COMPOSITION AND SOURCES OF MINERAL-FORMING FLUIDS OF THE ORLOVKA OROGENIC GOLD DEPOSIT (Southern Urals)
S.E. Znamenskii1, N.N. Ankusheva2,3, T.A. Velivetskaya4, S.N. Shanina5
1Institute of Geology, Ufa Scientific Center, ul. K. Marksa 16/2, Ufa, 450072, Russia
2Institute of Mineralogy, Ural Branch of the Russian Academy of Sciences, Il'menskii Zapovednik 1, Miass, 456317, Russia
3Department of South Ural State University, ul. 8 Iyulya 10, Miass, 456304, Russia
4Far East Geological Institute, Far Eastern Branch of the Russian Academy of Sciences, pr. 100-letiya Vladivostoka 15, Vladivostok, 690022, Russia
5Institute of Geology, Komi Scientific Center, Ural Branch of the Russian Academy of Sciences, ul. Pervomaiskaya 54, Syktyvkar, 167982, Russia
Keywords: Orogenic gold deposit, fluid inclusions, REE, oxygen and carbon isotopes, Southern Urals
Subsection: PETROLOGY, GEOCHEMISTRY, AND MINERALOGY
Abstract
Fluid inclusions, REE and Y patterns, and carbon and oxygen isotope ratios in the minerals of sulfide-carbonate-quartz mineralization of the Orlovka orogenic gold deposit were studied. We have established that fluid inclusions in calcite and quartz homogenize in the same temperature range 217-170 ºC and contain aqueous Mg-K-Na solutions with salinity of 3.0-6.4 wt.% NaCl equiv. According to the results of gas chromatography of inclusions in quartz, the gas phase is a mixture H2O (79-977 ppm) + CO2 (2.64-5.35 ppm) + CH4 (0.002-0.018 ppm) ± N2 (0-1.22 ppm). The REE pattern of calcite shows accumulation of LREE ((La/Yb) N = = 1.28-7.18), (La/Lu) N = 1.10-6.58 (indicating a predominance of REE sorption in the fluid), and weak negative Ce and positive Eu anomalies. Negative Ce anomalies in calcite might be due to the interaction of the fluid with limestones and to the presence of a small amount of meteoric water in it. The positive Eu anomalies reflect the high-temperature environment (>200-250 ºC) that existed in the fluid system before the crystallization of calcite. The δ13CCO2 (-2.0 to 0.9‰) values of the fluid, close to the carbon isotope composition of carbonates of the host rocks (-2.3 to 1.9‰), testify to the metamorphogenic source of carbon. The δ18OH2O values of the fluid depositing quartz (3.1 to 4.5‰) and calcite (4.0 to 4.6 ‰; one sample has 6.6 ‰) suggest that metamorphic water with an impurity of meteoric water prevailed in the fluid system. We propose a model for the gold deposit formation, which takes into account the generation of a mineral-forming fluid at the progressive stage of greenschist dynamometamorphism of the host rocks and the formation of gold mineralization at the regressive stage.
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