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《Geochimica》 2018-02
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Mineral chemistry of hornblende in the Chihu-Fuxing copper district,Xinjiang,and its geological significance

GONG Lin;CHEN Hua-yong;XIAO Bing;WANG Yun-feng;ZHAO Lian-dang;Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences;University of Chinese Academy of Sciences;Guangdong Provincial Key Laboratory of Mineral Physics and Materials;  
The Chihu and Fuxing copper deposits are located in the Dananhu-Tousuquan island arc belt of Eastern Tianshan. This study focuses on the hornblende found in the intermediate-acidic igneous rocks. Using electron microprobe analyses(EPMA), we study the characteristics of hornblende and constrain the tectonic setting and physicochemical conditions related to the pluton formation. In addition, we discuss the process of magma evolution and its relationship with Cu mineralization. The EPMA data show that hornblende is composed mainly of magnesiohornblende, tschermakitic hornblende, and secondary actinolite. These components were primarily formed by magmatism and part of them were altered. The mantle materials were possibly involved in the formation of these plutons during subduction. The values of crystallization pressure, temperature, lgfO2 and H2 O content of the hornblende in the melt of diorite porphyry(Chihu) are 244~451 MPa or 2.44~4.51 kbar,(equivalent to 8~15 km), 880~918 ℃, –10.2 ~ –11.1, and 6.4%~7.0%, respectively. The corresponding values pertaining to the melt of granodiorite(Chihu), quartz diorite(Chihu and Fuxing), and diorite(Fuxing) and their hornblendes are 30~90 MPa or 0.3~0.9 kbar,(equivalent to 1~3 km), 640~785 ℃, –12.3 ~ –13.8, and 3.6%~4.8%, respectively. Thereby, we conclude that the hornblendes might have formed in two different magma chambers at different depths. Mantle-derived magma might have migrated from depth into the deep magma chamber and formed the hornblende of the diorite porphyry; thereafter, the residual magma carrying the hornblendes ascended. this was accompanied by the exsolution of fluid from the magma and the migration of ore-forming elements. Granodiorite, quartz diorite, and diorite and their hornblendes might have formed in the shallow magma chamber and copper mineralization might have occurred at the top.
【Fund】: 国家重点基础研究发展计划(2014CB440802);; 中国科学院“百人计划”项目(Y333081A07)
【CateGory Index】: P588.125;P618.41
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