Geological And Geochemical Characteristics And Genesis Of The Shuiyindong Gold Deposit,Zhenfeng County,Guizhou Province

The Shuiyindong gold deposit is a super-large concealed gold deposit.A detailed geological,fluid inclusion,isotopic geochemical and geochronological study has been carried out on the Shuiyindong gold deposit,with a focus on an analysis of the source of ore-forming fluid and materials and genesis of the deposit.The ore bodies,which occur within the bioclastic limestone of the Permian Longtan Formation and Sbt,are mainly stratiform,stratoid and lenticuar ones,with the attitude in consistency with the strata.The hydrothermal alteration is dominated by silicification,decarbonation,pyritization,arsenopyritization.Based on grain size and structure of pyrite,mineral assemblages and crosscutting relationships,the metallogenic process can be divided into three stages: quartz-fine grained pyrite,quartz-pyrite-arsenopyrite-native gold and calcite-realgar-stibnite stages.The second stage is the main metallogenic stage.Three types of fluid inclusions have been identified in the Shuiyindong gold deposit,based on their characteristics at room temperature: two-phase aqueous,CO₂-bearing three-phase and pure liquid-phase aqueous inclusions.Microthermometric data show that the homogenization temperatures and salinities vary within the range of 132²89 ? and 0.02⁷.59 wt.% NaCleq.,respectively.Thus,the ore-forming fluid was a medium-low temperature and low salinity fluid.The Sm-Nd isochron age of hydrothermal calcite is 86±3 Ma.And it presumably represents the upper limit of metallogenic age of this deposit.Sulfur,lead and carbon isotope results indicate that the ore-forming materials derived mainly from the strata.Helium,argon,hydrogen and oxygen isotopes indicate that the ore-forming fluid was dominated by basinal fluid,with little contribution of magmatic water.Based on the geological,fluid inclusion,isotopic geochemical and geochronological study,a metallogenic model has been establish as follows: Marine sedimentation formed the original protore strata in the Permian.In the early Yanshanian period,the evolution history of the basin ended.In addition,the Au,As and Sb-bearing basinal fluid was formed.During the Late Yanshanian,this region was in the extentional state.The ore-forming fluid migrated a long distance along the deep faults.When the metallogenic fluid reached the primary protore strata,the immiscible process occurred.Meanwhile,the original protore beds were superimposed and reformed to form the Shuiyindong gold deposit.