Deposit Geology,Fluid Inclusion Characteristics And Ore Genesis Of The Matoushan Cu-Au Deposit In Mianning,Southwestern Sichuan Province

Since the beginning of the 21st century,China's economy has entered a stage of rapid development,and the demand for metal minerals,especially precious metals,has continued to increase due to the increase in national economic production and construction.Sichuan province is a famous polymetallic metallogenic province in China.The Matoushan Cu-Au deposit is a newly discovered medium-sized copper-gold deposit in southwestern Sichuan province.It is located in a special geotectonic location,located in the western margin of the Yangtze Platform,in the northern part of the Kangding-Yunnan axis,at the junction of multi-level faults.Folds,faults and joints are well developed in the mining area,which were provided favorable conditions of the enrichment of metal elements and the sedimentation of minerals.The multi-stage magmatism in the region provides sufficient mineralizing material and metallogenic power for the formation of the deposit.Based on detailed field geological survey and systematic sampling,this paper uses the techniques of macroscopic observation and microscopic observation,microscopic temperature measurement of fluid inclusions and modern geochemical analysis to analyze the geological characteristics and mineralization of the Matoushan Cu-Au deposit.The characteristics of fluids and sources of ore-forming materials were analyzed and studied,the metallogenic background,metallogenic processes and metallogenic mechanisms were discussed and the genetic types of the deposits were determined.It provided theoretical basis for the subsequent theoretical research and actual exploration and mining work of the deposits.The main results and understanding are as follows:?1?The ore bodies of the Matoushan Cu-Au deposit is occur in Devonian clastic rocks and carbonate rocks,Permian argillaceous slate,crystalline limestone,metamorphic sandstone and slate,basalt,Triassic schist and slate.The deposit is divided into three ore sections from north to south.A total of six industrial mineralized bodies are encircled.The main metal elements are gold,copper and a small amount of silver.The ore bodies are produced in veins,and the strike is consistent with the tectonic line.It is strictly controlled by NNE-trending fault structure,but the fluctuation of hydrothermal activity and the difference of surrounding rock lithology cause uneven distribution of mineralization.?2?The main metal minerals in Matoushan Cu-Au deposit are gold,chalcopyrite,bornite,chalcocite,tetrahedrite and pyrite,and a small amount of atacamite and covellite.The ore types are divided into three types:carbonate quartz vein type ore,metamorphic type ore and albite type ore.The ore texture includes crystalloblastic texture,metasomatic texture,palimpsest texture and deformation texture,and exsolution texture and cataclastic texture are also relativetly developed.The structure of ore is mainly disseminated,veined,reticulated,massive,flaky and slate.it surrounding rock alteration of the deposit is generally developed,pyritization,carbonation,silicification,chloritization and sericitization,with albitization and baratization in locally visible.?3?According to the sequence of mineral formation,the symbiotic combination of minerals in ore bodies,interpenetrating relationship and metasomatic filling,the Matoushan Cu-Au deposit is divided into two metallogenic period and five metallogenic stages,namely hydrothermal mineralization period and supergene period.Among them,hydrothermal mineralization period is divided into S1 quartz-medium-coarse grained pyrite stage,S2 quartz-fine vein pyrite stage,S3 quartz-polymetallic sulfide stage,S4 carbonate stage.The supergene period is divided into supergene oxidation stage.?4?The petrography of fluid inclusions shows that there are two main types of fluid inclusions in the Matoushan Cu-Au deposit:H₂O inclusions?type L?and CO₂bearing inclusions?type C?.The microscopic temperature data of inclusions show that the average temperature of fluid inclusions in the S3 main metallogenic stage is 206.9?,the average salinity is 11.3%Na Clevq,the average density is 0.89 g/cm³.It is characterized by medium-low temperature,medium-low salinity,low density and rich in CO₂.During the whole metallogenic process,the fluid inclusions in the Matoushan Cu-Au deposit have the characteristics of temperature rising to falling,salinity and density decreasing continuously.The fluid evolution process from the early metallogenic stage to the main metallogenic stage is from acidic oxidation fluid to alkaline reduction fluid.?5?The stable isotope geochemical characteristics show that the ore-forming fluids of the Matoushan Cu-Au deposit is magmatic water-mixed with meteoric water and brine water in Sichuan basin,and the ore-forming materials mainly come from mantle-derived magma,the Permian basalt,metamorphic slate and seawater sulfate strata in the region also provide some ore-forming fluids.?6?The metallogenic background and metallogenic mechanism indicate that the Matoushan Cu-Au deposit was the product of the Himalayan neotectonic movement.During this period,the Yangtze block was inserted into the Longmenshan crust as a wedge-shaped body,resulting in the overthrust and subduction of the upper slices and the middle and lower crusts respectively,forming mantle-derived alkaline magmatic activity,and the magma carrying mineralizing substances continuously extracted the mineralization and mineralization of the strata during the upwelling process.Agent,because of the fluid boiling lead to copper and gold deposits,eventually forming a large-scale mineralization.Based on the geological characteristics,fluid inclusion characteristics and isotope geochemical characteristics of the deposit,the Matoushan Cu-Au deposit can be determined as a medium-low temperature hydrothermal vein type copper-gold deposit.