The Juelotage tectonic belt lies between the Tuha Basin and the Central Tianshan Massif, within the Eastern Tianshan of XinJiang, where the geological structures are very complicated and rich in mineral resources, and the mineralization is closely related to the magmatic activity. Based on detailed petrographic observation, the authors analyzed the compositions of amphibole from the intrusive rocks by electron microprobe analysis (EMPA). The critical factors for calc-alkalic magmas such as temperature and pressure conditions, oxygen fugacity and water contents of the magmas are estimated, which provide the mineralogical constraints on the environments of magmatism, magmatic evolution and metallogenic processes in the Juelotage tectonic belt. The EMPA data show that the amphibole is rich in magnesium (MgO 5.82%-18.04%), calcium (CaO 9.91%-12.56%) and sodium (Na2O/K2O>1.0), belonging to calcic amphiboles. The chemical compositions of amphibole reveal that the host intermediate-acid intrusive rocks were derived from a hybrid of melts of the mantle wedge and the continental crust under subduction setting. The amphibole is characterized by crystallization temperatures of 751.88-887.46 ℃, crystallization pressures of 62-248 MPa, with magma emplacement depth of 2.35-9.4 km. The oxygen fugacity of calc-alkalic magmas defined by amphibole components varies from ΔNNO+0.30 to ΔNNO+2.48, and H2O contents of the melts when amphibole crystallized are higher than 5%. Through analysis, it is known that the calc-alkalic magmas in the Juelotage tectonic belt are characterized by high oxygen fugacity, water-rich and shallow emplacement, which is beneficial to the enrichment of Cu and other elements in the ore-forming fluids, and consistent with the metallogenic conditions for porphyry copper deposits. Therefore, it is suggested that this belt has great prospecting potential for porphyry copper deposits. © 2021, Science Press. All right reserved.
