Petrogenesis of the late Yanshanian Laba granite in northwestern Yunnan Province and its metallogenic implications: Evidence from mineral chemistry of biotites and amphiboles
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P575.1;P581;P611

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    Abstract:

    The late Yanshanian Laba porphyritic granite, associated with a superlarge Mo(-Cu)-polymetallic deposit, was recently identified by drilling exploration in Shangrila area of northwestern Yunnan Province. The magmatic biotites and amphiboles have recorded the detailed petrogenesis information including the temperature, pressure, oxygen fugacity, and the source origin of the parent magma. The authors investigated the mineralogical composition of the biotites and amphiboles in the porphyritic granite from the Laba Mo(-Cu) deposit, and constrained the physico-chemical conditions of the ore-bearing magmatic rocks as well as the metallogenic potential. Electron microprobe analyses (EMPA) show that the biotites have uniform Fe2+/(Fe2++Mg) values, without or with minor CaO, and the Ti cation number is 0.31~0.52, indicating that they are of magmatic origin. The Si, Ti cation num-bers of the amphiboles are 6.68~7.20 and 0.09~0.13 respectively, indicating that they are also of magmatic origin. The authors have reached the conclusion that the formation temperature, pressure and depth of the porphyritic granite are 705~903℃, 59~449 MPa and 2.2~17.0 km respectively. The features of mineral geochemistry of the biotites and amphiboles suggest that the porphyritic granite belongs to the I-type granite with the addition of mantle-derived materials, and was formed in an environment with high oxygen fugacity. The values of F and Cl in the biotites are 0.17%~0.58%, showing that the fluids exsolved from the granitic magmas were rich in F and Cl, which was beneficial for enrichment and mineralization of Mo and Cu. These results shed light on the correlation between the rock-forming and ore-forming processes for the superlarge Laba Mo(-Cu)-polymetallic deposit. Meanwhile, they also indicate that the Laba orefield has a giant potential for future exploration.

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向坤,薛传东,谢志鹏,来瑞娟,2019,滇西北拉巴燕山晚期花岗岩岩石成因及其成矿指示——黑云母和角闪石矿物化学证据[J].岩石矿物学杂志,38(1):34~46. XIANG Kun, XUE Chuan-dong, XIE Zhi-peng, LAI Rui-juan,2019,Petrogenesis of the late Yanshanian Laba granite in northwestern Yunnan Province and its metallogenic implications: Evidence from mineral chemistry of biotites and amphiboles[J]. Acta Petrologica et Mineralogica,38(1):34~46.

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History
  • Received:April 17,2018
  • Revised:November 07,2018
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  • Online: January 19,2019
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