THE KYZYL-TASHTYG ORE DEPOSIT IN EASTERN TUVA, A STANDARD FOR THE ANCIENT VOLCANOGENIC FORMATION OF PYRITE-POLYMETALLIC ORES
The Kyzyl-Tashtyg deposit and the Kyzyl-Tashtyg ore field are included in the Kyzyl-Tashtyg ore cluster, which is located in the southeastern part of the Ulugoi structure-metallogenic zone. The geologic section of the ore field is composed of lower Cambrian terrigenous and volcanic deposits of the Tumat-Taiga and Tapsa Formations that include a homodromous sequence of early basaltic andesites transitioning to felsic dacite-rhyolite rocks with widespread subvolcanic intrusions. The pyrite-polymetallic mineralization of the ore field spatially associates with a central-type volcanic structure and is localized within the «motley» unit consisting of three lithologic/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 are 650 m in length and 60-65 m in width. The reserves of commercial ore are 12,920 mln tons, with the following average contents of ore metals: Pb-2.8%, Zn-10.3%, Cu-0.65%, Au-1.03 ppm, and Ag-48.71 ppm. The ores have typically simple mineral compositions: pyrite, chalcopyrite, sphalerite, galena, and baryte. Secondary minerals include enargite, hessite, sylvanite, proustsite, and native silver. Based on the dominant mineral or groups of minerals, the ores are classified into sulfur-pyrite (pyrite), copper-zinc (pyrite-chalcopyrite-sphalerite), polymetallic (sphalerite-galena), and baryte-polymetallic (baryte-sphalerite-galena) varieties. The main commercial type is copper-zinc mineralization. The widest range of impurity elements and their highest contents have been identified in copper-zinc and polymetallic ores, in which the main mineral is sphalerite, the carrier of the largest amount of impurity elements. In these ores, commercial contents of gold and silver have been detected: Au-0.8 and 2.3 ppm and Ag-26 and 78 ppm, respectively. Formation temperatures of different types of ores of the deposit range from 400-305 to 270-150 °C. The formation temperatures regularly decrease from sulfur-pyrite to copper-zinc and to baryte-polymetallic ores. This temperature pattern forms a vertical mineralization zoning from bottom to 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 hydrothermal and hydrothermal-sedimentary genesis on the floor of a sea basin. The occurrence of tube-like orebodies in the root area of the mineralization zone with veinlet-disseminated and massive ore structures indicates a hydrothermal-metasomatic origin.