Geological Characteristics And Discussion On Genesis Of The Fangyangshang Cu-Pb-Zn Polymetallic Mineral Deposit In Zhenkang,Western Yunnan Province,SW China

The Fangyangshan Cu-Pb-Zn polymetallic deposit is tectonically located in the Sn-Pb-Zn-Fe-Cu-Au polymetallic ore concentration area in the southern part of the Baoshan block,"Sanjiang" metallogenic belt,SW China.The deposit and the Luziyuan deposit which is a super large-size Pb-Zn-Fe(Cu)deposit both lie at the core of the Zhenkang anticlinorium,with distance of only about 6 km.The Fangyangshan deposit is a Cu-enriched(Cu>1.70%)Pb-Zn deposit and this type is the first time to be found in Zhenkang area recently.Trends of these ore bodies are NE-EW-NW,with their outline arching from the west to the east and clearly different from the direction of overall structure line in this area(Mainly to NE).Restricted by poor geographic factors,previous works only covered mineral exploration and survey,but the basic geology research,such as geographical conditions of the deposit,the mining area and etc.are currently only gap.What causes its Cu-enrichment? What is the reason of obvious change of ore bodies' strikes? On that account,this paper took the Fangyangshan deposit as a object,based on the detailed geological research of the deposit,systematically analyzing sulfide minerals' trace elements(REE)and gangue minerals' C,H,O isotopic composition characteristics,took a further discuss in the source of ore-forming materials and the change of ore-forming physicochemical conditions in the Fangyangshan deposit.Meanwhile,according to the comparision of information reflected by the geochemical characteristics from the Fangyangshan deposit and other typical deposits,the following understandings have been identified:(1)The formation of the Fangyangshan deposit experienced mineralization of the hydrothermal stage and superposition stage,and the Cu-enrichment of deposit is the result of the reactivation and enrichment of the minerals caused by the hydrothermal fluid in the superposition stage.The NW-EW-NE arc-like outline of ore bodies in the mining area from west to east was caused by the coupling of the Wumulan anticlinorium and the Luziyuan anticlinorium.The position of structure superposition is the key target for ore prospecting in this area.(2)The research of typical mineral trace elements Y/Ho,H and O isotopes in quartzs,and C and O isotopes in calcites,which indicate that the formation of the Fangyangshan deposit was closely related to the deeply Magmatic-hydrothermal activities.The fluids of hydrothermal stage and superposition stage all mainly came from deeply magmatic hydrothermal fluids,and the hydrothermal fluid was partly mixed with the upper crust fluid,while the fluid of the superposition stage had the participation of meteoric water.The C and O isotopes from these two stages have uniform compositions which show the fluids of these two stages were mainly from the deep magmatic hydrothermal hydrothermal.(3)The metallogenic materials in the hydrothermal stage in the Fangyangshan deposit were mainly formed in an oxidizing environment at relatively low-temperature,and the fluid was mainly Cl-rich.The fluid of superposition stage was from the reductive environment at medium-high temperature and characterized by F-rich,activating and migrating minerals deposited in the former stage.(4)The formation of the Fangyangshan Cu-Pb-Zn polymetallic deposit was controlled by strata,lithology and structure,and it was the result of the coupling of multi-period tectonic movements.The nearby deposits such as the Luziyuan deposit,the Shuitoushan deposit,and the Wenkong deposit were regarded as the products of contemporaneous tectonic movement.The Fangyangshan deposit is now considered as a medium-low temperature hydrothermal polymetallic deposit,which was superimposed and transformed by the later tectonic movements.