Geology and Mineral Resources of Paraguay A Reconnaissance

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