Geology and Mineral Resources of Paraguay A Reconnaissance

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geology and mineral resources ofParaguay, it is essentially a compilation and interpretation ofexisting published and unpublished information on the subject.The rocks can be divided into five major classes, depending onage and mode of origin.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