Study On The Magmatic Processes And Cu-Mo Mineralization In The Lailigao'er-Kendenggaoer Region, Western Tianshan, Xinjiang, China

As a important Cu-Mo ore concentration area in western Tianshan, the Lailigao`er-Kendenggaoer region is paid much attention to. Based on regional geology and mine geology, the magmatic processes and Cu-Mo mineralization by petrography, mineralography, geochemistry of petrology and ore deposit, geochronology of Lailisigao`er-3571 Cu-Mo deposit and kendenggaoer Cu-Mo deposit are studied in this paper.In the Lailisigao`er-3571 Cu-Mo deposit, the Cu-Mo sulfide ore-body with veins, tabular and lens in shape occurring in the top or edge parts of the granodiorite porphyry, contact belts and the wall-rock nearby, shows the typical mineralized alteration zoning characteristics of Porphyry deposit. The Kendenggaoer Cu-Mo ore bodies with tabular, laminated and lenticular shape occurs in the outer contact belt between late Carboniferous granodiorite and carbonate rocks of Upper Carboniferous, controlled by contact zone structure. The Kendenggaoer Cu-Mo sulfide endogenic mineralization has obviously experienced two stages,skarn stageand quartz-sulfide stage, showing the characteristics of skarn-type Cu-Mo deposit.Geochemical analysis shows that the Lailisigao`er granodiorite porphyry is rich in Si, Al, K and Na, and poor in Mg, with high-K calc-alkaline characteristic and the Kendenggaoer granodiorite has a relatively high quantity of SiO₂, Na₂O+K₂O and CaO, and low quantity of MgO, with metaluminous and high-K calc-alkaline characteristic. The characteristic of petrology geochemistry shows that the high-acid, rich-alkali, high-potassium magma is beneficial to the Cu-Mo enrichment, and the formation of rock mass happened after Junggar oceanic crust subducted to Kazakhstan-Yili plate.The analysis of the microthermometry and Laser Raman spectroscopy shows that the ore-forming fluid of Lailisigao`er-3571 Cu-Mo deposit in the early stage is a NaCl-H2O system, which has high-middle temperature, mid-low salinity, and then evolves a H2O-NaCl-CO<sub>2</sub> system, which has high-middle temperature, low salinity, and continuing evolves into a NaCl-H<sub>2</sub>O system, which has middle temperature, low salinity. The main ore-forming fluid of Kendenggaoer is a NaCl-H<sub>2</sub>O system, which has mid-low temperature, low salinity and density. The study of H<sup>-</sup>, O-isotopic composition shows that the ore-forming fluid is originated from magmatic water, with a little mixing of precipitate water in the late stage.The study of S-, Pb-isotopic composition and the Re content of the molybdenite of Lailisigao`er-3571 Cu-Mo deposit and Kendenggaoer Cu-Mo deposit shows that the ore-forming process is related to magmatic activity in the process of ocean crust subduction, and the ore-forming metals may come from the subduction ocean melting magma.The forming of the Ores-Bearing Porphyries and ore-bodies in the Lailisigao`er-3571 Cu-Mo deposit occurs in the late Devonian or early Carbiniferous. In the Kendenggaoer Cu-Mo deposit, the granodiorite is dated as 313±4Ma by Zircon SHRIMP U-Pb method, and the model age and isochron age of molybdenite Re-Os are 315.4±1.8Ma and 313.9±2.5Ma. The study of chronology shows rock mass and ore body are formed in the late Devonian or late Carbiniferous in the Lailisigao`er-Kendenggaoer region.To sum up, the high-acid, rich-alkali, high-potassium rock mass in the late Devonian or late Carbiniferous has indicative significance for the exploration of prophyry - skarn type Cu-Mo deposit.