Abstract

RIOS-GUERRERO, Johanna  and  BALLESTEROS-CAMARO, Carlos Andrés. Chemical classification and geothermometric of sulfides from the Pilar Mine gold deposit (Greenstone Belt, Quadrilátero Ferrífero, Brazil). Bol. geol. [online]. 2021, vol.43, n.1, pp.147-161.  Epub Jan 01, 2021. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v43n1-2021007.

The Quadrilátero Ferrífero is widely known for its world-class epigenetic and orogenic gold deposits of Archean ages. These are hosted in a sequence of meta-volcano sedimentary rocks of the Nova Lima group, mainly with the Banded Ferriferous Formations (BIF) and strongly sulfured with pyrite ± pyrrhotite ± arsenopyrite ± chalcopyrite + Au, where many of the mineralized bodies are structurally controlled due to the influence of regional NE structures and related to strongly hydrothermal zones. At the Pilar deposit, gold is disseminated in the Banded Iron Formation sequences and as free gold in quartz + carbonate veins associated with sulphides, mainly arsenopyrite. The main sulphides correspond to pyrrhotite, pyrite, chalcopyrite, and arsenopyrite, oriented according to a mylonitic S3 foliation of the rocks. Three halos of hydrothermal alteration are identified, distributed according to the position of the mineralized bodies, being chloritization zone (distal), carbonatization (intermediate) and sericitization (proximal). Chemical compositions of the sulfides associated with the hydrothermal mineral phases were carried out from the results obtained by electron microprobe analysis. The hydrothermal processes associated with the formation of mineralization, according to the paragenesis of sulphides (arsenopyrite ± pyrrhotite ± pyrite ± gold (electrum)) reveal a chemical equilibrium in the temperature range between 363°C to 471°C.

Keywords : Quadrilátero Ferrífero; Sulphides; Mineral chemistry; Geothermometry.

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