Quartzo magmático e hidrotermal do depósito de ouro São Jorge, província aurífera do Tapajós-PA: petrografia, MEV-CL e implicações metalogenéticas

Abstract

The São Jorge Deposit (DSJ), located in the municipality of Vila Riozinho, Gold Tapajós Province, southwest of Pará state, is hosted on 1.89 Ga monzogranite rocks, hydrothermalized at different intensities, belonging to the Younger São Jorge granite. Four morphologicaltextural types of quartz (Qz1, Qz2, Qz3 e Qz4) were identified through images of scanning electron microscopy-cathodoluminescence (SEM-CL) in the mineral assemblages proposed by Borges et al. (2009) to the area of the São Jorge gold deposit. In the most preserved rocks (assemblages 1 and 2), rich in amphibole and biotite, occur anhedral crystals of primary magmatic quartz, with moderate to high luminescence (Qz1). In the altered rocks (assemblages 2 and 3), post-magmatic to hydrothermal fluids affected the granite and percolated fractures in Qz1 and crystallized Qz2 not luminescent (dark). In the most intensely altered rocks (assemblage 4), successive alteration, dissolution and recrystallization processes gave rise to zoned subhedral (Qz3) and euhedral (Qz4) quartz crystals, typically hydrothermal, the latter being host of the gold mineralization. The textural evolution of quartz is directly related to hydrothermal fluids that affected the rocks of the Younger São Jorge granite. Backscattered electrons images (ERE) and semiquantitative analysis by energy dispersive spectroscopy (EDS) identified two generations of gold: Au1, enriched in Ag (4.3 to 23.7%) and included or associated to crystals of Py; Au2, enriched in Te (1.1 to 17.2%) and included in Qz4. The study of quartz crystals by SEM-CL provided important morphological and textural information for understanding of the hydrothermal processes that acted in the mineralized area of the São Jorge gold deposit, allowing the application of this methodology in studies of quartz of other hydrothermal deposits.