| The Dihu-Jiuxing copper polymetallic deposits of Congjiang country,southeast Guizhou province,are located in the southwest Jiangnan orogenic belt,which are important ore-forming represents of Congjiang Cu-Au-Ag-Pb-Zn-Fe polymetallic ore-forming area.On the basis of field geological survey and sample collection,we carry out petrology and mineralography observation of the samples to classify the ore-forming stages.And then carry out microscopic temperature measurement of quartz fluid inclusions,analysis of the Laser Raman spectroscopy,H-O isotopic and quartz in-situ geochemistry.The research of fluid inclusions and in-situ element geochemistry provides a basis of ore deposit genesis,and the results are as follows:(1)According to orebody,ore structure and mineral intergrowth association,the ore-forming process of both Dihu and Jiuxing copper polymetallic deposits can be divided into four ore-forming stages:quartz+magnetite and pyrite stage(S1 stage),quartz+copper sulfide stage(S2 stage),quartz+polymetallic sulfide stage(S3 stage),quartz+a few magnetite or pyrite stage(S4 stage).(2)Petrographic characteristics show that fluid inclusions can be classified into four types:pure liquid inclusions(?type),liquid rich inclusions(?a type),gas rich inclusions(?b type)and pure gas inclusions(?type).The liquid rich inclusions(Gd A type)are the most developed in the two deposits and can account for more than 50%of the total in each stage.The temperature measurement results show that the average temperature of fluid inclusions from S1 to S4 stage of the Dihu copper polymetallic deposit decreases from244?,229?,209?to 208?,and the temperature of the whole stages is 126??370?,with an average of 225?.The average temperature of fluid inclusions from S1to S4 stage of the Jiuxing copper polymetallic deposit increases firstly and then decreases from 218?,230?,209?to 208?,and the temperature of the whole stages is 113??380?,with an average of 217?.Most of the fluid inclusions in the two deposits also fall in the temperature range of 160??260?,showing the ore-forming characteristics of medium-low temperature,and the ore-forming temperature of the Dihu copper polymetallic deposit(225?)is slightly higher than that of the Jiuxing copper polymetallic deposit(217?).The average salinity of fluid inclusions from S1 to S4 stage of the Dihu copper polymetallic deposit is 9.57%Na Cleqv,9.61%Na Cleqv,9.48%Na Cleqv and 8.02%Na Cleqv,respectively,and the salinity of the whole stages is 3.71%?20.67%Na Cleqv,with an average of 9.23%Na Cleqv.The average salinity of fluid inclusions from S1 to S4 stage of the Jiuxing copper polymetallic deposit is 10.35%Na Cleqv,9.33%Na Cleqv,9.98%Na Cleqv and 8.45%Na Cleqv,respectively,and the salinity of the whole stages is2.90%?19.45%Na Cleqv,with an average of 9.55%Na Cleqv.Fluid inclusions of the two deposits are medium-low salinity,and the salinity of the Jiuxing copper polymetallic deposit is slightly higher.Meanwhile,the salinity of both deposits decreases in the S4stage(average value<9%Na Cleqv).The average fluid density of the Dihu copper polymetallic deposit is 0.905g/cm3,the average pressure is 222bar,and the average ore-forming depth is 837m.The average fluid density of the Jiuxing copper polymetallic deposit is 0.913g/cm3,the average pressure is 217bar,and the average mineralization depth is 821m.It shows that the two deposits belong to shallow deposits with medium density fluid.(3)The results of Laser Raman component analysis show that the fluid inclusions in the S1-S4 stage of the Dihu copper polymetallic deposit all contain H2O,CO2 and N2.And CH4 appears in the S1-S3 stage.The fluid inclusions in the S1-S4 stage of the Jiuxing copper polymetallic deposit all contain H2O,CO2 and N2.And CH4 is only found in the S1 stage,but the signal strength is extremely weak.Therefore,the ore-forming fluids system of both Dihu and Jiuxing copper polymetallic deposits is Na Cl+H2O+CO2+N2ąCH4,and the fluid may have migrated and evolved from Dihu to Jiuxing mining area.(4)The results of H-O isotopic analysis show that the water in the hydrothermal fluids of the two deposits mainly derive from the metamorphic water.In the H-O isotope discriminant diagram,the water in S3-S4 stage of the Dihu copper polymetallic deposit and S4 stage of the Jiuxing copper polymetallic deposit is slightly out of the metamorphic water range.It may be the metamorphic hydrothermal fluids react with the surrounding rock,which makes the?18O value in the fluids slightly lower,and the water-rock reaction of the Dihu copper polymetallic deposit may be stronger than that of the Jiuxing copper polymetallic deposit.(5)The results of in-situ geochemical analysis show that the content of Ti in quartz is less than 10ppm,indicating that the formation temperature is less than 350?.The content of Al varies in a small range(1.9ppm?24.9ppm),indicating that the p H value of the fluids is relatively stable during the ore-forming process,and the content of Al in the Dihu copper polymetallic deposit is slightly lower than that of the Jiuxing copper polymetallic deposit in each stage or the whole stages,indicating that the p H value of the Jiuxing copper polymetallic deposit is slightly higher.The Dihu-Jiuxing copper polymetallic deposit is similar to the epithermal deposit in geochemical characteristics according to the variation of vein forming temperature and Al content.(6)In conclusion,the ore-forming fluids of Dihu and Jiuxing copper polymetallic deposits are characterized by medium-low temperature(160??260?),medium-low salinity(<10%Na Cleqv),shallow ore-forming depth(<1000m).And the water in the fluids is mainly derived from metamorphic water.The genetic type of two deposits is hypabyssal medium-low temperature metamorphic hydrothermal deposit. |
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