Geology and Mineral Resources of Paraguay A Reconnaissance

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,