Geology and Mineral Resources of Paraguay A Reconnaissance

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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.
20 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYFIGURE 11. Typical weathering profile on Precambrian quartz porphyry on thehighway between Caapucu and Quyquyo.FIGUEE 12. Partly weathered Precambrian quartz porphyry at same locationfigure 11. showing characteristic weathering out of quartz phenocrysts.tion of the distribution of rocks by interpretation ofaerial photographs, by use of sketch cross sections publishedby Carnier (1913c), and by Boettner (1947),and by piecing together scattered observations recordedin the literature.The western part of the main area of Precambrianrocks is a relatively high and rugged chain of hills thattrends northward to and beyond the Rio Apa. Tt iscalled the "Apa Bergland" by Carnier (1913c) andother authors. The Paraguayan part, marked by theeminences of Cerro Paiba and Loma Pora, is alsoknown as the Cordillera de las Quince Puntas. Eastof this chain is a rolling upland, known as the Satyplateau or Potrero Saty.Biotite and hornblende gneiss, mica schist, andgranite make up most of the area. Associated withthese rocks are aplite, pegmatite, argillite, quartzite,hematitic schist, and other rocks. Lineations in themetamorphic rocks trend northeastward in general anddip steeply either northwest or southeast. Many ofFIGUEE 13. Brown variety of quartz porphyry (specimen P-67) from Quiindyroadside north of Caapucu. Shows weathered aspect of hand specimen. The projectionsare quartz grains.the rocks are much fractured, principally along N. 30°-50° W. trending zones. The northward-trending faultshown on plate 1 is based on interpretation of photographsand may well be in error.
Page 1 and 2: Geology and MineralResources of Par
Page 3 and 4: UNITED STATES DEPARTMENT OF THE INT
Page 5 and 6: IVCONTENTSMineral resources._______
Page 8 and 9: GEOLOGY AND MINERAL RESOURCES OF PA
Page 10 and 11: INTRODUCTION(1947, 1952) are the on
Page 12 and 13: GEOGRAPHYFIGURE 1. Index map showin
Page 14 and 15: GEOGRAPHYbisects the Republic of Pa
Page 16 and 17: GEOGRAPHY 9thorny semidesert plants
Page 18 and 19: GEOLOGY 11chiefly logs, rough lumbe
Page 20 and 21: IGNEOUS AND METAMORPHIC ROCKS 13and
Page 22 and 23: 15FIGURE 7. Arkosic sandstone (spec
Page 24 and 25: IGNEOUS AND METAMORPHIC ROCKS 17FIG
Page 30 and 31: IGNEOUS AND METAMOEPHIC ROCKS 23TAB
Page 32 and 33: 25FIGURE 18. Ehyolite (specimen P-3
Page 36 and 37: IGNEOUS AND METAMORPHIC ROCKS 29PET
Page 38 and 39: IGNEOUS AND METAMORPHIC ROCKS 31DIA
Page 40 and 41: IGNEOUS AND METAMOEPHIC ROCKS 33a d
Page 42 and 43: GEOLOGICAL SURVEY PROFESSIONAL PAPE
Page 44 and 45: 36 GEOLOGY AND MINERAL RESOURCES OF
Page 50 and 51: 42dated by two kinds of porphyry. O
Page 52 and 53: 44FJGTJEE 34. Porphyry (specimen P-
Page 68 and 69: 60lower third of the series consist
Page 74 and 75: 66possible Cretaceous age. Baker (1
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68 GEOLOGY AND MINERAL RESOURCES OF
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174 GEOLOGY AND MINERAL RESOURCES O
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MINERAL RESOURCES 87a pivot, show s
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MINERAL RESOURCES 89of the bright r
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Geology and Mineral Resources of Paraguay A Reconnaissance

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