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Petrografia, química mineral e processos hidrotermais associados ao depósito de ouro São Jorge, Província Aurífera do Tapajós, Cráton Amazônico

2009; Sociedade Brasileira de Geologia; Volume: 39; Issue: 2 Linguagem: Inglês

10.5327/rbg.v39i2.1466

2317-4889

Régis Munhoz Krás Borges, Roberto Dall’Agnol, Cláudio Nery Lamarão, Marco Aurélio Figueiredo, Albano Antônio da Silva Leite, Carlos Eduardo de Mesquita Barros, Hilton Túlio Costi,

Geochemistry and Elemental Analysis

The Paleoproterozoic Sao Jorge gold deposit is situated in the Tapajos Gold Province of the Amazonian Craton. The deposit is hosted by an amphibole biotite monzogranite, composed of quartz, potassic feldspar, plagioclase, amphibole, biotite, titanite and opaques. Four dominant mineral assemblages were recognized in the deposit. Assemblage 1 was formed during the magmatic stage and is characterized by the presence of amphibole and andesine-oligoclase. Assemblage 2 shows the total replacement of the amphibole and intense saussuritization of the primary plagioclase, epidote is a ubiquitous phase and biotite is partially chloritized. Assemblages 3 and 4 are related to the hydrothermal processes, which generated the sulfide and gold mineralization. Assemblage 3 is dominated by chlorite and albitic plagioclase with subordinate white micas and, sometimes, biotite. Assemblage 4 is dominated by white micas, carbonates and pyrite. It is a result of a phyllic alteration, with associated carbonatization. Chlorite geothermometer suggests temperatures of 300±40 °C for the 3 and 4 assemblages. Al in hornblende geobarometer indicates low pressures, around 1 kbar for the crystallization of the mineralized granites. Oxidizing conditions, above NNO, prevailed during the genesis of the deposit. The hydrothermal assemblages of Sao Jorge differ from those described at Joel and Davi and are not dominated by epidote minerals as registered in other areas of the Tapajos province. A porphyry model or intrusion-related model are best adapted for the Sao Jorge deposit. The latter has similarities with the Serrinha deposit in the Juruena province and Batalha in the Tapajos province but it has more strong analogies with the Volta Grande hydrothermal system in southern Brazil.