Study On The Geological Characteristics And The Genesis Of Caiyuanzi Gold Deposit In Eastern Kunlun Orogenic Belt,qinghai Province

Caiyuanzi gold deposit is located in Golmud city,Qinghai province.The geotectonic location of the deposit is in the Southern Kunlun composite collage belt,eastern Kunlun orogenic belt.The deposit is also divided into copper,cobalt,gold,lead,zinc,PGE,chromium,iron metallogenic belt located in the south of Eastern Kunlun orogenic belt.The major outcropping layer of mining area is Ordovician-Silurian Halabai Gully Formation,Naij Tal Group,which contains siliceous albite rock related to hydrothermal exhalative sedimentation.The dominating trend of fracture is NE-SW direction and a small amount of Naij Tal Group chlorite schist and late Triassic granodiorite porphyry(210.4±1.9Ma)are exposed in the mining area.Geochemical of the rocks indicated that the protolith of Naij Tal Group chlorite schist is tholeitic basaltic rock,which was formed in Ordovician,in the setting of seafloor spreading back-arc basin.While granodiorite porphyry was formed in late Triassic,originating form the thicken lower crust which was formed in the setting of extensional post-collisional orogeny.One iron-gold,three iron,five copper mineralized bodies and two copper ore bodies are delineated in the mining area.The ore bodies appear in near bedded and lenticular shapes,controlled by fracture,showing the dominating trend of NE-SW direction.The main ore minerals include pyrite,magnetite,chalcocite,chalcopyrite and natural gold and the main gangue minerals include quartz,iron dolomite,calcite,sericite and chlorite.The main texture of ore includes hypidiomorphic-allotriomorphic granular texture and metasomatic texture and the main structure of ore includes disseminated structure and massive structure.The main alteration of country rock includes silicification,carbonation,sericitization and chlorinization.Temperature measurement of fluid inclusions showed that the main metallogenic stage fluid of gold deposit has the feature of medium-low temperature,medium-low salinity,medium-low density.The ore-forming pressure is 46-147 MPa and metallogenic depth is 5.39-10.13 km.The main metallogenic stage fluid of copper deposit has the feature of medium-hihg temperature,medium-low salinity,medium-low density.The ore-forming pressure is 120-180 MPa and metallogenic depth is 9.11-11.20 km.Pressure reduction is the main factor of gold mineralization,while temperature reduction is the main factor of copper mineralization.The results of hydrogen and oxygen isotope analysis indicated that the ore-forming fluid of gold deposit was mainly composed of magma water and metamorphic water,the results of sulfur and lead isotope analysis indicated that the metallogenic material of gold deposit came form the deep,mixed with crustal material,and the results of carbon and oxygen isotope analysis indicated that the carbon in the gold deposit came from the dissolution of regional marine carbonate rocks,and the ore-forming fluid was added with meteoric precipitation in later period.Combined with geological characteristics of the deposit and regional tectonic evolution,we conclude that Caiyuanzi gold deposit is a tectonically controlled mesothermal vein deposit and deep fluids participate in mineralization and the metallogenic depth of copper deposit is deeper.The formation time of ore deposit is later than that of granodiorite porphyry,and the deposit was formed in late Triassic,in the setting of changing from compressional regime to extensional regime after continental collision orogenesis of eastern Kunlun orogenic belt.