Metallogenic Fluid Characteristics And Implications For Ore Genesis Of Chalapu Gold Deposit In South Tibet

The Chalapu gold deposit is located in longzi county,shannan region,Tibet autonomous region.The tectonic structure belongs to the eastern section of the northern Himalayan tectonic belt.The region is controlled by the lint-gufu fault in the east-west direction.Based on the field geological work,this paper studies the geological characteristics and fluid inclusion characteristics of Chalapu gold deposit,constrains the genesis and metallogenic mechanism of Chalapu gold deposit,and obtains the following understanding:The geological characteristics of the Chalapu gold deposit are similar to that of the carlin type gold deposit.The surrounding rock of the host is the upper Triassic nieru formation,which is a set of shallow metamorphic black rocks rich in organic matter.The orebody is mainly controlled by fold and fracture,and the boundary between orebody and surrounding rock is unknown,which can only be defined by chemical analysis.Gold mainly exists in the form of microscopic-submicroscopic invisible gold in pyrite,arsenic-bearing pyrite,and a small amount in the form of natural gold in quartz veins.Pyritization,arsenopyritization,silicification,sericitization,chloritization,visible carbonization;The metallogenic stage can be divided into sedimentary metamorphism stage,hydrothermal stage and epigenetic stage,among which the hydrothermal stage can be further divided into arsenic-pyrite alteration stage,quartz-arsenic-arsenic-rich pyrite stage and natural gold stage.Four types of fluid inclusions were developed in the fluid:liquid-rich(L_H2O+V_H2O)two-phase inclusions and three-phase inclusions containing CO₂(L_H2O+L_CO2+V_CO2),followed by CO₂-rich(L_CO2+V_CO2)two-phase inclusions and gas-rich(L_H2O+V_H2O)two-phase inclusions.The average temperature ranged from 215.2?to 419.9?,concentrated in 300?to 320?,with an average of 314.5?.The salinity ranged from1.2 to 10.8wt%Na Cl.eqv,which was concentrated between 4 and 5wt%Na Cl.eqv.The primary inclusion groups with different types and filling degrees indicate that the fluid boils.The ore-forming fluid is rich in CO₂,medium and low temperature and low salinity.The ore-forming fluid mainly comes from the earth's crust.The mineralization process is dominated by tectonic water,with the participation of metamorphic fluid and meteoric water.The evolution process is as follows:Printed stretch after the collision of continental collision stage lower crust of metamorphic molten,cause local temperature increase at the same time form rich CO₂ metamorphic fluid,in the north and the south under the action of compressive stress and high temperature storage building in formation water activation and mixed with metamorphic fluid,extraction formation of Au ore-forming elements,formation of ore fluid migration along structural fissure,the participation of the near-surface atmospheric precipitation,make the fluid composition change,a sharp drop in temperature and pressure at the same time,the p H value increases,the massive sulfide formation,the Au supersaturated precipitation.Chalapu gold deposit is a reformed hydrothermal ore control deposit,and its genetic type belongs to Carlin type gold deposit.