The Kyzyl-Tashtyg Ore Deposit of Eastern Tuva-A Standard for the Ancient Volcanogenic Formation of Pyrite-Polymetallic Ores

摘要

The Kyzyl-Tashtyg deposit and the ore field of the same name are included in the Kyzyl-Tashtyg ore cluster, which is located in the southeastern part of the Ulugoi structural-metallogenic zone. The geological section of the ore field consists of lower Cambrian terrigenous and volcanogenic deposits of the Tumat-Taiga and Tapsa Forniations that include a homodromous sequence of early andesite-basalts transitioning to acid dacite-rhyolite rocks with widespread subvolcanic intrusions. The pyrite-polymetallic mineralization of the ore field associates spatially with a central-type volcanic structure and is localized within the "motley" unit, consisting of three lithological-stratigraphic horizons. The Kyzyl-Tashtyg pyrite-polymetallic deposit is the main ore occurrence of the ore field, which contains the main reserves of pyrite-polymetallic ores. The mineralization outcrops on the surface are 650 m in length and 60-65 m wide. Reserves of commercial ore arc 12,920 min tons with average concentrations: Pb-2.8%, Zn-10.3%, Cu-0.65%, Au-1.03 ppm, Ag-48.71 ppm. The ores have typically simple mineral compositions consisting of pyrite, chalcopyrite, sphalerite, galena and barite. Secondary minerals include enargite, hessite, sylvanite, proustsite, and native silver. Ores are classified based on the dominant mineral or groups of minerals into sulfur-pyrite (pyrite), copper-zinc (pyrite-chalcopyrite-sphalerite), polymetallic (sphalerite-galena), and barite-polymetallic (baritesphalerite-galena) varieties. The main commercial type is represented by the copper-zinc mineralization. The widest range of impurity elements and their highest concentrations have been identified in copper-zinc and polymetallic ores, where the main mineral is sphalerite-the carrier of the largest amount of impurity elements. In these ores, commercial concentrations of gold and silver have been detected: Au-0.8; 2.3 ppm, and Ag-26; 78 ppm correspondingly. Formation temperatures of different types of ores of the deposit range from 400-305 degrees C to 270-150 degrees C. There is a pattern of decreasing formation temperatures from the sulfur-pyrite to the copper-zinc and to the barite-polymetallic ores. This pattern forms a vertical mineralization zoning from the bottom to the top of the deposit The formation of the deposit was related to early Cambrian volcanism and included different mechanisms of ore deposition. The hill-like shape of the main ore lode with intense hydrothermal alteration of rocks in its base indicates a mineralization zone with veinlet-disseminated and massive ore structures, which indicates a hydrothermal-metasomatic origin.