MINERAL FEATURES OF THE COPPER ASSOCIATION OF THE BARANEVSKOE EPITHERMAL DEPOSIT (CENTRAL KAMCHATKA)

The relevance of this study is determined by lack of information of the behavior and accumulation of non-conventional metals (-oids), such as tellurium, bismuth, selenium (TBS-microelements), involved in modern industries, as well as the limited information about deposits, in which they are able to accumulate significant concentrations, including in association with native gold. Such objects are represented by some epithermal deposits. Russia's share in the total balance of these deposits accounts for a negligible number, although in some regions, such as the Arctic, Siberian and Far East, they have a significant role. The key task of this research is to investigate the material composition and conditions of gold and TBS-microelements formation in an exotic for the low sulfidation type «copper mineral association» of the Baranyevskoe Au-Ag epithermal deposit (Central Kamchatka). The objects of the research are ores and their host altered rocks in the form of core-, hand-and-chip-samples. Research methods. Minerals, ores, and host altered rocks were studied by electron and optical microscopy, as well as by X-ray diffraction analysis, microthermometry, Raman and infrared spectroscopy. To determine the temperatures of phase transitions, salinity and composition of gas-liquid inclusions, microthermometry and Raman spectrometry of bipolished plates were carried out. It was established that the main volume of the «copper mineral association» with gold enriched in tellurium, selenium, bismuth is associated with illite-muscovite quartz formed in modern altered rocks of late Miocene–Holocene age. The composition of copper mineralization is represented by copper sulfides (geerite (Сu8S5), sometimes with impurities of Pd (up to 0,8 wt. %) and Te (up to 1,9 wt. %), chalcopyrite, bornite, tetrahedrite fahlore with Bi impurities (up to 11,16 wt. %), wittechenite (Cu3BiS3), emplectite (CuBiS2), miharaite (PbCu4FeBiS6), aikinite (CuPbBiS3), finegrade gold (Au 920–980), gold and silver tellurides, telluro-selenides Bi and Pb, including non-stoichiometric (unknown), to a lesser extent, pyrite sporadically enriched in Cu (up to 0,9 wt. %), galena enriched in Se (up to 8,5 wt. %). As a result of the data obtained, it was established that the gas-liquid inclusions in quartz and calcite, the hydrothermal-ore process proceeded at temperatures of 250…305 °C at a salinity of 0,5…1,2 wt. % NaCl equiv. As a result of studying the material composition of ore and vein mineralization, it is assumed that aqueous H3TeO3+ and H2TeO3, chloride BiCl3(aq) (III) solutions, and carbon dioxide participated in ore formation.