Ore-bearing fluids of the Eldorado gold deposit (Yenisei Ridge, Russia)

Abstract

The Eldorado low-sulfide gold–quartz deposit, with gold reserves of more than 60 tons, is located in the damage zone of the Ishimba Fault in the Yenisei Ridge and is hosted by Riphean epidote–amphibolite metamorphic rocks (Sukhoi Pit Group). Orebodies occur in four roughly parallel heavily fractured zones where rocks were subject to metamorphism under stress and heat impacts. They consist of sulfide-bearing schists with veins of gray or milky-white quartz varieties. Gray quartz predominating in gold-bearing orebodies contains graphite and amorphous carbon identified by Raman spectroscopy; the contents of gold and amorphous carbon are in positive correlation. As inferred from thermobarometry, gas chromatography, gas chromatography–mass spectrometry, and Raman spectroscopy of fluid inclusions in sulfides, carbonates, and gray and white quartz, gold mineralization formed under the effect of reduced H2O–CO2–HC fluids with temperatures of 180 to 490 °C, salinity of 9 to 22 wt.% NaCl equiv, and pressures of 0.1 to 2.3 kbar. Judging by the presence of 11% mantle helium (3He) in fluid inclusions from quartz and the sulfur isotope composition (7.1–17.4‰ δ34S) of sulfides, ore-bearing fluids ascended from a mantle source along shear zones, where they “boiled”. While the fluids were ascending, the metalliferous S- and N-bearing hydrocarbon (HC) compounds they carried broke down to produce crystalline sulfides, gold, and disseminated graphite and amorphous carbon (the latter imparts the gray color to quartz). Barren veins of milky-white quartz formed from oxidized mainly aqueous fluids with a salinity of < 15 wt.% NaCl equiv at 150–350 °C. Chloride brines (> 30 wt.% NaCl equiv) at 150–260 °C impregnated the gold-bearing quartz veins and produced the lower strata of the hydrothermal-granitoid section. The gold mineralization (795–710 Ma) was roughly coeval to local high-temperature stress metamorphism (836–745 Ma) and intrusion of the Kalama multiphase complex (880–752 Ma).

Ore–Bearing Fluids of the Blagodatnoye Gold Deposit (Yenisei Ridge, Russia): Results of Fluid Inclusion and Isotopic Analyses

“…A similar pattern was revealed at the Olympiada giant gold deposit in the depth interval from 4.5 m (well 503) to 817 m (well 510) of ore body No. 4 in the Eastern area of the deposit [19], at the Panimba deposit at the depth up to 692.5 m (well 145) [18], and at the Eldorado gold deposit [20].…”

“…The ore field of the deposit is located in the Severo-Yeniseisky district of the Yenisei Ridge on the southeast wing the Panimba anticlinorium bounded by the Tatarka deep fault in the west and Ishimba deep fault in the east (Figure 1a). ridge [18][19][20][21]. The aim of our work is to reveal the physicochemical properties of orebearing fluids that formed the Blagodatnoye deposit in the Yenisei Ridge, which ranks the second in gold reserves.…”

“…Recently we developed a special device that is used for gas mixture injection upon shock destruction of a sample, which in combination with a highly sensitive gas chroma tography-mass spectrometer allowed obtaining original results on the composition of gas component of fluids in native gold, quartz and sulfides from gold deposits of the Yenisei ridge [18][19][20][21]. The aim of our work is to reveal the physicochemical properties of ore-bearing fluids that formed the Blagodatnoye deposit in the Yenisei Ridge, which ranks the second in gold reserves.…”

Location Peculiarities and Evolution of Koshkarchay Copper-Porphyre Field (Lesser Caucasus, Azerbaijan)

“…Для Rye, 1979;Taylor, 1986;Goldfarb et al, 1991). Обогащенная тяжелым изотопом сера могла образоваться при гидролизе сульфидов, содержащихся во вмещающих осадочных породах (Ohmoto and Rye, 1979).…”

“…Обогащенная тяжелым изотопом сера могла образоваться при гидролизе сульфидов, содержащихся во вмещающих осадочных породах (Ohmoto and Rye, 1979). При этом не наблюдается характерных различий в соотношениях изотопов серы в пирите из вкрапленности в околорудных измененных породах, из прожилков во вмещающих породах и пирите из наиболее обогащенных частей минерализованных зон (Goldfarb et al, 1991). Таким образом, допускается, что имелся единый источник серы пиритов, образованных в сходных условиях, а отсутствие сульфатов в непосредственной ассоциации с сульфидами, сравнительно однородный изотопный состав пирита, наконец, отсутствие направленного разделения изотопов в ходе рудообразующего процесса, указывают на гомогенизацию тяжелой серы при определенных высокотемпературных условиях (Ohmoto and Rye, 1979;Taylor, 1986).…”