Geology and Mineral Resources of Paraguay A Reconnaissance

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