Discovery and Genesis of Telluride in a Gold Deposit from the Danghenanshan Area of Gansu Province

Based on Electron Probe Micro-Analysis(EPMA), tellurides such as petzite, hessite, calaverite, hessite, tellurbimuth were found in a gold deposit in the Danghenanshan area of Gansu province for the first time. According to electron probe microscopic image observation, these telluride minerals are relatively small and have no intergrowth. However, there is a close relationship between telluride minerals and pyrite. Telluride minerals are mainly included in pyrite and some exists among the grain of pyrite and quartz or the crack of pyrite. Based on the association of different telluride and pyrite, this study speculates that the mineral precipitation sequenceis is calaverite, petzite, hessite, tellurbimuth, and hessite. According to the mineral assemblage characteristics and ore-forming temperature, the values of fTe₂ and fS₂ during ore forming are limited.The range of lgfTe₂ of ore forming fluids is -15.2 to > -11.2 and the range of lgfS₂ is -16.7 to-14.4. The source of gold and tellurium significantly associates with adakitic plagiogranite which is formed by the partially melting of subducted slab occurred during the Caledonian.Ore-forming elements are thus concentrated and brought to the near surface to form the telluride-bearing gold deposit.