Chemical Composition Of Biotites In Woergei Granodiorite,Gansu Province:Implications For Petrogenesis And Mineralization

West Qinling orogenic belt is one of the most important part of the Central orogenic belt.Woergeixiaka gold deposit located in the western West Qinling orogenic belt and the northern Lishishan-Weidangshan fault zone.Xitufang-Dakuiguo fault zone,which almost is controlled by EW and traverses the gold deposit.Based on the 1:10000 soil geochemical survey on the gold deposit of Woergei in Gansu Province.With the R-model factor analysis method was used in the evaluation of geochemical anomalies.Cluster analysis ofthe soil geochemical data obtained from the gold deposit of Woergei shows that eight kinds of elements can be grouped into three categories,i.e.,?1?Sb,As,Au,Pb,Ag;?2?Cu,Zn;?3?Hg.Combined with favorable ore-controlling factors such as lithology and structure,the authors applied the system core theory to synthetically evaluate main ore-forming elements and the abnormal element combination,and then selected three prospecting target areas.In No.?,? and ? anomaly target zone,the system of nuclear respectively are {Au,Pb},{Au} and {Cu},the system stability are strong,among which abnormal ? and? area were verified by drilling and pit engineering.The mineralization location,size and element anomaly concentrated heart position are in good agreement,in the two abnormal zone,suggesting that soil geochemical survey is effective in the study area.However,No.? anomaly target zone,the system of nuclear is {Cu},attached the anomaly in the area to display the main ore-forming elements Cu,Au abnormalities.This article selects the biotites of granite as the research object,which are closely associated with mineralization space within the mining area.Through the detailed petrographic observation and the analysis of its mineral chemistry composition by electron Microprobe,in order to discuss the forming conditions of the biotite from hydrothermal fluid,and it is vital that identifying the mamagic source natures.The results illustrate that the bioties are rich in Mg?w?MgO?=9.20%¹1.06%,the value of Mg/?Mg+Fe?of biotites is 0.42⁰.52?,which belong to Mg-biotite.According to the logfO2-T temperature diagram of biotite to estimate its crystallization temperature varied from 670? to 715?,and combine the logfO2-T temperature diagram with the Fe²⁺-Fe³⁺-Mg triangular diagram to estimate the range of oxygen fugacity?logfO2?that biotite formed is 10-11 10-13.Mineral geobarometer,which calculated by the TAlchemical composition of biotite,showed that pluton consolidation pressure is 1.56².04 kbar.And the pluton is equivalent to a depth of 5.91 7.72 km.chemical composition of biotite suggest the pluton is I type granite formed in orogenic Zone environment and the mixture of crust and mantle.In this paper,we centre on the investigation of relationship between the alkalinity rock mass and mineralization.Based on the statistics of the chemical compositions of biotite,the biotite came from 52 kinds of different deposits in China.According to we analyzed the basicity of host rock,the metallogenic elements Cu and Au existed rock mass that were located in high basicity area.The rock mass almost was related to the formation of Sn deposits which were belonging to the low alkalinity rock.The period of magmatic melt transformation process was from early to late.The oxygen fugacity had been changed from high to low cause on medium alkalinity increased.The formation of Cu and Au deposits was also followed the process with diagenetic mineralization.However,the low Oxygen fugacity and the high basicityare are advantageous to the activation and migration of element Sn in early magmatic crystallization process.The high oxygen fugacity and the lower alkalinity are advantageous to the precipitation of cassiterite in magmatic hydrothermal-fluid stage.Due to the precipitation of cassiterite constantly consumed oxygen in this process,which leading to the higher oxygen fugacity is significant reduction than before.The interaction will happen between the oxygen fugacity and the basicity resulting in mineralization.