Source And Evolution Of Ore-Forming Fluid In Xinqiao Deposit,Tongling,Anhui Province

Tongling ore concentration area in Anhui Province is an important polymetallic metallogenic area in the middle and lower reaches of the Yangtze River metallogenic belt.The ore concentration area has large-scale mineralization and multiple types of complex metallogenic system evolution,with great prospecting potential and high degree of research.A series of layered sulfide deposits are widely developed in the area,and their genesis has been controversial.The focus of controversy is whether there is late Carboniferous seafloor exhalative strata(SEDEX).The Xinqiao deposit,a representative stratabound Cu Au Fe s polymetallic deposit in the area,is selected as the research object in this paper.The authors try to trace the source of ore-forming fluid and its evolution process and determine the genesis of the deposit through the determination of lithium and oxygen isotopic compositions of mineral fluid inclusions and Re-Os isotopic dating of pyrite.The micro temperature measurement results of fluid inclusions show that the ore-forming fluid system of Xinqiao deposit belongs to Na Cl-H₂O composition system.The homogenization temperature is 150??450?and the salinity varies from 0.88 wt%to 59.76 wt%Na Cl eqv.Some fluid inclusions contain daughter crystals.The boiling of ore-forming fluid occurred at240??250?.The melt fluid separation of magma and the liquid immiscibility of ore-forming fluid played a leading role in the enrichment of copper mineralization.By measuring the lithium and oxygen isotopic compositions of hydrothermal quartz in different positions of the mining area,the proportion of magmatic water in ore-forming fluid is calculated quantitatively,and the contribution of seawater and magmatic exsolution fluid to the ore-forming system is obtained.The composition of ore-forming fluid in adjacent rock bodies indicates that the hydrothermal fluid is mainly from ore-bearing magma,and the ore-forming fluid is mainly magmatic hydrothermal fluid,With the decrease of magma proportion of ore-forming fluid far away from the rock mass,Yanshanian magmatism played an important role in the enrichment of ore-forming metals(especially Cu and Au)in Xinqiao deposit.The Re Os isotopic dating of pyrite indicates that the skarn was formed at an age of 150.7±8 Ma(initial ¹⁸⁷Os/¹⁸⁸Os=1.183±0.012;MSWD=0.000,2?),The mineralization age of the layered ore body is 133±52 Ma(initial ¹⁸⁷Os/¹⁸⁸Os=0.59)±0.69;MSWD=33,2?),It provides geochronological constraints for the Yanshanian Mineralization of the Xinqiao deposit.In recent years,the age data of pyrite quartz veinlets in the sandstone below the stratabound ore body in Xinqiao mining area have been continuously appeared in Hercynian period.Therefore,the layered ore body may have Hercynian genesis,but the large scale and rich copper of Xinqiao deposit is closely related to the Yanshanian magmatic hydrothermal activity,In addition,the age obtained in this paper is still uncertain,which puts forward higher requirements for the metallogenic age,genesis and metallogenic process of Xinqiao deposit.