Metallogenesis of the orosirian epithermal coringa gold-silver (Cu-Pb-Zn) deposit, southeastern Tapajós mineral Province, Amazonian craton, Brazil

Abstract

The Coringa gold-silver (Cu-Pb-Zn) deposit, in southeastern of Tapajós Mineral Province, is hosted in felsic volcanic rocks the Vila Riozinho Formation (1996 ± 21 Ma) and in the Serra Alkali Feldspar Granite (1999 ± 25 Ma), and has been interpreted to have formed in a post-collisional volcano-plutonic setting. The mineralized shear-vein system follows the NNW-SSE trend of the main regional structures and is coincident with a magnetic trend that can represent a crustal discontinuity at the boundary zone between a magnetic pyroclastic facies of the Vila Riozinho Formation and the pluton of the Serra Alkali Feldspar Granite. The hydrothermal alteration stages comprise: (a) proximal chlorite-hematite alteration, (b) intermediate-proximal sericite-pyrite alteration, with an estimated temperature of 400 °C (white mica chemistry), and (c) late, distal Mn-carbonate-chlorite-epidote alteration, with an average temperature of 234 °C (chlorite chemistry). There are discontinuous massive barren quartz veins (veins type 1), and two types of quartz-sulfide veins (veins types 2 and 3). The veins type 2 are sulfide-poor, gold-bearing, open-space filling veins with pyrite, galena, and hematite, with an average temperature formation of 243 °C (fluid inclusions in quartz). The veins type 3 are sulfide-rich, and gold-bearing quartz veins with sulfide phases represented by pyrite, galena, sphalerite, and chalcopyrite and presented a minimum temperature of 340 °C (fluid inclusions in quartz). Chemical analyses of the sulfides detected significant Mo, Bi, Ni, and Co, with decreasing contents according to the crystallization sequence of the sulfide phases (pyrite-chalcopyrite-sphalerite-galena-gold). The mineralizing fluids are H2O-rich and CO2-poor, low salinity, and the stable isotope compositions of the alteration minerals are mostly consistent with a magmatic source that mixed with a diluted and colder meteoric fluid. The geological setting, the timing of mineralization being nearly contemporaneous with the host rocks (given by previous works), the genetic characteristics, and the local presence of adularia and Mn-carbonate led us to classify Coringa as formed by an intermediate-sulfidation epithermal system.