Fluid inclusion and sulfur and oxygen isotope studies on quartz-carbonate-sulfide veins of the Carvoaria Velha deposit, Corrego do Sitio gold lineament, Quadrilatero Ferrifero, Minas Gerais, Brazil

摘要

The Corrego do Sitio lineament is defined as a 16-km long, NE-SW-trending ductile shear zones, which controls fourteen gold deposits, including the Carvoaria Velha deposit. The dominant lithotypes of this deposit are metagrewackes with subordinate carbonaceous phyllites lenses of the Archean Rio das Velhas greenstone belt, which host gold mineralization. Metamafic dikes and sills are parallel and crosscut the host metasedimentary sequence. All these rocks exhibit alteration to quartz, carbonate and sericite, besides sulfides and sulfosalts. The main gold mineralization styles at the Carvoaria Velha deposit, and at Corrego do Sitio as a whole, are quartz-carbonate-sulfide +/- sulfosalt veins of varied distribution. The veins are classified as: V1 veins - quartzankerite-pyrite-berthierite-gold - parallel to the main regional foliation S-n,; V2 veins - quartz-ankerite-pyrite - developed at extensional crenulation cleavage S-n (+) (1), and rarely gold mineralized; V3 veins - quartz-ankerite - filling Sn + 3 fractures, usually free of sulfides and sulfosalts; V4 veins - quartz-calcite - of restricted occurrence in metamafic dikes and sills. The latter crosscut the metasedimentaty sequence, are extensional and display no preferential orientation. The most common ore minerals in all vein types are arsenopyrite, pyrite, berthierite, and pyrrhotite. Microprobe analyses reveal the presence of metallic phases rich in Sb, Pb and Co, such as stibnite, ullmanite, tetrahedrite, galena, cobaltite, which commonly overgrow the sulfides. Fluid inclusion studies trapped in quartz from V1, V2 and V4 veins have identified a H2O-CO2 +/- CH4-NaCl mineralizing fluid that may contain KCl, MgCl2 e FeCl2. The presence of CH4 in fluid inclusions of the V1 and V2 veins reflect interaction of the fluid with the Corrego do Sitio and Santa Quiteria carbon-bearing metapelitic host units.