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《Acta Petrologica Sinica》 2017-10
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Relation between magmatic processes and porphyry copper-gold ore formation,the Duolong district,central Tibet

SUN Jia;MAO JingWen;YAO FoJun;DUAN XianZhe;MLR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences;School of Nuclear Resource Engineering,University of South China;  
The Duolong ore district,comprising four significant deposits(Duobuza,Bolong,Naruo,and Rongna) with a total resource of approximately 16 megatons of copper and 200 tons of gold,is located in the western part of the Bangong-Nujiang suture zone,central Tibet.This study attempts to investigate the relation between magmatic processes and porphyry copper-gold ore formation in the Duolong district,and to discuss the igneous and geochemical characteristics that might be used as exploration tools for future exploration.Whole rock geochemistry,Sr-Nd-Hf isotopic compositions,as well as geochemistry of igneous minerals collectively indicate that ore-related igneous rocks were sourced from mixing of mantle-derived mafic,and crust-derived felsic melts with the input of oceanic sediments.Magmas also experienced crystallization fraction and recharge of mafic magmas upon subsequent ascending.This study suggests that metal-rich magma was mainly sourced from mantle region,metals were transferred through highly oxidized(ΔNNO0.5)and water rich(≥4% H_2O) magmatic environment to the shallow level magma chambers(2.5~7.5 km in depth).Since copper,gold and water solubilities in silicate melts decrease with falling temperatures and pressures,ore formation tends to be associated with magma chambers emplaced at shallow levels.We also outline three steps for future exploration of porphyry copper(gold) system along the Bangong-Nujiang suture zone.The first step is to identify regions with mantle-derived component by Nd-Hf isotopic mapping at regional scale,and regions with well exploration potential might also be characterized by the occurrence of mafic microgranular enclaves(MMEs).The second step is to narrow the prospecting area to district scale by magmatic oxidation mapping through igneous minerals(i.e.,zircon and amphibole),meanwhile the presence of igneous amphibole could be considered as an indicator for a potential porphyry system.The third step is to assess the mineral potential of porphyritic intrusion by measuring V,Ti contents of igneous magnetite as magnetite crystals of economically ore-bearing porphyries tend to contain lower V,Ti contents.Additionally,igneous rocks,characterized by presence of amphibole,chalcopyrite,vapor and brine inclusions,and secondary biotite and chlorite,also indicate a well exploration potential for the porphyry copper(gold) system.
【Fund】: 国家重点研发计划项目(2017YFC0601403);; 中国地质调查局地质调查工作项目(1212011120994);; 中央级科研院所基本业务费项目(K1501);; 国家留学基金委员会《国家建设高水平大学公派研究生项目》联合资助
【CateGory Index】: P588.1;P611
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