Sulfide Microanalysis And The Indication Of The Genesis Of The Xiyi Lead-zinc Ore Deposit In Yunnan

The Xiyi lead-zinc ore deposit is located in the central-northern Baoshan Block in Yunnan.It is a large lead-zinc-silver polymetallic deposit that have been found in recent years,making a breakthrough on prospecting lead-zinc concealed orebodies.On the basis of detailed field investigation and microscopic observation,this paper carried out EMPA and LA-ICP-MS analyses on sphalerite,galena,pyrite and arsenopyrite from V3 orebody.These results were used to throw light on the metallogenic environment and genetic type of the Xiyi deposit,which is significant to guide future prospecting.The strata-bounded orebodies are hosted in the Lower Carboniferous Xiangshan Formation(C₁x),controlled by NE-striking faults and secondary faults.Lead-zinc mineralization is closely related to carbonate rocks.Ore minerals are mainly sphalerite,galena,pyrite,arsenopyrite and chalcopyrite.Gangue minerals include abundant calcite and quartz,and minor barite.Wall-rock alteration is dominated by calcilization,pyritization and baratization.The ore-forming process can be divided into four stages,including calcite-pyrite stage(?),sphalerite-galena-calcite stage(?),galena-sphalerite-arsenopyrite-calcite stage(?)and calcite-pyrite-quartz stage(?).Electron microprobe(EMPA)analysis data show that sphalerite of stage?at Xiyi has average Zn content of 59.3%,S of 32.9%,and Fe of 6.8%.The sphalerite of stage?has average Zn content of 61.1%,S of 33.1%,and Fe of 5%.The average Pb/S ratio of galena in both two stages is 1.01.The pyrite of stage?has average Fe of 45.9%,S of 52.7%with S/Fe ratio of 2.0.The pyrite of stage?has average Fe of 46.0%,S of 52.9%with S/Fe ratio of 2.0.The arsenopyrite has average As content of 45.4%,S of 20.5%with S/As ratio of more than 1.LA-ICP-MS analysis data show that the early-stage sphalerite are enriched in Fe,Cd,Mn,Pb,Cu,and depleted in Zn,Ag,Ge,and Ga.In contrast,the late-stage sphalerite shows significant depletions in Fe,Cd,Mn,Pb and Cu,and enrichments in Zn,Ag,Ge,Ga.The contents and ratios of trace element in sphalerite indicate that the ore formation temperature at Xiyi is low(200?300?).The sphalerite diagram and similar geological features with other typical lead-zinc deposits from China and abroad show that the Xiyi deposit has the features of Mississippi valley-type(MVT)deposit.The Co/Ni ratio of these two-stage pyrites is about 1,showing that they were formed at low temperature of sedimentary origin.Combined with the geological features and mineral geochemistry of the Xiyi lead-zinc ore deposit in Baoshan,Yunnan,it is suggested that the Xiyi deposit could be attributed to the MVT Pb-Zn deposit.