云南大理笔架山铜矿区斑岩成因与动力学背景:年代学和地球化学制约

Petrogenesis and Dynamic Background of Porphyry in Bijiashan Cu Deposit, Yunnan Province, China: Geochemistry and Geochronology Constraints

大理笔架山铜矿区位于金沙江-红河富碱斑岩成矿带中部,与斑岩有关的铜（金）矿找矿取得了新突破。本文在详实的成矿斑岩岩相学观察基础上,开展了系统的岩石地球化学和年代学研究。与成矿相关的石英二长斑岩具有富碱（K2O＋Na2O均值为9.97%）、富钾（K2O/Na2O均值为2.34）和准铝质（A/CNK均值为0.89）特征,属准铝质钾玄岩系列;微量元素具LILE（Rb、Ba、U、Th和Sr）富集和HFSE（Ta、Nb和Ti）亏损特征,与大陆地壳特征相似;稀土元素具LREE富集和Eu（均值0.73）弱负异常特征,与壳幔混合型花岗岩相近。岩石地球化学特征表明,石英二长斑岩源区具典型壳-幔混合特征,其中以部分熔融的古老地壳物质为主。LA-ICP-MS锆石U-Pb年龄（35.6±0.19 Ma）与金沙江-红河富碱斑岩带岩浆活动高峰期（45~30 Ma）一致。研究结果进一步佐证了本区富碱斑岩是在印-欧板块后碰撞伸展背景下,由加厚下地壳和上地幔部分熔融形成的,与金沙江-红河断裂的走滑构造事件相关。

Located in the middle of Jinshajiang-Red River alkali-rich porphyry metallogenic belt, Bijiashan copper deposit in Dali City, Yunnan province, China has made new breakthroughs associated with the porphyry Cu/Au ore prospecting. Based on detailed petrographic study, the paper carries out system geochemistry and geochronology of Bijiashan Cu deopit. The quartz-monzonite porphyry（QMP） associated with Cu/Au mineralization belongs to the quasi-aluminous and high-K series with alkali-rich（the average K2O＋Na2O value is 9.97%）, K-rich（the average K2O/Na2 O ratio is 2.34） and quasi-aluminous（the average A/CNK values is 0.89） features. Trace element spider diagram displays enrichment of LILE（Rb, Ba, U, Th and Sr） and depletions of HFSE（Ta, Nb and Ti）, which is consistent with continental crust. The rock displays Eu negative anomaly（the average value is 0.73）, which is consistent with crust-mantle mixed granite. Litho-geochemical features suggest that the quartz-monzonite porphyry has crust-mantle mixing characteristics, of which the old crustal material melt partially is important. The zircon U-Pb dating（35.6±0.19 Ma） of quartz-monzonite porphyry by LA-ICP-MS is consistent with the magmatic period（45 to 30 Ma） of Jinshajiang-Honghe alkali-rich porphyry belt. The results further indicate that quartz-monzonite porphyry formed from the thickened lower crust and upper mantle melt partially under the tensional setting in India-Eurasian plate post-collision, which is related to the strike-slip tectonic events of Jinshajiang-Honghe fault.