Volcanogenic-related origin of sulfide-rich quartz veins: evidence from O and S isotopes at the Géant Dormant gold mine, Abitibi belt, Canada

• Published in: Mineralium deposita Vol. 35; no. 1; pp. 21 - 36
• Main Authors: Gaboury, D, Daigneault, R, Beaudoin, G
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer Nature B.V 2000
• Subjects: Dikes; Geology; Gold; Isotopes; Mineralogy; Ocean floor; Oxygen isotopes; Pyrite; Quartz; Seawater; Sulfides; Sulfur; Veins (geology); Volcanoes; Canada; Canada, Quebec, Abitibi
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s001260050003

The Géant Dormant gold mine is a sulfide-rich quartz vein gold deposit hosted by a volcano-sedimentary sequence and an associated felsic endogenous dome and dikes. The auriferous quartz-sulfide veins were preceded by two synvolcanic gold-bearing mineralizing events: early sulfidic seafloor-related and later disseminated pyrite in the felsic dome. This deposit differs from classical Archean auriferous quartz vein deposits by the low carbonate and high sulfide contents of the veins and by their formation prior to ductile penetrative deformation. The δ^sup 18^O values of quartz associated with seafloor-related auriferous sulfides average 11.9±0.6[per thousand] (n=3). The seafloor hydrothermal fluids had a δ^sup 18^O value of 3.2[per thousand] calculated at 250°C. The oxygen isotope composition of quartz and chlorite from veins average 12.5±0.3[per thousand] (n=20) and 5.9±1.1[per thousand] (n=4) respectively. Assuming oxygen isotope equilibrium between quartz and chlorite, the veins formed at a temperature of 275°C, which is consistent with the calculated temperature of 269±10°C from chlorite chemistry. The gold-bearing fluids had a δ^sup 18^O value of 4.7[per thousand] calculated at 275°C. The δ^sup 34^S values of sulfides from the three gold events range from 0.6 to 2.8[per thousand] (n=32) and are close to magmatic values. Sulfur isotope geothermometry constrains the sulfide precipitation in the gold-bearing veins at a temperature of 350°C. The similarity of the isotope data, the calculated δ^sup 18^O of the mineralizing fluids and the likely seawater fluid source suggest that the three mineralizing events are genetically related to a volcanogenic hydrothermal system. The high value of the auriferous fluids (δ^sup 18^O=4.7[per thousand]) is attributed to a significant magmatic fluid contribution to the evolved seawater-dominated convective hydrothermal system. The two-stage filling of veins at increasing temperature from quartz-chlorite (275°C) to sulfides (350°C) may reflect the progressive maturation of volcanogenic hydrothermal systems. These results, together with field and geochemical data, suggest that formation of gold-rich volcanogenic systems require specific conditions that comprise a magmatic fluid contribution and gold from arc-related felsic rocks, coeval with the mineralizing events. This study shows that some auriferous quartz-vein orebodies in Archean terranes are formed in volcanogenic rather than mesothermal systems.[PUBLICATION ABSTRACT]