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Mineralogical Features of Porphyries in the Narigongma Mo(-Cu) Deposit,Southern Qinghai and their Implications for Petrogenesis and Mineralization

HAO Jin-hua1,2,CHEN Jian-ping1,2,TIAN Yong-ge3,LI Yu-long3,YIN Jing-wu1(1. State Key Laboratory of Geological Processes and Mineral Resource,China University of Geosciences,Beijing 100083;2. Institute of Land Resources and High Techniques,China University of Geosciences,Beijing 100083;3. Qinghai Geological Survey Institute,Xining 810012)  
This paper focuses on the study of the ore-bearing porphyry of the Narigongma deposit through mineralogical and geochemical analyses. The result reveals that the biotite phenocrysts in the deposit are ferri-phologopite or magnesium-rich biotite and the amphiboles are magnesium amphiboles,tremolites or actinolites. The porphyry should be classified as I-type granite,which was originated from the mantle,meanwhile assimilated crustal material is also present. The crystallization pressure of the porphyry is 1.18~1.39×108Pa. The crystallization temperature of the biotite porphyry is estimated to be 550℃~650℃,whereas that of the leucogranitic porphyry is about 500℃~550℃. The geochemical characteristics regarding ratio Mg/Fe and contents of Ti,Al,K,Na,Ca,F and Cl suggest favorable ore-forming potential in the Narigongma deposit. The crystallization temperature and pressure are both lower than that in the Yulong ore-forming belt,which indicates that the former was probably developed shallower than the latter. Besides,the inferred difference in the forming depth also suggests that more crustal material had contributed in the formation of the shallower Narigongma deposit.
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