Geology And Geochemistry Of Igneous Rocks And Ores In The Kochbulak Gold District Uzbekistan

Kochbulak deposit is a typical of the hydrothermal epithermal type gold deposit in The Uzbekistan Almalyk area,which is a world-class copper and gold deposit area.The geology and geochemimistry study of the gold deposit has important reference for the prospecting work of the West Tianshan gold mine in China.Gold mineralization occurs mainly in the silicified and sericite andesite and dacite.Three kinds of geological occurrences in the gold ore body:(1)high angle steeply dipping vein orebodies;(2)gently-dipping orebodies;(3)tubular,pipe-like bodies.The ore is mainly massive,disseminated,fine vein and banded structure.The mineralization period is divided into three phases through the mutual cutting relationship between the ore bodies.The first metallogenic stage is the silicification period of the andesite,forming the metallic mineral assemblage of natural gold-pyrite-chalcopyrite-galena–sphalerite-telluride.The second phase is quartz sulfide,forming the metallic mineral assemblage of natural gold-pyrite-chalcopyrite-bismuth telluride and so on.The third phase is mainly composed of sulfide veins and contains a large number of tellurides and bismuth,forming a combination of pyrite-chalcopyrite-tetrahedrite-telluride-bismuth and so on.In the mining area,there is the I type granite.The ore-bearing rocks are andesite and dacite,which have similar geochemical characteristics with Kochbulak mine granite syenite.All of thembelong to the high potassium calc alkaline?shoshonite series and are Typical potassium igneous rocks.There are loss in high field strength elements such as Nb,Ta,Ti,andheavy rare earth element,enriched in light rareearth elements and Pb.Kochbulak deposit showed island arc magmatism with The characteristics of rare earth elements and trace elements in the subduction zone.The initial values of(⁸⁷Sr/⁸⁶Sr)i of granodiorite and andesite and andesite fall in the range of 0.705680?0.708090,and the?Nd(t)values of-2.7?-3.91,and the second stage mode of Nd isotope is between 1285Ma?1383Ma.At the same time,the zircon(¹⁷⁶Hf/¹⁷⁷Hf)i ratio of granodiorite and dacite isotope falls in 0.282567?0.282704,the?Hf(t)values of-0.24?4.19,and the variation range of crustal mode age(TDMc)is1047Ma?1345Ma.The LA-ICP-MS U-Pb dating of zircons from granodiorite and andesite yielded ages of the 315.8±1.1Ma and 299.7±1.3Ma,which indicate a large-scale magmatic activity product of the Middle-Late Carboniferous in the Almalyk area.The Kochbulak deposit was formed in the transition period of Turkestan ocean subduction and collision.The original magma comes from partial melting of subduction plate and entry of oceanic crust sediments.The rocks of Kochbulak deposit are all derived from the mixing of subduction oceanic crust and mantle.