Ore mineral assemblage, pyrite geochemistry and fluid inclusion data track multi-stage metallogenesis in the Kochbulak Au-Ag-Te deposit (Chatkal-Kurama, Uzbekistan)

The Kochbulak epithermal gold-telluride ore field is located in the eastern part of Uzbekistan, in the Middle Tien Shan Metallogenic Belt. One of the largest gold deposits in Uzbekistan, Kochbulak hosts a variety of Te-bearing minerals, representing an ideal case study to unravel the complex and partially obscure mechanisms forming Au-Ag-Te ores. In this work, we focused on the Kochbulak breccia pipe orebodies. We carried out an integrated micro-textural study and in-situ trace element analysis of pyrite, with the aim to provide, together with fluid inclusion study, new insights on fluid evolution and ore-forming mechanisms leading to the formation of the deposit. The trace element composition and micro-texture of pyrite has proved to be a very useful tool to track the geochemical evolution of fluids in hydrothermal ore deposits. Our results allow proposing a model for Kochbulak high-grade Au-Ag-Te ore formation based on the superposition of two different mechanisms: 1) gentle boiling and gold scavenging from a gold-undersaturated hydrothermal fluids by Te-rich melts (LMCE melts), 2) vigorous boiling causing abundant native Au precipitation during hydrothermal breccia formation. The transition is marked by a decrease in f Te2 and f S2. Defining the genesis of the Au-Ag-Te Kochbulak ore deposit significantly contributes to the understanding of the metallogeny of the epithermal deposits present in the Chatkal-Kurama region. Furthermore, the results of this study can give useful insights on the interplay of boiling and gold scavenging by LMCE melts as genetic mechanisms leading to the formation of epithermal gold-telluride ore deposits elsewhere.