Geochemical and Isotopic Properties of Fluids from Gold-Bearing and Barren Quartz Veins of the Sovetskoye Gold Deposit (Siberia, Russia)

This paper reports on the comparative study of fluids trapped in inclusions in gold-bearing and barren quartz veins at the Sovetskoye gold deposit, Yeniseisky ridge, Siberia, Russia. The host rocks are greenschist facies metasedimentary rocks of Upper Proterozoic age. Within the deposit, some veins contain 10 to 25 ppm of Au (gold-bearing veins); others contain Jess than 1 ppm of Au (barren veins). Fluid inclusions trapped in barren veins are predominantly low-salinity-H20 (4.0—8.0 mass % NaCl equiv.) with variable contents of dissolved C02 (<12.5 mol 070), CH4 (<1.3 mol 0/0), and N2 (<1.7 mol 070). Homogenization temperatures vary from 2000 to 4100C, and the calculated pressures of entrapment are <1.5 kbars. Inclusion fluids trapped in the host schists are predominantly aqueous (97.6 —99.3 mol % HO), with C02 contents below 2.4 mol percent. The fluids trapped in ore-bearing quartz inclusions are different. Inclusions show higher homogenization temperatures (up to 6300C) and salinity (up to 20—25 mass % NaCl equiv). Calculated pressures range from 0.7 to 2.0 kbars. Bulk gas chromatographic data of fluids extracted from native gold have contents of C02 that range from 29.3 to 62.0 mol percent, N2 from 2.7 to 13.2 mol percent, and CH4 from 0.0 to 2.8 mol percent. In gold-bearing quartz the contents of C02 range from 18.0 to 41.0 mol percent, N2 from 0.1 to 0.2 mol percent, and CH4 from 0.3 to 3.0 mol percent. Raman spectroscopic data of fluid from gold-bearing quartz revealed C02 contents of individual inclusions as high as 98.2 mol percent, N2 up to 66.4 mol percent, and CH4 up to 88.7 mol percent. Fluids of the country-rock schists which host gold-bearing quartz veins are also enriched in C02 (up to 49.5 mol 0/0). The host rocks for both barren and gold-bearing quartz veins show consistent REE patterns characterized by a negative Eu anomaly. Fluids from barren quartz veins show similar REE patterns although with a less conspicuous negative Eu anomaly, whereas fluids from gold-bearing quartz show a marked positive Eu anomaly. Similar isotopic values of sulfur in pyrite, pyrrhotite, and arsenopyrite disseminated in country rocks (ð34S = 14.7—21.6%0), and in barren (ð34S = and gold-bearing quartz veins (ô34S = suggest that sulfur in sulfides was derived from the same source, most likely being the adjacent country rocks. C02 trapped in fluid inclusions of barren and gold-bearing quartz has distinct isotopic compositions (ð 13C = —8.1 to —10.2 and —4.9 to +5.2 700, respectively), and the ð 13C values are positively correlated with Au contents in veins. Helium isotope composition of both types of quartz veins (3He/4He = 0.04—0.05 Ra for gold-bearing veins and 3He/4He 0.02 Ra for barren veins) indicates a crustal provenance of mineral-forming fluids. The 40Ar/39Ar dating of sericite demonstrates that the barren veins (890—850 Ma) are significantly older than the gold-bearing veins (830—730 Ma). On the basis of their ages, barren veins are interpreted as symmetamorphic. The age of the gold-bearing veins corresponds to the age of the local granitoids (850—720 Ma), suggesting that the origin of the Sovetskoye deposit is related to the tectonic activity syntetctonic magmatism

Metal-bearing fluids and the age of the Panimba gold deposit (Yenisei Ridge, Russia)

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.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)

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

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.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 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)

Cr-rich rutile : a powerful tool for diamond exploration

Mineralogical studies and U–Pb dating have been carried out on rutile included in peridotitic and eclogitic garnets from the Internatsionalnaya pipe, Mirny field, Siberian craton. We also describe a unique peridotitic paragenesis (rutile + forsterite + enstatite + Cr-diopside + Cr-pyrope) preserved in diamond from the Mir pipe, Mirny field. Compositions of rutile from the heavy mineral concentrates of the Internatsionalnaya pipe and rutile inclusions in crustal almandine-rich garnets from the Mayskaya pipe (Nakyn field), as well as from a range of different lithologies, are presented for comparison. Rutile from cratonic mantle peridotites shows characteristic enrichment in Cr, in contrast to lower-Cr rutile from crustal rocks and off-craton mantle. Rutile with Cr₂O₃ > 1.7 wt% is commonly derived from cratonic mantle, while rutiles with lower Cr₂O₃ may be both of cratonic and off-cratonic origin. New analytical developments and availability of standards have made rutile accessible to in situ U–Pb dating by laser ablation ICP-MS. A U–Pb age of 369 ± 10 Ma for 9 rutile grains in 6 garnets from the Internatsionalnaya pipe is consistent with the accepted eruption age of the pipe (360 Ma). The equilibrium temperatures of pyropes with rutile inclusions calculated using Ni-in-Gar thermometer range between ~ 725 and 1030°C, corresponding to a depth range of ca ~ 100–165 km. At the time of entrainment in the kimberlite, garnets with Cr-rich rutile inclusions resided at temperatures well above the closure temperature for Pb in rutile, and thus U–Pb ages on mantle-derived rutile most likely record the emplacement age of the kimberlites. The synthesis of distinctive rutile compositions and U–Pb dating opens new perspectives for using rutile in diamond exploration in cratonic areas.8 page(s