Geology And Fluid Geochemistry Of The Jinziwei Skarn Cu-Mo Polymetallic Deposit,Anhui Province

Jinziwei deposit is located in the Tongling ore-concentrated district of Anhui province.It is a skarn-porphyry multiple Cu-Mo deposit newly discovered and appears special and typical in the Middle-Lower Yangtze metallogenic belt.This deposit is dominated by skarn orebodies.A comprehensive study has been carried out on the ore deposit geology and fluid geochemistry of this deposit in order to ascertain its geological background and fluid mineralization process.According to the crosscutting relationships of the veinlets combined with the ore texture,structure and mineral assemblages,the alteration and mineralization process of the Jinziwei skarn Cu-Mo deposit can be divided into high temperature pneumatolytic,middle to high temperature hydrothermal,and low temperature hydrothermal periods.The high temperature pneumatolytic period can be further divided into early skarn,late skarn,and oxide stages,and the middle to high temperature hydrothermal period into quartz-molybdenite and quartz-Cu-polymetallic sulfides stages.The low temperature hydrothermal period includes carbonate stage.Cu-Mo mineralization mainly took place in the oxide,quartz-molybdenite,and quartz-Cu-polymetallic sulfides stages.The fluid inclusion analyses show that from the high temperature pneumatolytic period through the middle to high temperature hydrothermal period to the low temperature hydrothermal period,temperature of ore-forming fluid varies from 380.3~560.6 ? through 262.7 ~ 385.6 ? to 136.4 ~ 209.2 ?.Correspondingly,its salinity changes from 7.6 ~ 50.4 % NaCleqv through 2.2 ~ 40.2 % NaCleqv to 0.7 ~ 6.6 %NaCleqv,and its pressure from 16.2~60.6MPa through 14.8~39.8MPa to 9.4~20.1MPa.The hydrogen and oxygen isotopic analyses indicate that the ore-forming fluid from the early skarn stage to quartz-molybdenite stage is predominated by magmatic water,whereas the ore-forming fluid from the quartz-Cu-polymetallic sulfides stage to the carbonate stage is a mixing fluid of magmatic water with meteoric water.The geological and geochemical analyses support the occurrence of unmixing,boiling,and mixing during the evolution of ore-forming fluid in the Jinziwei ore deposit.The unmixing occurring mainly at the early skarn stage leads to the great enrichment of ore-forming elements in the ore-forming fluid.The boiling occurring mainly at the oxide and quartz-molybdenite stage is responsible for the formation of scheelite and molybdenite by precipitation of W and Mo from the ore-forming fluid,and the mixing occurring mainly at the quartz-Cu-polymetallic sulfides stage results in the formation of Cu-polymetallic sulfides by precipitation of Cu,Pb,and Zn from the ore-forming fluid.