces of thePrecambrian rocks and is overlain gradationally bycoarse-grained crossbedded sandstone. According toHarrington, it is exposed along the entire length of theYpacarai depression, from San Bernardino to Paraguari,at the foot of the Cordillera de los Altos thatforms its eastern side. Harrington, who thinks that aconglomerate at Pirayu, on the west side of the depression,may belong to this unit, also mentions theexposures farther south that are described below.The typical conglomeratic rock consists of a greatnumber of pebbles in a coarse-grained sandy matrix.The pebbles are smooth, ellipsoidal to well-rounded,and 1 to 30 centimeters in diameter. They consistexclusively of siliceous materials vein quartz, quartzite,and various forms of chert and jasper. There areno igneous and metamorphic rocks except quartzite.The most easily studied exposure of the conglomerateis probably that at the north edge of San Bernardino.a resort town on the east shore of Lago Ypacarai.Even here the actual contact with underlying rocks ispoorly exposed. The lower part of a small hill at SanBernardino is made up of coarse Precambrian granite,fresh near the lake level, but strongly weathered andcrumbly upward. The top of the hill is made up ofcoarse-grained brown to red-brown sandstone, at least7 meters thick. It is strongly crossbedded and containsmany thin lenses of conglomerate with pebbles1 to 2 centimeters in diameter. Between the weatheredgranite and the conglomeratic sandstone there is acovered interval less than 6 meters thick. The soiland slope wash in this interval, as well as on the uppermostpart of the granite slopes, contain an abundance olpebbles, 2 to 10 centimeters in diameter, of quartz,chert, and quartzite. These indicate that at least apart of the interval is made up of a true basal conglomerate,though it seems probable that even here there isa considerable amount of sandstone matrix.The basal conglomerate is well exposed in manyplaces along the highway between Quiindy and Caapucu,at Quyquy6, south of Acahay, and elsewhere.At all of these places it marks the contact betweenPrecambrian igneous and metamorphic rocks anderosional remnants of the lower part of the Caacupeseries. Nowhere in this southerly area does theconglomeratic horizon appear to be much more thanone meter thick. It grades upward to typical brownor red-brown sandstone of the Caacupe, and itsweathered surfaces are liberally strewn with roundedto semirounded pebbles of quartz, quartzite, andvaricolored chert. As elsewhere, pebbles of graniteand quartz porphyry, that form the surface on whichthe conglomerate was deposited are conspicuouslyabsent in the conglomerate.Arkosic sandstone. The arkosic sandstone, whichmakes up more than half of the Caacupe series, constitutesthe bulk of the rocks that are called the Piribebuysandstone by Harrington. It grades downwardto the basal conglomerate of the series and is overlain,with little or no gradation, by the thick white saccharoidalsandstone unit. The unit consists almost

54 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYentirely of a monotonous succession of arkosic sandstone,mostly light brown to light reddish brown butmarked by thick dark brown to dark-red soils in manyplaces. It is coarse grained locally but mostly fine tomedium grained, is usually poorly cemented, and consistsof well rounded grains of quartz and feldspar, withconsiderable quantities of mica. It occurs in thinbeds, most of them strongly crossbedded.At several places along the western side of theYpacarai depression the sandstone beds contain intercalatedlayers of light-colored fossiliferous clay severalmeters thick, probably the partly weathered productof soft gray or black shale. According to the author'sinterpretation of the structure, all of these are in thelower part of the unit.The arkosic sandstone unit is exposed along theentire western front of the Cordillera de los Altos; itsupper part is most accessible and most easily studiedin the cuts along the main Asuncion-Caacupe highwaywhere it traverses this front and rises more than 200meters between the lake level and the crest of the hill.The unit also makes up the western part of the Cordillerade los Altos, where it extends a little east of Caacupe,as well as most of the area between Asuncion andYpacarai. Except for one hill just southeast ofCarapegua, which is capped by the white saccharoidalsandstone unit, all the southern body of Caacupe rocksis made up of the arkosic sandstone unit, underlain bythe basal conglomerate. (See fig. 44.)The following more detailed descriptions of specificlocalities give some picture of the nature of the intercalatedclay layers mentioned above and of the enclosingsandstone.One clay deposit that was examined is on the westside of tbe railroad, 1 to 2 kilometers southeast ofAregua. There, clay underlies a low-level bench, 100meters or so wide, that parallels the shore of LagoYpacarai. Clay is exposed in a large number of pits todepths of 3 to 4 meters. It is very micaceous, white tolight gray and mottled near the surface with brown andred; it is used for making bricks of excellent qualityand rich-red-brown color. In the dense woods at thebase of a slope just above the broad bench, hence justabove the clay stratigraphically, there is a small building-stonequarry in buff to brown, fine-grained mica­ceous sandstone in beds 1 to 2 meters thick. Thissandstone, which yielded a few poorly preservedfossils and which strikes N. 65° W. and dips 32° SW., isoverlain by thin-bedded, very shaly sandstone that isalso micaceous but redder in color than the lower beds.Rocks that form the upper parts of the hill are poorlyexposed, but fragments in the soil and slope wash makeit evident that there is a series of buff-colored sandstonebeds, at least 60 meters thick, fine to medium grained,quartzitic in places, and locally rich in iron oxides. Anintermediate bench suggests that there is at least onemore thick bed of clay like the one near lake level, butit is not exposed.The Vargas Pefia clay pit, 2 kilometers northwest ofthe town of Ypacarai, which is described by Harrington(1950, p. 21-22, 48) and is one of the key fossil localitiesnow known in Paraguay, provides another good exampleof the relations of clay beds and sandstone.The beds strike N. 55° W. and dip 12° SW. Clay isexposed in two pits, about 25 meters apart vertically.The clay is white, very micaceous, containsHUttle or noFIGURE 44. Sandstone hills of the Caacupe' series southeast of Paraguari. The dark hill at the left is basal conglomeratic sandstone of the series.

SEDIMENTARY ROCKS 55sand, and is richly fossiliferous. In places it is stainedred, yellow and brown and contains an abundance oflayers and veinlets of siderite, which is largely alteredto limonite. Massive, crossbedded micaceous lightbrownto red sandstone crops out between the upperand lower clay pits. Similar sandstone appears tooverlie the clay in the upper pit. The relations are notclear, but it is believed that the lower sandstone liesbetween two distinct layers of clay, each severalmeters thick. Possibly, however, the clay representsa single bed of altered shale that has been repeated bydropping along a northwestward-trending fault.The two series of sandstone and clay just describedprobably belong in the lower part of the arkosic sandstonemember of the Caacupe series not far above itsbase. The one near Aregua is probably a few meterslower in the section than that near Ypacarai, but theymay be actually or very nearly equivalent.White saccharoidal sandstone. The white saccharoidalsandstone is one of the most striking and mosteasily recognized of all the sedimentary rocks in Paraguay.About 100 meters thick, it rests on the arkosicsandstone unit and is overlain by a unit of alternatingclay and sandstone. Its main outcrop is a broad, southward-trendingbelt on the eastward flank or dip-slope ofthe Cordillera de los Altos, and along the west side ofthe Rio Piribebuy valley. Thus it extends through thetowns of TobatI and Piribebuy and thence southwestwardto make up the prominent hills east of Paraguari.The southeastward-trending hill just south of Carapeguais capped by an outlier of the same unit.The sandstone is so friable, at least near the surface,that it fails to crop out in many places, but on some ofthe hills east of Caacupe and in the general vicinity ofPiribebuy, it forms extensive outcrops. Probably thebest exposures are near TobatI (see figs. 45 and 46).There the road from Tobati to Caacupe crosses the baseof the unit about 3 kilometers north of Caacupe. Thecontact itself is obscured, but it is marked by an abruptchange from the red sandy soil derived from the arkosicsandstone unit to white or light-gray sandy soil. Fromthis point to Tobati the road skirts prominent and impressivehills, roughly 50 meters high, that are made upof the white sandstone. Near the base the sandstoneis thinly bedded in layers 15 to 60 centimeters thick, butthe remainder of the unit is in massive beds, locallycrossbedded, and as much as 17 meters, thick. Thebeds dip at low angles toward the east and southeast,with occasional minor rolls. A series of vertical eastward-trendingjoints, 3 to 70 meters apart are so erodedFIGUBE 45. Typical weathering pattern, resembling mudcracks on case-hardened joint faces of white sandstone unit of Caacupfi series of Silurian age.Three kilometers west of Tobati.

56 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 46. Typical joint pattern and pitted surface of the white sandstone unit of the Caacupe series near Tobati.as to form flutings and deep, almost vertically walledravines that give the outcrops the appearance of limestoneweathered in an arid climate (fig. 46). Along afew of the joints the sandstone contains much whiteand ocherous clay, possibly of hydrothermal origin,which forms the basis of a tiny industry at Tobati formanufacture of ocher, laundry bluing, and billiardchalk. (See figs. 47 and 55.)Except for the few clay-bearing localities just mentioned,the sandstone is made up of clean quartz sandwith a little calcareous cement and no other impuritiesexcept widely scattered fine grains of magnetite. Thefine quartz grains are uniform in size, but very irregularin shape, ranging from round grains to euhedralcrystals. The surface of the rock is commonly casehardenedto depths of 5 to 30 centimeters but its interioris saccharoidal. It may well be that the friablenature of the rock as seen in outcrops is a near-surfacefeature, caused by solution of the intergranular cement,and that the rock is better consolidated at depth.There are no available facts to confirm this possibility,however. Many of the surfaces, especially horizontalones, exhibit polyhedral cracks, resembling mudcracks(fig. 45), that seem to be as characteristic of the unitas are the weathered joints and pitted, limestonelike,weathered surfaces elsewhere.Upper shale and sandstone unit. The uppermost unitof the Caacupe series, about 200 meters thick, is evenless well known that the other units. Scattered informationsuggests that the lower half is made up largelyof soft shale or clay, with thin beds of sandstone,whereas the upper half is largely micaceous sandstonewith comparatively little clay or shale. The followingnotes, arranged stratigraphically, represent all the informationon this unit that is available.Just east of the town of Tobati the white saccharoidalsandstone unit dips beneath the surface of thebroad valley of the Rio Piribebuy. The underlyingbeds are covered almost everywhere by as much asC meters of river-deposited clay, silt, and sand. A fewlow forested hills, or "islas," and occasional outcrops inthe banks of the main stream serve to give some ideaof the older rocks. They consist of brown, fine-grainedcross-bedded sandstone, dipping eastward at low anglesand directly overlying the white saccharoidal sandstone.Despite the evidence of these exposures, the generalcharacter of the valley, as well as the rarity of exposuresmake it appear probable that the valley is carvedin a series of very soft shale or shaly sandstone beds,with only a few relatively thin beds of harder sandstone.Cerro Aparipi, from which Beder and Windhausen(1918) and later Harrington (1950) collected an exten-

SEDIMENTARY ROCKS 57of red ochre that it gives a bright-red greasy streak.Poorly preserved fossils are widespread. At the northeastend of this exposure, 2.5 kilometers southwest of.Arroyos y Esteros, a fairly large collection of fossilswas made from a freshly quarried pile of building stoneidentical with that just described.Stratigraphically above the red micaceous sandstone,and extending 2 kilometers northeast of Arroyos yEsteros, is massive quartzose sandstone with little micaor feldspar. It is yellow to brown, but weathers to soilthat is nearly as red as that on the underlying red sandstonefarther southeast. This sandstone dips beneaththe valley of Rio Manduvira. It probably marks thetop of the Caacupe series and is overlain by softer andmore shaly beds of the Itacurubi series of DevonianFIGURE 47. Ocher quarry near Tobati. The white sandstone unit of the Caacupfiseries contains ocher-yellow clay between interstices of the sand grains.sive fauna, is on the east side of the Piribebuy valley,hence the beds described by these authors would seemto be stratigraphically above those of the main valley.Cerro Aparipi, which was not visited by the presentauthor, is a conical hill, 30 meters high and 300 meterslong, about 4 kilometers north of Rio Piribebuy andalmost due north of Tobati. According to Beder andWindhausen, the lower part of the hill is made up ofvery fine grained, highly micaceous sandstone, with afew intercalations of white to gray clay. This sandstoneis succeeded by 20 meters of white to grayishwhitefossiliferous clay, locally tinted yellow by veinletsof limonite. The layer of clay is overlain by mediumgrainedgrayish-red, thick-bedded sandstone that capsthe hill.The beds exposed on Cerro Aparipi are overlain by athick massive sandstone. This is exposed in a numberof places along the road between Tobati and Arroyos yEsteros between points 2.5 and 6.5 kilometers southwestof the latter town. The sandstone is soft, dullred, very micaceous, and contains such an abundanceThe author's interpretation of the Caacupe series, asgiven in preceding paragraphs and shown on the geologicmap, plate 1, differs somewhat from that of Harrington(1950, p. 19-24, fig. 3, and geologic map). The differenceshave to do with the place of the two major fossiliferouslocalities in the stratigraphic section, and withthe relative stratigraphic position of the white saccharoidalsandstone unit.Harrington's general description of the rocks of theCaacupe series is essentially the same as that givenabove. He says it is made up of a succession of lightcoloredsandstone beds that commence with a stronglydeveloped basal conglomerate. These basal beds hecalls "Paraguari conglomerate," using the name "Piri­bebuy sandstone" for the main part of the series. HisPiribebuy sandstone beds are crossbedded in the lowerpart and contain a few thin laj^ers of clay. They gradeupward to light-colored saccharoidal sandstone, whichcaps the Caacupe series.Harrington believes the fossiliferous clay of CerroAparipi and of the Vargas Pena clay pit at Ypacaraito be at or about the same stratigraphic horizon, whichhe places as probably high in the crossbedded sandstoneseries but beneath the saccharoidal sandstone unit.Unfortunately, the faunas from the two main localitiesshed no light on the problem. Unless there is an undiscoveredfault along the Rio Piribebuy that broughtthe beds at Cerro Aparipi up on its east side, and anotherbetween Arroyos y Esteros and the Rio Manduvira thatagain dropped the whole Caacupe section beneath thesurface, the facts available indicate that the fossiliferousclays at Cerro Aparipi are near the top of theseries and well above the saccharoidal sandstone unit.The place of the clay beds at Ypacarai is much moreopen to question than those just discussed. The authorbelieves they are very near the base of the Caacupeseries, but this is based more on his interpretation ofthe structure than on real knowledge of the stratigraphy.

58 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYIf, as shown on plate 1 and discussed in the section onstructural geology, Harrington's concept of a grabenalong the depression is correct, then the fossiliferousbeds at Ypacaral may be anywhere within the Caacupeseries though almost certainly within the main arkosicsandstone unit and beneath the white saccharoidalsandstone.Paleontology. Much confusion exists as to the age ofthe Caacupe series and of the Itacurubi series, describedon succeeding pages. Available facts on identificationsand age assignments of the few fossils from these seriesthat have been made by various paleontologists aregiven below. It is evident from these conflicting reportsthat no satisfactory definition of the ages of the Caacupeand Itacurubi series can be made without studies oflarge collections of fossils that are tied to detailedgeologic maps. Indeed, it seems probable that solutionof the paleontologic problems may well have to awaitthe establishment, somewhere in South America, ofsome standard section of the Paleozoic rocks that canbe used as a point of reference throughout the continent.The first known fossils from what is here called theCaacupe series were from Cerro Aparipi, south ofArroyos y Esteros. They were collected and describedby Beder and Windhausen (1918). These authors alsocollected fossils from a pile of building stones in thetown of Arroyos y Esteros which they say were takenfrom a quarry a few kilometers north of the town.They identified the following species:Leptocoelia flabellites ConradCalmonia subseciva ClarkeTentaculites crotalinus SalterTropidoleptus carinatus ConradBeder and Windhausen's assignment of the bedsthat yielded these fossils to a Devonian age stood in theliterature until Harrington (1950) visited the samelocality and recognized the fauna to be of lower Silurianage. Harrington describes the following species fromCerro Aparipi and from the Vargas Peiia quarry atYpacarai:CerroAparipi YpacaraiLingula sp__________________________________ _ _ _ _ XAtrypina(!) paraguayensis Harrington__________ X _____Ctenodonta(l~) sp_____________________________ XPalaeoneilo constrictiformis Harrington________ ____ XNuculites opisthoxystomus Harrington__________ X XHyolithes sphenomorphus H arrington ___________ ____ XCalymene boettneri H arrington _________________ X XDalmanites sp_______________________________ ____ XClimacograptus innotatus var brasiliensis Rued- X XemannDiplograptus modestus Lapworth var ___________ ____ XHarrington points out that the trilobite describedby Beder and Windhausen as Acaste (Calmonia)subseciva Clarke is in reality the form he describes asCalymene boettneri Harrington.A J. Boucot of the U. S. Geological Survey has thefollowing comment concerning the faunal lists justgiven:The faunal list in Beder and Windhausen indicates lowerDevonian age for the Cerro Aparipi, and it is difficult to seehow they could have misidentified Leptocoelia flabellites. Onthe other hand the graptolites identified by Btilman (Harrington,1950) are certainly not of Devonian age. Is it possiblethat the flat-lying beds on the top of the hill are Devonian andthat the Silurian fossils could have been obtained from thebottom of the hill?Boucot's question can be answered in the negative.Harrington, in written communication to the author,states that there is but one tiny quarry on CerroAparipi and that it is certainly the place that yieldedBeder and Windhausen's collection as well as his owncollection that contained graptolites. He adds thathe is personally convinced that Beder and Windhausen'sidentification of Leptocoelia flabellites was in error.The present author, in company with Kicardo MazoU., failed to find the Cerro Aparipi locality, but likeBeder and Windhausen, did make a collection of fossilsfrom a large pile of building stone in a field 2 kilometerssouth of Arroyos y Esteros. Quite possibly thesestones came from the same quarry mentioned by theearlier workers. The rich fossil locality at the VargasPeiia clay pit near Ypacarai was found, quite accidentally,and a few fossils were found in a stone quarry1.5 kilometers southeast of Aregua and in pottery clayreported by the owner to come from a clay pit 3 kilometersnorth of Itaugua. The latter locality isprobably at about the same stratigraphic horizon asthat at the Vargas Pena quarry. The fossils collectedfrom these localities were examined by paleontologistsof the U. S. Geological Survey, whose reports follow:A. J. Boucot reports on a small lot of poorly preservedfossils from the stone quarry 1.5 kilometers southeastof Aregua as follows:This lot contains an unidentified plicated brachiopod, probablya rhynchonellid, whose brachial valve bears a median septum.It resembles the genus Camarotoechia. Also present is anunidentified smooth pelecypod and Tentaculites sp.A. K. Palmer reports as follows on trilobites fromthe same collection just noted:This collection contains a cephalon of a Phacopid trilobitethat could belong to either the subfamily Acastinae or Calmoninae.Trilobites of this type have not been reported fromrocks younger than lower Devonian. If a pygidium in thecollection belongs with the cephalon, then the general lack ofspines on the species would eliminate the subfamily Calmoninaefrom consideration.It is not possible to identify the genus within the Acastinaeto which the Paraguayan specimens might belong. The cephalon

SEDIMENTARY ROCKS 59shows resemblances to the Silurian genus Scotiella and theDevonian genus Phacopina. Again, if the pygidium belongswith the cephalon, then its lack of a median spine would eliminateit from comparison with Scotiella. Because of the uncertaintyof association of the parts and the imperfect nature of thespecimens, they cannot be dated more closely than Silurian orlower Devonian.R. J. Ross reports as follows on a collection from thelower Vargas Pena quarry, 2 kilometers northwest ofYpacarai:The fauna secured from this collection is:1. Climacograptus innotatus var. braziliensis Ruedemann2. Calymene cf. C. boettneri Harrington3. Anabia cf. A. paraia Clarke4. CleidophorusC?) cf. C. brasilianus (Clarke) (this speciesmay be referable to Nuculites.)5. Anodontopsis(?) cf. A. austrina Clarke6. Small taxodont concentrically ornamented pelecypcd.7. UlrichospiraC?) sp.8. Gastropod with general form of Flormotoma.This fauna is strikingly similar to that described by Clarke(1897) from the "Middle" Silurian of the Rio Trombetas, a northerntributary of the Amazon; although his studies lacked graptolitesand trilobites, the occurrence of the same species ofClimacograptus was reported in 1922 from what is presumed tobe the same locality. The presence of this genus and specieseliminates the possibility of a Late Silurian dating; in fact otherspecies of its are known from Middle and Upper Ordovicianstrata elsewhere. A species of the trilobite genus Calymene ishere present and appears to be conspecific with that described byHarrington as C. boettneri from the same Paraguayan locality.None of the specimens is as well preserved as Harrington's andall lack the critical frontal portion of the cephalon by whichvarious subgenera are distinguished. There is nothing to suggestthat they are not assignable to Calymene sensu strictu, which isnot found below the Silurian in Great Britain.There can be little doubt that this Paraguayan fauna is correlativewith that from Rio Trcmbetas, Brazil; the age of thelatter has been redesignated as Early Silurian by Maury (1929),and there is no reason here to question this dating, which agreesalso with that of Harrington for this locality.A. J. Boucot reports on the author's collection offossils from a pile of building stone 2 kilometers southof Arroyos y Esteros:This lot contains an unidentified orthoceracone, a pelecypodpossessing taxodont dentition which may belong to the genusNuculites, several other fragmentary pelecypods, two gastropods(one possibly belonging to the genus Bucanella whereas the othermay belong to the genus Tropidodiscus), and several unidentifiedbrachiopods. The brachiopods may possibly belong to the genusSchuchertella, in which case the fauna is probably not any olderthan the Devonian, or to a strophomenoid resembling Leptostrophiaalthough identity with an orthoid-like Rhipidomellacannot be ruled out because of the poor quality of the fossils.A. R. Palmer reports as follows on the trilobites inthe same collection:DalmanitesC?) sp. Homalonotus sp. Lack of associated pygidiaof DalmanitesC?) sp. makes generic identification difficult. Thereis no surety that this collection is Devonian, but it is probablyas good an assignment as can be made with the material andpresent knowledge.465871 50 5This collection has a distinctly Siluro-Devonian aspect, butit is not possible to make any definite age determination basedon the available collection.DEVONIAN SYSTEMTTACUEUBI SERIESA series of micaceous shale and arkosic sandstonebeds, that contain marine fossils of Early Devonian agein places, extends in a comparatively narrow bandbetween the Silurian and Pennsylvania!! beds andtrends northwestward from the Rio Tebicuary-mi tothe Rio Paraguay not far below Rosario. They werenamed the Itacurubi series by Harrington (1950,p. 24-27) for the town of Itacurubi, sometimes knownas Itacurubi de la Cordillera; they are seemingly equivalentto the Furnas sandstone and the Ponta Grossashale of southeastern Brazil and possibly to the LosMonos and Iquiri beds of the Andean foothills ofBolivia (Ahlfeld, 1946). They are stratigraphicallyabove the beds near Arroyos y Esteros that were designatedas Devonian by Beder and Windhausen (1918)and are here included in the Caacupe series of EarlySilurian age.Several outcrops of quartzitic sandstone in the northernpart of the Gran Chaco, west of the Rio Paraguay,are correlated with the Itacurubi series. In addition,two exploratory wells, the Santa Rosa and the Picuiba,demonstrated that the Lower Devonian beds lie beneatha part of the Gran Chaco sedimentary basin, wherethey are a variable, but locally great, thickness of marineshale, siltstone, and sandstone (p. 74).The distribution of the Itacurubi series in easternParaguay, as shown in plate 1, is based largely onHarrington's map (1950) with some changes and additionsfrom the present author's field observations andhis interpretations of aerial photographs. The seriesis best exposed in a belt 10 to 20 kilometers wide and50 kilometers long that extends from, near Caraguatayto a point south of San Jose. In this area, cuts alongthe roads that connect Eusebio Ayala with Itacurubiand Caraguatay, as well as the road between Itacurubiand Santa Elena, present the best and most easilyaccessible exposures.There are a few isolated hills of these beds south ofSan Jose, but generally speaking the series is lostbeneath the swampy lowlands of the Rio Tebicuary-midrainage basin and the distribution shown on the mapis very largely imaginative. North of Caraguatay thebeds are again obscured beneath the swampy alluviumof the Arroyo Yhaguy and the Rio Paraguay, thoughsandstone that may belong to the lower part of thesection is poorly exposed just east of Arroyos y Esteros.The series is about 250 to 300 meters in thickness.Harrington (1950, p. 24-27) gives a good descriptionof its general characteristics. According to him, the

60lower third of the series consists largely of yellow tocream fine-grained sandstone, crossbedded in places,and with some intercalations of shale. The sandstoneunits are thin-bedded near the base but become thickerbeddedupward. The middle third of the series consistslargely of sandstone in thin beds; they are shalythroughout and become more so up\vard. Theseargillaceous beds, characterized by lilac, purple, andyello\v colors, contain ferruginous concretions inplaces. The upper third of the series is friable, yellowish-whiteto purple micaceous sandstone in thin beds.It contains intercalated varicolored shale in placesbut the sandstone tends to be considerably coarser ingrain than the lower units. This unit has yielded mostof the fossils reported from the series.The author's random observations along the highwaybetween Eusebio Ayala and San Jose confirm Harrington'sthree-fold division of the series in a general way.and add a few details as to parts of the section. Thehighway mentioned crosses the series diagonally fromits base to its top, so that the following notes must bein approximately the correct stratigraphic order.From a point 4.6 kilometers southeast of EusebioAyala to the broad valley of Arroyo Yhaguy, 5 kilometerswrest of Itacurubi de la Cordillera, the mainhiglrvvay traverses rolling grasslands marked by lightcoloredsoils. Several road cuts present excellentexposures of a small part of the section traversed (seefig. 48). In these, the rocks are seen to consist ofalternations of buff to light-reddish-brown soft shaleand very shaly micaceous sandstone in beds 1 to 5centimeters thick. A few of the beds, notably someof the micaceous sandstone, contain poorly preservedfossils.Alluvial material masks the Devonian rocks in thevalley of Arroyo Yhaguy where the main highwaycrosses it, but the beds are fatfly well exposed a shortdistance south of the highway in the vicinity of theMinas-cue or "Lopez" sulfur deposits. These depositsconsist of widely scattered concretions of marcasite inshale. The enclosing rock, which doubtless correspondsto Harrington's shaly middle part of the Itacurubiseries, consists of alternating beds of blue-gray shaleand mudstone, with local splotches of red and pink.The shale is sparsely fossiliferous.There are no good exposures along the highway nearItacurubi but \valls, buildings, and piles of rock invarious places suggest that there is a nearby source ofFIGUKE 48. Minor thrust fault in sandy micaceous shale of the Itacurubi series, Devonian age. View eastward on the highway 6 kilometers southeast ofEusebio Ayala. The beds at left have been pushed up and over the horizontal beds at right.

SEDIMENTARY ROCKS 61fine-grained olive-brown sandstone probably in thehills just south of town. This rock, which containsmuch clay-sized material, splits into solid but easilyworkable blocks from 12 to 30 centimeters thick.At a point about 10 kilometers southeast of Itacurubide la Cordillera, the surface is covered by 1 to 2 metersof lateritic iron ore, on thin-bedded alternations ofmicaceous sandstone and clay. The sandstone ispurplish gray, very soft, and contains at least 50percent fine-grained muscovite mica. The clay, nodoubt a weathered shale, is reddish brown and is farless micaceous than the sandstone.Two kilometers farther southeast, or 3 kilometersfrom San Jos6, a shallow road cut exposes an extensivebody of white, fine-grained micaceous sandstone thatbreaks along joints and horizontal bedding planes intosmooth but relatively soft flagstones, from 2 to 6centimeters thick. The vertical joints in this rock areseamed with brown limonite and many blocks of sandstoneshow diffusion banding that has worked awayfrom the joints. Several poorly preserved fossils werefound at this place.The Itacurubi series rests on the Caacup6 series oflower Silurian age and is overlain by the Tubaraoseries of Pennsylvania!! age. Neither contact hasactually been observed, but both evidently are markedby unconformities. There is, indeed, some evidence ofa major erosional unconformity at the base of theDevonian beds. Harrington states that the Itacurubiseries rests directly on the Piribebuy sandstone thewhite saccharoidal member of the Caacup6 series andeven considers the possibility that this sandstoneshould be grouped with the Devonian rocks. Therelationship described by him is quite possibly true inthe area directly west of Itacurubi and near Valenzuela.Farther north, however, the fossiliferous beds in thevicinity of Arroyos y Esteros, which are definitely partof the Caacupe" series, are stratigraphically above thewhite sugary sandstone and beneath the Itacurubi beds.These relationships are discussed on pages 56-57.If the present author's concepts are correct, the relativelythick section of upper Caacup6 beds that ispresent between Tobati and Arroyos y Esteros mustbe missing in the latitude of Itacurubi. This stronglysuggests the presence of a major erosional unconformitybetween the Silurian and Devonian rocks.Harrington (1950) lists the following fossils from aquarry at Cariy Loma, a few kilometers east of Itacurubide la Cordillera. These fossils were found in sandstonenear the top of the series.Favosites sp. indet.Schellwienella inca (d'Orb.)Australostrophia conradii HarringtonChonetes falklandicus Morris and Sharpe465871 59 6Spiroaphe(?) sp. indet.Tentaculites crotalinus SalterPhacopina itacurubensis HarringtonCalymene sp. indet.A small collection of fossils was made by the authorand Ricardo Maz6 U. from micaceous sandstone nearthe base of the series, 8 kilometers southeast of EusebioAyala. A. J. Boucot reports as follows:This collection contains an unidentified plicated brachiopod,probably a rhynchonellid, whose brachial valve bears a medianseptum. It resembles the genus Camarotoechia. Another finelyplicated brachiopod is possibly an orthoid belonging to theWattsellidae, Silurian or Devonian.A. R. Palmer reports on trilobites from the samecollection:Hadrorachis(!) sp., cranidium; Homalonotus sp., thoracic segment.Similar forms have been described from the Devonianof adjacent South American countries; however, neither genusis necessarily definitive of a Devonian age. On the basis of thetrilobites, this collection cannot be more closely dated thanSilurian-Devonian.At the "L6pez" sulfur workings, in the middle shalymember of the series, the author found one fossil,identified by R. J. Ross as follows:A single partial specimen of an orthoconic nautiloid possessingthe ornamentation of the "form genus" Spyroceras. Similarforms are known in North America from mid-Ordovician toDevonian strata.Boettner (1945) describes a single specimen of Homalonotussp. from this same locality.The white flaggy sandstone mentioned above as 3kilometers west of San Jos6 yielded an unidentifiedsmooth pelecypod and fragments of Homalonotus sp.and Dalmanites(?) sp. as identified by A. R. Palmer.Fossils that were found in the Santa Rosa and Picuibaexploratory wells in the Gran Chaco, and that areascribed to the Devonian by Harrington are listed inthe tables on pages 73 and 74.These faunas, which contain species that are typicalof the classic Devonian localities of Brazil, Uruguay,and Argentina, indicate the Early Devonian age of theItacurubi series of Paraguay, as well as its generalcorrelation with the Devonian sedimentary rocks ofthe surrounding countries.GONDWANA (SANTA CATARINA) BEDSThe Paraguayan equivalent of the widely distributedGondwana beds consists of a thick series of continentaland epicontinental sedimentary rocks that overlie themarine Devonian beds unconformably (Du Toit, 1927;Oliveira and Leonardos, 1943; Harrington, 1950). TheGondwana of Paraguay is 1,000 meters (3,280 feet)or more thick, including its extensive cap of basalt.Because the name Gondwana is still widely used bygeologists in Brazil and other parts of the world it is

62 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYretained here. The name "Santa Catarina system" is,however, used parenthetical!}*. It was applied byI. C. White (1906, p. 378) to the Gondwana beds ofsouthern Brazil, and its use was extended to Paraguayby Harrington (1950).In Paraguay, the following groups of Gondwana(Santa Catarina) rocks can be distinguished: theTubarao series, of Pennsylvanian or Permian age andlargely of glacial and fluvioglacial origin; the Independenciaseries, of Permian age and made up ofsandstone with some shale; the Misiones sandstone ofTriassic age; and the Serra Geral basaltic lavas ofTriassic or possibly Jurassic age. The latter rocksare described above in the section on igneous rocks;the others are described in order below. So far asknown, the carbonaceous and coal-bearing sedimentsthat are present in the Gondwana beds elsewhere arenot represented in Paraguay.PENNSYIVANIAN OR PERMIAN SYSTEMSTUBARAO SERIESThe distribution of the Tubarao series, as shown onplate 1, is based almost entirely on Harrington's map(1950) with a few refinements by the author based onstudy of aerial photographs and maps. The seriesis shown as covering a northward-trending belt,of variable width, from the swampy basin of the RioTebicuary as far north as the Rio Apa boundary ofParaguay and Brazil, just west of Bella Vista. Actually,almost all this belt of "outcrop" is occupiedby marshes and swamps and virtually the only exposuresthat have been studied are in the central region,in a belt that extends from near Caraguatay southeastwardto the vicinity of Villarrica. Much farthernorth, and thus providing a good deal of justificationfor mapping the series over such a large area, Boettner(1947, p. 11) found undoubted glacial deposits betweenthe Rio Apa and Toldo-cue. He also found striatedpebbles from the same series in the vicinity of Concepci6n.Even in the central zone, where they are best known,the Tubarao rocks are poorly exposed, and it is impossibleto study or measure a complete section.Harrington, who believes the entire series to be about250 meters (820 feet) thick, found three distinct kindsof interstratified sediments in the series glacial tillite,light-colored sandstone, and compact, laminated olivegreenshale.Tillite, according to Harrington, is exposed in anumber of road cuts from the outskirts of Caraguatayto a point just north of the Rio Tebicuary-mi betweenCoronel Oviedo and Villarrica. These beds were examinedat only one part of this stretch in the last8 kilometers of the main highway between San Jos6and Coronel Oviedo, or just west of the place wherethe highway forks lead to Coronel Oviedo and Villarrica.The grassy flats along the road are conspicuouslycovered with pebbles, mostly from 1 to 5 centimetersin diameter. A few of the pebbles are well roundedbut nearly all are subangular with 2 or 3 flat sidescharacteristic; a few are typically scratched by ice.Most of the pebbles are of very hard, brown quartzite,but a considerable number are made up of varicoloredagate or chert. One pebble of pink quartz porphyry,identical in appearance and microscopic character tothe Precambrian porphyry near Caapucu, was found.The matrix that yields the pebbles is exposed in roadcuts to a maximum depth of a little more than 1 meter.It is white to light-gray structureless clay, typical oftillite, in which the pebbles are randomly but sparselydistributed.Toward the east end of the exposures, road cutsshow several thin, lenticular beds of sandstone, someextremely fine-grained and dense, interbedded withlayers of the tough clay.In addition to pebble materials mentioned above,Harrington noted pebbles of granite and diabase. Healso mentions pebbles as much as 50 centimeters indiameter and even a few much larger erratics.Harrington (1950) also describes red fossiliferoussandstone that he believes to be either interstratifiedwith the tillite, or to "represent part of the Bonitosandstones which according to many Brazilian geologistsform a distinct group overlying the glacial beds." Onesuch exposure is on top of a large hill immediatelysouth of Villarrica, where it has been worked in severalsmall quarries, now abandoned. The sandstone is thinbedded, red to gray, strongly arkosic, and fine tomedium grained. Beder (1923) found well-preservedremains of Mesosaurus, probably M. tumididus Cope, intwo of the quarries on this hill and also found similarremains at Jhovy, a town 2 kilometers northwest ofVillarrica. Harrington found a few poorly preservedvertebrae in a quarry 1 kilometer west-southwest of theVillarrica railroad station.Harrington found banded shale, which he believesto be at or near the top of the Tubarao series, exposed ina low hill on the north edge of Coronel Oviedo. Thisrock is hard, grayish-green, and typical of varved clay.Harrington (1950, p. 31-32, 49-50) describes an exposureof hard olive-green varved shale in the vicinityof Paraguari, far from the main belt of Tubarao rocks,that he believes represents this same series. It is thissingle exposure, plus considerations of the geologicstructure, that led Harrington to map the entireYpacarai depression as underlain by Tubarao beds(pi. 1). The shale forms a small conical hill at thewestern edge of Cerro Jhu, an eminence that is 2

SEDIMENTARY ROCKS 63kilometers north of Paraguari. The gap between thesmall hill and Cerro Jhu is traversed by the main roadbetween Paraguari and Piribebuy. The western footof Cerro Jhu is made up of Paraguari conglomerate,surmounted by arkosic sandstone typical of the Caacupeseries. These beds strike about N. 30° E. and dipabout 45° SE.; the varved shale of the smaller hill, onthe other hand, strikes about N. 70° W. and dips about45° SW. These relationships convince Harrington, aswell as the present author, that the Tubarao beds tothe west must have been downfaulted against theCaacupe beds to the east along a northeastward-trendingfault that traverses the gap between the two hills.The correlation of the tillite and related sandstoneand shale with the Tubarao series of Brazil, as made byHarrington, seems to be entirely justified on the basisof lithologic and paleontologic evidence available. Theage of these beds in South America, and of theirprobable or possible correlatives in South Africa andAustralia is still in dispute. Many geologists believethem to be of Permian age, whereas others assign themto the Pennsylvanian. This question is left open here.PERMIAN SYSTEMINDEPENDENCE SERIESThe Independencia series, named by Harrington(1950) for Independencia, 25 kilometers northeast ofVillarrica, is about 400 meters (1,310 feet) or less thickand made up very largely of sandstone. It containssparse fauna and flora of late Permian age.The distribution of the series as mapped is basedlargely on Harrington's map; the rocks have only beenstudied in the central region, in the general vicinityof Villarrica, and Harrington himself expresses somedoubts as to the extension of the belt of outcrop as farnorth as Bella Vista on the Rio Apa. As shown onplate 1, the series is about 400 meters (1,310 feet) thickin the mountainous area east of Villarrica but elsewhereit is less than half this thickness in almost all places.How much of this apparent difference is real and howmuch is due to gross errors on the topographic orgeologic maps is not known.The best exposures known are in Sierra Ybyturuzuand its vicinity, but Harrington maps a number ofknown outcrops in the mountains north of Caaguazu.The series is described by Harrington, from his studiesalong the road between Mbocayaty and Independencia,as consisting of two thick sandstone units, separatedby a thinner unit of alternating shale and sandstone.Only the lower sandstone was examined by the presentauthor, and this only in one place, at the west baseof Sierra Ybyturuzu, almost due east of Villarrica.There, the basal part of the sierra, which rises abruptlyfrom the plains of Tubarao tillite, is massive sandstone,60 to 90 meters (200-300 feet) thick, that forms steepto vertical cliffs (see figs. 49 and 50). The sandstonehas siliceous cement and is light reddish brown, mediumgrained and moderately hard. Individual layers areless than 1 centimeter thick, but the bedding planesare tight so that the rock appears from a little distanceto be made up of massive beds from 2 to 8 metersthick. Near the top of the unit the sandstone hascharacteristic deltaic crossbedding, with topset andforeset beds ranging from 1.5 to 5 meters thick.Above the rock are about 60 meters (200 feet) ofsandstone that is similar in most respects but somewhatredder in color and softer so that it forms gentler slopesand supports heavier vegetation. The rocks above thissecond unit are concealed, at least in that part of themountain that was examined, by soils and dense forestgrowth. The slopes are moderate to steep and mostof the upper part of the section is probably made upof sandstone similar to that lower down.Harrington's description of the lower sandstoneunit, which he found exposed 10 kilometers east ofMbocayaty, is substantially like that reported aboveexcept that he found the rock to be somewhat coarsergrained, less well cemented and more arkosic thanthat seen by the author.FIGURE 49. Coarse-grained arkosic, crossbedded sandstone of the Independenciaseries of Permian age, 13 kilometers east of Villarrica. The dark slotlike ravine isin a deeply weathered dike of basic alkalic rock that contains much biotite. Seefigure 28.

64 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 50. Unusually good outcrop of crossbedded sandstone of the Independencia series of Permian age in the hills east of Villarrica. Vegetation istypical of the hilly parts of eastern Paraguay.Above the lower sandstone Harrington found aunit, about 50 meters (165 feet) thick, of thinly alternatingsandstone and shale. The sandstone is finegrained, feldspathic and shaly, generally light gray toyellow, and occurs in beds only a few centimeters thick.The units are interbedded with thin layers of cream,yellow, and gray shale.The upper unit of the series, which contains little orno shale, is according to Harrington, fine to mediumgrained, strongly arkosic, crossbedded, and slightlycemented to friable. It ranges from light red to yellowishred and is mottled locally. About 200 meters (660feet) thick, it has yielded most of the fossils reportedfrom this series.The Independencia series overlies the Tubarao andolder rocks disconformably and is unconformablyoverlain by the Misiones sandstone of probable Triassicage. The angular disconformity at the base of theseries is indicated in at least two places mentioned byHarrington. Just south of Villarrica the Tubarao bedsdip southwest, whereas the Independencia beds, lessthan 2 kilometers east, dip eastward. Moreover, asmall outlier of fossiliferous Independencia rocks, discoveredby Windhausen in 1924 and first described byKeed (1935) is known about midway between Valenzuelaand San Jose, where it rests directly on Itacurubibeds of Devonian age.The first undoubted fossils of any kind to be discoveredin Paraguay were found by Carnier (1911b)in what are here called the Independencia beds. Thefern and conifer fossils, the latter said to be abundant,were found in two creeks crossed by the road fromVillarrica to Mbuvevo. The location of the latter placeis not known, but the fossil locality is near the footof Sierra Ybyturuzu. It is quite possibly the samefossil-wood locality described by Harrington (1950,p. 35) as 6 kilometers west of Independencia; he placesthis locality as probably near the base of the uppersandstone unit of the Independencia series. Schuster(1911) describes and figures the fern materials collectedby Carnier as Osmundites carnieri Schuster and thesilicified conifer remains, some of them trunks 15centimeters in diameter, as Dadoxylon sp. He felt thatthese plants indicated a Tertiary age, a mistake thatwas corrected by Beder (1923).Carnier (1911b) also mentions fossil wood from nearMaciel, southwest of Villarrica, and from near theKio Parana at Villa Azara. Some existing maps showa town of this name in the general vicinity of Foz deIguagu. There is some doubt that this is indeed thelocality noted by Carnier, for it is in an area mappedas Serra Geral lavas by all investigators whose workis known to the author.Fresh-water invertebrate fossils have been found in

SEDIMENTARY ROCKS 65at least three different localities in the Independenciabeds near Villarrica, in the small outlier betweenSan Jose and Valenzuela, and near Independencia.The stratigraphic position of these fossils within theseries is not known accurately, but those at Independenciaand perhaps the others, are believed byHarrington to be in the upper sandstone unit, not farabove the plant-bearing horizon.Beder (1923) found lamellibranchs on the southeastedge of Villarrica at a point where the road is cut inreddish-gray sandstone. This is 2 kilometers east ofthe Mesosaurus locality mentioned above in the descriptionof the Tubarao series. The fossils, which arepoorly preserved, were identified by Beder as Solenomorpha,probably S. similis Holdhaus and S. intermediaHoldhaus. Gerth (1932, pt. 2, p. 209-210) says thatBeder's Solenomorpha was later redescribed by Reedas Myophoria. Solenomorpha similis Holdhaus is nowcalled Leinzia similis (Holdhaus) Camargo Mendes(1951). Leanza (1948) calls attention to the fact thatWindhausen in 1931 added Sanguinolites to the list offossils from Villarrica; it accompanies Beder's Solenomorpha.Reed (1935, p. 41-42) describes and illustrates fossilscollected in 1924 by Windhausen from an outlier ofIndependencia beds between San Jose and Valenzuela.The only description of the geology is ofpinkish or buff-colored fine-grained sandstone containingnumerous poor impressions and internal casts of one or morekinds of small lamellibranchs.Reed classes these as Pinzonella cf. Ulusa Reed.Harrington (1950, p. 35) describes pelecypods from asmall abandoned quarry 800 meters south of HotelTilinsky in Independencia. The fossils are stratigraphicallyabove the plant-bearing beds but still inthe lower third of the upper sandstone unit. They weretaken from a light-gray to reddish-gray layer of sandstone,only 20 centimeters thick, that lies betweencrossbedded sandstone units. There are many individualfossils, but Harrington found only two speciesPinzonellopsis occidentalis (Reed) Camargo Mendesand pseudocorbtda anceps Reed.The paleontologic evidence, though somewhat sparse,convinces Harrington (1950) that the Independenciabeds of Paraguay are of late Permian age and stratigraphicallyequivalent to the Rio do Rasto group andthe Estrada Nova formation of the Brazilian Passa Doisseries (Gordon, 1947).TEIASSIC SYSTEMMISIONES SANDSTONEThe Misioiies sandstone was named by Harrington(1950, p. 37-40) for the Misiones region, between theRio Tebicuary and the Rio Parana, where it is particularlywell exposed. It consists of homogenous redsandstone, and probably of red clay or shale, and overlapsall, or nearly all, of the older rocks in the country.It is overlain by the Serra Geral basalt, and is possiblyinterbedded with it in part.One very large area of outcrop and several smallerones are shown on plate 1. The main outcrop occupiesa southward-trending band, 20 to 70 kilometers wide,that extends through the eastern part of Paraguay fromthe Rio Apa to the Rio Parana. At the latitude ofCaazapa the lower boundary of the belt trends abruptlywestward and the belt is broader, covering most of theextreme southwestern part of eastern Paraguay. Thedistribution as mapped is based partly on Harrington'smap, partly on sketch maps and descriptions by Carnier(191 Ic) and other earlier workers, and partly on observations,interpretations, and guesswork. The contactbetween the Triassic sandstone and the Serra Geral lavais believed to be one of the most accurate shown on theentire map (see p. 26 and pi. 1). The broad expanse ofTriassic rocks shown in the southwestern corner of thecountry is almost pure guesswork, however, for nearlyall of this area is marshland. Similarly, the northernhalf of the belt of outcrop is drawn as essentially conformableon the Independencia rocks; there are no mapsor descriptions known to the author to help determinewhether the Misiones beds there are conformable orwhether they overlap the older beds as they do farthersouth.A second fairly large area of outcrop lies in the areabetween Asuncion and Ypacarai, and extends as farsouth as Paraguari (pi. 1). Exposures are poor in mostof this area, and the soils are redder and thicker than inmany parts of the country. Good outcrops of massive,thick-bedded, reddish-brown sandstone are known atYaguaron, at Itapitapunta (a cliff on the Rio Paraguaysouth of Asuncion), in road cuts in and near Asuncionitself, and at a few other places. Harrington describesa striking angular unconformity between the Misionessandstone and the underlying Caacupe series. In aravine almost midway between Itaugua and Ypacarai,and about 200 meters north of the highway, he foundthe strike of the Misiones sandstone was almost duenorth and the dip 42° W. The actual contact is not exposed,but below the Misiones beds Harrington foundtypical Caacupe sandstone light-colored, crossbedded,and strongly brecciated that appeared to dip at 70° orhigher angles toward the west.A small inlier of sedimentary rocks along the RioParana near the colonies of Jesus and Trinidad (pi. 1)is referred to the Triassic with considerable hesitation.On the basis of several specimens of coal reported tohave come from that area, Harrington (1950) mappedthese rocks as above the Serra Geral lavas and as of

66possible Cretaceous age. Baker (1923) also mentionssedimentary rocks younger than the lava in the samearea. Consideration of the structure, as well as observationsby others, suggest that the rocks constitute awindow of Triassic red beds as provisionally shown onplate 1. DeMersay (1860) and other writers describethe remarkable masonry churches and other early missionbuildings as having been built of resistant finegrainedred sandstone that is abundant in the environsof Jesus and Trinidad. DeMersay also notes the presenceof a white tough sandstone, suitable for whetstones,between the two missions and along the Argentinebank of the Rio Parana. These observations aresubstantiated by those of Robert M. Miller, who reportedorally that the rocks in and near these coloniesare largely red beds, capped by basalt on the higherridges.As described by Harrington (1950), and substantiatedby the author's few direct observations, the Misionessandstone is probably between 150 and 200 metersthick and is dark red, uniformly colored where fresh,but weathered to pink or gray in places. It is mediumto coarse grained and made up almost entirely of quartzgrains that are well rounded to spherical and havepitted or frosted surfaces. Generally the sand grainsare poorly cemented by hematitic clay, but locally therocks are silicified to form tough quartzite. Most of thebeds are massive and thick, but here and there, as in thevicinity of San Juan Bautista, they are thin bedded orcrossbedded. For example, at a point 9 kilometerswest of San Juan Bautista and 1 kilometer north of theroad, there are some small quarries that produce ex-cellent red flagstone, almost quartzitic in character,from the lower beds of the Misiones sandstone (seefig. 51).Occasional small pebbles of quartz and quartzite,ranging from well rounded to subelliptical, are scatteredthrough some of the more massive beds. Though notabundant, there are some true conglomerate beds in afew places. At a point 3 kilometers west of San JuanBautista, for example, a coarse conglomerate withrounded pebbles of quartzite and chert is exposed inroad cuts.Harrington describes a similar conglomerate, 1 meterthick, near San Juan Bautista, with a few pebbles aslarge as 15 centimeters in diameter, with fully 15 percentof the smaller pebbles of banded agate. He also describesthe sandstone on the hill 7 kilometers east ofSanta Rosa as containing abundant nodules of epigeneticagate. These nodules, as much as 20 centimetersin diameter, are very irregular in shape and show blue,light yellow and white in concentric bands. Their relationto the surrounding sandstone is such that they arecertainly concretionary in nature and probably relatedto hydrothermal activity associated with the SerraGeral lavas.Though clay or shale are not described in the literatureas an important constituent of the Misiones section,there must be considerable quantities of such material,for a large part of the outcrop area betweenCarmen del Parana and Yhu appears from the air to beunderlain by red clay or shale. In the immediatevicinity of Yhu, moreover, workable deposits of whitepottery clay and red clay suitable for brick manufacture,are well known (see fig. 52).Because of its stratigraphic position between theIndependencia series and the Serra Geral lavas, Harringtonbelieves that the Misiones sandstone is of lateTriassic age and is correlated directly with the Botucatusandstone of southeastern Brazil.TERTIARY AND QUATERNARY SYSTEMSFIGTJKE 51. Typical flagstone quarry, 3 kilometers west of San Juan Bautista. Therock is well-cemented coarse red sandstone of the Misiones series of Triassic age.A very large part of eastern Paraguay is covered byalluvial deposits of clay, silt, and fine sand of Tertiaryand Quaternary age. The deposits are probably asmuch as several hundred meters thick in places, as inthe vicinity of Pilar in the extreme southwestern cornerof eastern Paraguay where they are known to containpeat deposits, at least locally. Elsewhere their thicknessprobably ranges from 1 to 20 meters in mostplaces. Virtually every swale in the country containssome alluvium but the larger deposits are, of course,along the broad, nearly level valleys of the majorstreams. There they are almost invariably marked bypoor drainage conditions or by permanent or intermittentswamps. The boundaries of the alluvial materials

SEDIMENTARY ROCKS 67FIGURE 52. White pottery clay interbedded with red shale and sandstone of the Misiones sandstone of Triassic age. Air view near Yhu.shown on plate 1 are drawn almost entirely by connectingareas shown as "swamp" or "subject to flood" onexisting base maps, particularly the U. S. Air Forcepreliminary charts.A few fossil discoveries have been reported from, theTertiary deposits along or near the east bank of theRio Paraguay. Vellard (1934) says that many mammalianfossils, similar to those from, the Gran Chacothat are noted on page 75, have been reported from thevicinity of Trinidad just northeast of Asuncion, especiallyalong the banks of Arroyo Teju-cuare. None ofthese finds were seen by Vellard. He also says thatmany fragments of mammal bones have been foundalong Arroyo San Javahy, 6 kilometers west of Ypane,and 30 kilometers south of Asuncion. Except forTrinidad, none of these features are shown by nameon plate 1.Mastodon andium, Glyptodon, Toxodon, Macrauchenia,and Megatherium, mammals of Tertiary age, were reportedby A. de W. Bertoni (1939) as found in 1910from "below" Asuncion, quite possibly from theArroyo San Javahy locality noted by Vellard.A. de W. Bertoni (1939) also mentions the discoveryof Tertiary invertebrate fossils in limy rocks at Villeta,25 kilometers south of Asuncion. He identified Turritella,probably T. americana, fragments of Ostrea, anda few remains of nummulites. He believes that thesefossils record marine invasions during Oligocene andlate Eocene times.GRAN CHACOGENERAL FEATURESThe Gran Chaco is a deep, elongate sedimentary (andprobably structural) basin that lies between the Andeson the west and the much lower ranges along theAtlantic Ocean side of the continent.The geology of the Gran Chaco, the part of Paraguaythat lies west of the Rio Paraguay, is even less wellknown than the eastern part. Except for a few comparativelysmall outcrops near its northern and easternborders, the entire area is covered by unconsolidatedalluvial materials. The only known facts about thesubsurface character of these materials and the olderbeds that underlie them are those recorded by the logsof five deep drill holes, scattered through a very largearea.OUTCROPS OF CONSOLIDATED ROCKSThere are several large outcrops of sandstone in theextreme northern part of the Paraguayan Gran Chacothat are probably related to the Itacurubi series ofEarly Devonian age (pi. 1). There are also a fewsmall outcrops of other rocks at various places along the

68 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYEXPLANATIONOrihuelaChaco sediments, Tertiary to Recent ageUnconsolidated to semiconsolidated sand and clay,mostly red and of continental origin. Total thicknessand position of lower contact not known with anyRed beds, Pennsylvanian to Late Tnassic ageSemiconsolidated shale and sandstone, mostly red andof continental origin. Probably includes Tubarao andIndependencia seiies and Misionessandstone ofeastern ParaguayMarine beds, Silurian and Devonian age,showing recorded fossil horizonsSoft to hard dark-gray shale and fine-grained sandstone.Probably represents the equivalents of Itacurubi andCaacupe series of eastern Paraguay in large part. AHbut the uppermost 120m (375 ft) of these beds inLa Paz well appear to be different from, and olderthan, beds grouped here in other wellsQuartzitic rocks, Cambrian and Ordovician ageHard quartzite and sandstone, with some hard shale anddolomite. Possibly equivalent to sandstone andquart zite of supposed Cambrian and Ordovician agethat crop out in northern part of the Gran ChacoCollar altitudes of wells are approximate8000-9000-10,000 J- 3000FIGUEE 53. Sketch showing the major rock units in exploratory wells drilled in the Paraguayan Gran Chaco. See plate 1 for location of wells.

SEDIMENTARY ROCKS 69west bank of the Rio Paraguay. Some belong to thePrecambrian basement complex that doubtless underliesthe entire Gran Chaco basin; others belong to theItapucumi series of probable Cambrian and Ordovicianage. Those near Villa Hayes are reportedly of redsandstone and are mapped as belonging to the Misionessandstone of Triassic age. The outcrop between PuertoGuarani and P6rto Murtinho is an extension of thesupposedly late Tertiary syenitic body of the Paod'Agucar on the Brazilian side of the river.There are several outcrops of sandstone and possiblyof quartzite in the extreme northern part of the GranChaco, west of the Rio Paraguay. None of them wasseen by the author except in very distant air views andthere are no known geologic maps that show them withany exactitude.The largest outcrops make up Cerro Leon and CerroCristian (pi. 1). In addition to the several smallerbodies sketched on the map, there are a number ofsmall hills on both sides of the Bolivian border that arereportedly made up of the same rock. Some of thesehills have been used as triangulation points in boundarysurveys.In written communication to the author, Harringtonreports that the rock of Cerro Leon is a medium-grained,reddish-brown ferruginous sandstone. From this rockthe geologist for Union Oil Company collected a fewwell-preserved fossils that were identified by Dr. Har­rington as Leptocoelia flabellites. This identificationleaves no question as to the lower Devonian age of therocks, which would appear to be about equivalent tothe Itacurubi series; they are so mapped on plate 1.The quartzite and sandstone beds of eastern Boliviaand extreme northern Paraguay are briefly describedby F. Prieser (in Ahlfeld, 1946, p. 32-36). They arenearly horizontal in most places and form vast tablelandssome distance north of the international border.Some of the hills in and near Paraguay maybe erosionalremnants of these tablelands, but Prieser thinks someof them may represent uplifted fault blocks, or horsts.In Bolivia, the sandstone beds are slightly ferruginousand yellow or orange to white. They are mediumgrained, crossbedded, and cemented with secondaryquartz. Their total thickness is about 200 meters.Several thin conglomerate beds are known. The rocksare provisionally assigned to the Ordovician period byPrieser, but on admittedly thin evidence; Dr. Harringtonbelieves that they, like the rocks of Cerro Leon inParaguay, are probably of Early Devonian age.The sandstone and quartzite deposits are overlain inBolivia by shale and sandstone of possible Permian andCretaceous age locally, but by the Chaco formation ofTertiary and Quaternary age in most places. In northernParaguay these rocks are everywhere overlain orsurrounded by the Chaco sediments.SUBSURFACE ROCKSWELL RECORDSThe well records that follow are translations andcondensations of the logs furnished officially by theUnion Oil Company to the Government of Paraguay atthe close of the exploratory campaign for petroleumin the Gran Chaco; they were made available to theauthor by the Paraguayan Ministerio de Obras Publicasfor use in this report. They have doubtless beenchanged in condensation, as well as in a series of translationsfrom English to Spanish and again to English.Nevertheless, they contain some hitherto unavailablefacts as to the subsurface character of the Gran Chaco.The logs are given below; the author's attempt at theirinterpretation and correlation is sketched in figure 53.Records of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive[Translated and condensed by Eicardo Mazo U. from logs transmitted by thecompany to the Government of Paraguay.]_. ., -Picuiba well B-l:Thickness(feet)Depth(feet)Sand, yellow, fine- to medium-grained,grades downward to darker sand withlaminae of clay and pebbles cemented byred or gray clay_____.---------------- 1,008 1,008Sand and sandstone, dark-red, with claycementedangular to rounded pebbles ofquartz and other materials--___________ 87 1, 095Sand, light-green, uniform grain size withsome pinkish-brown grains_____________ 125 1,220Sand and siliceous siltstone, bluish-gray,very fine grained, some incrustations ofpyrite at 1,400 ft_-_----------_------- 300 1,520Quartz sand, fine- to medium-grained, withmuchpyrite------------------------- 260 1,780Sand, pale-greenish-gray, medium-grained;contains pyrite and one 1-ft bed of wellstratifiedsandstone- __________________ 487 2,267Sand, gray, medium-grained, with abundantsmall rounded pebbles.________________ 10 2,277Sand and sandstone, pale-greenish-gray,with some pebbles and siltstone________ 163 2,440Siltstone, olive-green, with streaks of sandand of pyrite ----------------------.- 70 2,510Sand and sandstone, greenish-gray, fine- tomedium-grained, with some pebbles and alittle shale__.------------------------ 363 2,873Sand, siltstone, and shale, brick-red, withpale-green nodules of shale_____________ 227 3, 100Sandstone, fine-grained, silty, pale-red andgreen, with some grains of coarse sand_ _ _ 44 3, 144Shale, lustrous, dark-purple-red, with partingsof fine sandy shale____-_-_-----__- 316 3,460Sand, gray, fine- to medium-grained_____ 15 3, 475

70 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYRecords of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive ContinuedT>- -i n T> i n j_- i Thickness DepthPicuiba well B-l Continued(feet) (feet)Silt-stone, micaceous, pale bluish-gray togray, with fine- to medium-grainedpebbly sandstone, lime-cemented andmicaceous; some pyrite_ _______________Sandstone, very hard, crossbedded, lightgray,fine- to medium-grained; containssome pebbles, interbedded with micaceousshale and sandy siltstone; some pyrite___Shale, hard, sandy, dark-brown, slightlymicaceous- ___________________________Sandstone, gray, fine- to medium-grained,and brick-red siltstone with gray micaceousSpots__ _ _-__-_-______-___-_____Sandstone, same as above, but containinghard marine shale, becoming more abundantdownward, ______________________Shale, hard, micaceous, gray, with laminae801011273, 5553, 5653, 5693,5803,607of firm, very fine grained sandstone.Sandstone below 3,845 ft yields strongodor of petroleum and gives other positivetests for petroleum________________ 248 3, 855Shale, hard, dark-olive-gray, with a fewlaminae of hard, gray, fine-grained sandstone.No evidence of petroleum_______ 135 3,990Shale, hard, dark, with dark stains oforganic material; some gray very finegrained sandstone; yields slight odor ofpetroleum,-- _ _________________________Shale, same as above but no odor of petroleum;highly micaceous in interval 4,060-4,070 ft______________________________Shale, same as above, with strong odor ofpetroleum in interval 4,168-4,175 ft andslight odor at interval 4,460-4,470 ft;contains one 2-in layer of limestone at5,207 ft______________________________3014813774,0204, 1685,545Shale, dark-gray, hard, very little sandstone______________________________Sandstone, friable, gray, fine- to mediumgrained;yields odor of petroleum.______Shale, micaceous, gray; with fine-grainedsilty light-gray sandstone ______________630409446, 1756,2157, 159Shale, soft micaceous dark-gray; slightodor of petroleum in one 1-ft zone neartop...______________________________ 356 7,515Santa Rosa well 1:Clay, varicolored_______________________ 810Sand, gray, fine-grained, silty, with streaksof waxy-green and red clay near base_ _ 30Clay, varicolored.______________________ 20Sand, gray, fine-grained_________________ 43Clay, red and green_____________________ 55Sand, gray, fine-grained, with sandy claybetween 974 and 980 ft_____________.__ 37Clay, blue and red______________________ 10Sand, bluish-gray, firm; silty and very finegrained, ____________________________ 10Clay, red and blue, firm, sandy; containsinclusions of hard limestone ___________ 108108408609039589951,0051,0151,025Records of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive ContinuedThicknessSanta Rosa well 1 Continued(feet)Sand, gray, friable, very fine grained andwell-sorted_-___----_------__-----_--- 30Clay, blue and red, firm, sandy to verySand, gray, fine-grained, well-sorted andwith well-rounded grains. _ ____________Clay, blue and red, mostly firm and sandy,with limy material in places. __ _ ________Sand, blue-gray, firm, with a few smallClay, red and blue, mostly firm and sandy. _Sand, white, fine-grained, firm limy _______Clay, blue and red, sandy in lower 10 ft. __Conglomerate of well-rounded black andred pebbles in matrix of blue and red14010290101203020Depth(feet)1,0551,1951,2051, 4951,5051, 6251, 6551, 675sandy clay-_____---_-----_--_-------- 10 1,685Clay, blue and red; mostly firm and sandy;contains many small concretions of limymaterial and a few pebbles. ____________ 645 2, 330Sand, gray, fine-grained _ ________--_-__-_ 50 2,380Clay, red and blue, mostly firm and sandy;contains limy concretions in places. _____ 175 2,555Sand, gray, fine-grained, soft_____-____-_- 10 2,565Clay, blue and red; firm and very sandy,with medium- to coarse-grained sand;many limy concretions in places ________ 30 2, 595Sand, gray, coarse-grained. ______________ 40 2,635Clay, blue and red; very firm, sandy _ _____ 10 2, 645Sand, bluish-gray, fine- to coarse-grained,friable to firm; clayey in many places;contains abundant small pebbles ofvarious colors almost throughout; limynodules abundant in places. One 1-ftcore of hard sandy blue-green to purplelimestone near bottom, __ _____________ 90 2,735Limestone, firm, sandy, nodular, light-gray _with streaks of red; contains large angularred and light-gray pebbles of quartziteand smaller well-rounded pebbles; top 2 ftappears weathered; grades downward tomassive white to light-gray limestone.Limestone contains 87.5 percent CaCOs,11.5 percent insoluble, and traces of MgOand FejO8 ------------------------ 10 2,745Limestone, white to gray to red, hard, massiveto nodular; sandy in places _ ______ 10 2, 755Sand, friable to firm, white to gray, fine- tomedium-grained; mostly silty; containsnodules of hard massive limestone and afew large pebbles--------------------- 80 2,835Clay, red, firm, sandy; alternates with grayfirm coarse-grained sand; many pebbles ofquartzite in lower 10 ft-__- ------------ 130 2,965Sand, red and blue, firm, fine- to mediumgrained;silty and clayey with small angularpebbles throughout- _______-_____-- 20 2,985Conglomerate, containing pebbles of sandstone,shale, and siliceous material inmatrix of sandy clay, interbedded withreddish-white hard sandstone containingmany small rounded pebbles. __________ 8 2, 993

SEDIMENTARY ROCKS 71Records of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive ContinuedThicknessSanta Rosa well 1 Continued(feet)Clay, red, yellow, and purple, firm._______ 12Shale, red and lavender, laminated, mica­Depth(feet)3,005ceous, with irregular bedding planes_____ 16 3,021Shale, light-greenish-gray, lavender, andyellow, soft to firm, with thin layers ofred, harder shale. Pyrite clusters at3,022ft____-_----__-_________________ 12 3,033Shale, dark-gray, firm to hard; poorly laminatedin large part but upper layers neartop are well-laminated and locally crossbedded.One megascopic fossil at 3,058ft (see p. 74 for list of fossils here and inlower part of well) ____________________ 249 3, 282Shale, hard, dark-gray, poorly to welllaminated,very micaceous; silty in part_ 1, 086 4, 368Sandstone, hard, dark-gray, micaceous, veryfine grained and poorly sorted __________ 6 4, 374Shale, hard, dark-gray, micaceous, poorlybedded to massive with a few thin layersof silt--_-__-____-___-_____-..--__-___ 98 4,472Recovered 2 ft of core: 1 ft of hard, veryfine-grained sandstone and 1 ft of hardmassive dark-gray shale _______________ 10 4, 482Shale, hard, massive, dark-gray, interbeddedin lower part with equal quantities of hardfine-grained silty sandstone, ___________ 72 4, 554Shale, hard, dark-gray, micaceous, interlayeredwith hard dark-gray micaceoussiltstone-_--_----_____._.__--__-____- 144 4,698Shale as above, interbedded with an equalquantity of hard gray very fine grainedsandstone in layers as much as 1 in thick. 10 4, 708Sandstone, hard, gray, very fine grained andsilty, with 10 to 20 percent of shale in thinlayers.__---____-__-_______--________ 40 4,748Shale, hard, dark-gray, massive to wellbedded,with considerable quantities oflight-gray micaceous crossbedded siltstonein upper half__________________ 639 5, 387Shale as above, interbedded with hard, veryfine grained silty and micaceous sandstone______________________________18 5,405Shale, hard, dark-gray, micaceous; massiveto poorly bedded, with silty and sandymaterial in places. Odorless gas bubblesfrom fresh core at 5,606 to 5,723 ft; noevidence of petroleum.________________ 500 5,905Sandstone, hard, gray, very fine grained,micaceous, crossbedded and silty, interbeddedwith equal quantity of hard graymicaceous shale. Sandstone shows gas infresh cores but no evidence of petroleum. 50 5, 955Shale as above with fine-grained sandstonein lower few feet; gas shows when fresh__ 50 6, 005Sandstone as above with a little shale; gasshows when fresh_____________________ 10 6, 015Shale, hard, dark-gray, micaceous, with afew thin layers of siltstone; and someclusters of pyrite crystals ______________ 1,071 7,086Records of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive ContinuedThicknessSanta Rosa well 1 Continued(feet)Shale as above with a few layers as much as0.4 ft thick of very hard massive gray limyand sandy "sheH"_____-_----_--_--_-_- 20Limestone, 0.2 ft, hard, massive, gray, and2.3 ft of shale as above---------------- 14Shale, hard, dark-gray, micaceous, with afew thin layers of siltstone; much pyrite 37Shale, very hard, dense, gray, micaceous,and very sandy, with irregular layers ofhard gray siltstone and sandstone___-_--Siltstone, very hard, gray, sandy, micaceous,crossbedded with irregular streaks ofvery hard dense shale, grading downwardto shale with some siltstone- ___________Limestone 0.3 ft, hard, gray, massive; sandstone0.4 ft; siltstone 0.2 ft; very hard,fine-grained and limy, micaceous, andcrossbedded sandstone 1.5 ft; very hardmicaceous siltstone 2.1 ft_ _______-_----Sandstone, very hard, gray, silty, finegrained,micaceous, with thin streaks ofshale-_______-__-___--------_-------- 10Shale, very hard, gray, sandy, and micaceous___ -___ _________--_---------Sandstone, fine-grained, silty, and micaceous,approaching quartzite in hardness________________-_--__-_-_------Shale, very hard, dark-gray, sandy, andmicaceous, with irregular streaks of veryhard fine- to medium-grained quartziticsandstone, especially abundant in upper25ft_ -La Paz well D-l:Silt, sandy, soft, reddish, and siltstonewith some small pebbles __________----Silt and fine sand, green-blue; with redClay, red and greenish-blue __________-_--Sand, medium- to fine-grained, greenishgraywith some red clay _ ______________Sand, fine to coarse, light-brown; containsfragments of limy material and some siltandclaySand, white, quartz, clean- _ ________--_--Sand, white, quartz; mixed with red andgreenish-blue sand..-----.------------Clay, dark red; with a little green-blue clayand some sand_______---_--_---------Silt, fine sandy, light-red, with white quartzsand; a little light-green clay_ ______-_--Sand, fine, light-brown; some sandy blueClay, dark-red; and sandy silt _ ____---_Clay, dark-red, sandy, with streaks ofbluish-green clay __ -_________--_-__--Clay, dark-red; with sandy silt and somewhitelime----Silt and clay with fine sand- _____________Silt and clay with gray lime _ ___________Depth(feet)7, 1067, 1207, 15712 7, 1698108070540102902401402704501608003022 7, 1915 7, 1967,2067,21320 7,233346 7, 579810890960140 1, 1001,6401, 6501,9402,1802, 3202,5903, 040170 3,2103,3704, 1704, 200

72 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYRecords of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive ContinuedLa Paz well D-l Continued**$§)"'Sand, silty, red and green; with somelime ________ ___381Shale, black to gray, hard, unstratified;with abundant mica __ _ _ __ 275Shale as above, with nodules of pyrite andcalcite-filled fractures144Sandstone, fine, hard, gray, micaceous;with some shaleShale, hard, and sandstone, both micaceous.343682Shale, dark-gray to black, medium-hard,laminated, micaceous; some fine sandstonein lower part _ _ _ _1, 133Sandstone, coarse; interbedded with shale;some fragments of black dolomite _ 10Shale, dolomite, and fine sandstone withpyrite29Shale, dark-gray, interbedded with lightgraysandstone55(Hole ended in hard quartzite.)Pirizal well D-l:Clay, pale- red; with a few layers of finesand; veinlets and crystals of gypsumlocally _ __ ____ _____Clay, same as above, with green clayeysiltstone and some gray sandy mudstone_Siltstone, red; with about 30 percent green,fine sandy siltstone __ _____ _ __Siltstone, green, red, and brown; someamorphous gypsum _____Siltstone, greenish-blue; alternating withbrown siltstone that contains thin sandylavers __ __________ _____Siltstone, clayey, red and green; with partingsof sand __ _ __ _ ___Quartz sand, gray, fine- to medium-grained.Siltstone, sandy, red; with a few greenstreaks and fragments of anhydriteSandstone, dark-gray, fine-grained; upperpart is hard and crossbedded, lower partvery friable _______ ___ ____Sand, dark-gray, silty __ __ _ _ _ _ _ ___Shale, pebbly, conglomeratic sandstone andsilty gray sand; small particles of carbonaceousmaterial. __ ____ ___ ___Sand, fine-grained, chestnut-brownSand, friable, fine- to medium-grained, gray;with carbonaceous material along beddingplanes. __ ______ _ ___Siltstone, sand and gypsum, gray, green, anddark-red _ __ _ ___Sandstone, dark-red, fine-grained, silty; containssome gypsum crystals; friable inpart _ __ __Siltstone, red; with sandy streaksSand, dark- red, fine-grained; with siltystreaks _ __ ______Siltstone and sandstone, dark-red1,7101,400248922200310306405101020303020102943Depth(feet)4, 5814,8565,0005,3436,0257, 1587, 1687, 1977,2521,7103, 1103,3584,2804, 4804,7904,8205,4605,4655,4755,4855, 5055, 5355,6655, 5855, 5955,6245,667Records of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive ContinuedT-,. . , n-r-vi /-( j.- iPinzal well D-l ContinuedThickness(feet)Depth(feet)Siltstone, sandy, red to chestnut-brown;with intervals of fine red sand at 5,750,5,770, and 5,800-5,840 ft; clean mediumtocoarse-grained quartz sand at 5,710-5,740 and 5,870-5,910 ft_______ __ 271 5,938Sand and siltstone, fine-grained, silty red_ _ 72 6, 010Siltstone, sandy, red to chestnut-brown;with fine-grained red sand at 6,050-6,090ft and 6,160-6,170 ft and clean mediumtocoarse-grained quartz sand at 6,040-6,050, 6,100-6,120 and 6,180-6,220 ft.. ._ 270 6, 280Sandstone, fine-grained, silty, red; with redsiltstone at 6,300-6,310, 6,350-6,370 and6,470-6,490 ft and abundant quartz sandat 6,370-6,380 and 6,400- 6,410 ft. _ - - - 260 6, 540Siltstone, red to chestnut-brown; with finegrainedred sand in lower 20 ft_ ________ 94 6, 634Conglomerate of fine to coarse sand andwell-rounded quartz pebbles.._______--- 30 6,664Siltstone, sandy, red___.____________ 20 6,684No recovery,__________________-__-_--- 16 6,700Siltstone, sandy, red; with thin layers of finesand. ._.________-_________________ 500 7,200Siltstone, red and chestnut-brown; with afew fragments of anhydrite___________ 1,086 8,286Siltstone, sandy, pale, red______________ 20 8, 306Sandstone and siltstone, fine-giained, red tochestnut-brown; with some fragments ofanhydrite,._________________ 773 9,079Shale, hard, varicolored______-___---_---_ 21 9, 100Siltstone, red to dark-red; with some sand-_ 946 10,046Siltstone and hard shale, red to chestnutbrown;with some gray-green nodules. 285 10, 331Orihuela well B-l:Clay, yellowish- to greenish-blue; with finetomedium-grained sand_______________ 1,100 1,100Quartz sand, medium-grained; with someyellow clay___________________--_--- 150 1,250Sand, muddy, fine- to medium-grained,yellow to dark-red____-___-_--_------- 80 1,330Mud and clay, red to yellow; with a littlequartz sand-_________--__--______- 1,170 2,500Mud, sandy, soft, light-red. -_________-_- 20 2, 520Mud and clay, dark-red; with quartz sand__ 750 3, 270Mud and clay, dark-red; with fine- to medium-grainedquartz sand and streaks ofwhite bentonite or ash__ __________---- 60 3, 330Mud and clay; same as above, with layersof white calcareous sandstone and one2-in layer of sandy conglomerate______ 190 3,520Mud, sandy, dark-red; with laminae of verysoft dark-red clay-____--_------------- 10 3,530Mud; same as above, with one 4-in layer ofsoft pebbly sand__--__----_----------- 20 3,550Sand, light red, muddy, fine-grained-_____ 30 3, 580Sandstone, soft, friable, fine- to mediumgrainedreddish-gray, with pebbles-_____ 300 3, 880

SEDIMENTARY ROCKS 73Records of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive ContinuedOrihuela well B-l Continued(fee?) SSSand, muddy, 1.5 ft, red, fine- to mediumgrained;1.5 ft red siltstone and shale,with some quartz pebbles._____________ 10Sand, fine-grained, silty, and sandy siltstone-_ ______________________________ 10Sand, soft, micaceous, brilliant red, finegrained______________________________40Sand, soft, friable, red, fine-grained_ _ -____ 110Shale, red____________________________ 40Siltstone, sandy, light-red; fairly hard attop, grading downward to softer andsandier material____________________-_ 70Sand, soft, friable, silty, brilliant-red-__-__ 60Siltstone, sandy, soft fine sand, and thinlayers of clay, all bright red; a little hardDepth(feet)3,8903,9003,9404,0504,0904, 1604,220limy sandstone 10 to 20 ft above base___ 240 4,460Sand, silty, bright-red, fine- to mediumgrained____________________________770 5,230Sandstone, hard, fine-grained, light-red-___ 10 5, 240Sand, soft, friable, silty, bright-red, micaceousnear base_____--__-_---__-__--__ 50 5,290Siltstone, sandy, hard, red; with black stainsof an unknown mineral._______________10Sand, silty, bright-red___________________ 150Sandstone, hard, fine-grained, light-red-___ 10Sand, silty, soft, red; with laminae of clay__ 50Siltstone, sandy, bright-red; with laminaeof clay ______________________________Sand, soft, friable, silty, fine-grained;with a few laminae of clay_____________ 170Shale, dark-red_________________________ 10Sandstone, fine- to medium-grained, reddish-gray.- __ _________________________Sand, soft, friable, silty, fine-grained, lightred_______-__________________46Siltstone and shale, bright-red.___________ 94Sand, soft, friable, red, fine- to mediumgrained-_____________________________ 180Siltstone, sandy, bright-red; with abundantanhydrite and pebbles of quartz ________ 150Sand, soft, silty, fine-grained, red; withangular pebbles of quartz______________ 60Siltstone, sandy; with laminae of red shaleand abundant pebbles of quartz ________ 465,3005,4505,4605,51010 5, 5205,6905,70010 5, 7105,7565,8506,0306, 1806,2406,286Records of wells drilled by Union Oil Company in the Gran Chaco,western Paraguay, 1944 to 1949, inclusive ContinuedOrihuela well B-l Continued(fee()Quartz, white, and quartzitic sandstone,with fragments of red siltstone and ofpale-green shale. __ ___________________ 255Sandstone, quartzitic, fine-grained; withstains of iron oxide____________________ 174FOSSILSDepth(feet)6,715The following record of fossils recovered from thePicuiba well was given to the writer by Dr. Horacio J.Harrington and is published with his permission.Fossils from Picuiba wellMetersDepthsFeetTop of Devonian_-___________________ 1,187 3,893Plant remains, indet-_________________ 1,207 3,959Calamitean stems and wormburrows__ _ 1, 273- 4, 175-4, 1791,274Cyclostigma sp______________________ 1,290 4,231Palaeoneilo sp________________________ 1,333 4,372Crinoid stems (very similar to thosedescribed by Steinmann from the lowerDevonian of Bolivia)________ 1, 394-1, 398 4, 572-4, 585Wormburrows and very small Cruzianaliketrails______________________ 1,490 4,887Brachiopod indet. and plant remainsindet__________________________ 1,502 4,926Crinoid stems, like those of level 1,394__ 1, 509 4, 949Hadrorhachus australis (Clarke)_______ 1, 561 5, 120Crinoid stems, like those of level 1,394__ 1, 628 5, 340Tentaculites crotalinus Salter and Australostrophiamesembria (Clarke)____ 2, 020-2, 022 6, 625-6, 632This record indicates that the Lower Devonian bedsextend downward at least as deep as the 2,022-meterlevel and Harrington writes that he "would not besurprised to learn that the lowermost 500 meters of thewell are also lower Devonian." The following tableshows that there is also a very thick section of LowerDevonian beds in the Santa Rosa well. This recordis taken from a report made to the Union Oil Companyby Harrington and made available to the presentauthor by the Paraguayan government.

174 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYDistribution of species of fossils in Union Oil Company's Santa Rosa No. 1 well[Determinations by Dr. Horacio J. Harrington, Universidad de Buenos Aires, who states in a report to Union Oil Company that all fossils are marine and of EarlyDevonian age]Depth in feetSpecies3,055-3,0653,600-3,6023,615-3,6254,423-4,4335, 472-5,4825, 492-5,5025, 522-5,5305,530-5,5405,6255,960 6,2906,3306, 391-6,4016,688-6,6986,698-6,7076,698-6,7076,698-6,707. Ch.skottsbergi..^ . . _____ ___. Leptaena sip ____ ______ _____). Spirifer sp _________________ __ ___ __ ___. Trilobite?-__-_________-__-__-______-__-______ _________XXXvXXX?Xv?XXX?______XXXXXXXXXX9~x~"XX?XXX?______XXINTERPRETATION OF WELL RECORDSThe following broad generalizations can be interpretedfrom the facts available in the well records above andfrom the few surface outcrops.The entire Gran Chaco basin is doubtless underlainby Precambrian basement rocks, but their surface isprobably everywhere at considerable depth except inthe extreme northeastern part of the Gran Chaco; theyare very deeply buried more than 3,289 meters (10,331feet) in the southwestern part, near the Pirizal well.The Itapucumi series of limestone and dolomite ofCambrian and Ordovician age probably overlies thePrecambrian rocks directly in places; how far it extendswest of the outcrops along the Rio Paraguay is unknown,but it was not recognized in the drill holes nordoes it reappear at the surface in the Andean foothillswest of the Gran Chaco (Ahlfeld, 1946, fig. 23). On theother hand, quartzitic rocks, not known in easternParaguay, extend beneath the younger rocks at leastas far south as the Santa Rosa, La Paz, and Orihuelawells.A thick series of dark-colored marine shale and sandstonebeds rests directly on the older quartzitic rocks.These beds, which are more than 1,200 meters (4,000feet) thick in the Picuiba and Santa Rosa wells, thinto less than 800 meters (2,600 feet) in the La Paz wellonly 70 kilometers east of the Santa Rosa well; mostof the rocks there appear to be older than those in thePicuiba and Santa Rosa wells. They appear to beentirely missing in the Orihuela well and, if there atall, are below the 3,289 meters (10,331 feet) bottom ofthe Pirizal well.There can be little doubt that these marine beds areat least in part the equivalents of the Caacupe andItacurubi series of eastern Paraguay and of the LosMonos and Iquiri groups of beds assigned to the Devonianin eastern Bolivia (Ahlfeld, 1946, p. 58-62, fig.23), where they reappear at the surface in a series ofanticlines that parallel the front of the Andes. Thefossils identified by Harrington in cores from the SantaRosa well are evidence for this correlation. It shouldbe noted, however, that according to Union Oil Companyreports to the Paraguayan Government, the Devonianbeds in the La Paz well are only about 120meters (400 feet) thick; these are underlain by a sequenceof Paleozoic beds that were not in the SantaRosa well and with very hard quartzite at the base.The older Paleozoic beds are covered by a greatthickness of unconsolidated and semiconsolidated bedsof sand, clay, sandstone, shale, and conglomerate.They are largely red and, so far as can be told, representall the Gondwana or Santa Catarina beds (except forthe Serra Geral lavas) of eastern Paraguay, as well asa Tertiary to Recent series that is not known in theeastern half of the country. The total thickness ofthis accumulation is not known, but it is certainly morethan 3,000 meters (10,000 feet), for in one well, thePirizal, these beds were not penetrated at a depth of10,331 feet. There is nothing in the well logs to showthe break between the Gondwana beds and the youngerChaco sediments, although, on the basis of recordedchanges of color and degree of consolidation, it appearslikely that the Chaco beds are about 650 meters (2,000feet) thick, underlain by beds that tend to be harderand redder than those above.CHACO SEDIMENTSThe outcrops of igneous and sedimentary rocks describedabove make up only a tiny fraction of the surfaceof the Gran Chaco. The remainder of this vastplain, which rises gently from a minimum altitude of

STRUCTURAL GEOLOGY 7555 meters along the Rio Paraguay to a maximum ofonly about 400 meters along the western border of thecountry,is covered by unconsolidated alluvial materialshere called the Chaco sediments. These materials,called the Chaquena formation in Bolivia (Ahlfeld,1946, p. 52, and Oliveira and Leonardos, 1943, p. 780)and the 'Pampa formation in Argentina (Stappenbeck,1926, p. 68-170) are little known even at the surface.The Chaco sediments, that is, those above the Gondwanaor Santa Catarina sediments, are probably similarto those of northern Argentina, described in considerabledetail by Stappenbeck (1926, p. 68-170). There, theyrange from Miocene to Recent, are largely unconsolidatedclay with some sand, and include both marine andcontinental deposits. The amount of material of eolianorigin included in these beds is unknown. Sand dunes,some stabilized and some active, are known at the surfacein the extreme northwestern corner of Paraguay.Kanter (1936) failed to confirm the presence of trueloess in his travels through the Paraguayan GranChaco, but as Ahlfeld (1946, p. 53) points out it ispossible that some of the material at the surface, as wellas in the deeper beds, is loess, deposited by the strongwinds that blow northward from the Argentine pampasat present and probably also in the past.Four known occurrences of fossil mammals are re­ported from the Gran Chaco by Vellard (1934). Oneof these is near Reventon, on the lower Rio Pilcomayo;the other three are along the upper Pilcomayo nearthe forts of General Bruguez, General Delgado, andSalto Palmares. Not all of these localities are shownon plate 1. Vellard also notes unconfirmed reports ofsimilar fossils on the banks of the Rio Negro.None of these localities have been explored; the findshave been made by soldiers assigned to the militaryposts. The fossils are said to be exposed in the bedsof rivers or along their banks; new exposures are madeat frequent intervals by the constantly changing streamchannels. Vellard says that bones from Reventonhave been identified by A. de W. Bertoni as those ofGlyptodon clavipes, Mastodon andium, and Machrancheniaboliviensis.STRUCTURAL GEOLOGYGENERAL RELATIONSParaguay occupies parts of two great sedimentary andstructural basins the Parand basin of southern Brazilto the east and the Gran Chaco basin of Paraguay,Bolivia, and Argentina to the west. In its grossaspects, the geologic structure amounts to a deepsyncline beneath the Gran Chaco whose western limbrises gradually toward the Andes Mountains and whoseeastern limb rises to a gentle northward-trending anticlinethat is parallel to and only a short distance eastof the Rio Paraguay. The easterly limb of this anticlinedips at very low angles eastward toward theBrazilian center of the Parana basin.The major structural features shown on the geologicalcross sections that accompany plate 1 are based moreon the distribution of the major rock units and theirrelationship to the topography than on detailed observationsor other knowledge of structural features them­selves. In many places there are, however, bits ofdetailed evidence as to local geologic structures. Theyare all shown on the map and many of them are mentionedin the text. Thus, the local attitudes of bothmetamorphic and sedimentary rocks, as observed bythe author or recorded in the literature, are known atmany widely scattered localities throughout easternParaguay. A few faults are also shown on the map,though most of them are mapped on very scanty evi­dence. There is good evidence of minor thrust faultingin the Itacurubi beds south of Eusebio Ayala (seefig. 48); the importance of thrusting in the structuralhistory of the region is quite unknown, however.ANTICLINE BETWEEN RIO APA AND SAN JUAN BAUTISTAThe anticlinal flexure that separates the two basinsexposes the older Precambrian and Early Paleozoicrocks from the Rio Apa as far south as San Juan Bautista,where it appears to die out or to plunge southward,for the southward-dipping Triassic rocks coverthe older rocks south of that point. The sedimentaryrocks and the overlying Serra Geral lavas on the eastlimb of the anticline dip generally at very low anglestoward the east, but there are reversals of dip locally.Most of the rock units probably also thicken eastwardfor although there is little known local evidence of this,the entire sedimentary-volcanic section is thicker insoutheastern Brazil than it is in eastern Paraguay.Available data indicate that the western limb of theanticline is much steeper than the eastern one, for thebeds that occur at the surface along the anticlinalaxis are more than 3,000 meters (10,000 feet) deepbeneath the central part of the Gran Chaco basin.It is entirely possible that this drop, or part of it, isdue to a major fault or faults that parallel the generalcourse of the Rio Paraguay, evidence being maskedby the Chaco alluvial sediments. It seems moreprobable that folding has played a more importantrole than faulting in development of the structure butthis statement is based on little evidence. Strongfaults with downthrow to the west are known along theRio Parana in Argentina, south of Paraguay (Harrington,oral communication). Somewhat similar faultsystems are also known north of Paraguay in thegeneral vicinity of Corumbd, Brazil (Almeida, 1945,and Dorr, 1945). Possibly these fault systems also

76 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYcontinue in Paraguay, roughly parallel to the RioParaguay. If so, they must be somewhat west of thepresent stream and buried by the Chaco alluvialsediments. Only further subsurface data, geologic orgeophysical, will solve the problem.Ther£ is some evidence that the anticline has been inexistence, though intermittently, since early in Paleozoictime. This would account for the sandy nature, as wellas the relative thinness of most of the Paleozoic andMesozoic sedimentary units along its axis as comparedwith their apparent correlatives in the Gran Chacobasin and as they are described in the Parana basin ofBrazil and in the Andes of Bolivia (Oliveira and Leonardos,1943, and Ahlfeld, 1946).The Rio Apa and San Juan Bautista anticline isdoubtless far more complex than described in the lastparagraphs, as indicated by the several faults and thediversity in attitudes of the Precambrian and Itapucumirocks near the Rio Apa and by the absence of olderrocks at the surface between Asuncion and Concepcidn,suggesting a sag in the structure in that area. The complexityis also indicated by the interesting but incompletelyunderstood structural and topographic featurecalled the Ypacarai depression. As described by Harringtonand shown on his map it is a rectilinear valley,65 kilometers long and 6 to 8 kilometers wide, thattrends northwestward from the vicinity of Paraguaripast the northern end of Lago Ypacarai. It is characterizedby a nearly flat floor, covered almost everywhereby swampy alluvium or by the shallow waters ofthe lake. It is flanked on both sides by relatively highabrupt hills whose faces suggest fault scarps or faultlinescarps in many places.Harrington believes that the depression is a long,very narrow graben bounded along its sides by majorlongitudinal faults and probably by a strong transversefault at its southeast end. As evidence of the grabenstructure, Harrington cites the presence, 2 kilometersnortheast of Paraguari, of varved clay and of a graniteerratic boulder seemingly belonging to the Tubaraobeds of Pennsylvanian age but in juxtaposition to bedsof the Caacupe series of Silurian age. He also givesevidence of strong faulting along the western side ofthe depression, marked by fault breccia, locally as muchas 300 meters wide, at a number of places from Paraguarito some distance northwest of the Vargas Penaclay pit near Itaugua. In. addition, he saw strong fracturesalong the eastern side of the depression.In short, Harrington believes that the Ypacaraidepression represents a downfaulted block that hasdropped the rocks several hundred meters, thus bringingthe Tubarao beds within it down to the level of thelower Caacupe1 beds along its sides. There is littleevidence of a transverse fault to close the southern endof the depression but there may be one. As mentionedby Harrington (1950, p. 51) such a fault, extendingfrom Caballero northwestward past Paraguari towardthe Rio Paraguay near Villeta, would explain the abruptdisappearance of the Misiones sandstone south ofa line between Villeta and Yaguaron.GRAN CHACO BASINStudies of the outcropping rocks of eastern Paraguayand of the records of the deep exploratory wells in theGran Chaco indicate the presence of a very deep basinthat centers in southeastern Paraguay, not far northof the Pirizal well. From this center the rocks risenorthward toward the outcrops of Devonian sandstoneand quartzite near the northern edge of the country.They also rise eastward, for some of the same rocks, orthen- close correlatives, appear at the surface alongthe Rio Paraguay and east thereof. Within a few tensof kilometers west of the Paraguayan border, in Bolivia,the rocks rise in a series of anticlines, some of themoil producing, along the eastern flank of the Andes.Available evidence is far too scanty to determine theage of the Gran Chaco basin or how much of it is dueto folding and how much to erosion and subsequentfilling. Nor are there any available facts as to the presenceor absence of older structures within the Paleozoicbeds of the basin as distinct from the broad downfoldindicated on section A-A', plate 1, which, as drawn,involves the Mesozoic beds as well as the Paleozoic ones.It seems likely that the major folding took place intwo stages once after the Devonian marine sedimentshad been laid down but before the red beds of Pennsylvanianthrough Triassic age were formed, and onceduring the Tertiary. The latter folding, associated withthe major uplift of the Andes, involved the continentalred beds as well as the older rocks.GEOLOGIC HISTORYGENERALIZED ACCOUNTWith the exception of the paragraphs below on theGran Chaco plains and on the Alto Parana valley,most of the following summary of the geologic historyof Paraguay is generalized from that given by Harring­ton (1950). During Precambrian time a series ofclastic sediments of unknown thickness was foldedand metamorphosed before being invaded by graniteand other acid rocks. Most of the acidic rocks weredeep-seated intrusives, but at some time during thisperiod there were extensive surface flows and nearsurfaceintrusions of porphyry. Between the formationof the granitic rocks and Late Cambrian or Ordoviciantime there must have been strong uplift anderosion followed by subsidence, permitting depositionof the Itapucumi limestone beds under marine con-

GEOLOGIC HISTORY 77ditioiis, on an erosional plane carved on the Precambrianrocks.In late Ordovician time there was widespread upliftand regression of the sea, followed by an erosion periodthat permited removal of the limestone, and probablythe quartzite, in southern Paraguay and quite possiblyin parts of the area beneath the Gran Chaco. In EarlySilurian time there was a general depression again,resulting in marine invasion of the Parana basin anddeposition of the Caacupe sediments. Whether theGran Chaco basin was connected with the Parana basinat that time is not known, but marine sediments thatappear to be equivalent to the Caacupe series areknown there. Quite possibly the two basins were onlypartly connected, with shoreline conditions, or atleast shallower waters, between them in most places.Toward the close of the Silurian there was reneweduplift and erosion, followed in Early Devonian timeby a new invasion by the sea, this time probablyinitiated in the Andean geosyncline so that depositionof the Itacurubi series preceded from west to east,or from the Gran Chaco toward the Parana basin.Middle Devonian time essentially marked the lastof marine conditions in Paraguay. From that time toLate Pennsylvanian or Permian time there was apparentlya period of extensive erosion and near-pene-planation. A glacial period followed, during whichthe tillites, varved clays, and other sediments of theTubarao series were laid down over most of easternParaguay, possibly over the Gran Chaco as well.The glaciation was followed by renewed uplift anderosion until some time in the Permian, when theIndependencia series was laid down under continentalconditions. This period of deposition was againfollowed by erosion that led to complete removal ofall the sedimentary rocks in places, notably in southernParaguay. During Late Triassic time the Misionesseries of red beds was laid down on the new erosionsurface. The new red beds were soon covered byoutpourings of Serra Geral basaltic lavas fed by fissuresthat centered in the Parana basin. The lavas didnot extend much farther west than is indicated bytheir present outcrop pattern. The lava flows wereaccompanied or closely followed by small intrusionsof diabasic rocks in many places. At some time ortimes, from Late Triassic to late Tertiary, there wereintrusions and volcanic eruptions of alkalic rocks.Some, like the caldera at Acahay and its nearby volaniccones still retain most of their original form, hencewould seem to be very young, but other bodies ofalkalic rock, such at that at Mbocayaty, are of quiteindeterminate age.The sparse evidence at hand suggests that there wereno major periods of strong faulting or folding duringthe entire time from the close of the Precambrian untilthe Triassic. Instead, the entire region that is nowParaguay seems to have been the scene of a successionof gentle risings and lowerings of the crust, each markedrespectively by periods of erosion and marine or continentaldeposition. The enormous thickness of continentalred beds in the central Gran Chaco, however,strongly suggests that a major downwarp, perhaps accompaniedby faulting, began at some time after theclose of the Devonian. It probably reached its maximumduring the Triassic, but may well have continuedinto the Tertiary, when it reacted to the major upliftof the Andes Mountains by renewed downwarping.Except for the scattered volcanic rocks, and theswampy alluvium in many places, little or nothing isknown of the geologic history of eastern Paraguay fromthe beginning of the Cretaceous to the present. Thepresent upland topography is carved by subaerialweathering and erosion on rocks of Jurassic or olderages; the lowlands are largely filled, or at least thinlycovered, by fine debris washed from the uplands ordeposited by overflows of the Rio Paraguay. The factthat Jurassic and younger sedimentary rocks are knownin nearby Brazil suggests that similar rocks may havebeen deposited in eastern Paraguay; if so, they havesince been removed completely.In discussing the valley of the Alto Parana, and particularlythe Salto del Guaira and other waterfalls,Baker (1923) indicates convincingly that the SerraGeral lavas have been exposed at the surface ever sincethey formed in Late Triassic or Jurassic time. He feelsthat the upland surface of the Parana basin, incised bythe narrow gorges of the Rio Parana and its tributaries,represents one of the "oldest known youthful topographiesin the world" and ascribes the cataracts to headwarderosion along the axis of the synclinal basin whichwas followed by the Rio Alto Parana. Washburne(1930, p. 117-122), however, believes the valley of theRio Alto Parand to be very late Pleistocene or, moreprobably, Recent in age. The narrow gorges in theSerra Geral lavas he ascribes to simultaneous erosionalong great lengths by constricted rapids rushing downdip. The cataracts he believes to be due to downfaultingof the lavas toward the downstream side or toabrupt upstream dips of the flows.GRAN CHACO PLAINSThe Gran Chaco, once a structural and sedimentarybasin, is now an aggrading alluvial plain that is beingbuilt up with fine debris from the Andes to the west,distributed by the many meandering streams thatwander across it toward the Rio Paraguay. How longor how continuously the alluviation has been going onis unknown. It probably began at some time in the

78 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYlate Tertiary; certainly it is continuing today. Thefull answer must await further detailed studies of theGran Chaco alluvial sediments themselves and of thegeomorphologic history of the eastern Andes.To the author's knowledge, Johnston (1876, p. 499)was the first to suggest that the Rio Paraguay is inprocess of being shifted toward the east as a result ofthe uplift of the Andes. There is considerable evidenceto support his belief that the river once flowedsome distance west of its present course and it is beingpushed eastward by the growing alluvial plains of theGran Chaco. This evidence lies chiefly in the relationsof the river to the outcrops of Itapucumi limestonefrom, the Rio Apa southward to San Salvador. On theeast bank of the river the limestone forms almost continuouscliffs, 3 to 30 meters high, along this entirestretch; in addition there are a number of small butsignificant hills made up of Itapucumi limestone alongthe Gran Chaco side of the river from near PuertoCasado northward (pi. 1). As seen in the field in thevicinity of Vallemi, as well as by aerial observation andstudy of aerial photographs farther south, the riverfollows almost exactly the curves in the strike of theItapucumi beds for the entire distance. The limestonecliffs along the river are almost everywhere steep; theirsurfaces are rough and pitted (see fig. 43).A few of the stronger joints in the rock are markedby narrow, steep to vertical-walled ravines, most ofthem choked by large joint blocks that have slid intothem. Most of the steeply dipping joints, however,are tight and almost imnoticeable on upper parts of thecliff faces. Yet within a few tens of centimeters of theriver level many of these joints have been wideneddownward by solution into open caves, shaped likeinverted Vs. This feature was also described andsketched by Carnier (1911c).In addition to the small tent-shaped caves along jointsthere is a striking series of longitudinal notchlike caves,that extend back beneath the cliffs from 60 centimetersto as much as 15 meters. As seen in April 1952, whenthe river was at a fairly high stage, these notches occurredat intervals from the water surface to a levelabout 5 meters above it; all were parallel to the watersurface. The upper limit marks the highest river levelin recent history. The solution notches are continuousacross different beds, though they tend to cut deeperinto the purer limestone beds than they do in thedolomitic ones.The relationship of the river to the general structureof the rocks, as well as to the solution features, seems tomean that the river is pushing against the limestone outcropslaterally, rather than that it has cut its way downthrough them in more orthodox fashion. Had it cutdownward,the limestone, which is extremely soluble inrelatively lime-free, carbon dioxide-rich water such asthat of this tropical stream, should have been dissolvedalmost completely. Outcrops, had they survived at all,should have been low and rounded, and joints shouldhave been widened into broad valleys. It seems morereasonable to suppose that until comparatively recentlythe Rio Paraguay flowed across the alluvium of theGran Chaco, west of its present course, and that theItapucumi rocks were subject only to subaerial erosion.Then, as the alluvium encroached eastward, it pushedthe river sidewise against the higher lands of what isnow eastern Paraguay, leaving "islands" of limestoneprotruding through the alluvium farther west, and allowingthe river to begin to gnaw away at the mainoutcrops.The only other explanation that occurs to the authoris that the Gran Chaco plains were once higher andmore extensive than they are at present and that theGran Chaco basin was then dropped relative to the rocksof eastern Paraguay. This would, it is true, expose thelimestone suddenly to solution by the river, but it failsto explain the outcrops of limestone on the Gran Chacoside of the river nor does it account for the sinuouscurves of the river that conform to the structure of thelimestone.MINERAL RESOURCESSUMMARYParaguay possesses large quantities of certain nonmetallicmineral resources, notably clays suitable forbrick, tile, and pottery; limestone and other raw materialsfor portland cement and for lime; common andornamental building stones; glass sand; talc; and mineralpigments. Supplies of all these materials appear tobe more than sufficient to meet all conceivable domesticrequirements.Except for iron ore, of which there are many small butrich deposits, the country appears to be very poorlyendowed in most other mineral resources, metallic andnonmetallic. It has a little manganese, copper, mica,and beryl, but unless larger and richer deposits arefound in the future than have been in the past, none ofthem seem to offer much promise. There is some slightchance that rumors of the existence of gold, tin, tungsten,lead and mercury, and gem stones may yet besubstantiated by actual discoveries or rediscoveries, butthe possibility of finding large or rich deposits of any ofthem is rather remote. There are, however, goodgeologic reasons for hoping that worthwhile deposits ofsalt, gypsum, and bauxite may yet be uncovered.Even if rich mineral resources were to be discovered,the general lack of fuels and power would preclude thedevelopment of manufacturing industries on a largescale. Aside from wood and water power that is both

MINERAL RESOURCES 79remote and totally undeveloped the only known sourceof fuel or energy in the country lies in the peat depositsin the vicinity of Pilar. There is a fair chance thatpetroleum resources may exist beneath the Gran Chaco,but if so, their discovery and development will requirethe investment of many million dollars in the searchfor them.Available facts on all the known and reported mineralresources are given in the following paragraphs; thesection on "Future of the mineral industry" containssuggestions for making the most of the resources thatthe country is known to possess and for searching forothers.BARITEA vein or veins of barite reportedly exists at or nearFuerte Olimpo, on the upper part of the Rio Paraguay.The deposit is probably in one of the bodies of igneousrock ("porphyry") that are shown on most maps justsouth of the fort (pi. 1). It was reportedly examined bythe Union Oil Company as a possible source of materialfor heavy drilling mud, but was not developed by them.Some studies have also been made by other groups, buthigh costs of transportation, tariff difficulties, and othereconomic factors have discouraged any active exploration.BAUXITEBauxite, the ore of aluminum, is reported from SanJuan Nepomuceno, Altos, Piribebuy, and Paraguari,according to notes in the files of the Departamento deGeologia, Ministerio de Obras Piiblicas. No bauxitewas seen, but in view of the deep weathering and laterizationof most of the rocks in eastern Paraguay,deposits of bauxite or of high-alumina clay are to beexpected. The alkalic rocks, such as the shonkiniteat Mbocayaty and the phonolite and nepheline syeniteelsewhere, are of special interest in this regard. Weatheringand laterization of similar rocks in Brazil and inother parts of the world have yielded large deposits ofbauxite of commercial grade. The author knows of noplaces in Paraguay where these alkalic rocks are weatheredto laterite, but it would be surprising if no suchweathered zones exist. All the bodies of alkalic rocksshown on plate 1 are potential sources. Because of thelack of fuel and power locally, only large deposits thatcould form the basis of an export industry would be ofinterest. A determined search for such deposits appearsto be worthwhile.BERYLBeryl is reported by Boettner (1947) in pegmatitedikes near Caracol, not far from the Rio Apa. It isassociated with mica and quartz. Occasional crystalsof beryl are also reported by others from various partsof the Precambrian terrain in northeastern Paraguay,465871 ^59 7but no deposits that might be workable have come tothe author's attention.CEMENTThe country's one portland-cement plant, whichfirst went into production early in 1952, is at Vallemi,on the east bank of the Rio Paraguay, not far south ofthe Rio Apa. The wet-grind, rotary-kiln processadopted is similar in all respects to modern practice inEurope and the United States except that pulverizedcharcoal is used for fuel. The plant itself is an oldBelgian plant, reconstructed at Vallemi by native laborunder the training and supervision of a German cementspecialist. When visited in April 1952, only one kiln,with a daily capacity of 100 tons, was in operation, butparts and plans were available for more than doublingthe capacity in future. Except for bags, gypsum, andballs for grinding, which must be imported, the plantshould be self-sustaining, as raw materials and fuel arepresent in abundance and the company has plans forreforestation as the existing forests are used up. Fromthe purely technical standpoint, therefore, there isevery reason to believe that the operation could supplyall of Paraguay's .requirements for portland cement andcould even produce some surplus for export. Whetherit continues to do so will depend on the company'ssuccess in replacing worn plant parts and on economicor political factors. The Itapucumi series, of Cambrianand Ordovician age, provides part of the raw materialsfor the plant. The deposits consist of limestone andrelated rocks that crop out prominently along this partof the Rio Paraguay. (See fig. 43.) Both argillaceousand calcareous rocks come from the same quarry, whichis parallel to the river and immediately in back of theplant so that the quarried rock needs only be moved afew meters. The quarry face in early 1952 was about20 meters high and between 100 and 200 meters long.The lowest and oldest rock exposed in the quarry,at its extreme north end, is hard light-red silty limestonethat contains much fine-grained mica. Although soimpure that it resembles argillite in the field, in thinsection it is seen to be a slightly siliceous dolomiticlimestone. It is quarried separately from the limestonethat overlies it and is used as the aluminous portionof the cement mix. It is thinly bedded, strikes nearlydue east and dips south about 20°. It is regularlybedded but has been sufficiently metamorphosed tohave a slaty cleavage which makes it difficult to breakit along bedding planes, as the rock tends to fractureinto elongate pencillike splinters. The uppermost 2meters of this argillite unit is yellow instead of red andthe top 30 centimeters consist of soft yellow clay thatcontains irregular masses of white to yellow, soft butcoherent, granular calcium carbonate. This yellow

80 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYclay zone may represent weathering along an unconformitybetween argillite and limestone, particularlysince the overlying beds differ in attitude from thosebelow. It is equally possible, however, that the discolorationand softening are due to weak hydrothermalalteration.A series of limestones, some dolomitic, overlie theargillite. The entire series is about 50 meters thick,but only the lower 15 meters are exposed in the quarryface. The series has been sampled at the surface andis reported to be comparable in composition to therocks exposed in the quarry. No drilling or samplingof the beds in depth has been attempted. The bedsstrike northeastward and dip southeast, or into the hill,at a rather regular angle of 15°. They are 30 centi­meters to 1.30 meters thick. There are several continuousbeds of dolomitic limestone that are characteristicallyflesh pink to white in color and streakedor mottled. They are called "bacon rock" locally.The remainder of the series is made up of alternationsof dark-blue-gray crystalline limestone and greenish-gray limestone. The blue-gray rock, which is cut byveinlets of white calcite, is reported to contain anaverage of 95 percent CaCO3 . The greenish-gray rock,which has an average content of 80 to 85 percentCaCO3 , is made up of white to dark-gray crystallinelimestone with many irregular slickensided streaksand nodules of dark-dull-green chloritic material.Much of this rock could be mistaken easily for ser­pentine marble. All the rocks in the series are partlyto entirely recrystallized and many of them wouldform excellent ornamental marble.A series of strong, nearly vertical joints that trendnortheastward, 1 to 3 meters apart, cut all the beds.Some appear to be minor faults, with the beds droppedfrom a few centimeters to as much as 2 meters on thesoutheast sides. Many of the joints have been openedby solution, especially near the surface. The resultantopenings, 4 to 75 centimeters wide, are filled with coarsegrainedgranular calcium carbonate (caliche) thatcements a breccia of rock fragments. The caliche,which also coats the surface in places, is too high inmagnesia and silica to be used for cement; it, and thedolomite in the quarry, must be removed by handor avoided by selective quarrying.The rocks are cut by many irregular veinlets of whitecalcite, with an opening here and there that is linedwith crystals of calcite, dolomite, or mixed carbonate.One small grain of chalcopyrite was seen in one of theseveinlets and one irregular mass of white quartz, about12 centimeters in diameter, has been found. Thesefacts indicate rather clearly that the rocks have beensubjected to mild hydrothermal alteration.On the assumptions that the present practice ofsorting out the dolomite by hand continues to besuccessful, and that the higher beds, which will bereached soon in quarry operations, are no more dolomiticin depth than they are at the surface, the Vallemioperation seems to be assured of adequate raw materialsfar into the future. Even should these assumptionsprove incorrect it is certain that sufficient limestoneof usable grade can be found somewhere within the beltof outcrop of the Cambrian and Ordovician rocks.CLAYClay is one of the most widespread and abundantmineral resources of Paraguay, and the brick and tileindustry is by far the most important mineral industryat the present time. In addition to the common clays,there are many deposits of clay of pottery grade;they form the basis of a moderate-sized industry thatcould be much expanded.There are a few relatively modern plants that employsome machine methods. Good examples are the VargasPefia plant near the town of Ypacarai, which produceshollow structural tile, sanitary porcelain, sewer pipe,and other ware and the large plant at Aregua, whichproduces a large variety of cheap pottery. A greatmajority of the scores of brick and tile plants throughoutthe heavily populated regions, however, are tinyfamily affairs, producing only a few thousand brick peryear. In these, the clay is dug by hand from shallowpits, and moved by wheelbarrow to a central pointwhere it is thoroughly trodden by oxen attached to along sweep. For some purposes, straw or grass isadded to the clay at this stage. The clay is thenfurther kneaded by hand in small quantities, and packedtightly into crude wooden or metal molds. After therough tops are cut off by means of a wire the bricksare carried directly to an open grass-thatched dryingshed; thin slabs for tiles are first bent over a woodenform to give them the proper shape. After severalweeks of drying in the air the products are burned ina small wood-fired kiln. The final products vary considerablyin quality, but most are at least fair to good,and have a pleasing buff to light red color. Consideringthe amount of hand labor that must be expended oneach individual brick it is not surprising that bricksare roughly twice as large as the standard size usedin the United States and in Europe.REFRACTORY CLAYGood refractory clay, suitable for firebrick and otherhigh temperature uses, seems to be relatively scarce,but this may be due more to lack of adequate searchand testing than to actual scarcity. Some of theknown clay deposits have at least moderately goodrefractory properties. For example, the local clay nearthe old Quyquy6 iron furnace is reported to have yielded

MINERAL RESOURCES 81as good refractory bricks as those imported fromEngland. The glass plant at Eusebio Ayala uses localclay for its furnaces, though it has been found best toburn part of the clay first, regrind it, and then mix itwith unburned clay to get the best results.ALLUVIAL, CLAYMost of the small cottage-type clay plants depend onshallow accumulations of clay that characterize nearlyall of the topographic swales in the country. Clay isnaturally far more abundant in the areas underlain byshale, but nearly all the sandstone contains interstitialclay material that is released on weathering and concentratesin topographic depressions. These near-surfaceclay deposits are commonly gray to black becauseof a high content of carbonaceous material, but a feware colored red to brown with iron oxides.WEATHERED SHALEIn contrast to the comparatively small and thinsurface accumulations of clay, most of the larger andbetter-grade deposits represent beds of shale, usuallyinterbedded with sandstone, that are more or lessthoroughly weathered and bleached. More study ofthe geologic nature of the clay deposits is needed, butit appears that all the sedimentary formations yieldworkable clay in some places. The deposits along thewest side of Lago Ypacarai, between the towns ofAregua and Ypacarai are perhaps typical.There are a number of clay pits from 1 to 2 kilometerssoutheast of Aregud. on a broad bench just west of therailroad. The pits expose white to light gray claystrongly mottled with brown and red to depths of 3 to 4meters. The clay is very smooth to the touch and isstrongly micaceous. Bricks made from it are a richred brown and are of as good quality as any seen inParaguay. The clay, which has the appearance ofsoftened and weathered shale, is overlain by a series ofmassive, buff to red, fine-grained, micaceous sandstoneand shaly sandstone beds. The lower beds contain afew fossils of Silurian age and the entire series of clayand sandstone is mapped as part of the Caacupe serieson plate 1. The beds strike N. 65° W. and dip 32° SW.Even though the clay deposits thus dip beneath thesurface, hasty examination indicates that a littleexploration would prove the existence of enormousquantities of good clay within easy reach of the surface.The Vargas Pena clay pit 2 kilometers northwest ofYpacarai works beds that seem to be stratigraphicallyequivalent with those at Aregtia. The beds strikeN. 55° W. and dip 12° SW. Clay is exposed in twopits, one above the other. The lower one is 60 to 80meters long, 10 meters deep, and 15 meters wide; theupper one is shorter but wider than the lower. The clayin each of the pits is white, very micaceous, containslittle or no sand, and is richly fossiliferous in places.Locally it is stained brown and contains layers as muchas 10 centimeters thick and a few narrow steeplydipping veins of light-gray iron carbonate, or siderite,largely altered to brown limonite. Massive, crossbeddedmicaceous sandstone, about 25 meters thick,crops out between the upper and lower clay pits. Therelations are not clear but it is believed that the sandstonelies between two separate layers of clay. It ispossible, however, that the clay represents a single bedof altered shale that has been repeated by droppingalong a steep northeastward-trending fault.Samples of clay from the Vargas Pefia pit wereexamined microscopically by Charles Milton. Hefound that they contained quartz and altered mica,with disseminated grains of rutile. The altered micaappears to be the major constituent of the rock, whichpossesses an obscure lamination, with some segregationinto relatively mica-poor, quartz-rich areas. X-rayexamination of the same samples by J. M. Axelrodshowed that the material was made up of quartz,kaolinite, and muscovite; no montmorillonoid materialswere found.Other deposits of clay, some pure white and of excellentquality, are known to exist at a point 10 kilometersnorth of Tobati and at Iturbe, Yegros, San Pedro delParana, Piribebuy, Yhu, in the Gran Chaco, anddoubtless at many other places. The deposits at Yhu,which are reported to be very good for pottery, areinterbedded with red sandstone of Triassic age (seefig. 52). The geologic setting of most of the others isnot known, but their geographic distribution indicatesa wide stratigraphic range.A sample of washed pottery clay from Piribebuyproved, on X-ray examination by J. M. Axelrod, toconsist of relatively large flakes of kaolinite with alittle mica, quartz, and an unidentified mineral.According to the report on Concurrencia del BancoAgricola del Paraguay (Anon., 1911), tobacco pipeswere made successfully from Paraguayan clays in 1903.The report contains the following chemical analysesof clays used for this purpose. Of these, the clay fromTobati is said to have been the best.SiOj.. . . .. . .AljOa.CaO .-_ _ .MgO.~ .-.K2O.. . __ -_-. .NajO. ...... .- .~H.tO. ............................Chemical analyses of Paraguayan days[Ovldio Rebaudl, analyst]VilletaNo. 152. 36738.8332.800.380.120.372.230.1843.739.975100.00VilletaNo. 249. 69336. 9104.1201.810.130.298.196.1205.1231.600100.00Chaco53.44740. 152.657.410.198.650.210Tr.3.2761.000100.00Tobati55.10040.322.210.298Tr..310.200Tr.2.932.630100.00

82 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYCOPPEROf the several copper deposits that are more or lessreliably reported, only one the Paso Plndo depositnear Villa Florida was seen by the author. Smallamounts of malachite, azurite, and native copper arepersistently and apparently reliably reported from thevicinity of Encarnacion. Copper is also reported inand near Colonia Fram, 15 kilometers northeast ofCarmen del Parana, at a place 40 kilometers due eastof San Pedro del Parana, and from many other placeswhere Serra Geral basalt covers the southeastern partof the country. The widespread popular belief thatParaguay is rich in copper is supported hi part by reportssuch as these and in part by the legend that theearly Jesuits produced bronze implements of manykinds.Small amounts of copper are unquestionably presentin some places, but most of the reported occurrences areunsubstantiated by specimens or assay results. Itseems almost certain that many, if not most, reportsare based on the fact that the cavity fillings of bright- todull-green chlorite that are so widespread and socharacteristic of the Serra Geral basalt has been mistakenfor malachite or other green minerals of copper.It is reasonable to suppose that the reported productionof bronze implements by the Jesuits represents remeltedand recast Spanish bronze rather than that thealloy was made from local materials, particularly aseven the legends fail to account for the tin that is anessential constituent of bronze.The Paso Pind6 deposit is 8 kilometers N. 18°E. of Villa Florida and 5 kilometers due east of kilometerpost 157 on the Villa Florida-Caapucii highway.It can be reached from the highway by an unimprovedsecondary road. The country rock is largely a dense,fine-grained aplite that forms broad northeastwardtrendingdikes in coarse Precambrian granite. Thedeposit is on a weak nearly vertical shear zone, severalmeters wide, that trends N. 65° E. and extends atleast as far southwest as the main highway, whereit is well exposed in road cuts. It was not tracedfarther in either direction.The deposit has been explored over an area of 50to 100 square meters by 3 test pits, each 3 to 4 metersdeep, and by several shallow opencuts. Copper occursas malachite and other green oxidation products ofcopper sulfides, as films, and as veinlets along seamsand joints of the slightly brecciated aplite. There isno well-defined vein and little or no evidence of strongalteration or of large openings that would have permittedthe entrance of ore-bearing solutions in volume.A few pounds of high-grade carbonate ore has beenmined and sorted by hand in the past. More mayyet be found in depth or along the strike of the fracturezone, but the outlook for a large or rich deposit isdistinctly unpromising.FUEL RESOURCESSOLID FUELSAs noted in the introduction, the chief known fuelresources are wood and charcoal. Comparativelysmall amounts of heat and energy are obtained fromalcohol, hulls of cottonseed and palm nuts and byproductsof the sugar and vegetable oil industries.Inasmuch as the Gondwana beds contain coal inother parts of South America and elsewhere, it isentirely possible that some of those beds in Paraguayare also coal bearing. No authenticated occurrenceshave ever been reported, however.Deposits of peat are known in some of the swampyareas along the Bio Paraguay near Pilar. None wereseen by the author, but they are reported to be large.During 1952 plans were being laid to develop andexploit these deposits. In view of the serious shortageof fuel in the country and of the bearing of this shortageon the total national economy, such plans seem todeserve continued and strong support. The extent,fuel value, and usability of the peat resources shouldbe determined, and other deposits should be sought insimilar geologic settings.PETROLEUM AND NATURAL GASExcept for one or two reported oil seeps in easternParaguajr, and showings of oil and gas in one deepwell in the Gran Chaco, Paraguay has no knowndeposits of petroleum or natural gas. There are somereasons for believing, however, that resources of thesecommodities may yet be discovered beneath the GranChaco plains.From December 1944 through November 1949, theUnion Oil Company carried out a rather costly andelaborate prospecting campaign in the Gran Chaco.Its work included a considerable amount of geologicmapping and very extensive geophysical studies thatincluded almost the entire Gran Chaco. Five testwells, ranging in depth from 2,048 to 3,150 meters,were drilled. The approximate locations of thesewells are shown on plate 1; partly condensed logsappear in the section on rocks of the Gran Chaco,and a generalized interpretation of the logs is givenin figure 53.The results of the drilling were almost more confusingthan enlightening as to the subsurface geology of theGran Chaco. In the two north westernmost wells,Santa Kosa and Picuiba, great thicknesses of marineshale and sandstone of Devonian age beneath more

MINERAL RESOURCES 83than 1,000 meters (3,000 feet) of continental red bedswere found. The La Paz well, only 70 kilometerseast of the Santa Rosa well, showed that the Devonianshale had thinned from more than 1,200 meters toonly 120 meters in that distance, but that it wasunderlain by a thick series of Paleozoic beds, reportedlyvery different in appearance from, any of those in theSanta Rosa well. Conversely, the 3,149-meter Pirizalwell, 130 kilometers south of the La Paz well failed toreach the marine sediments, demonstrating an enormousthickness of continental red beds there. In theOrihuela well, 210 kilometers east of the Pirizal, nearly2,000 meters of red beds were penetrated and the drillpassed directly into an old quartzite, probably Cambrianand Ordovician in age, thus proving the absenceof Silurian and Devonian marine sediments in this area.Evidence indicates a deep basin in the marinesediments, filled with continental red beds of Mesozoicand Cenozoic age that centers somewhere near thesouthwestern border of Paraguay, not far from, thePirizal well. Whether this depression is due to foldingor to erosion and removal of the older marine sedimentsis unknown to the author; nor is the structure withinthe older beds known. It is clear, however, that theseolder beds rise to or above the surface eastward aswell as toward a large domelike structure that has anapex near the extrem.e northwest part of the republic.Despite the fact that only one well of the Union OilCompany the Picuiba found positive indications ofthe presence of oil and gas, the possibilities of eventualdiscovery of commercial petroleum or gas have not beenexhausted. Very thick carbonaceous marine shalebeds, possible sources for petroleum, are known in thearea. An extensive structural basin filled with alternatinglayers of shale and porous sandstone, which couldunder favorable circumstances serve admirably as rereservoirrocks for accumulations of petroleum, is alsoknown to exist in the area. Moreover, oil is producedin Bolivia in the anticlines on the western flank of thisbasin. The existence or location of minor folds, ancientshore lines, or other possible stratigraphic orstructural traps within the basin is of course quiteunknown, but it seems reasonable to suppose that suchfeatures may exist and may have been missed by theinadequate exploration that has taken place to date.Only further exploration can discover the unknownstructural features. Such exploration would necessarilybe both extensive and expensive; it would alsorequire larger amounts of equipment and technicalskills than were available in Paraguay when this reportwas written. The discovery of petroleum resourceswould mean so much to the national economy, however,that serious consideration should be given to developingthe ways and means of making further search for them.GEM STONESThere is a possibility, though only a remote one, thatsmall quantities of precious or semiprecious gem stonesmay someday be found in Paraguay. The reportedberyl in some of the pegmatites in the Rio Apa regionnaturally indicates the possibility that, as in Brazil,some may be in the form of emerald or of aquamarine,though admittedly no reports of such occurrences havecome to the author's attention.Similarly, comparison of the general geologic relationsin eastern Paraguay with some of the diamond-bearingareas farther north in Brazil, suggests that the basalconglomerate beds of the Lower Silurian Caacupe series,which locally mark the contact between these beds andthe Precambrian granitic rocks, might yield streamworndiamonds to thorough search. Such search, ifattempted, should be done in the full realization thatthe chances of finding diamonds are extremely slim,particularly since there is little or no knowledge as tothe sources of the Silurian conglomerate.Many of the beautiful amethysts and agates thatare produced in Brazil and Uruguay are derived fromcavity fillings in the Serra Geral basalts that are apparentlyidentical with those that cover a large part ofsoutheastern Paraguay. Some beautifully coloredagates and a few pale but otherwise gem-qualityamethysts have indeed been collected from the Para­guayan rocks from time to time. Active search amongthe basalt outcrops themselves or among the pebblesalong the Alto Parana and other streams that drain thebasalt area, would doubtless serve to discover additionalmaterial, though it is impossible to say in what quantityor quality.Some of the younger volcanic rocks, such as those atCerro Tacumbii in Asuncion, contain crystals of cleargreen olivine, or "evening emerald" as much as 1 centi­meter and more in diameter. It is probable that most,if not all, such crystals are so cracked or otherwiseflawed as to be worthless for gem material, but it wouldseem worthwhile to check this conclusion by furtherexamination of the rocks and of soils derived from them.GLASS SANDThe local glass industry depends almost entirely onalluvial deposits of fine sand that accumulate as barsin some of the streams. These form an inexhaustiblesupply of fairly good material, though none of thoseseen are clean enough to yield high quality glass. Thebest apparent source of cleaner material known to theauthor is the white saccharoidal sandstone member ofthe Caacupe series. This sandstone, which could bevery easily crushed, appears to be made up almostentirely of quartz grains in most places except for sma1 !

84 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYspecks of magnetite that could be easily removed bymagnetic or gravity methods.The best single source of pure silica for high-qualityglass making now known is the large body of white veinquartz in the Precambrian rocks north of San Miguel.This body, described in the section on the older Precambrianrocks, would yield large quantities of quartzof extreme purity. Extraction and crushing would bevery expensive as compared to the sandstones andalluvial sands. Quite possibly other sources of goodquality siliceous material will be discovered as thegeology of the country becomes better known.GOLD AND SILVERThere are, almost inevitably, many legends to theeffect that rich deposits of gold and silver were foundby the early explorers and priests who settled Paraguay.De Mersay (1860), for example, says that the earlyJesuits are supposed to have taken fabulous quantitiesof gold from San Miguel. He notes the presence ofdeposits of white vein quartz there as supporting thepossibility that at least small quantities of gold mayactually have been found.Though it is certain that these people sought theprecious metals vigorously, and that they enlisted theoriginal inhabitants to aid them in their search, thereare no authentic records known to the author that theywere successful. More important, there are no knownevidences of old placer or other mine workings.Reports of gold and silver discoveries are still madeoccasionally, but so far as known, none have been substantiatedby samples or by assay results showing morethan traces of either metal. The possibilities that preciousmetals exist in paying quantity cannot be denied,but in view of the record to date the outlook is distinctlyunpromising.GYPSUMNo commercially valuable sources of gypsum (calciumsulfate) are known to exist, yet the same reasoningapplies here as to that for salt deposits (p. 91).Sporadic crystals of clear gypsum, or selenite, occur insome of the clay soils along the Rio Paraguay nearConcepcion and south of Asuncion. De Mersay (1860),for instance, notes the presence of blocks of gypsum,used to whitewash houses, in the banks and bed of theRio Paraguay at latitude 26°17 / S., not far fromAlberdi; he mentions several other localities along theRio Paraguay and the Parana. A little gypsum coulddoubtless be found elsewhere, though it is improbablethat extraction from such sources could ever be madeto pay. It seems entirely possible, however, that gyp­sum, like salt, might be found somewhere within thecontinental beds that underlie the Gran Chaco. Inview of the comparatively small but continuing needfor gypsum for plaster and for cement-making, cautiousexploration by means of deep, carefully drilled wellsmay eventually be justified.IRONMany rich but comparatively small deposits of hematiteand magnetite iron ore are known to exist inParaguay. Most of them are in the Precambrian rocksthat extend southward from Quiindy to near San JuanBautista, but others are known in the Cordillera deAmambay and still others may exist in the body ofPrecambrian rocks just south of Rio Apa.So far as is known, there are no extensive depositsof bedded iron ore such as constitute resources of majorimportance in Brazil and in Venezuela. Nevertheless,the hematite-magnetite deposits of Paraguay do haveconsiderable potential value, at least to the local economy.As described below, all the iron needed by Paraguayduring the War of the Triple Alliance (1865-70)was successfully produced by a small charcoal-firedfurnace that used locally produced ores. There isevery reason to believe that similar but more modernfurnaces would be as successful today and that thecountrv could thus supply a part of its needs for iron(p. 96)".In addition to the veinlike deposits of hematite andmagnetite, there are several other possible sources ofiron. None are as promising as those just mentioned.A curious and little-known deposit of earthy lodestoneoccurs near Yuty (p. 86). Moreover, the lateriticmaterial represents a very large reserve of low-gradeiron ore whose chief constituent is hydrous iron oxide,or limonite. It ranges from a few centimeters to sev­eral meters in thickness and is widespread. Becauseof its availability and of the relative lack of gravel orother surfacing material it is used extensively for roadmetal. The laterite unquestionably contains an enormousamount of iron in the aggregate and a few schemesto use it as iron ore have been proposed from time totime. No analyses are available, but it appears almostcertain that it contains too little iron probably notmore than 25 percent at best and too much silica andalumina, to be usable as ore with present reductionmethods.EARLY IRON INDUSTRYThe following description of the early iron industryis taken largely from De Mersay (1860) and Du Graty(1865). The iron deposits in the general vicinity ofCaapucu were discovered in 1847 but their existencewas kept secret until 1854 when the Government establishedthe iron industry as a monopoly. There are norecords of the total production nor of the life of theenterprise, but it was continued at least through 1870,

for it furnished most of the iron for cannon, cannonballs, and other weapons throughout the bitter War ofthe Triple Alliance (1865-70).The furnace was established at Ybycui, 15 kilometersnortheast of Caapucu, apparently because there was astream there, which, when dammed, could furnishadequate waterpower to operate the crushers and theblower. Clay for refractory bricks was found in thesame valley in which the furnace was located. Experienceshowed that the bricks were better and longerlived than those that had been imported from England.The iron ore first used came from Caapucu but afterthe mines there reached water level they were abandonedand most of the ore used in later years consistedof three parts specular hematite from near Quyquyoand one part magnetite from San Miguel. This latterore was used because it was easily melted, even thoughit contained less iron than the hematite. The followinganalysis of San Miguel magnetite, quoted byDu Graty (1865), shows that it contained 31.91 percentof metallic iron compared with 40 to 50 percent in theores from Caapucu and Quyquyo.Analysis of magnetite from San MiguelPercentSiO250. 29A1203 ------------------------------------------- 4. 57MnO2------------------------------_-------------- 1. 73FeO___--_-_______--________-_-_-__---_____--__-- 21. 28Fe2O3 ___________________________________________ 21. 95Loss (ignition)_--__-_________-________-____-________ . 18MINERAL RESOURCES 85100. 00The furnace, at which 119 men were employed,had a capacity of 5,000 pounds of ore and flux andconsumed an equal quantity of charcoal, producing1,000-1,100 pounds of iron per 12-hour charge. Theflux was a limy marl from near Paraguari; because ofits low lime content, it was used in the proportion ofone part flux and two parts ore.The iron produced was of very good quality, beinglow in silica and carbon and containing no sulfur orphosphorus. The following analyses of typical ironmade from different ores, are given by Du Graty (1865).Analyses of iron produced at Ybycui

MINERAL RESOURCES 87a pivot, show sufficient polarity to act as compass"needles." Unfortunately, it was not possible to retainspecimens for study, nor was it possible to visit thedeposit.According to Albert Morris, the deposit occurs as anear-surface bed that crops out along the banks of theRio Pirapo for a distance of 8 to 10 kilometers. Whetherthe bed is a part of the Triassic red beds shown onplate 1 to underlie this area, or is associated withyounger alluvial materials along the river is unknown.The thickness, areal distribution, and origin of thedeposit are also unknown, though from the above indicationsit seems worthy of examination. Small quantitiesof the lodestone should find a ready sale to mineralmuseums and it is conceivable that there is sufficientmaterial available to be workable as iron ore.LEADLead "ore," probably in the form of galena, is quitereliably reported from Pedro Juan Caballero, from LaColmena a farm colony midway between Acahay andYbytymi and from a few other places. Pottery madefrom the clays 60 kilometers north of Yhu are reportedto "sweat out" globules of native lead when the potteryis fired. The only lead mineral seen was one small blebof galena in the body of white quartz just north ofSan Miguel.LIME AND LIMESTONEThe Cambrian and Ordovician limestone beds thatcrop out along the east bank of the Rio Paraguay fromSan Salvador to the Rio Apa constitute an inexhaustiblesupply of lime and limestone for all purposes. Somelime is imported from Argentina, but most of Paraguay'sneeds for the past 100 years have been met by a seriesof small quarries and charcoal-fired kilns at PuertoFonciere, Itapucumi, and several other places. Thelime is shipped by boat to Asuncion in metal drums.Most of that seen contained large amounts of unburnedlimestone, but it would be a simple matter to improvethe product greatly by better methods of calcinationor merely by screening the burned lime.Small but appreciable quantities of ground marble,presumably for use in the sugar industry, are importedregularly by Paraguay. With the raw materials andthe crushing and grinding equipment currently availableat the Vallemi cement plant, such requirementscould be met locally. The same reasoning should applyto fragmental limestone, marble, and other rocks thatare imported for use in terrazzo work.The following paragraphs are condensed from, aFebruary 5, 1953, memorandum report by Dr. KlareS. Marldey, vegetable oil specialist. The original is inthe files of the Asuncion office of the Institute ofInter-American Affairs.465871 59 8Among the basic needs of Paraguayan agriculture are mineralfertilizers and agricultural limestone. Many of Paraguay's soilsare highly acid and generally low in available phosphorusalthough they may be relatively high in total phosphorus. Thishigh acidity limits the type of crops that can be grown, especiallylegume crops which are intolerant of high acidity. Innoculationof legume crops with nitrogen-fixing bacteria is often uselessbecause the bacteria cannot establish themselves in highly acidsoils. Proper liming of the soil will increase its fertility byreleasing unavailable phosphorus, will make it possible to growcrops which are intolerant to acid soils, and to establish nitrogenfixingbacteria in the soils which are now too acid to permitthem to become established.Pedro Tirade has shown that the Alto Parana soils require2.5 to 7.0 metric tons of lime in the form of limestone or dolomiticlimestone to bring them to proper acidity (about pH 6.5).The deposit of limestone which is now being worked at Vallemifor the production of cement is actually a mixture of limestoneand dolomitic limestone. Only the former can be used for makingcement, consequently the two minerals have to be separatedwhich is done entirely by hand after partially cracking thequarried stone. This is the most costly operation carried outat Vallemi and the rejected dolomite or dolomitic limestone hasno present use. This type of limestone is ideal for agriculturaluse and need only be crushed to pass a 10-mesh screen. Forsome special applications a finely ground limestone (50 to 200mesh) might be preferable but is not absolutely essential.I feel that the production and distribution of limestone inParaguay could be one of the greatest contributions to agriculturethat could be made short of the introduction of balancedchemical fertilizers.MANGANESEManganese deposits are reported in many parts ofthe country, notably along the Rio Apa, in the vicinityof Villarrica, at Emboscada, at Yaguaron, and throughoutthe highland that extends from north of SanBernardino as far south as Paraguari. Only theYaguaron deposit, which is unpromising, was seen bythe author.It is, of course, conceivable that workable depositsof manganese exist in the country, particularly in thenortheast, but no such deposits have yet been found,despite the fact that manganese oxide is resistant toweathering, hence should accumulate on the surfacein easily visible and identifiable form.EMBOSCADA DEPOSITThe manganese deposit at Emboscada is generallyconsidered to contain the richest ore now known inParaguay. It was not visited but many small specimensof very rich manganese oxides from there wereseen. Emboscada (Wright, 1940) is only 65 kilometersnorthwest of Asuncion, but because of poor roads, it ismost easily reached by boat to Puerto Minas, a smallvillage not far above the mouth of the Rio Piribebuy,thence via horseback about 5 kilometers to Emboscada.The country rocks are sandstone of the Caacupe seriesof Early Silurian age (pi. 1), which dip toward thenortheast at low angles. A northwestward-trendingzone of hard mano;aniferous sandstone can be traced for

88 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYseveral kilometers. It has been explored by one pit 6meters long, 4.5 meters wide, and 3.6 meters deep.This excavation exposes veinlets of pyrolusite 2 centimetersor more in thickness; locally there are masses 6to 10 centimeters thick, but even the best specimenscontain considerable amounts of silica. Results ofchemical analysis of one specimen, doubtless carefullyselected, were seen, which showed the material to contain85.65 percent MnO2 (equivalent to 54.90 percentMn), 6.94 percent BaSO4 and 0.23 percent SnO2 . Thepresence of tin in this material is surprising. There isno doubt that some manganese ore of commercial gradeexists at Emboscada. However, the available evidencemakes it seem very unlikely that any large quantitiesof ore will be found there.YAGUARON DEPOSITThe deposit, which is not believed to be of commercialsize or grade, is in a prominent but relatively smallhill just southwest of the town of Yaguaron (fig. 54).The steep slopes of the hill expose a total thickness ofabout 50 meters of brown, thick-bedded and crossbedded,very fine grained arkose. This rock, shown onplate 1 as part of the Triassic Misiones sandstone issomewhat soft in places but elsewhere it is cemented bysilica to a hard quartzite.The manganiferous material forms an irregular pipelikezone a few meters in diameter that extends almostvertically to near the top of the hill. Within this zonemany joints are filled with narrow irregular veinlets ofblack oxides of manganese. The sandstone itself is alsoimpregnated with small spherical bodies of similaroxides. There is no visible major fracture or fault; themanganese mineralization seems to have concentratedin the zone of joints."Mining" consists of the breaking off of pieces of outcroppingrock and collection of loose fragmental mate­rial from the surface. The material so gathered iscobbed to pieces 4 to 10 centimeters in diameter andsorted by hand on the basis of color. None of the sortedmaterial appeared to contain more than 10 percentMnO2, and it is very doubtful that any quantity ofbetter grade material could be produced.MERCURYDe Mersay (1860) reported that mercury ore wasfound in 1779 at San Miguel. He stated further thatsamples that were sent to Spain for analysis gave unsatisfactoryresults and that no further development orexploration was attempted.It is problematical whether the reported material consistedof the red sulfide mineral, cinnabar, or was someFIGUKE 54. Coarse-grained, coarse-bedded, manganiferous arkose, believed to be part of the Misiones sandstone just west of Yaguaron. The beds dip 1° W.;the eastward slope of the hill is controlled by crossbedding. Just left of the central palm tree, joints and interstices in the sandstone are impregnatedwith manganese. Mandioca, a staple starch crop of Paraguay, in the foreground.

MINERAL RESOURCES 89of the bright red iron hydroxide material that characterizesthe weathered rocks in some parts of the country.MICAMica is reported to occur in many pegmatitic bodiesin the northeastern part of the country, between Concepcionand the Rio Apa. Several have been exploredto some extent and have been examined by competentmining engineers, but no detailed descriptions or reportshave become available. However, many selectedspecimens of mica were seen in sheets as much as 5centimeters in diameter and there were many reports ofsheets 2 to 3 times as large as this. All of those seenwere so full of structural flaws or of dark inclusions offoreign ferruginous material that they would have littleor no value as sheet mica.Even though available evidence is scanty, it seemsreasonable to assume that mica is widely, and perhapsabundantly, distributed in the Precambrian rocks in thenorthern part of the country. It seems probable thatmost of the material will be suitable only for scrap mica,which brings very low prices on the world market. Itis possible, however, that good grades of sheet mica,which would bring much higher prices if competentlyextracted and graded, may exist in some places. Evenif promising deposits should be found, questions of economics,of transportation, and of living conditions inthis remote and largely unsettled region might play alarger part in the workability of the deposits than wouldthe intrinsic value of the mica itself.The most persistent and reliable reports of mica occurrencesrefer to the small area of Precambrian rocks10 kilometers north of Concepcion, and to the followingplaces near the Rio Apa: between "Reyes Cue" andArroyo Seco, near Arroyo Caracol, at Puente Sinho,and close to Bella Vista. All but the last of these aresketched and described by Boettner (1947); he saysthat the pegmatite dikes at Arroyo Caracol containlarge, badly flawed books of muscovite, associated withwhite and pink feldspar, quartz, beryl, and graphicgranite.In addition to the above localities, mica is also reportedfrom Estancia Hermosa, from Potrero Bocaya,from Estancia Saty y San Bias all localities in the RioApa region and from San Estanislao. This last reportis the only evidence known that suggests the presenceof Precambrian rocks in the vicinity of SanEstanislao.PIGMENTSMany materials that could be used as pigments in themanufacture of paints are known in various parts ofParaguay. The only source known to have beenworked in recent times is a deposit of ocher about 1,500meters southwest of Tobati. It is in the white sandstonedescribed (p. 55) as the white saccharoidal memberof the Caacupe series. Along several of the strongvertical, northeastward-trending fracture planes thatcharacterize the sandstone there are irregular areas inwhich the sandstone grains are cemented with ocherinstead of the more usual calcareous or siliceous cement.This ocher, which makes up approximately 2 to 7 percentof the rock, appears to be a finely divided clay thatis impregnated and colored by secondary limonite.The largest deposit, and the one that was being workedin 1952, is about 30 meters long, 2 to 3 meters wide and3 to 5 meters high. Part of it is shown in figure 47.The rock is soft and easily worked. Blocks are priedout with hand tools, hammered to small pieces, andthen disintegrated by soaking in water (fig. 55). Theheavier sand sinks to the bottom and is removed withshovels; the ocher is decanted off. The decantationprocess is repeated in 3 to 5 operations in small woodentroughs, and the resultant ocher, when dried in the sun,FIGURE 55. Quarry and paint factory near Tobati. The sandstone at the rightcontains yellow ocherous clay interstitial to the sand grains The yellow ocher isrecovered by crushing the sandstone and washing it in shallow trays beneath theshed.

91rectangular outline showing coarser platy crystallization.Small opaque areas strewn through the sectionare leucoxene. One specimen (fig. 57) shows considerableamounts of fine-grained diaspore under themicroscope.The pyrophyllite appears to be derived by hydrothermalalteration of volcanic tuffs that are probablyinterlayered with the quartz porphyry.In view of the very large indicated size of the deposit,continued search for material of good grade and color,would appear to be worthwhile. Studies should alsobe made of possible markets for the product, both as asubstitute for talc and for other uses such as refractories.QUARTZ CRYSTALSQuartz crystals are reported to Robert M. Miller bylocal residents to occur on the ridge 6 kilometers northeastof Caapucu. Nothing is known of their size oroptical quality. It seems probable that they are smalldoubly-terminated crystals similar to those thatweather out of miarolitic cavities in Precambriangranite in many places. If so, they have little or novalue.SALTNo commercially valuable deposits of common salt(NaCl) are known to exist in the country, yet theuniversal need for this commodity (evidenced here byan annual importation of nearly $200,000 worth) plusknown geologic conditions that should be favorable tosalt accumulation, would seem to make a vigoroussearch worthwhile. Three possibilities are known tothe author recovery from surface efflorescences andfrom brine wells in central Paraguay and recovery fromdeep wells in the Gran Chaco.Pfotenhauer (1891) notes that the early Jesuits had amonopoly on extraction of salt from the salt playas(salinas) of San Jose and Santiago (now in Bolivia) inthe northern part of the Gran Chaco and that theyprovided all the salt needed by Paraguay and neighbor­ing provinces of Argentina and Brazil. Much later,De Mersay (1860) and Du Graty (1865) record theextraction of salt from salty earth, efflorescences, anddried ponds in the vicinities of Fuerte Olimpo, Concepcion,the Rio Piribebuy, the Rio Salado (which drainsLago Ypacarai), the Rio Negro (in the Gran Chaco),and Lambare (just south of Asuncion). Du Graty^mffFIGURE 57. Pyrophyllite with diaspore (specimen P-91) from 5 kilometers northwest of Caapucfl. The light-colored groundmass, p, is pyrophyllite andthe dark gray is diaspore, d. A few small dark areas are leucoxene, I. X 20,

92 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYstates further that these sources furnished a part of thecountry's salt requirements and could have met thementirely if necessary. He quotes an analysis of the saltfrom Lambare, by M. Parody, as follows:PercentNaCl____--________-___________________ 91. 40MgCl_-_____________-_________________ 2. 95MgSO4-___________________ ____ . 90CaSO4______________________ 4. 23Difference_____________________________ . 52100. 00There are persistent reports of the existence ofrelatively shallow wells in the area south of, and onlya few kilometers from Asuncion, that yield strong saltbrines. None of these reports could be verified.Nearly all the Gran Chaco is underlain by manyhundreds of meters of sediments that were depositedunder continental, and in part desert, conditions. Itseems reasonable to suppose, therefore, that somewherewithin this sequence of beds there may be beds orlenses that represent the evaporation of desert lakesthat were high in sodium chloride. Whether this isso or not cannot be determined from present evidence.It is known that most of the streams in the Gran Chaco,as well as most of the near-surface ground water, arerich in dissolved mineral matter though there appearsto be more magnesium sulfate (epsom salts) thansodium chloride in most of them. The logs of thedeep holes drilled by the Union Oil Company summarizedabove do not record the presence of salt beds.This is weak negative evidence, however, for discoveryof soluble salts by the usual water-filled wells drilled inthe search for petroleum are rare indeed.SAND AND GRAVELFine sand is extremely abundant in almost all partsof the country. Coarse sand and gravel, on the otherhand, are almost equally rare. Some of the sandstoneunits, notably the white saccharoidal sandstone memberof the Caacupe series and the red sandstone units inthe Misiones and Independencia series might be easilyquarried and crushed to yield medium- to coarse-grainedsand suitable for concrete and other purposes. Unfortunately,few of these units occur in areas where thereis the greatest demand. Gravel is even scarcer thancoarse sand. A few stream beds contain some gravelbut most do not. The basal conglomerate beds of theSilurian and Triassic rocks yield some excellent gravellocally, but these beds are too thin, too discontinuousand too poorly exposed in most places to yield largequantities either locally or in total. Most of the requirementsfor coarse aggregate for concrete are met bycrushed igneous rocks. The basaltic rocks, such asthose at Tacumbu and Lambar6 on the outskirts ofAsuncion, are most widely used, but this is because theyare close to the centers of population and of greatestdemand. The Serra Geral eruptive rocks, the Cambrianand Ordovician limestone units, and many of thePrecambrian rocks would be equally useful if there werelocal need for them, and some of them would be moreeasily quarried and crushed than the extremely toughvolcanic rocks.Limonite, in nodules or fragments from the lateritezones that make up the surface in many parts of thecountry, is very widely used, particularly in the centralregion, for gravel-size material for road surfaces. It isin large part responsible for the general impression,acquired by travelers who follow only the main roads,that Paraguay is characterized by red colors. Thelimonite has fairly good cementing properties, but is toosoft and dusty to be particularly desirable if any bettermaterial were available.STONESupplies of stone for either ornamental or roughconstruction purposes are more than adequate for anyconceivable requirements.Tough, durable rock for paving blocks, rubble masonry,and the like is produced in rather large quantitiesfrom a number of the volcanic deposits. Among thosethat were being worked in 1952 or had been recentlyworked are the deposits on Lambare and several otherhills close to Asuncion, those just south of Ypacarai thatyielded most of the stone used on the paved highway,the flow rocks along the highway near Carapegua, andthe body of shonkinite at Mbocayaty. Almost anyof the other igneous rocks shown on plate 1 would besuitable sources of good stone. The deposits of"pseudo-trachyte" near Luque and Aregua, which formnicely shaped polygonal columns from 4 to 15 centimetersin diameter, are used widely for walls and walksof many buildings in Asuncion and its vicinity. TheSerra Geral eruptive rocks of the Alto Parana regionprovide attractive semidressed stone for buildings; thephases that contain green chloritic amygdules areparticularly pleasing to the eye.Several sandstone units are worked in places forflagstone and building stone. One of the most attractivecomes from quarries near Emboscada from bedsbelieved to belong to the Caacupe series. These rocks,which split easily to form good but somewhat softflagstones, are nearly white in background color, butbeautifully mottled with light tones of rose and brown.The lower beds of the Misiones sandstone are quarriedin a number of small pits in the vicinity of San JuanBautista (see fig. 51). They have a pleasing uniformred color, and are almost as hard and durable as

MINERAL RESOURCES 93quartzite. They consist of well-rounded frosted quartzgrains, with interstitial cement made up of silica,sericitic mica, and other minerals.Among the rocks that have not been worked commerciallyto any extent, but which offer considerablepromise, are the marble, hard limestone, and dolomiteof the Cambrian and Ordovician rocks, the Precambriangranite and quartz porphyry near Caapucii, andthe 2honkinite, or "black granite" of Mbocayaty.Any of these rocks would yield good decorative stoneif properly worked; except for the Mbocayaty depositthe reserves of material are virtually unlimited.SULFURAt least two deposits of iron sulfide minerals, fromwhich small amounts of sulfur might be recovered incase of extreme need, are known. No deposits ofnative sulfur have ever been reported.One of the known deposits is the Del Puerto vein,near Caapucii (p. 85). The leached outcropping materialof this vein contains a little pyrite, as well asevidence that pyrite once existed there in considerablequantity but has since been removed by solution. Itseems possible that further and deeper explorationmight uncover bodies of pyritic ore sufficiently largeand rich to provide some sulfur. It is very unlikely,however, that any very large bodies of pyrite will bediscovered.The second known source of iron sulfide minerals isat the Minas-cue, or Lopez, mine near Arroyo Yhaguy,about 5 kilometers southwest of Itacurubi. Thisdeposit is reported to have furnished most, if not all,of the sulfur needed for gunpowder during the War ofthe Triple Alliance. It is possible that other depositsof the same kind may also have been worked during thewar, but if so, there is no reliable record of them.The Minas-cue deposit is on a nearly level plain thatis cut by many small arroyos tributary to ArroyoYhaguy. The "ore" consists of widely scattered concretionsof marcasite in shale of the Itacurubi series ofEarly Devonian age. These shale beds underlie theentire grass-covered plain of Arroyo Yhaguy. Nearbyhills consist of sandstone, also part of the Itacurubiseries, that overlies the shale. The alternating beds ofshale and mudstone are nearly or quite horizontal andare blue gray with local splotches of red and pink.They are strongly jointed along several sets of crisscrossing,nearly vertical joints that cause the beds toform vertical walls along the arroyos. The uppermostI to 2 meters are weathered to soft plastic clay, mottledin shades of yellow, white, and brown, surmounted by20 to 60 centimeters of brown clay soil that containssparse pebbles of quartz, quartzite, and agate.Concretions of marcasite and siderite, or iron carbonate,are sparsely scattered throughout the shale.Some of the siderite occurs as oval concretions 1 to 7centimeters in diameter but most of it forms smallvertebralike cylinders that break easily into thin disks.In the weathered zone most of the siderite is altered todeep-purplish-red limonite but fresh material is denseand gray to buff in color.The marcasite in the concretions occurs both asclusters of crystals and as irregularly oval masses.Some is pure iron sulfide, but some is earthy andprobably contaminated with clay or with siderite.None of the masses seen was more than 7 centimetersin greatest dimension, and they are so widely scatteredthat none of the rock could possibly contain much morethan 1 kilogram of marcasite to the cubic meter.The main Lopez workings appear to have consistedof a shallow opencut along one of the arroyos, about2 to 3 meters in depth, 10 to 15 meters wide, and 150meters long. One shaft in the bed of the arroyo, longsince filled with water and debris, is said by localinhabitants to have been 20 meters deep and to havethe richest concentration of marcasite in the entireworkings.About 1,000 laborers, mostly women, are reported tohave worked the deposit during the war period of 1865-70. Apparently they dug vast amounts of the shale,sorting out the sparse marcasite concretions by hand.The material was roasted at the mine in a small brickfurnace.There is no question that very large amounts ofmarcasite are present in the shale in this place andquite possibly elsewhere in the shale units of theItacurubi series. The marcasite is so widely scattered,however, and would require moving and treatment ofsuch enormous amounts of barren shale to yield evensmall amounts of marcasite, that it cannot be regardedas a resource except under the most extreme conditionsof economic or military emergency. If any such needsshould develop, it is suggested that the shale be investigatedover wide areas and to depths of 10 to 20meters by means of earth augers or other drills. Suchexploration might possibly serve to discover zoneswhere the marcasite concretions are relatively abundant.TALCKnown talc deposits are confined to a small partof the belt of lower Precambrian rocks that are exposedalong the highway from the center of San Miguel toa point 5 kilometers north of that town. As describedabove, this belt comprises alternating bands of a widevariety of rocks, ranging from quartz veins throughgranite and aplite to mica schist and altered ultrabasicrocks. All are strongly crushed, and component mineralsare strung out and flattened parallel to the

94 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYbanding, which trends N. 40° E. and dips 30°-60° NW.Talc occurs in three distinct zones in this series, from30 to 50 meters apart and each 2 to 3 meters thick.The talc is well exposed in the roadside ditch at kilometerpost 176 (see fig. 5) and in a prospect shaft about15 meters deep that is a few meters southwest of thatpoint (see fig. 58), or along the strike of one of thetalc-bearing zones. The material ranges from whiteto greenish gray and from very smooth or soapy togritty. Here and there it contains a few veinlets ofwhite quartz, and microscopic grains of chromite arewidely but sparsely disseminated through it. Veinletsof cross-fiber talc that has the megascopic appearance ofasbestos, from 5 to 15 millimeters in thickness, characterizesome of the talc taken from the prospect shaft.The texture, as well as the presence of chromite,strongly indicate derivation from serpentine or otherbasic rock, but no other evidence of its origin was seen.The talc near the surface is somewhat iron-stainedand is variable in texture and composition. It seemsto be fairly extensive laterally, however, and to bealmost certainly due to extensive hydrothermal alteration.In view of the potential local market for commercialgrades of ground talc, further exploration with thehope of finding better grade material in depth seemswarranted.TINTin, possibly in the form of cassiterite, is reportedto have been found in the white pottery clay fromnear Tobati, in the manganese ore from Emboscadaand from near Panambi, a village in the vicinity ofCaaguazu that is not shown on available maps. Noneof these reports appear to be very reliable.TUNGSTENWolframite, or some other ore minerals of tungsten,are persistently reported to occur on the Estancia SanLuis near Concepcion and elsewhere. Even thoughexport licenses for tungsten have been granted and somepurported tungsten ore has been actually shipped, thereis considerable evidence that these actions were taken inerror or chicanery and that no material containingappreciable quantities of tungsten has ever beenproduced in Paraguay.MISCELLANEOUS MINERALS, LOCALITY UNKNOWNSpecimens of the following minerals, said to be fromParaguay but with no localities given, were displayedat the Buenos Aires exposition in 1910 (Anon., Concurrenciadel Banco Agricola del Paraguay, 1911):stilpnosiderite, native iron, millerite, sphalerite,pyrite, galena, magnesite, serpentine, sulfarsenateFIGUKE 58. Test pit on outcrop of talc, 3 kilometers north of San Miguel. The larger rocks in the spoil pile are relatively high-grade talc. The terrainand vegetation are typical of Precambrian areas of southern Paraguay.

MINERAL RESOURCES 95of lead and silver, patrinite, antimonite, and six unidentifiedcopper minerals. Some of these mineralnames suggest the possibility that they representspecimens that originated in Bolivia or Peru ratherthan Paraguay.FUTURE OF THE MINERAL INDUSTRYGENERAL STATEMENTAvailable facts indicate that Paraguay is very poor inmineral resources except for certain nonmetallic materials,such as clay, limestone, talc, sand, and variouskinds of building and ornamental stones. It is possiblethat further exploration will serve to uncover otherresources. Even if such hopes should prove to beill-founded, however, there is every reason to believethat profitable local industries could be established thatwould provide some or all of the nation's requirementsfor certain commodities and would conserve some of itsforeign exchange.The author's pessimistic conclusion as to Paraguay'srelative poverty in minerals is not reached lightly norwithout reluctance. Nor is it based entirely on theresults of the present 6-month reconnaissance that wasinadequate to examine more than a small fraction ofthe mineral possibilities. Instead, it is based in parton history and in part on generalized knowledge ofthe geology of the country.For nearly four and a half centuries, many men,some highly skilled in their profession, have soughtmineral wealth in Paraguay. It is easy to believe thatall of them may have missed the obscure or the deeplycovered deposit, but almost inconceivable that allwould have failed to discover obvious deposits thatwould be most easily found and developed. The factthat they have not done so is in itself strong presumptiveevidence that easily discovered deposits do notexist.So far as the geology is now known, the Precambrianrocks offer the best chances of discovering depositsof metallic minerals. Unfortunately, these rocks arecovered in most places by barren sedimentary rocks,or by swamps and many of the exposures that do existare remotely situated and difficult to explore. Noneof the younger igneous rocks appear to be of the kindswith which ore-bearing solutions are usually associated.As a result, neither they nor the surrounding sedimentaryrocks, none having been fractured or metamorphosedenough to make them promising receptaclesfor ore deposits, seem to be of much promise.These conclusions are at variance with widespreadpopular beliefs within the country that are based inpart on the inevitable enlargement of legends withtime, and in part on failure to distinguish betweenmineral occurrences and mineral resources. The beliefin existence of gold and silver resources, for example,seems to be based entirely on stories that theearly Jesuits found and produced fabulous quantities ofthese metals. Actually, there are no authentic recordsof such production and no assay reports or other proofthat paying quantities of gold have been found sincethe time of the Jesuits. Again, the almost universallyheld belief that Paraguay is rich in iron is based onthe well-known fact that local mines and furnacesproduced all the iron needed in Paraguay's epic struggleagainst three powerful adversaries Argentina, Brazil,and Uruguay during the War of the Triple Alliance.As a matter of fact, Paraguay does possess rich irondeposits, but there are many reasons, geologic andotherwise, for believing that they are far too small,individually and collectively, to form the basis of anexport business. Too, many beliefs in mineral richesare based on small specimens, with little or no proofthat they represent workable quantities of ore. Thus,though manganese and copper are undeniably presentin several places, there is no evidence known to theauthor that bodies of commercially workable size andgrade have ever been discovered or developed. Similarly,though specimens of sheet mica can be seen inmany private and public collections, none of those seenwere of much more than scrap quality; moreover thereis little more than hearsay evidence that large depositsof mica, regardless of grade, have been discovered.Part of the author's pessimism is based on the merefact that most specimens of metallic and other mineralsor ores seen are far below commercial standards. It isonly human nature to select better-than-averagematerial for specimens; if all specimens of such easilyrecognized materials as gold, mica, manganese, andcopper ore are mediocre in quality, it is difficult tobelieve that the deposits from which they came aremuch, if any, better. This reasoning does not apply, ofcourse, to the less-easily recognized minerals, such as theores of tin and tungsten, nor to such things as petroleumthat can only be discovered by extensive undergroundexploration.SUGGESTIONS FOB PROSPECTINGPresent knowledge strongly indicates that Paraguayis relatively poor in mineral resources. Details of thegeology are but imperfectly known, however, and manyparts of the country are so inaccessible as to haveescaped very careful search for minerals. Furtherexploration, therefore, seems justified.Many suggestions for prospecting are offered on precedingpages in descriptions of individual commodities.These suggestions are only summarized here.In searching for deposits of the metallic minerals,and many of the nonmetallic ones, it is always well to

96 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYproceed from the known to the unknown. The bestchances of discovering more iron ore, for example, willlie in further exploration, in depth or laterally, of knowndeposits. This should be the first rule; the second shouldbe to confine the search to favorable geologic settings.So far as is now known, nearly all the metallic deposits,as well as all the talc, pyrophyllite, beryl, and mica, areassociated with Precambrian rocks in the Rio Apa andAmambay regions and in the general vicinities ofCaapucu and San Miguel. This fact alone shouldlimit the search to a very small part of the country'sarea. In this connection, however, the geologic mapshould be only a guide (pi. 1), for it is entirely possiblethat fairly large areas of Precambrian rocks may existthat are not shown on it. Conventional methods ofprospecting should be followed in most cases; in thesearch for iron ores, it is probable that geophysicalmethods that take advantage of their magnetic propertiesmight serve to discover ore bodies that are notexposed at the surface.Few, if any, guides can be given for hunting newdeposits of clays, building stones, or bauxite. Onlydetailed geologic mapping of large areas would providesuch guides. It is suggested, however, that seriousprospectors take account of the deep weathering thatcharacterizes most of the rocks, and prepare to exposeunweathered material by trenches, pit, or soil augers.Mazo (1952) outlines procedures for exploring commonclay deposits that might be applied to other materials.The shortages of fuel and power in Paraguay are soacute that serious efforts to alleviate them seem justified.There is a good possibility that commercialquantities of petroleum exist in places beneath theGran Chaco. In view of its potential importance tothe national economy, serious efforts to search for itshould be encouraged. Present efforts to develop thepeat deposits near Pilar deserve strong support.There is little reason to expect authentic discoveries ofcoal, but every reported discovery should be followedup, as should reports of salt and sulfur deposits.DEVELOPMENT OF LOCAL INDUSTRIESThere is an excellent possibility of establishing severalsmall new industries, or of modernizing existing ones,using local mineral resources and producing goods forlocal consumption. Such industries, whether fosteredby the Government or by private enterprise, wouldresult hi freeing Paraguay from dependence on importsfor some of its requirements and would, of course, conservecorresponding amounts of the nation's foreignexchange. They would also have long-range advantagesin encouraging the search for mineral resources and indeveloping skills on the part of Paraguayan workers inmining and treating mineral products.IRONBecause the known reserves of iron ore appear to besmall, both as to total and as to individual deposits,and because of the lack of fuel, the possibilities of developingan export trade in iron ore or of developing alarge local iron and steel industry are definitely notencouraging. On the other hand, there does seem to bean excellent chance of developing a small local industry,capable of supplying at least a few hundred tons peryear of wrought iron and related forms of iron and evenof steel. This iron could be made locally into suchthings as plowshares, crowbars, chains, machetes,anchors, ornamental grillwork, and many other itemsthat are normally imported. Moreover, all such itemshave enormously higher value than the raw iron orefrom which they are derived, so that the country'seconomy would benefit by the difference between themoney that would be received from exporting raw oreand that which would be spent on importation offinished products.The kind of iron works envisioned would be smallmodern blast furnaces or perhaps small Bessemer converters,both fired with charcoal, and similar to thosethat are in successful use in Brazil. Such furnaces arethe modern descendants of the primitive furnaces orforges that were used in Paraguay during the War ofthe Triple Alliance and in Texas and Alabama duringthe War Between the States. Small modern furnacescould be constructed cheaply and quickly, largely fromnative materials, so that capital outlay and imports ofmaterials would be small. Charcoal for fuel and limestonefor flux are available in Paraguay in unlimitedquantity, hence no imported materials would be neededafter the furnaces were in operation.If it is not already available in Paraguay, the requisitetechnical knowledge to build and operate the furnacesmight come from Brazil. That country produces atleast 500,000 tons of iron and steel per year from smallcharcoal furnaces; it has done and is doing a great dealof research on the technology and economics of suchfurnaces.BUILDING AND ORNAMENTAL, STONESParaguay possesses a great variety of rocks thatcould easily supply all local needs for ornamental stoneand that could even be developed into an export tradeif regular production of superior material could be assured.Even if production of finished ornamental stonewere undesirable or impossible for any reason, there isno apparent reason why a single kilogram of crushedmarble for terrazzo floor tiling and the like, of powderedmarble, or of lime or limestone in any form should everbe imported by Paraguay.Many types of sandstone are already being produced.

MINERAL RESOURCES 97These range from white to red in color and many ofthem form very attractive stone for flagstone walks,walls, and exterior facing for buildings. Large quantitiesof broken stone, mostly basalt or other darkcoloredigneous rocks, are used for street paving, forrough wall construction, and for foundations of allkinds. All these materials are quarried by very simplemethods and little or no attempt is made to improvetheir natural appearance by cutting, polishing, or otherdressing.In addition to the rough building stones mentionedabove, it should be possible to produce many kinds ofmarble from the large deposits that outcrop along theRio Paraguay from the mouth of the Rio Apa southwardto San Salvador. These rocks range from uniformwhite or gray through mottled and striped rocks ofvarious shades to what should be an excellent verdantique serpentine marble. Crushed and powderedmarble of a high degree of chemical purity could beproduced as a natural byproduct of a small marbleindustry, or could be easily produced by the Vallemicement plant, which already has all the requisite crushingand grinding equipment. The possibility of usingthe waste products from the Vallemi plant for agriculturallimestone is discussed on page 87.Several distinct types of light-colored granite withvery attractive texture, all durable and suitable forornamental stones, exist in the general vicinity ofCaapucii and Quyquyo, and probably elsewhere. Thereis also some strikingly beautiful and extremely toughblack "granite" (alkalic shonkinite) at Mbocayaty.The establishment of an ornamental stone industrywould require, in addition to technical knowledge thatis probably not now available in the country, a considerableinvestment in equipment for quarrying, cutting,and polishing the stone, Once the industry wereestablished, however, about the only continuous importrequirements would be small amounts of explosives forquarrying and abrasives and acids for cutting andpolishing.GLASSWAREExcept for three plants that produce common bottlesand jugs, virtually all of Paraguay's requirements forglass are imported. This is a particularly unfortunatesituation because, with such a fragile and bulky commodity,transportation charges necessarily form a highproportion of the final costs. Paraguay could probablynot compete successfully at this time with foreign producersof plate glass or the finer grades of domesticglassware, but there is no reason why it could not producemost of its requirements of the common grades ofglass for commercial and domestic use, such as heavywater glasses, bottles, jars, and other containers. Acheap local source of glass jars would remove one of thechief obstacles in the way of preserving more fruits andother foods for domestic use and even for export, thanis done at present. It would also provide a constantsource of supply for the local bottling industry, whichis now forced to shut down from time to time becauseof a lack of containers.Silica sand is the main ingredient of all glass. Sandand sandstone are abundant in most parts of Paraguay.Much of it is of excellent quality and purity for glassmaking,although most of the sand contains enoughiron to tint the glass green or yellow. This difficultycan be avoided by careful selection of iron-free sandor by the addition of small quantities of manganeseoxide, also available locally. Most of the white ornearly white sandstone, such as that near Tobati andPiribebuy, contains iron in the form of distinct particlesof magnetite (iron oxide); it should be easy to produceiron-free sand from such material by crushing andwashing, thus separating the iron particles by meansof gravity. In places where electricity is availablemagnetic methods of separating the iron-oxide mineralscould be employed.In addition to silica sand, the chief ingredients ofglass are feldspar and soda ash. Adequate suppliesof feldspar can almost certainly be found in the pegmatitesbetween Concepci6n and the Rio Apa. If not,or if transportation costs from that region are excessive,feldspar is a far cheaper commodity than finished glassand the requisite amounts could be imported. Thesame reasoning applies to soda ash, which is used inrelatively large amounts in glassmaking. There areno known deposits of sodium carbonate in Paraguay,but this is a cheap commodity and it would certainlybe cheaper to import soda ash than glassware.Glass factories require comparatively small capitalinvestments for machinery, and either wood or charcoalare adequate as fuels. Existing plants would requiremodernization, particularly in improved chemical controlof the raw materials and in control of temperaturesif any serious attempt is made to supplant imports.It is probable that the necessary technical skills arealready in the country, either among Paraguayanswho have learned glassmaking techniques in the existingfactories or among some of the immigrants fromGermany and other European countries.MINERAL PAINTSParaguay uses comparatively large quantities ofpaint for both exterior and interior decoration. Virtuallyall the paint needed is imported, either as pigmentor as prepared paints, yet there is abundant materiallocally to supply all the requirements for yellow, orange,pink, red, and brown colors that are used. This materialexists in the form of the rich iron ores near Caapucii, in

98 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYthe low-grade lateritic iron ores that cover the surfacein much of central Paraguay, as concretions of ironcarbonate in some of the clay deposits, and in variousother forms. The only treatment needed to produceexcellent mineral pigments from such materials consistsof washing, roasting under carefully controlled conditions,grinding, and grading as to color. The resultantpigments should be equal in most respects to importedproducts.The suggestion that Paraguay could produce muchof its own paint is not original; DeMersay (1860) inhis description of the red soils of the Misiones, nearEncarnacion, Trinidad, and other towns along the AltoParana*, says that the early Jesuits used local materialsin decorating their churches and colleges. He saysthat "clay veins" in the soils yielded red ochre, whichwas calcined, ground, washed, and mixed with amucilage made from the juice of a local cactus (Cactusperumanus). He adds that yellow and white paintswere made in the same way as the red ones.A small pigment industry would require only afew hundred dollars worth of washing, grinding, androasting equipment. Technical knowledge can beeasily gained by experiment and from the literature, or,perhaps better, by sending a technician to Brazilwhere there is a well-developed though primitivepigment industry. Except for the initial machinery,no raw materials would need to be imported in orderto produce pigments regularly.Production of pigments alone would save manydollars of foreign exchange annually. The saving couldbe increased several fold if finished paints, instead ofpigment, were produced. Locally produced tung,linseed, and castor oils could be easily and economicallytreated to produce excellent vehicles for paints. Ifthese oils were used, a fair share of the country'spaint requirements could be met with no importsother than turpentine, small amounts of dryer, andcontainers for the final product. High-grade modernpaints would, of couse, also require the importation ofwhite lead, lithopone, and other ingredients. As notedabove, glass containers could be produced locally,saving additional amounts of foreign exchange.PORTLAND CEMENTThe portland cement plant at Vallemi has alreadydemonstrated that it is technologically possible to producegood portland cement in Paraguay. Large reservesof raw material and fuel are available locally.Except for machinery parts and balls for grinding, theonly materials that must be imported are a few tonsof gypsum per year and paper bags for sacking thefinished product. Paper bags could be replaced bylocally made cotton bags or wooden kegs if that shouldseem desirable to conserve a little additional foreignexchange.As this is the only large-scale mineral industry nowin Paraguay, except for brick and tile, and as it iscapable of producing all of the vitally needed cement,it would appear advisable for the Government to useall possible means to encourage and maintain regularproduction and to place the venture on a sound financialfooting. This is even more desirable if the Vallemiplant is capable of producing an exportable surplus ofcement over Paraguay's requirements.POTTERY AND CLAY PRODUCTSParaguay contains abundant deposits of clay suitablefor most grades of pottery, earthenware, and manyother products, yet it still imports a large proportionof its needs of finished goods. Many of these needscould be produced locally with adequate modern machineryand careful technical control throughout themanufacturing process. Probably the initial investmentwould be relatively large, but continuing imports ofraw materials would be small and would be confinedessentially to coloring materials and to ground feldsparfor glazes. As suggested in the paragraph on glassmaking,there is a strong probability that requirementsof feldspar can be met locally when more is known aboutthe bodies of granitic rock near the Rio Apa and elsewherein the country.TALC AND PYROPHYLLITETalc, which is used as a filler in insecticides, soaps,paints, and many other products, is imported in comparativelysmall, but nevertheless important, quantity.One deposit of talc is known near San Miguel and wasbeing actively explored in 1952; other deposits willdoubtless be found. As described above, there is alsoat least one very large deposit of pyrophyllite, whichis adaptable to most of the same uses as talc, north ofCaapucu.It is doubtful that the local material is of sufficientlyhigh grade to be used in preparation of toiletries, butit should certainly be able to compete successfully withimported talc for most commercial purposes. Moreover,if a cheap local source of talc were available, thedemand for it would probably increase.WATER RESOURCESWater is unquestionably the most valuable single resourcein Paraguay. There are possibilities of developinghydroelectric power at the Sal to del Guaira on theRio Parana and at smaller falls on several major tributariesof that stream. Were it not that all the potentialsources of water power are so remote from centers ofpopulation, such possibilities doubtless would have beenrealized long ago. In addition to this potential use, wa-

WATEE RESOURCES 99ter provides dependable transportation routes throughmost of the country, and is essential for the farmingand livestock industries on which the livelihood of thecountry depends.EASTERN PARAGUAYBecause of the heavy annual rainfall (see fig. 3) andthe numerous perennial streams (pi. 1), virtually allof eastern Paraguay is abundantly supplied with waterfor all agricultural and stockraising pursuits. Even so,some crops suffer from drought damage at times, andin parts of the area it is necessary to build small earthenstorage dams to provide water for cattle throughdroughts that may last 6 months or even more. Inmany areas, however, the problem is one of too muchwater, rather than too little. A glance at plate 1 revealsenormous areas that are swampy or marshy during atleast parts of every year. Some of this marshy groundis well adapted to rice culture. Most of it, however, issuitable only for grazing land and is not even verydesirable for that purpose because the grass it supportsis inferior in nutritive value and there is danger of mir­ing of stock. Recent experiments at the stock ranchof the Institute of Inter-American Affairs at Barrerito,12 kilometers east of Caapucu, have shown that theswampland there can be easily converted to excellentgrazing land, and at comparatively low cost, by meansof drainage ditches. Similar experiments in drainageappear to be justified elsewhere in eastern Paraguay. Itis to be expected, though, that some of the poorlydrained soils that are derived from shale and similarrocks may not be as easily drained as the soils at Barrerito,which are derived from granite.Virtually all the water needed for domestic andindustrial use in eastern Paraguay comes from wells or,to much less extent, from stored rainwater. It isdifficult to understand why surface water is not usedmore widely. Nearly all the larger communities areon the banks of the Paraguay or Parana rivers, or ontheir major tributaries. All these streams carry asuperabundance of water that could be recovered atlittle cost. All doubtless are bacterially contaminatedand would require treatment, but it is certain that nonecan possibly be as contaminated as are many of theraw surface-water supplies in, for example, the UnitedStates.In Asunci6n, much of the water for domestic usecomes from shallow dug wells that depend on near-surface seepage for their supply. There are also afew deep wells, drilled to depths of 60 to 100 meters,which yield adequate supplies of good water fromwhat appears to be the principal zone of saturation inthis vicinity. A few deep wells in Asuncion have beenfailures because they were drilled into sills of basalticrock similar to that exposed on Cerro Tacumbu, butapparently most of the wells that are more than 60meters deep are successful in finding water. Bothdug and drilled wells are, of course, subject to contaminationfrom surface wash unless they are properlyprotected.Ground water conditions in most other communitiesare believed to be similar to those in Asunci6n. Generallyspeaking, moderate to large supplies of fresh groundwater will be found in all the alluvial materials andsandy rock formations throughout eastern Paraguay.Formations that are made up principally of shale orclay will yield little, if any, water. The same statementis probably true of some of the volcanic rocksand of the rocks in parts or all of the Precambrianareas. The only known exception in the latter categoryis at the Barrerito ranch east of Caacupe. There,a well at the ranch headquarters tapped a good supplyof water after almost 70 meters of solid granite hadbeen penetrated. It is believed that the water occurredalong one of the major northeastward-trending faultzones shown on plate 1 in that vicinity.GRAN CHACODespite the innumerable streams that meander overthe surface of the Gran Chaco (see pi. 1), water, andlack of water, are the chief obstacles in the developmentof its vast lands for agriculture, stockraising, or otheruses. This paradox is caused by the fact that in thisarid tropical climate the surface waters tend to alternatebetween states of flood and of drought, when moststreams and waterholes become dry. A closely relatedand no less important factor is that most of the water,both surface and underground, is reportedly so highlymineralized as to be unfit for most uses. Bad water,as well as the periodic lack of water of any kind, isgenerally supposed to have caused more casualties toboth sides during the Bolivian-Paraguayan Chaco Warof the 1930's than did enemy action. Similarly,scarcity of water for both drilling and for camp usewas one of the greatest problems met by the UnionOil Company in its exploration for petroleum duringthe midforties.There are a few relatively deep water wells in theGran Chaco, both in the Mennonite colonies in theinterior and in several of the settlements along thewest bank of the Rio Paraguay. Except for these,most of the scattered army posts and ranches dependon shallow dug wells, on natural waterholes, or onsmall earth-clammed reservoirs for domestic suppliesand for cattle. Such supplies are unsatisfactory atbest and are of course unreliable during prolongeddroughts.The few facts available suggest that the water-

100 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYsupply problems of the Gran Chaco are not necessarilyinsurmountable. A vigorous but careful effort tosolve them might well result in development of sufficientwater to make the Gran Chaco outstanding in meatproduction and possibly agricultural food products.The ideas presented here are nebulous in the extreme,because of lack of specific local knowledge. They aresupported, however, by many facts from the ArgentinePampa, which is the southerly extension of the ChacoBoreal of Paraguay and where the geologic conditionsare similar. Stappenbeck (1926) gives many detailsof the geologic and ground water conditions in themuch more highly developed and more thickly populatedPampa. His work includes many well logs andchemical analyses, as well as a small-scale map showingthe distribution of artesian conditions not far south ofthe Paraguayan Gran Chaco.In any attempt to develop water supplies in the GranChaco, ground water must be used rather than themore obvious surface supplies. Even though the surfacewaters are abundant and of good chemical qualityduring wet seasons, the topography is such that nolarge or deep reservoirs are feasible. It thus seemsimpracticable to count on storage of fresh flood watersfor use during droughts when the streams dry up orbecome too salty even for cattle. Instead, it wouldseem that the principal problem offered by the surfacewaters is one of drainage and of flood-protection. Suchworks, desirable though they may appear, are doubtlessbeyond the ability of the Paraguayan economy in theforseeable future.Too little is known of the geology of the Gran Chacoto permit pinpointing of the area or areas that mightyield usable supplies of ground water or formulation ofany detailed suggestions as to the best methods fordeveloping it. Two possible geologic sources of waterare apparent, however, and both include very largegeographic areas.One source is the great sedimentary basin thatoccupies all but the northern part and the easternmostfringe of the Gran Chaco. The subsurface geology ofthis basin is known in a most general way from therecords of the few deep exploratory wells put down bythe Union Oil Company. No records are available tothe author as to the quantity or chemical quality ofany water that may have been in these wells. Anysuch information would be of doubtful value, for wellsdrilled in search of petroleum are notably prone to missevidence that bears on water supplies.It is known that the Gran Chaco basin contains athick series of unconsolidated sediments and sedimentaryrocks, that many of the rocks must be permeableto water, and that some crop out at the surfaceand, hence, provide catchment areas in Bolivia andnorthern Paraguay. Owing to the basinal structure,artesian conditions probably are widespread, thoughwhether flowing wells can be obtained even on lowground is not known. Both the quantity and quality ofthe water in these sediments are of course conjectural,but by analogy with other sedimentary basins throughoutthe world it is reasonable to suppose that they containfresh water in places, which might be recoverableby pumping or artesian flow from deep wells. Anymore definite knowledge as to the availability of waterat depth must await much more detailed knowledge ofthe subsurface geology of the Gran Chaco than ispresently available. Considering the number of aquifersthat must be present, it is entirely possible thatwildcat wells might strike fresh water. The knowledgegained by means of such wells could be made the basisof a deep-well drilling program, backed by thoroughgeologic and geophysical studies.The chances of developing fresh-water supplies fromshallow aquifers in the Gran Chaco are somewhat morepromising and easier of accomplishment than are thechances from deeper parts of the basin.In a few parts of the Gran Chaco, the permanentwater table is relatively near the surface and yieldsfresh water readily to pumped wells. In some placesthe lower part of the fresh-water zone grades downwardwithin a few tens of centimeters to water that isso highly mineralized as to be unfit for use; elsewherethe fresh water is separated from underlying mineral­ized water by impermeable layers of clay. The fewavailable analyses of "salt" waters in the Gran Chacoindicate that the principal constituents are of sulfatesand chlorides of sodium and magnesium. No informationis available as to whether any fresh-waterzones exist beneath the "salt" waters.The near-surface stratigraphy of the Gran Chaco is,of course, no better known than is the stratigraphy ofthe deeper and older beds. Because of the continentalalluvialconditions under which the younger beds weredeposited, it is likely that most if not all of the youngerbeds are decidedly discontinuous, and, hence, thatconditions found in any one well could not be extrapolatedmore than a few kilometers at most from thepoint of discovery.If any serious attempt is made to develop nearsurfacesupplies of fresh ground water in the GranChaco, the first necessary step would be to make an inventoryof available information on all existing wells.On the basis of the data so derived, a series of exploratorywells 30 to 100 meters deep could then be drilled,with provision for offsetting any successful wells so asto delimit the areas that yield fresh water at reasonabledepths. Any such program should be under the directsupervision of a geologist experienced in ground-water

SOILS OF PARAGUAY 101investigations, for, in the absence of surface exposures,useful information as to existence or distribution of freshwater can be gained only from close observation andcontrol of the drilling operations and from study of therecords so obtained. Once some guides are establishedby the suggested exploratory wells, geophysical methodsmight be used to trace out fresh-water-bearinghorizons. Careful attention to and experimentationwith methods of drilling, casing, and screening are atleast as important as is geologic control, for there isalways grave danger of missing fresh-water aquifers entirely,or drilling through them and contaminating thefresh water with underlying salt waters.This suggested program of exploration has the virtueof flexibility as to scope; it could easily be restricted tosmall areas where the need for water is the greatest.Moreover, whatever its scope, it bears promise ofpossible reward far beyond its cost.SOILS OF PARAGUAYBY PEDEO TIRADO SULSONAAbout 70 percent of eastern Paraguay is covered byrelatively deep residual soils that range from loamy sandto sandy clay in texture. They are classified in sevenmajor soil series, the differences between them moreclosely related to the parent materials from which theywere derived than to any other single factor. The remainderof eastern Paraguay is covered by transportedsoils, divided into four series; like the residual soils, allare sandy. As would be expected from its geologichistory, virtually all of the Gran Chaco is covered bytransported soils ranging from sandy loam to clay thatare classed in six major soil series, with distinctionsbased more on drainage and topographic position thanon parent materials or other features. The soils ofParaguay are described briefly in the accompanyingtable; their general distribution is shown in plate 3.The soils of eastern Paraguay provide favorableto adequate conditions for root penetration, aeration,and water absorption and retention. The areas oftransported soils, however, are generally characterizedby a water table near or at the surface.The residual soils are low in exchangeable calciumand phosphorus, and low to adequate in organic ma­terial and in nitrogen. They are commonly acceptableto high in exchangeable magnesium and potassium.Most are acid, the pH ranging from 5.8 to 6.8. Thealluvial soils are higher in all nutrients than are theresidual ones and can generally be considered as adequatefor agricultural purposes if proper drainage canbe attained.All the eastern soils, transported and residual, tend tobe very low in the minor elements, such as copper, zinc,manganese, and cobalt, which are known to be essentialto healthy plant or animal growth. This shortcomingis doubtless a dominant factor in the slow growth andmaturity of cattle, and perhaps it even contributes tothe comparatively small stature of most of the people.The absence of minor elements, as well as the lowcontent of such elements as calcium and phosphorus, isa direct result of the geologic and soil-forming historyof the region. As most of the soils are derived fromsandstone, whose constituents represent long periods ofweathering and of rather thorough sorting, it is only tobe expected that they contain much smaller amounts ofmany essential elements than would soils formed fromthe weathering of rocks or mineralized zones that werericher in such materials. Moreover, all the easternsoils have evolved under tropical conditions, with heavyprecipitation, so that much of the nutrient materialthey may have had originally has long since been removedby leaching.The Gran Chaco soils are, as would be expected,richer in all the essential chemical elements than arethose of eastern Paraguay. They represent alluvialmaterial that, geologically speaking, has been freshlywashed down from a great variety of rocks in the Andesand that has had little opportunity to lose these ele­ments by leaching. Were it not for the high watertable and the abundance of magnesium sulfate andother salts, there is little doubt that the Gran Chacosoils would be far more amenable to agriculture and tostockraising than are those east of the Rio Paraguay.REFERENCES AND ANNOTATED BIBLIOGRAPHYAhlfeld, Federico, 1936, Ein neues Nutzglimmer Vorkommen inBolivia: Zeitschr. filr prakt. Geologic, v. 44, p. 143-145.Mica deposits in northeastern Bolivia.1946, Geologfa de Bolivia, Re vista de museo de la Plata:Sec. Geol., v. 3, p. 5-370, La Plata, Argentina, 1946. Alsopublished separately by Univ. de Econ. Nac., DireccionGeneral de Minas y Petroleo, La Paz, Bolivia.Excellent summary of Bolivian geology.Almeida, F. M. de, 1945, Geologia do Sudoe"ste Matogrossense;Dept. Nac. da Produgao Min. Div. de Geol. e Min., Bull.116, 118 p., Rio de Janeiro.Detailed description of stratigraphy in vicinity of Corumba,with maps.Azara, F. de, 1790 (republished 1904), Geografia fisica y esfericade las provincias del Paraguay y Misiones Guara.nies; An alesdel Mus. nac. Montevideo, Sec. his.-filos., v. 1.Quoted extensively by Carnier (191 Ic) with regard to geologyof central Paraguay. (Not seen.)Baker, C. L., 1923, The lava field of the Parana basin, SouthAmerica: Jour. Geology, v. 31, p. 66-79.Clear description of the Serra Geral lavas, their environmentand history.

102 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYBarclay, W. S., 1909, The River Parana: an economic survey:Geog. Jour., v. 33, p. 1-40, map, London.Interesting account, with notes on the lavas and on geologichistory of cataracts along the Parand and its tributaries.Beder, R., and Windhausen, H., 1918, Sobre la presencia delDevonico en la parte media de la Repiiblica del Paraguay:Bol. Acad. Nac. Cienc. de Cordoba, 23, p. 255-262.Describes fossils from near Arroyos y Esteros; notes on geologicsetting.Beder, R., 1923, Sobre un hallazgo de fosiles permicos en Villarrica:Bol. Acad. Nac. Cienc. de Cordoba, 27, p. 9-12.Brief descriptions of several building-stone quarries thatyielded vertebrate and invertebrate fossils of Santa Catarina(Gondwana) age.Bertoni, A. de W., 1939, Informe sobre rocas conchilianas deVilleta: Rev. de la Soc. Cient. del Paraguay, tomo 4, no. 4,p. 61.Brief notes on fossils of Tertiary age near Villeta.Bertoni, G. T., 1940, Geogr&fia econ6mica nacional del Paraguay:Biblioteca de la Soc. Cient. del Paraguay, Asuncion, Paraguay,235 p., no maps.Chapter 13 (p. 130-139) on "Estructura geologica del Paraguay"summarizes available knowledge of geology. Chapter 17(p. 189-212) on "Las producciones minerales del Paraguay" presentsmany data on metallic and industrial mineral resources,mostly taken from DuGraty (1865),'also contains good discussionof possibility of finding mineral fuels and excellent dataon water power resources.Bertoni, M. S., 1921, Datos preliminares sobre la geologia delParaguay: Rev. de la Soc. Cient. del Paraguay, v. 1, no. 2,Asunci6n.Not seen.Boettner, Ricardo, 1945, Homalonotus en el Paraguay: Re vistaFacultad de Quimica Farmacia, Univ. nac. del Paraguay,Asuncion, Paraguay, v. 1, no. 2, p. 25.Describes Homalonatus sp? from Minas-cue near Itacurubi.1947, Estudio geologico desde Puerto Fonciere hastaToldo-Cue: Rev. Facultad de Quimica Farmacia, Univ.nac. del Paraguay, Asuncion, Paraguay, v. 3, no. 6-7, p.9-14.Description of rocks along a traverse a short distance south ofthe Rio Apa.1952, Fosiles Paraguayos: Rev. del Centro ParaguayoIng., v. 1, p. 31-7, Asuncion.Summary of existing knowledge of Paraguayan fossils andgeologic history of the country.Bottignoli, P. J., 1926, Diccionario Guarani-Castellano y Castellano-Guarani:Asunci6n, 114 p.Bilingual dictionary, useful in translating names of places andnatural features.Bowman, Isaiah, 1909, The physiography of the Central Andes:Am. Jour. Sci., 4th ser., 28, p. 197-217, 373-402.Camargo, Mendes, J., 1951, Estratigrafia e malacofauna daformacao Corumbatai: Div. Geol. Min., Mon. 13, Rio deJaneiro.Carnier, Karl, 191 la, Reisen in Mato Grosso und Paraguay,Mitt, der Geog. Gesell, Miinchen, v. 6, p. 18-44.Superseded by Carnier, 191 Ic, which has many more details.1911b, Uber das Alter Holzer aus dem Randgebiet vonVilla Rica in Paraguay. Mitt, der Geog. Gesell., Munchen,v. 6, p. 430-431.Brief description of fossil woods from Villarrica, Maciel, andnear the Rio Parana.191 Ic, Paraguay, Versuch zu einer morphologischenBetrachtung der Landschaftformen, Mitt. Geog. Gesell.(fur Thuringen) v. 29, p. 1-50, Jena.Excellent description, with sketch cross sections and geologicmap, of geology and physiography particularly between Rio Apaand Rio Aquibadan, but including discussion of Amambayregion and area between Villarrica and Asuncion. Petrology ofsamples collected by Carnier described by Goldschlag (1913a).1913, Einige Bemerkungen uber die isolierten Gebirge imTieflande des Paraguay: Mitt, der Geog. Gesell. (furThuringen), v. 8, p. 7-17, Jena.Brief description of parts of northern Paraguay and southernMato Grosso, Brazil, with notes on augite syenite of Pao d'Acucarand Tres Hermanos hills and porphyry of Fuerte Olimpo.Clarke, J. M., 1897, Afauna Siluriana Superior do Rio Trombetas,Estado do Para, Brasil: Archives do Mus. Nac. do Rio deJaneiro, v. 10, 1897-1899, p. 1-174, pis. 1-8.Conradi, Sergio, 1935, Informe sobre los trabajos geologicosrealizados en el viaje a Pedro Juan Caballero: Rev. delJardin Botanico y Mus. de Historia Nat., v. 4, p. 63-81,Asunci6n.Geologic notes, with several cross sections, of a traverse fromConcepci6n to Pedro Juan Caballero and along the SierraAmambay. Includes excellent descriptions of the Serra Gerallavas and of the subjacent sandstone in this area.Cross, Whitman, 1897, The igneous rocks of the Leucite Hillsand Pilot Butte, Wyo.: Am. Jour. Sci., ser. 4, v. 4, p.115-141.Describes an amphibole similar to that in shonkinite fromMbocayaty.Dana, J. D., 1914, System of mineralogy: New York, Wiley &Sons, 6th ed., p. 609.Describes hydronephelite.Decoud, Hector Francisco, 1906, Geografia de la Republica delParaguay, 5th ed., Leipzig, Brockhaus, 127 p.Not seen.DeMersay, Alfredo, 1860, Histoire physique, economique etpolitique du Paraguay et des etablissements des Jesuits:Librairie de L. Hachette et Cie, Paris, 486 p. plus atlas ofmaps.Interesting account, with many useful notes on geology andmineral resources.

REFERENCES AND ANNOTATED BIBLIOGRAPHY 103Derby, O. A., 1878, Geologia da regiao diamantifera da provinciado Parana no Brasil: Arch. Mus. Nac. v. 3, p. 89-96.First known description of Parana trap rock (here calledSerra Geral lavas). Not seen.1887, 1891. On nepheline rocks in Brazil: Quart. Jour.Geol. Soc. (London), v. 43, p. 457-473 and v. 47, p. 251-265.Excellent description of alkaline rocks in eastern Brazil.1898, A study in consanguinity of eruptive rocks: Jour.Geology, v. 1, p. 597-605.Principally a discussion of alkaline rocks in eastern Brazil butcontains brief mention of foyaite and augite-syenite from Paod' A§ucar.Dorr, J. V. N., 1945, Manganese and iron deposits of Morro doUrucum, Mato Grosso, Brazil: U. S. Geol. Survey Bull.946 A, p. 1-47.DuGraty, A. M., 1865, La Republique de Paraguay, 2d ed.,Brussels, C. Muquardt, 407 p.Includes many data on geography, hydrology and climate withnumerous notes on lithology and mineral resources (latter inchap. 6, p. 273-301). Also includes useful glossary of Guaraniterms.Du Toit, A. L., 1927, A geological comparison of South Americawith South Africa: Carnegie Inst. Washington Pub. no. 381,158 p.Eckel, E. B., and Maz6, Ricardo, 1952, Posibilidad de establecerindustrias minerales en el Paraguay: Rev. del CentroEstudiantes de Cienc. Econ. 13, no. 110, p. 45-51, Asunci6n.Preliminary report, superseded by this paper.Evans, J. W., 1894, The geology of Mato Grosso (particularlythe region drained by the upper Paraguay): Quart. Jour.Geol. Soc. (London), v. 50, p. 85-104.Includes brief description on page 100 of augite-syenite fromPao d'A§ucar and vicinity.Freitas, Ruy Ozorio de, 1944, Jazimento das rochas alkalinasno Brasil meridional: Minera§ao e Metal, v. 8, no. 43,p. 45-48.Fries, C., Schaller, W. T., and Glass, J. J., 1942, Bixbyite andpseudobrookite from the tin-bearing rhyolite of the BlackRange, N. Mex.: Am. Mineralogist, v. 27, p. 305-322.Discusses occurrences of pseudobrookite comparable withthat in Serra Geral lavas.Gerth, Heinrich, 1932-41, Geologic Sudamerikas: 3 v., GebriiderBorntraeger, Berlin.Excellent compilation of available geologic facts on SouthAmerica.Goldschlag, M., 1913a, Beitrag zur Kenntnis der PetrographieParaguays und des angrenzenden Gebietes von MatoGrosso: 59 p., Inaug. diss., Jena.Detailed petrologic description, with many analyses, of rocksamples collected by Carnier, 1911.Goldschlag, M., 1913b, Zur Petrographie Paraguays und MatoGrosses: Mitt, der Geog. Gesell., Miinchen, v. 8, no. 3,p. 293-301.Condensation of material given by Carnier (191 la) andGoldschlag (1913a).Gordon, Mackenzie, Jr., 1947, Classification of the Gondwanicrocks of Parana, Santa Catarina, and Rio Grande do Sul:Dept. Nac. de Produ§ao Min., Div. de Geol. e Min., NotasPreliminares no. 38a, 19 p., Rio de Janeiro.Guimaraes, Djalma, 1947, Origin das rochas alcalinas MinasGerais: Inst. Tech. Ind., v. 5, 104 p.Hanson, E. P., Editor, 1950, New World guides, III, LatinAmerican Republics: Duell, Sloan & Pearce, New York,3ded.Harrington, H. J., 1950, Geologia del Paraguay Oriental: Contr.Cient., ser. E, Geologia, Univ. de Buenos Aires, to mo 1,82 p., map and plates.Excellent modern description of geology, stratigraphy, andpaleontology, with geologic map (1 inch=47 mi.) of easternParaguay.1956, Paraguay, in Handbook of South Americangeology: Geol. Soc. America Mem. 65, p. 99-114.Contains essentially the same material, in English, as appearsin Harrington (1950).Hibsch, J. Em., 1891, Einige Gesteine aus Paraguay: TschermaksMineralog. Petrog. Mitt., 12, p. 253-255, Wien.Describes specimens of nepheline basalt from Cerro Ybytymiand quartz porphyry from near Lago Ypoa, collected by Jordan(1893).Jerman, Ludwig, 1898, Der Unterlauf des Igatimi: Mitt, derGeog. Gesell., Hamburg, v. 14, no. 4, 28 p.Not seen.Johnston, Keith, 1876, Notes on the physical geography ofParaguay: Royal Geog. Soc., Proc., v. 20, p. 494-504.Good general description; no geologic observations.Jordan, Paul, 1893, Ueber meine Reisen in Paraguay: Mitt, derGeog. Gesell., Wien, v. 36, p. 627-655.Includes description of Sierra Ybyturuzu; rocks collected byJordan are described by Hibsch (1891). Not seen.Kanter, Helmuth, 1936, Der Gran Chaco und seine Randgebiete:Hamburg, Hansiche Univ., 376 p.Good description of natural history, including surface geologyof the Gran Chaco and surrounding areas. Contains smallscalesketch map of geology.Kennedy, W. A., 1933, Trends of differentiation in basalticmagmas: Am. Jour. Sci., 5th ser., v. 25, p. 239-256.Kerr, Sir John Graham, 1950, A naturalist in the Gran Cbaco:Cambridge Univ. Press, 229 p., ills.Excellent background material on Gran Chaco natural history;contains a few minor notes on geology.

104 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYKrieg, Hans, 1931, Wissenschaftliche Ergebnisse der DeutschenGran Chaco Expedition: Geographisehe Ubersieht undillustrierter Routenbericht, Stuttgart, Strecker und Schroder,95 p.Excellently illustrated summary of geography and naturalhistory along a route up the Rio Pilcomayo, thence circling theGran Chaco. Many details of the regimen of the Pilcomayo.Extensive bibliography.Larsen, E. S.,Jr., 1940, Petrographic province of central Montana:Geol. Soc. America Bull., v. 51, p. 887-948.Leanza, A. F., 1948, El llamado Triasico marino de Brazil,Paraguay, Uruguay, y la Argentina: Soc. Geol. Argentina,Rev., v. 3, p. 219-244.Review of literature, with conclusion that marine faunas ofBrazil, Uruguay, and Paraguay, previously considered Triassic,are of Permian age.Lisboa, A. R., 1909, Oeste de Sao Paulo, sul de Mato Grosso,Typ. do Journal do commercio, de Rodriques & Co., 172 p.,Rio de Janeiro.Good descriptions of much of the geology of Mato Grossocontiguous to northeastern Paraguay.Mather, K. F., 1922, Front ranges of the Andes between SantaCruz, Bolivia, and Embarcaci6n, Argentina: Geol. Soc.America Bull., v. 33, p. 703-764.Maury, C. J., 1929, Uma zona de Graptolitos do Llandoveryinferior no Rio Trombetas, Estado do Para, Brasil: Mon. 7,Serv. Geol. Min. Brasil.Maz6, Ricardo, 1951, Posibles recursos minerales del Paraguay:typed, in files of Dept. de Geol., Min. des Obras Publicas yCommunicaciones, Asuncion.Brief summary of reported mineral occurrences.1952, Objecto e importancia de la delimitation de losdepositos arcillosos: Rev. del Centre Paraguayo Ing., v. 1,p. 49-50, Asunci6n.Methods of prospecting for clay deposits.Milch, L., 1895, Uber Gesteine aus Paraguay: TschermaksMineralog. und Petrog. Mitt, v. 14, no. 5, p. 383-394,Vienna.Detailed petrologic description, but no analyses of rocksamples collected by A. Lindner. Mostly sediments, butincludes limburgite from Tacumbii and phonolite from Ybytimi(near Sapucay).1905, Uber die chemische Zusammensetzung einesLimburgites, eines phonolithischen Gesteines und einigerSandsteine aus Paraguay: Tschermaks Mineralog. und Petrog.Mitt., v. 24, no. 3, p. 213-226, Wien.Chemical analyses of rocks described by Milch, 1895.Niederlein, Gustav, 1885, Reisen im nordlichen Argentinien:Verhandlungen der Gesellschaft fur Erdkunde zu Berlin,v. 12, p. 238-240.Describes basalt along Rio Parand briefly.by Carnier.Not seen notedOliveira, A. I. de, and Leonardos, O. H,. 1943, Geologia doBrazil: Rio de Janeiro, Servicio de Informac.ao Agricola,Ministerio da Agricultura, 2d ed., 813 p., maps and plates.Excellent general account of geology of Brazil, with extensivebibliography.Oppenheim, Victor, 1936, Geology of Devonian areas of Paranabasin in Brazil, Uruguay, and Paraguay: Am. Assoc.Petroleum Gecl. Bull., v. 20, p. 1208-1236.No original observations on Paraguay; extensive bibliography.Page, Capt. John, 1859, La Plata, the Argentine Confederation,and Paraguay: New York, Harper and Bros., 632 p., map.Good desciiptions of geography, with a few notes on geology.1889, The Gran Chaco and its rivers: Royal Geog. Soc.Proc., v. 11, no. 3, 129-152. Not seen.Pfotenhauer, J., 1891-93, Die Missionen der Jesuiten in Paraguay:C. Bertelsmann, Guterslogh, 3 v. in 1.Few notes on geology, including data on early sources of salt.Pohlmann, Robert, 1886, Gesteine aus Paraguay: NeuesJahrbuch fur Mineralogie, Geologic und Paleontologie,Stuttgart, v. 1, p. 244-248.Detailed petrologic description of hand specimens fromnorthern Paraguay. Includes sedimentary, metamorphic andigneous rocks, but gives few localities.Prider, R. T., 1939, Some minerals from the leucite-rich rocks ofthe west Kimberly area, Western Australia: Mining Mag.(London) v. 166, p. 373-387.Describes rocks similar to the shonkinites of Mbocayaty.(See also Wade and Prider, 1941.)Ramdohr, Paul, 1950, Die Erzmineralien und ihre Verwachsungen:Akad.-Verlag, Berlin, 826 p.Contains discussion of origin of pseudobrookite (p. 735-736)possibly applicable to that in Serra Geral lavas.Reed, F. R. Cowper, 1935, Some Triassic lamellibranchs fromBrazil and Paraguay: Geol. Mag. (London), v. 72, p. 34-43.Describes Pinzonella cf. P. illusa Reed from between San Jose"and Valenzuela.Ruiz de Montoya, Padre Antonio, 1876, Arte de la lenguaGuarani, O mas bien Tupi: (Vienna), 95 p., Buenos Aires,P. E. Coni, also published in Vienna, Faesy y Frick, 100 p.Guarani-Spanish dictionary and thesaurus.lating names of places and natural features.Useful in trans­Schuster, A. N., 1929, Paraguay, Land, Volk, Geschichte, Wirtschaftsleben,und Kolonization; Stuttgart, Strecker urdSchroder, 667 p., many illustrations and maps.Fine report on human and physical geography. Containsbrief descriptions of geology (after Carnier) and of mineralindustries.Schuster, Julius, 1911, Osmundites von Sierra Villa Rica in Paraguay:Ber. der Deutsch. Botanisch. Gesell., v. 24, no. 7,p. 534-539, 4 figs., 1 tbl., Berlin.Detailed description of fossil fern and conifer specimens collectedby Carnier (1911).

REFERENCES AND ANNOTATED BIBLIOGRAPHY 105Scorza, Evaristo Penna, 1952, Consideragoes sobre o ArenitoCaiua: Brazil. Div. Geol. Min. Bol. 139, Rio de Janeiro, 62 p.Sermet, Jean, 1950, Le Paraguay; Les Cahiers d'Outre-mer, v. 3,p. 28-65.Brief but reliable summary of geography. Contains smallscale,highly generalized geologic map and brief mention of mineralresources.Siemiradski, J. von, 1898, Geologische Reisebeobachtungen inSudbrasilien: Sitz. Ber. Akad. Wiss. Mat., Vienna, v. 107,p. 22-39.Records Permian marine fossils from Amambay plateau alongBrazilian border. Baker (1923) points out that these were wornas charms by Indians and may have come from distant sources.Not seen.Stappenbeck, Richard, 1926, Geologic und Grundwasser derPampa: Stuttgart, E. Schweizerbart'sche Verlagsbuchhandlung(E. Nagele) Gimibitt., 409 p.Stelzner, Alfred W., 1876-85, Beitrage zur Geologic und Paleontologieder Argentinischen Republik: Cassel und Berlin,T. Fischer. 2 v. in 1.Quoted by Carnier (191 Ic) as noting the equivalence of thePrecambrian quartz porphyry near Caapucu with similar rocksin the Andes. Not seen.Taylor, E. F., 1952, Geology and oil fields of Brazil: Am. Assoc.Petroleum Geologists Bull., v. 36, no. 8, p. 1613-1626.Small scale map shows general geologic relations along easternborder of Paraguay.Tbugutt, Stanislaw J., 1932, Sur Fepinatrolite, mineral composantPhydronephelinite: Arch. Min. Soc. Sci. Varsovie(Warsaw) 8, p. 141-143.The above paper in Polish is abstracted in Neues Jahrbuch fiirMineralogie, Geologie und Palaontologie 1, 534, 1933. (In German.)The abstractor (Stiitzel) considers hydronephelite to bea mixture and not a mineral species.Toeppen, Herman, 1884, Hundert Tage in Paraguay: Mitt, derGeog. Gesell., Hamburg, p. 1-264.Records travels over much of eastern Paraguay; few scatterednotes on geology. Contains 1: 200,000 scale hachure map ofeastern Paraguay.Troger, W. E., 1952, Tabellen zur optischen Bestimmung dergesteinsbildenden Minerale, Stuttgart, Schweizerbart, 147 p.Gives optical data on hydronephelite.Vellard, M. J., 1934, Sur quelques fossiles de Paraguay: Mus.Natl. d'Hist. Naturel, Bull. ser. 2, v. 6, no. 1, p. 150-152.Describes fossils of mammals from the Gran Chaco and fromseveral places in southeastern Paraguay.Wade, Arthur and Prider, R. T., 1941, The leucite-bearing rockof the west Kimberly area, Western Australia: Quart. Jour.Geol. Soc., London, v. 96, p. 39-98.Describes rocks similar to the shonkinites of Mbocayaty. (Seealso Prider, 1939.)Warren, H. G., 1949, Paraguay, an informal history: Univ.Oklahoma Press, Norman, Okla., 393 p.Absorbing and factual history.Washburne, C. W., 1930, Petroleum geology of the state of SaoPaulo, Brasil: Comm. Geog. e Geol. do Estado de SaoPaulo, Bull. 22, 282 p., map, Sao Paulo, Brazil. (Alsopublished in Portuguese, 1939, by Dept. Nac. da ProdugaoMin., Rio de Janeiro.)Includes good description of Salto del Guaira and of nearbygeology.Washington, H. S., 1917, Chemical analyses of igneous rockspublished from 1884 to 1913, inclusive, with a critical discussionof the character and use of analyses; U. S. Geol.Survey Prof. Paper 99, 1201 p.White, I. C., 1906, Geology of South Brazil: Science, v. 29, p.377-379.Wilhelmy, Herbert, 1944, Der Alto Parana und die Falle desYguazu: Zeitschr. fur Erdkunde, v. 12, p. 437-442.Brief description of the upper Parana valley and of the Iguassufalls.1948, Aufbau und Landformen des Alto-Parana Gebietes:Petermanns Geographische Mitt., v. 92, p. 32-38.Describes physiography, geology, soils, and ground water,particularly in eastern Paraguay.Willman, Karl, 1915, Zur Petrographie von Uruguay: Dissertation,29 p., Munchen.Describes a Pao d'Agucar in Uruguay that is remarkablysimilar to the one in Brazil on Paraguayan border. Erroneouslylisted in some bibliographies as "Zur Petrographie vonParaguay."Woodworth, J. B., 1912, Geological expedition to Brazil andChile: 1908-1909, Bull. Mus. Comp. Zoology, HarvardCollege, v. 56, no. 1, p. 1-116.Excellent descriptions of Permian glacial deposits and Triassiclavas of the Parana basin some distance east of Paraguay.Anonymous, 1911, Concurrencia del Banco Agricola del Paraguaya la exposicion international de agricultura de BuenosAires: en el centenario de la Revoluci6n de Mayo 1910(2d ed.) 256 p., Asunci6n.Notes on mineral and rock occurrences; history of early ironindustry.Anonymous, 1942, Antecedentes hist6ricos y solucion de lacuestion de limites entre las Republicas del Paraguay yla Argentina en el Rio Pilcomayo: Inst. Geog. Militar delParaguay, Asuncion.Includes description of geology, rainfall, hydrology and physiography.Not seen.

110 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYPageSanta Rosa well, fossils from___...________....__......._____. 74record of._____..__-_..____.__..___._...._____._ 70-71Sapucal, phonolite from ____________________________.. 37,47Schist. See Metamorphic rocks.Scoria, of Acahay caldera... --------___.._.__________..____ 38-39Seco, Arroyo, mica deposits near____________________________ 89Sedimentary rocks, of eastern Paraguay.....____._____________ 50-66Serra Geral lava, age_________..______________________ 28chemical analyses of__.._-_._..._____.______..._._.... 35description-------______...___________..__-____________ 26-27erosion of. _--.._ ...._.....______._.__...__ 28exposures..------- -... -._____.______ ._________. 28extent..--.._.--_-_-_.___________._._._._________________._. 26geomorphic character.,origin___._______.source of name ....stratigraphic relations,structure sections ...._______________.___.___._...._._._____._____. 26._-__.__________._._..._......_._______.___... 26._____________________________._.__........_.. 26.-_-_-_.________________________._....._._._.. 2828Shale, in the Caacupe series._______ _________._____.._____ 56-57of the Itacurubi series__... ...____ ____________._____ 59-61of Tubarao series.._________._______________________ 62-63weathered... ___ _ ___________ ____ _ 81Shonkinite, analyses of__._ . _____________________ 35,47,50description of samples.-. _ -__________.....___________ 45,46Siderite concretions_ _. ....________________._..... 93Silurian system, sedimentary rocks________...______________. 52-59Silver.. --._ ... . .. ._-... -................... 84Soils of Paraguay, by Pedro Tirado Sulsona.. ________._________ 101Southeastern Paraguay, igneous rocks._________________________ 15-19Precambrian rocks_.._____..._..__..____________ 13-15quartzite in ________________________ 13Spectrographic analyses, of alkalic rocks_________.____________. 50of Precambrian rocks___...........___...._....._._________. 24of Serra Geral lavas_______...._______________________ 35Stone ... . . ..... 11,16,34,92-93,96-97Structure, anticline between Rio Apa and San Juan Bautista_______________ 75faults .._.______-______________._.____....._____.__________. 63,76general relations _.. .....________.__.._._________._____ 75Gran Chaco basin. .- 76joints..___-.__- . . . 52,78,80Ypacarai depression-_----___-_----._____________________.____._________.. 76Subsurface rocks, in the Gran Ohaco__________...__________.. 69-73Sulfur...-_ 60,93Swampy lands___...____-.-.______________...___.. 8-9,62Syenitic rock, of Pao de Acucar, Brazil_________.____________ 36-37,69Tabapy. See Roque Gonzalez de Santa Cruz.Tacumbu, Cerro _- . _. 33,35,83,99Tarrant, L. N., density analyses by______....__...____________ 23,35,47Teju-cuarfi, Arroyo, fossils from._.__________________________ 67Temperature-.__ ._______________________.__... 7-8Tertiary system, sedimentary deposits..-.-____..._______________ 66-67Tillite, in rocks of Tubarao series.________________._______ 22,24,62Tin - . . -- . 94Tirado S., Pedro, Soils of Paraguay..... _. . ...........__ ... 101Tobati, clay deposits at_________________________________ 81deposits of ocher.________________________________ 56,89-90exposures of sandstone at_ - _________________ __ 55-56, 57Topography____________________________________.._._ 6Transportation.------______---_-__--_-..__.________._______.__._.___________. 9-10Tres Hermanos hills, rocks of.-..._-_____._.__._.__...____ 21-22Triassic system, igneous rocks.._...______-..._._______..._ 26-34sedimentary rocks of._______________...._________________ 65-66See also Misiones sandstone.PageTrinidad, fossils from__________________________________ 67sedimentary rocks near__________ _ ______.-.______ 65-66Trumbull, Lois D., chemical analyses by..___________________ 23,35,47Tubarao series, correlation ___ __ __ 63description-.._______.__________...________.______ 62-63exposures-...-_.____...-_. -___ .-._________. 62fossil 62tllliteln.... - . ... . 22,62Tungsten__._______-_______ __ -___ ________.__ 94Union Oil Company, well records._.________.___.---.________. 69-74Upper shale and sandstone unit of Caacupfi series ___ 56-58Vallemi cement plant._________.___________... ______ 79,87,98Vargas Pena clay pit.--_. - .- - 54-55,57,59,76,81Vargas Pena tile plant.____-----_. .. ..__ 80Vegetation..______-_____-____-_-__-__. .._______ 8-9Villa Florida, copper deposit near.._____________.____..._____ 82,90Precambrian rocks near.---- . - ___________ _ 13-15,23Villa Hayes, outcrops of red sandstone near... ___-_-___ _ ___-_-_ ______ 68-69Villarrica, mica porphyry from-----...----.---------- __________________ 37-38rocks of Tubarao series near__________._-_.___ . _________ 62Villarrica, Sierra. See Ybyturuzu, Sierra.Villeta, fossils found near _ _.. 67Volcanic rocks.. . ...- .. ._ _.-_ ________________ 12WWater resources, eastern Paraguay___________-___-_---_-_-_-_-_--.-._.______ 99in the Gran Chaeo_____. _______.____. _____ _____ _ 99-101possibilities for developing_-..._-..___..._----- . ...___ 98-99Well records, interpretation. _______ __.. .... ____________________ 74of wells in the Gran Chaco....._ ... . .__ ___ 69-74Yaguaron, granite near-..-..- -... __-_-_-___.___ ___________ _ __ 19Misiones sandstone at_-__- ___ _____ _. -___ ______ ___ . 65, 76manganese deposit_.____--__.._ _____________________________________ 88Yahape, Cerro_--_-_- ______________ ._.. _______ _ . _. 18Ybycul, early iron industry at _____ _ ________ ___________ ___.. 85Ybytymi, nepheline basalt at ...- __ __ _________ . __ 37Ybytymi, Cerro-.-----------.------------------------------------------------ 37Ybyturuzu, Sierra, olivine diabase on_-.._. _______________ _...... __ 32,35Yegros, clay deposits at_ . . . - -- 81Yhaguy, Arroyo, iron sulfide minerals near.. _ __________ __ _____ 93Yhu, clay deposits at 66,81Ypacarai, alkalic rocks near ______________ _ _ ___________ ____ 36,40-43analysis of rocks from. ____________ _.__ _. _ _________ 23arkosic sandstone near ___________________ ________________ -__ ____ 54-55Misiones sandstone near_______ ________ ___ ____ _______ ... 65paving stone from..-._________ __ _ ________________ ..____ 92tile industry at_-------- - ----- ___________ ___ 80Ypacarai, Lago.____ ___ _ ... . - 7, 53, 76Ypacarai depression.__________ __________ ______ ________________ 19, 76Ypacarai quarry._________ __________ _ ___________ ________ .. 40Ypane, fossils found near...... . ______ _ 67Ypoa, Lago.__-._. -... _ __-_____------------_ -... ._____. 7Yta-cue mine__ _ . . . - --- 86Yuty lodestone deposit._______.____- ___.__ - 86-87Zanji Moroti, analyses of rocks from ___ _ _- 23Precambrian rocks at ----- ------- - 21o