Metalogenia em terrenos de alto grau metamórfico estudo de caso: distribuição e controle das ocorrências auríferas na região compreendida entre Palma-MG e Laje do Muriaé-RJ.

Abstract

In Palma Capivara and Laje do Muriaé regions there are many gold occurrences, most of them from aluvionar character-type. Ferraz (1928), Freise (1908) and Oliveira (1936) were the main authors to register the presence of gold in the region; they describe gold and monazite presence in almost all the placer deposits from the area. Those authors also describe that the gold from this region is thin, and it shows bismuth impurities. Ferraz (1928) points a pyrite bearing granite-gneiss located 2km north from Palma as a possible source from the gold ore. Pathfinders and field geological evidences related to gold mineralization (e.g. milky quartz, smoky quartz, tectonized quartz veins, hydrothermal alteration zones) were used to try locate the mineralization. The main mined shafts were visited, a regional mapping was completed, and pan concentrate samples and stream sediments samples were collected. The regional mapping has showed the presence of graphite-and-sulphide bearing rock band (Murici A and Murici B). The sub band Murici A is composed of graphite-garnet-pyrite gneiss, where the pyrite contains inclusions of cobaltite, chalcopyrite, copper and nickel sulphide. And the subband Murici B is a pyrrhotite-garnet gneiss, where the pyrrhotite shows inclusions of pyrite, bismuth and nickel telluride, chalcopyrite, sphalerite and petlandite. 26 gold specks were observed on the sample collected from point CB-09 (Fazenda Boqueirão- Córrego Santo Antônio); while on the sample collected from CB-17 (Várzea Congelação- Ribeirão da Capivara) 21 gold specks were observed. Graphite has demonstrated to be the best field evidence to delimitate the mineralized band because it s easily observed on saprolite. The sulphide bearing graphite band is parallel to local ridges (e.g. Serra do Goiabal, Serra da Água Limpa and Serra do Boqueirão), where gold occurrence are found on the streams that cut those ridges. The graphite bearing gneiss was tested through LECO and has showed a 1.84% carbon concentration on the graphite rich portions. Due to those facts, it s possible to assume that the mineralization host rock is the sulphide-and-telluride graphite band.