The indicative significance of amphibole composition to magmatic process of copper-nickel deposits in eastern Tianshan

Tulaergen and Xiangshan, Tianyu and Baishiquan magmatic Ni-Cu sulfide ore deposits are located in Jueluotage belt and Central Tianshan Massif of eastern Tianshan, Xinjiang Province, respectively, and the amphibole is the common mineral through these areas. In this study, we use the characteristics of major and trace elements contents in amphiboles to discuss the property and the process of evolution of magma. All the amphiboles are mainly classified as pargasite, magnesiohastingsite, endenite, kaersutite, tschermakite and magnesiohornblende, forming at the range of 940 similar to 1080 degrees C, 250 similar to 450MPa, thus crystallizing at depths of 11 similar to 15km. Amphiboles in Tulaergen and Xiangshan deposits have been crystallized in lower temperature and pressure (1027 degrees C, 318 MP and 1013 degrees C, 313MPa, respectively), which can be a result of their tectonic background, Jueluotage belt, where there may be more fractures which is helpful for magma to ascend to shallow position to crystallize. H2O in co-existed melts of all four deposits when amphiboles crystallized is high (about 4%), which could be the result of both high water contents of mantel source due to subduction and late-stage of the amphibole crystallization. Compared with Tulaergen and Xiangshan deposits in Jueluotage belt (0 < Delta NNO < 1.7), the amphibole oxy-barometers suggested that Tianyu and Baishiquan in Central Tianshan Massif have a larger extent and lower value of oxygen fugacity (0.6 < Delta NNO < 1.7 in Tianyu and -0.4 < Delta NNO < 1.8 in Baishiquan, respectively). We can see the crustal contamination in Central Tianshan Massif is heavier from the massages indicated by the characteristics of oxygen fugacity and trace elements (the lower Ce/Pb value comparing to Jueluotage belt). Above all, though amphibole is the late-stage crystallization phase of basaltic magma, it can afford vital clues to trace magmatic evolution of copper-nickel deposits.