| The Yangshan gold deposit,lying in the trigonal area in northern Yangtze Plate,southern Sino-Korean Plate,and eastern Songpan-Ganzi fold systems,develops in the sedimentary rock systems bearing coal-silica-mud-dust materials in Devonian Sanhekou Group,is controlled by faults and occurs as veins and stratoid orebodies,the mineralizing phases of which can be subdivided into quartz-little pyrite,quartz-pyrite-arsenopyrite and quartz-stibnite in the early mineralizing period,and quartz-carbonate veins in the late mineralizing period with the middle two being the main mineralizing phases.Mineralizing fluids are characterized by middle-low temperature,low salinity and high CO2 contents,with the characteristics of isotope components as follows:(1)δ18Ow in the early phase varies from 1 i.01‰ to 13.21 ‰,averaging to 11.85 ‰;the main phase ranges from 5.94 ‰ to 11.04 ‰,averaging to 8.89‰;the late phase changes from 4.48 ‰ to 6.45 ‰,averaging to 5.36 ‰;(2)the δD of mineralizing fluids falls in between-82‰ and-569‰,averaging to-71.82‰;(3)δ13C varies from-2.5‰ to-5.3‰.Based on H-O isotope studies,mineralizing fluids in the early and main phases originating from metamorphic waters or strata transforming hydrothermal solutions and lots of atmospheric waters mixing in them in the late phase can be obtained.According to C isotope studies,we conclude that CO2 in mineralizing fluids may originate from multiple sources,with carbonate rocks being one of them.In addition,Sanhekou Group and late Proterozoic-Triassic strata in western Qiling Mountains both consist of carbonate(coal)-bearing phyllite,siltstone and silicalite,which coincides with the lithologic characters indicated by C-isotope studies,showing late Proterozoic-Triassic strata in western Qiling Mountains(mainly Bikou Group)and Sanhekou Group are the main sources of mineralizing fluids in Yangshan gold deposit.In light of sulfur,plumbum and strontium isotope researches,following results can be achieved:(1)34S of pyrite,stibnite and arsenopyrite range from-4.7‰ to-0.5‰,averaging to-1.77‰,showing the characteristics of magmatic sulfur.Combining former δ34S data,we conclude that there can be several provenances which are mainly stratigraphic and magmatic sulfur.(2)The 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb of above sulfides are 17.552～18.759,averaging to 18.316,15.538～15.928,averaging to 15.663 and 37.894～39.293,averaging to 39.094 respectively.Comparison with Sanhekou Group,Bikou Group and granite porphyries indicates the mineralizing materials are mainly originated from Sanhekou and Bikou Group.Sr value of sulfides vary from 0.70798 to 0.71697,averaging to 0.71204,showing composite sources of mineralizing materials which are mainly originated from crust and little show characteristics of crust-mantle composite sources,coinciding with Pb isotope studies.Based on the comparison of geological and geochemistry characteristics of Yangshan Gold Deposit with Carlin-Carlin-like and orogenic gold deposits,we attribute it to Carlin-like gold deposit. |
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