Compositions and metallogenic significance of biotite and amphibole from fertile porphyry in the Shuangyuangou copper deposit in South Qinling
The Shanyang-Zhashui area of ore concentration is located in South Qinling,which is the site of porphyry-skarn copper-molybdenum deposits in which the ore body occurs in the porphyries,and its zone of contact with the wallrock of the Cu deposit in the Shuangyuangou porphyry.In this study,we selected quartz diorite porphyry and granodiorite porphyry from the Shuangyuangou deposit,and subjected them to petrographic analysis,electroprobe-based micro-analysis,and LA-ICP-MS analysis to reveal their composition as well as the implications of the mineralization of biotite and amphibole.The biotites of quartz diorite porphyry and granodiorite porphyry in Shuangyuangou were found to have similar compositions:they were rich in Mg,Al,Ti,K,F,and Cl,and depleted in Si and Na.The major and trace elements of the amphiboles had different compositions,whereby the amphiboles in quartz diorite porphyry had higher contents of Si and Mg,and lower contents of Al and Fe than those in the granodiorite porphyry.The amphiboles in the two types of porphyries were rich in light rare-earth elements and depleted in heavy rare-earth elements.The quartz diorite porphyry had high oxygen fugacity,and was in the high-oxidation HM zone(Fe2O3-Fe3O4).Both porphyries were rich in volatile matter,and the magma of the granodiorite porphyry had a higher water content(average,5.30％).The latter had a higher potential for mineralization,which was primarily influenced by the water content of magma.
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