Geology And Ore-forming Fluids Geochemistry Of The Tongkuangli Molybdenum Polymetallic Deposit,Qingyang,Anhui Province

The Tongkuangli molybdenum polymetallic deposit in Qingyang,Anhui Province is a typical skarn molybdenum polymetallic deposit in the Middle-Lower Yangtze River Metallogenic Belt.In this paper,we present details of the geology and fluid inclusions of the Tongkuangli deposit,and then discuss the fluid evolution and ore genesis.The metal minerals in the deposit are mainly molybdenite,pyrite,pyrrhotite,chalcopyrite,etc.The gangue minerals are mainly garnet,diopside,calcite,quartz,feldspar,etc.,followed by sericite,epidote,chlorite,etc.The ore texure and structure and the cross-cutting relationship indicate that the ore-forming processes can be divided into the early skarn,late skarn,quartz molybdenite,quartz polymetallic sulfide and carbonate stages.The quartz molybdenum stage is the main stage of molybdenum ore formation.Microscopic observations show that the types of fluid inclusions in the Tongkuangli deposit are mainly liquid-rich,vapor-rich and three-phase inclusions.From the early skarn stage to the late carbonate stage,the fluid inclusions show homogenization temperatures of 500～520℃,380～400℃,360～380℃,300～320℃,200～220℃,respectively.Additionally,three-phase inclusions were found in garnet from the early skarn stage,with a salinity ranging from 43.54 to 46.68 wt%NaCl equiv.,while the calcite in the carbonate stage only contains liquid-rich inclusions with a salinity of 0.18～4.18 wt%NaCl equiv..The above results indicate that the early fluids in the Tongkuangli deposit are high salinity and high temperature,while the late fluids are low temperature and low salinity.This feature,combined with H-O isotope data,indicates that the early hydrothermal fluids in the Tongkuangli deposit were dominated by magmatic hydrothermal fluid,and that the magmatic water gradually mixed with circulating meteoric water during the late stages.The comprehensive analysis indicates that the Tongkuangli deposit is formed by the ore-forming fluids reacted with the host rocks along the contacts and interlayer faults,and the main mechanism of molybdenum precipitation in the deposit is fluid boiling.