Mineralogy of the Tumanny Au-Ag-Te-Hg epithermal veins, Western Chukchi Peninsula, Russia

Abstract

The Tumanny Au-Ag-Te-Hg epithermal prospect, Chukchi Peninsula, Russia is located in the near contact zone of the large Vuknei pluton, part of the Early Cretaceous Egdykgych Complex, which is related to the Peschanka porphyry copper deposit and the Nakhodka porphyry-epithermal ore district located 45 km north of Tumanny. Mineralization at Tumanny is characterized by an early carbonate-base metal and a late gold-silver-sulfosalt mineral assemblage. Pyrite of the first assemblage is unzoned and As-poor, and tennantite-tetrahedrite solid solutions (Ttrs) are characterized by a weak oscillatory zoning caused by variable contents of Sb and As, low Ag content, and the widely variable Sb/(Sb + As) values. Pyrite of the second assemblage is zoned and As-rich (up to 5.2 wt%) and Ttrs is weakly zoned and Ag-rich (up to 10.35 apfu) and has a comparatively narrow range of Sb/(Sb + As) value. Electrum, Au-Ag alloy (“küstelite”), Au-Ag-S phases, hessite, polybasite, and imiterite recognized at the prospect belong to the second mineral assemblage. The homogenization temperature of primary fluid inclusions in quartz ranges from 340 to 210 °C and decreased during the mineralizing process; fluid salinity varying from 0.8 to 5.2 wt% NaCl equiv is not evolved during the process. Cores of quartz crystals formed from a boiling fluid, whereas crystal rims appear to have formed from a lower temperature non-boiling liquid. LogfS2 decreased from −8 at the formation of carbonate-base metal assemblage to −16 at the deposition of gold-silver-sulfosalt assemblage as temperature decreased from 340 to 200 °C. Bulk ICP-OES analysis of mineralized samples indicated up to: 38 ppm Au, 908 ppm Ag, 154 ppm Mo, 106 ppm Te, 53 ppm Se, 9246 ppm As, 1284 ppm Sb, and 23 ppm Bi. Cluster analysis of the data obtained identified three geochemical associations corresponding the carbonate-base metal the gold-silver-sulfosalt, and to the overlapped mineral assemblages. The whole-ore composition is controlled by mineralogy of these assemblages. Taking into account the geological setting, mineralogy, composition of minerals, and fluid inclusion data, the Tumanny Au-Ag-Te-Hg prospect is characterized as intermediate sulfidation epithermal style.