Pegmatitos da região entre Rio Bonito e Saquarema, RJ: tipologia, química mineral e geocronologia

Abstract

The pegmatitic area Niterói - Rio Bonito is the most abundant in pegmatites in the Rio de Janeiro state. At this area there was a large exploratory activity of feldspar, quartz and kaolin for ceramics and glassworks industries, as well as the mining activity of beryl near Rio Bonito. The study pegmatites occur on the Northeast portion of the area mentioned above, along the Via Lagos Highway (RJ-124), between Rio Bonito and Saquarema counties, which emplace the Palmital Unit (supracrustal Cabo Frio Terrane), Cassorotiba Unit and Tingui Unit (both within the Oriental terrane). They were divided into two groups: early and late, being distinguished by different aspects. The mineralogy of the veins is basically composed of quartz, K-feldspar, plagioclase and the accessory minerals are apatite, muscovite, biotite, magnetite, ilmenite, diopside, epidote, garnet, hornblende, sillimanite, pyrite, zircon, spodumene and rutile, in addition to minerals with rare earth elements in its composition such as monazite, xenotime and columbite, spodumene and rutile, wich are considered tracers for petrogenetic classification pegmatites. The results suggest four classes (abyssal, muscovite, muscovite - rare element and rare element), with reservations concerning the last one, in addition to the petrogenetic NYF signature. U-Pb geochronological analyses were conducted in four pegmatites with results consistent with brasiliano magmatic bodies generated from collisional phase II to collisional phase III in a time interval between 597 to 537 Ma.