Geology and Mineral Resources of Paraguay A Reconnaissance

IGNEOUS AND METAMOKPHIC ROCKS 19accessory minerals. This rock is almost identical witha rock (specimen P-30, fig. 18) 9 kilometers south ofCaapucu and also resembles superficially but notmicroscopically that shown in figure 16 (specimen P-31),north of Caapucu.CENTRAL AREAAn exposure of granite at San Bernardino is smallbut nevertheless significant. The northern part of thetown is underlain by this rock; the freshest material isalong the eastern shore of Lago Ypacarai, where thereare nearly continuous exposures for a distance of about1 kilometer.The exposure, whose size is somewhat exaggeratedon the map, (pi. 1) is scarcely more than 1 squarekilometer in extent, as the rock is covered in mostplaces by sediments in the lake or by the basal beds ofthe Caacupe" group. Harrington (1950, p. 16) mentionshaving seen specimens of similar but coarsergrainedgranite said to have come from a small hill afew kilometers west of Yaguaron and a little south ofIta. This indicates that the granitic basement may berelatively close to the surface along both sides of theYpacarai depression.At San Bernardino the granite is pinkish brown andcoarse to medium grained in texture, with some suggestionof schlieren. It contains pink and white feldspar,a little interstitial biotite, and numerous glassyquartz "phenocrysts" thai are subspherical and uniformlyabout twice the size of the feldspar grains thatform the matrix.On the upper slopes of the hill at the north edge oftown the granite is very weathered and crumbly. It iscapped unconformably by the basal beds of the Caacupeseries.NORTHERN AREARIO APA REGIONA complex of Precambrian rocks occupies most ofthe area from the Rio Apa southward to the RioAquibadan, and between the latitudes of Centurionand Santa Luisa. Other outcrops of some of thesesame rocks, though not described in the literature, mustexist near Bella Vista and just north of Conception, forthere are authenticated reports of mica-bearing pegmatitesnear both places. Their probable positionsare sketched in plate 1. This area was not visited byEckel, but it was possible to draw a rough approxima-FIGURE 10. Fine, even-grained aplite (specimen P-74), a brick-red aggregate of flesh-colored orthoclase CO, somewhat perthitic, and glassy quartz (g), fromthe road between Villa Florida and Caapucu. X 20.