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).

—New thermobarogeochemical and isotope-geochemical data are presented, which show the intricate and long history of the formation of the unique Olimpiadinskoe gold deposit with predicted gold reserves of >1000 tons on the Yenisei Ridge. Metal-bearing oxidized water–carbon dioxide and reduced carbon dioxide–hydrocarbon fluids participated (at the same time or successively) in the formation of the deposit at 220–470 °C and 0.6–2.5 kbar. Fluids of gold-bearing mineral assemblages include CO2, hydrocarbons, and S-, N-, and halogen-containing compounds capable of transporting ore elements, including gold. Highly mobile carbon dioxide–hydrocarbon fluids were responsible for the appearance of disseminated gold mineralization in large bodies of quartz–carbonate–mica schists serving as geochemical barriers in the Olimpiadinskoe deposit. The deposit formed in the period from 817 to 660 Ma, which fits the time interval from crystallization to cooling (868–721 Ma) of the most proximal multiphase Chirimba granitoid pluton. The hydrothermal activity of the fluids that formed the Olimpiadinskoe deposit lasted at least 100–150 Myr year.

The Panimba gold deposit lies in the rocks of the epidote–amphibolite metamorphism facies and is confined to the exocontact zone of the Chirimba granitoid massif. Fluid inclusions in quartz and sulfides of two sites of the deposit, Mikhailovka and Zolotoi Brook, were studied by thermobarogeochemistry, gas chromatography, and chromatography-mass spectrometry. We have established that gold–quartz veins of the deposit were formed by metal-bearing Mg–Na–Cl-containing water–carbon dioxide–hydrocarbon fluids with salinity of 8–23 wt.% NaCl eq. at temperatures of 180 to 410 °C and pressures of 0.2 to 3.3 kbar. Hydrocarbons and nitrogen- and sulfur-containing compounds of the fluids can transport gold and might be positive indicators of the gold presence in quartz veins. Fluids with salinity of >30–40 wt.% and sulfur isotope values (δ34S) of 0.9 to 6.7‰ of sulfides are the result of the action of postmagmatic solutions of the nearby Chirimba granitoid massif. The age of hydrothermal gold–sulfide mineralization of the Panimba deposit is within 817.2 ± 5.3–744 ± 17 Ma and falls in the time interval of crystallization of the Chirimba intrusion, 868.9 ± 6.5 to 721.4 ± 1.6 Ma, but it is considerably younger than the age of the regional metamorphism (996.0 ± 32–889.0 ± 26 Ma).

––The first results on the composition of fluids from native gold and associated pyrite and quartz have been obtained. Despite the small amount of analytical data, these results are of scientific and practical interest. The identified geochemical criteria can be used for the assessment of gold ore shoots and the substantiation of prospecting in the region. The one-act shock-destructive extraction of volatiles from fluid inclusions and their pyrolysis-free gas chromatography–mass spectrometry analysis made it possible to determine the composition of fluids in native gold and in associated pyrite and quartz. Based on these data, we have first shown that fluids in native gold, pyrite, and quartz are a mineral-forming multicomponent system. In addition to water and carbon dioxide, the studied fluid inclusions contain representatives of at least 11 homologous series of organic compounds, including oxygen-free aliphatic and cyclic hydrocarbons (paraffins, olefins, cyclic alkanes and alkenes, arenes, and polycyclic aromatic hydrocarbons), oxygenated hydrocarbons (alcohols, esters, furans, aldehydes, ketones, and carboxylic acids), and nitrogened, sulfonated, halogenated, and siliconorganic compounds. The portion of hydrocarbons together with S–N–Cl–F–Si compounds reaches 52.0 rel.% in fluid inclusions from native gold, 10.1 rel.% in fluid inclusions from pyrite, and 18.0 rel.% in fluid inclusions from quartz. Gold-transporting gas fluids have reducing properties. Pyrite and quartz contain oxidized water–carbon dioxide fluids with low contents of hydrocarbons and nitrogen–halogenated compounds.

A superlarge gold-ore stockwork of the Vasil’kovskoe deposit (with gold resources of more than 380 tons) is located at the contact of porphyroblastic granodiorites and diorites in northern Kazakhstan. The specifics of the Vasil’kovskoe deposit is a wide occurrence of gray (so-called ore) gold-bearing quartz, which, together with white quartz, composes quartz–sulfide veins and veinlets in the stockwork. Based on thermobarogeochemical and isotope-geochemical data, we have established that gray quartz and arsenopyrite of the deposit formed with the participation of K–Na–Mg–Cl-containing aqueous CO2–hydrocarbon fluids at 250–550 ºC, 0.1–2.5 kbar, and salinity of 7.0–22.5 wt.% NaCl equiv. (seldom, >30–40 wt.% NaCl equiv.). The cyclic recurrence of parameter fluctuations was accompanied by the deposition of gold, which led to the formation of gold-rich veinlet ores in the stockwork core. White quartz formed at lower temperatures, 120–310 ºC, and 0.2–1.0 kbar, with the participation of Ca–Na–Cl-containing fluids with salinity of 2.0–11.0 wt.% NaCl equiv. In addition to H2O and CO2, hydrocarbons and their derivates (paraffins, olefins, arenes, alcohols, ethers, aldehydes, ketones, and carboxylic acids) as well as nitrogen-containing (C2H3N, C3H9N, C7H5N, and C8H5NO2) and sulfur-containing (CS2, COS, SO2, C2H6S2, etc.) compounds (indicators of reducing conditions) were involved in the ore formation. The sulfur isotope composition of sulfides (δ34S = +5.7 to + 11.8‰) and the carbon isotope composition of CO2 in fluid inclusions in gray (δ13C = –2.1 to –4.6‰) and white (δ13C = –11.0 to –21.4‰) quartz as well as its positive and negative anomalies of Eu point to the crustal source of the fluids. The gray color of quartz is due to abundant CO2–hydrocarbon-containing inclusions, carbon particles, and sulfides. Crystallization of ore-hosting granodiorites happened in the period from 490.0 ± 4.4 to 443.5 ± 4.1 Ma. The age of the areal K-feldspathization of granodiorites, preceding the ore formation, is 375.2 ± 3.7 Ma. Formation of gold-including parageneses took place in the period from 311.7 ± 6.4 to 279.2 ± 2.5 Ma, i.e., lasted no less than 30 Myr.