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sulphates
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abstract aynak is the largest known copper deposit in afghanistan, with indicated resources of 240 mt grading 2.3% cu placing it in the ‘giant’ category. host rocks are neoproterozoic metasediments comprising dolomitic marble, carbonaceous quartz schist and quartz-biotite-dolomite schist con- taining garnet, scapolite and apatite. chalcopyrite and bornite dominate the hypogene ore with lesser pyrite, pyrrhotite, cobaltite and chalcocite, and rare sphalerite, molybdenite, uraninite and barite. sulphides occur as bedding-parallel laminae, disseminations, metamorphic segregations and crosscutting veins. sulphide δ34s ratios range –14.5 to +17.3‰ in bedded and disseminated sulphides (n = 34). this broad range favours biogenic reduction of seawater sulphate as a major source of sulphur, although thermochemical reduction processes are not precluded. the narrower δ34s range of –6 to +12.2‰ in vein and segregation sulphides (n = 21) suggests localized redistribution and partial homogenization during metamorphism. geochemical associations sug- gest that al, p, ca, ti and fe were primary sedimentary constituents whereas cu, mg, s, se, as, co and bi were introduced subsequently. we infer that aynak originated as a shale- and carbonate- hosted stratabound replacement deposit, resembling orebodies of the central african copperbelt, although underlying red-beds are absent at aynak and mafic volcanics were the probable copper source. these giant deposits formed worldwide in the cryogenian probably due to marine enrich- ment in copper, magnesium and sulphate coincident with profuse basaltic volcanism and ocean oxidation.
چکیده عینک بزرگترین کانسار شناخته شده مس در افغانستان است ، با منابع مشخص 240 mt با درجه بندی 2.3٪ مس آن را در گروه "غول" قرار داده است. سنگهای میزبان فراسنجهای نئوپروتروزوییک متشکل از سنگ مرمر دولومیتی ، شیار کوارتز کربنی و شیست دولومیت کوارتز بیوتیت حاوی گارنت ، اسکاپولیت و آپاتیت هستند. کالکوپیریت و بورنیت با کمبود پیریت ، پیروتیت ، کبالتیت و کالکوسیت و اسفالریت نادر ، مولیبدنیت ، اورانیت و باریت بر سنگ معدن هیپوژن مسلط می شوند