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Characteristics and genesis of Kanggur gold deposit in the eastern Tianshan mountains,NW China:evidence from geology,isotope distribution and chronology

【摘要】:正The Kanggur gold deposit lies in East Tianshan mountains,eastern section of Central Asia orogenic belt.The gold mineralization occurs on the northern margin of the Aqishan-Yamansu island arc in the Tarim Plate.It is mainly hosted in Lower Carboniferous volcanic rocks,and controlled by syn-tectonic intrusions and the ductile shear zone. The host rock is a calc-alkaline volcanic rock series consisting of andesite,dacite,tuff and subvolcanic rocks.The gold ore bodies were distributed in transition zone from strong ductile deformation to weak deformation.Ore-controlling structure is EW-trending normal brittle-ductile shear zone.The gold ore bodies are composed of Au-bearing altered rocks and a few Au-bearing sulfide-quartz veins.The mineralization shows vertical zonation in which Au was enriched in the upper orebodies.Au-Pb-Zn were enriched in the middle and Au-Cu were enriched in the lower orebodies.According to mineral assemblages and alteration intensity,hydrothermal alteration could be divided into three zones:silicification.chloritization. pyrirization and magnetization zone(major ore body);pyrite-phyllic rock and/or sericite alteration zone;and sericite-chlorite alteration zone.Five mineralization stages are identified on the basis of mineral assemblage and crosscutting relationship of veins. Theδ~(34)S values of sulfide in the ores range from - 0.9‰to + 3.3‰,similar to those of the volcanic and subvolcanic rocks (-3.21~+1.3‰),indicating that the sulfur isotope composition is characterized by unfractionated mantle sulfur.The lead isotope compositions of ores are between those of the volcanic rocks and subvolcanic rocks.The initial ~(87)Sr/~(86)Sr ratios of the ores vary between 0.7077 and 0.7106,similar to those of the host rocks(0.7079-0.7125).According to the Sr,S and Pb isotopic data,it is indicated that the ore-forming materials were derived from the surrounding volcanic rocks and feature deep source.Theδ~(18)O values of the ore fluids vary from +3.83‰to - 1.77‰c and theδD values from - 46‰to - 66‰.Theδ~(18)O vs.δD andδ~(18)O vs.~(87)Sr/~(86)Sr diagrams indicate that ore fluids were derived from dynamic metamorphic water,magmatic water and meteoric water.The ore-forming ages of Kanggur gold deposit are determined by Rb-Sr and Sm-Nd isochron methods.The results show that the main ore-forming stages of Kanggur gold deposit are 290-282 Ma,secondary mineralization stages are 275-254 Ma.Studies on regional geology,ore geology,isotope geochemistry and ore-forming ages have proved that the Kanggur gold deposit was formed in the compression-extension transition stage during the latest Paleozoic continental collision,and is characterized by orogenic gold deposits.

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