Mineralogy, geochemistry, and genesis of gold-sulfide-selenide-telluride ores from the Kairagach deposit (Uzbekistan)

The Late Paleozoic Kairagach epithermal gold deposit belongs to the high-sulfidation (acid-sulfate) type. It is located at the northern slope of the Kuramin Ridge in the central Tien Shan, 3.5 km northwest of the Kochbulak deposit, being confined to the volcanic andesite-dacite sequence (C2-3) composing the northeastern segment of the Karatash caldera. Volcanogenic sequences are intruded by subvolcanic dacite-porphyry and diorite-porphyry intrusions, as well as granodiorite-porphyry and porphyritic diabase dikes of the northeastern strike. The gold-sulfide-selenide-telluride mineralization of the Diabazovaya zone, which encloses the main gold resources, associates with these dikes. Unlike typical epithermal deposits of the high-sulfidation type with Au-Cu geochemical specialization of ores, the Kairagach deposit is characterized by distinct Au-Sn-Bi-Se-Te mineralization, which includes over 80 ore minerals, including new and rare ones. This paper discusses data on the geological structure of the deposit, ore geochemistry, variations in chemical composition, mode of occurrence and parageneses of native elements (Au, Ag, Te, Sri, Bi); sulfides of Fe, Cu, Pb, Zn, and Ag; fahlores of the tetrahedrite-tennantite-annivite-goldfieldite series; bismuthinite-aikinite, junoite, and pavonite sulfosalts: Cu and Fe sulfostannate; various Au, Ag, Pb, Fe, Hg, Bi, and Sb tellurides and Bi sulfoselenides; and Fe and Sn oxides. The chemical composition of ordinary, high-grade, and bonanza ores and the vertical and lateral (including hidden) mineralization zoning, as well as the succession of mineral parageneses, P-T parameters, composition of mineral-forming fluids, and main factors and mechanisms responsible for the formation of gold-productive mineral associations, are considered. The variations in the S, C, 0, and H compositions of ore minerals are used to define probable sources of water and ore components in ore-forming fluids. The results of thermodynamic modeling of probable gold occurrence and transportation in the mineral-forming solution are also discussed.