EPITHERMAL Au-Ag-Se-Te DEPOSITS OF THE CHUKCHI PENINSULA (Arctic zone of Russia): METALLOGENY, MINERAL ASSEMBLAGES, AND FLUID REGIME
N.S. Bortnikov1, A.V. Volkov1, N.E. Savva2, V.Yu. Prokofiev1, E.E. Kolova2, A.A. Dolomanova-Topol'1, A.L. Galyamov1, K.Yu. Murashov1
1Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
2N.A. Shilo Northeastern Interdisciplinary Research Institute, Far Eastern Branch of the Russian Academy of Sciences, ul. Portovaya 16, Magadan, 685010, Russia
Keywords: Arctic zone, epithermal Au-Ag deposits, mineralogical features, selenides, tellurides, fluid inclusions, thermobarogeochemistry, ore formation, Chukchi Peninsula
Abstract
Numerous epithermal Au-Ag deposits and ore occurrences of the Chukchi Peninsula are localized in the Cretaceous Okhotsk-Chukotka (OCVB) continent-marginal and Late Jurassic-Early Cretaceous Oloi (OVB) island arc volcanic belts and in Early Cretaceous postcollisional volcanic troughs. Volcanotectonic depressions, calderas, and volcanic domes control the location of the deposits. The orebodies of the deposits are quartz-adularia veins, sometimes en-echelon ones forming extending vein zones, as well as isometric and linear stockworks. The auriferous veins of most deposits display complex breccia-crustification structures. The vein ores have rhythmically and colloform-banded structures, with a predominantly fine distribution of ore mineral grains, often with banded clusters of ore minerals (ginguro). Native gold is of low fineness; the dispersion of this index varies from low to high. Acanthite is widespread in the ores. Its highest contents are specific to deposits with the repeated redistribution of substance (Kupol, Corrida, and Valunistoe). Based on the results of mineralogical studies, most of the epithermal Au-Ag deposits of the Chukchi Peninsula can be assigned to the Se type. The ores of some deposits (Valunistoe, Dvoinoe, etc.) contain both Se and Te minerals. The telluride-richest sites of the Sentyabr’skoe and Televeem deposits are far from the main orebodies. Most of the Chukchi epithermal Au-Ag deposits have many common characteristics (low and moderate temperatures of fluids, low fluid salinity, domination of carbon dioxide over methane, etc.) typical of low-sulfidation deposits. The maximum temperatures and salinity are specific to fluids in the Central Chukchi sector of the OCVB and in the Baimka zone of the OVB, and the minimum ones are typical of fluids in the East Chukchi flank zone and inner zone of the OCVB. The average salinity of mineral-forming fluids in the inner zone of the OCVB is half as high as the salinity of fluids in the East Chukchi flank zone of this belt, although the sulfate content is higher. At the same time, the fluids in the inner zone of the OCVB are richer in carbon dioxide and bicarbonate ion than the fluids in the East Chukchi flank zone of this belt. The fluid inclusion data permit the Vesennee deposit (Baimka zone) to be regarded as an intermediate-sulfidation one and suggest the presence of epithermal high-sulfidation deposits in the inner zone of the OCVB.
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