The Ore-forming Fluids Of The Porphyry-skarn Type Cu-Mo Deposits In The North Of Western Tian Shan,Xinjiang

The Sailimu Block-Borohoro island-arc belt,located in the north of western Tian Shan,Xinjiang,holds many porphyry-skarn deposits.These deposits commonly contain many transparent and opaque solid minerals in their fluid inclusions and show a clear separation of Cu and Mo mineralization,which means they are ideal objects for understanding the mechanism of metal transport and precipitation in porphyry-skarn deposits.More over,different deposits have different ore-forming fluid systems,the mechanism of differences in fluid systems remains unclear.In this contribution,based on detailed field investigation and microscope observation,the Dabate porphyry Cu-Mo,Lamasu-Saibo skarn Cu,Lailisigaoer porphyry Mo and Kekesala skarn Fe-Cu-Mo deposits were selected to conduct research on the ore-forming fluids,the following achievements have been withdrawn in this study.1.A large number of chalcopyrite,anatase-bearing fluid inclusions are discovered in the quartz of molybdenite-quartz veins in the Lailisigaoer porphyry Mo deposit,and pyrite-bearing fluid inclusions are also discovered in the diopside of the Kekesala skarn Fe-Cu-Mo deposit.According to the volume of these solid phase,we have obtained the concentration of Cu,Ti,Fe in the fluids are 8901¹0186ppm,1974¹0652ppm and 69934¹06804ppm,respectively.The high concentration of Cu,Fe in the fluids,can analogy to the ore-forming fluids of many porphyry deposits?In addition,the high concentration of Ti in the fluids may indicate that Ti can be transported in H₂O-rich fluids.2.The Cu and Mo separation in the Dabate porphyry Cu-Mo deposit is due to the fluid immiscibility in the deap area and different physical-chemical conditions?oxygen fugacity,pH,temperture and pressure?for deposition of Cu and Mo;whereas the Cu and Mo separation in the Kekesala skarn Fe-Cu-Mo deposit may be mainly controlled by pH,temperture and pressure conditions of fluids rather than oxygen fugacity.3.The fluid systems of porphyry-skarn deposits in the north of western Tianshan,Xinjiang,can be divided into three kinds which are H₂O-NaCl-CO₂-CH₄?H2O-NaCl-hydrocarbon and H2O-NaCl systems.The property of magma?source materials and oxygen fugacity?may be a major contributor to differences in fluid systems:The magma which is mainly derived from oceanic crust,commonly exsolve a H₂O-NaCl fluid system;whereas the magma which is mainly derived from continental crust,commonly exsolve a H₂O-NaCl-carbon volatile?e.g.CO₂,CH₄?fluid system.In addition,the magma which has high oxygen can lead the carbon volatile in the form of CO₂,whereas the magma which has low oxygen can lead the carbon volatile in the form of hydrocarbon.