The Geochemical Characteristic And Genesis Of Boka Gold Deposit, Yunnan

Yunnan Boca gold deposit is a large deposit found in the metallogenic area of Sichuan-Yunnan-Guizhou.The tectonic location is located at the northern of the Yunnan section of the Kangdian axis which in western margin of the Yangtze Block.The deposit is located in the proterozoic Kunyang Group.Therefore,the reserch of Boka gold deposit is very important for the prospecting of the mining area.Based on the ananlysis of the ore-forming geological setting,geology characteristics,geochemical characteristics and fluid inclusion characteristics of the deposit,the source of ore-foeming materials,the genesis of deposit,ore-forming model and etc are studied.The main achievements are obtained as follows:(1)The Boca gold deposit is located on the western margin of the Yangtze Block,and the strata in the mining area are mainly the Mesoproterozoic Kunyang group.The main ore-occurred strata in the mine area are the Yinmin group,the Luoxue group and the Heishan group.The ore-bearing strata mainly distributed in metamorphosed rock series,which developed alteration breccia,carbonaceous siltstone and carbonaceous slate.The ore is mainly quartz vein type and pyrite type,type is mainly in the shear zone,the types of alteration are: silicification,albitization,pyritization,carbonatization,limonite mineralization,epidotization,malachite petrochemical and chlorite.The optimum combination of hydrothermal alteration is silicification,pyritization and carbonatization.(2)By studying the geochemical characteristics of major elements,the trace element and the REE in the Boca deposit,it's known that the intermediate-basic rock belongs to the alkaline gabbride and basaltic rocks(?Si O2=43.24%~52.05%,?=43.24%~52.05%,AR=1.14%~1.83%),that the LREE / HREE is from 0.34 to3.62,which means light rare earth element enrichment,and that ?Ce is from 0.61 to 0.94 respectively without obvious,and that ?Eu is from 0.67 to 1.03 exhibits weak depletion.The characteristics of trace elements and REE showt hat the magmas experienced assimilation and contamination of the crustal materials in the diagenetic evolution process,and the rocks occurred in the intiaplate-basalt tectonic setting.(3)The geochemical characteristics of trace elements and REE show that quartz has different multiphase,and the fluid may be the product of different stages of the same fluid system,and the fluid temperature of early stage is higher than the later stage.By studying the geochemical characteristics of the trace element and the REE of calcite,it's known that the calcite form of hydrothermal fluid.Consequently,Boka gold deposit belongs to the hyfrothermal genesis deposit.(4)Based on the analysis of the hydrogen and oxygen isotopes,helium argon isotopes and fluid inclusions in the Boca deposit,it is known that the ore-forming fluid is mixed fluid of the upeer mantle and crustal,as well the metamorphic hydrothermal and meteoric water.The studyingof metallogenic fluid inclusions indicate metallogenic fluid has high-temperature,high-salinity to low temperature,low salinity reduction.The characteristics of sulfur and plumbum isotopes show that the source of metallogenic material is complicated,and that mainly source on the upper mantle.The mentallogenic material is influence on other source,such as host rock(diabase and carbonaceous slate).(5)Based on the predecessors' study on the metallogenic chronology of Boca gold deposit,the ore age of is 40 ~ 59 Ma,which indicates that deposit formate at the time for the late paleocene to early Eocene.The tectonism and hydrothermal cation have an great influence on mineralization in the Himalayan stage.(6)Based on the analysis of characteristics of geology,Lithogeochemistry and fluid inclusion,ore-forming geological conditions,source of ore-forming matericals,ore-forming age and mineralization,Boka gold deposit belongs to low-middle hydrothermal deposit type controllde by he brittle-ductile shear zone.