CONDITIONS OF FORMATION OF GOLD-BEARING MAGNETITE-CHLORITE-CARBONATE ROCKS OF THE KARABASH ULTRAMAFIC MASSIF (South Urals)
V.V. Murzin1, D.A. Varlamov2, G.A. Palyanova3,4
1Zavaritsky Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences, ul. Akademika Vonsovskogo 15, Yekaterinburg, 620016, Russia
2Institute of Experimental Mineralogy, Russian Academy of Sciences, ul. Akademika Osip'yana 4, Chernogolovka, 142432, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
4Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Magnetite-chlorite-carbonate rocks, chloritolites, rodingites, gold-rare-metal-REE mineralization
Abstract
Ilmenite, apatite, monazite, aeshynite-(Y), zircon, baddeleyite, thorianite, uraninite, and copper-containing native gold have been revealed in specific magnetite-chlorite-carbonate rocks and chloritolites in the Karabash ultrabasic massif in the South Urals. Dolomite from the magnetite-chlorite-carbonate rocks are characterized by a rather uniform isotope composition (δ13С = -0.9 to -1.9‰, δ18О = 11.5-13.6‰, 87Sr/86Sr = 0.70422-0.70469) corresponding to a mixture of sources: marine limestones and mantle fluids. We determined the isotope compositions of antigorite from serpentinites (δD = -79.1 and -89.6‰, δ18O = 7.4 and 7.6‰), of chlorite from chloritolites (δD = -57.8‰, δ18O = 7.8‰), and of magnetite-chlorite-carbonate rocks (δD = -59.2 and -69.6‰, δ18O = 6.4 and 5.9‰). The latter probably formed by the mechanism of filling of the free space at 480-280 ºC, and chloritolites were developed after serpentinites. Oceanic serpentinites, gabbros, limestones, and mantle fluids can be considered the source of material during the formation of magnetite-chlorite-carbonate rocks. A comparative analysis of the latter and the massif rodingites (chlograpites) bearing copper-containing gold was carried out. The established common features of these types of rocks are the localization in zones of tectonic melange, the presence of chloritolite rims, geochemical specialization, thermal conditions of formation, and isotope parameters of minerals and fluids.
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