Geology and Mineral Resources of Paraguay A Reconnaissance

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