The study of VHMS deposits was based on the new principles of ore-facies analysis. The different ore facies were mapped and sampled in the open pits of Sybay, Yaman-Kasy, Molodeznoe, Alexandrinskoe, Barsuchiy Log , Jusa, Balta-tau, Tash-Tau VHMS deposits open pit and Talgan, Mauk underground shaft. The mineralogy and trace elements geochemistry for stockwork veins vent chimneys, hydrothermal-biomorphic, clastic and halmyrolitic ore facies have been studied.
Each ore facies of the Urals VHMS deposits are characterised by specific mineralogical composition. Hydrothermal ore facies contain diverse tellurides and native gold. Native gold, electrum and rare hessite assemblages are common for ggrey smokersh vent chimneys from Alexandrinka deposits. Numerous Pb, Bi, Hg, Au, Ag, Co tellurides, telluroarsenides and tellurosulpoarsenides, native tellurium, tellurium oxide native gold have been identified in Yaman-Kasy black smokers vent chimneys. Electrum and Ag-rich sulphotellurides, sulphides, sulphosalts of these metals are more common for the seafloor altered clastic sulphides from VHMS deposits of island arcs (Utrennee, Zvezdnoe, Uvaryazh, Balta-Tau). There is a high diversity of Co-Ni arsenides and suphoarsenides. Traces of Pd (up to 0.5%) have been found by microprobe analysis in coloradoite and pentlandite.
Minerals of each ore facies and microfacies yield signatures of trace elements evolution during hydrothermal, hydrothermal sedimentary, seafloor alteration and metamorphic processes. The study has shown a systematic distribution pattern within the chimneys for two groups of trace elements. Group 1 elements (Mn, As, Tl, Pb, Ag and Au) are enriched in colloform pyrite in the outer-most section of the chinmey wall. This enrichment probably results from rapid precipitation of colloform pyrite under low temperature conditions. Pyrite euhedra, which result from the recrystallisation of colloform pyrite toward the inner wall, are depleted in the Group 1 elements. Group 2 elements (Bi, Ag and Au) are enriched in chalcopyrite along the boundary between the chalcopyrite inner wall and the sphalerite filled central conduit, where Bi, Ag, Au, Pb tellurides have been precipitated in a zone of strong temperature gradients. The main zone of chalcopyrite within the central inner wall is depleted in Group 2 elements, probably due to the high temperature of formation, which is unsuitable for telluride precipitation. Generally, trace element concentrations of chimneys increase with the decrease in chalcopyrite content from pyrite-chalcopyrite- to marcasite-chalcopyrite-sphalerite- to marcasite-quartz-rich chimneys, due to the decrease in temperature and increase in Eh of the black smoker and seawater fluids mixtures.
Trace elements diagenetic partition has been studied in sulphide sandstones. Diagenetic and mesogenetic subhedral pyrite in comparison to hydrothermal-sedimentary colloform pyrite is depleted in Tl, Mn, Au, Ag and is sometime enriched in Co. The free visible native gold and electrum grains formed clastic sulphides due to this process of diagenetic recrystallisation. Pseudomorphous chalcopyrite which was formed after pyrite was enriched by Mn and As in comparison with hydrothermal chalcopyrite incrustation. Hematite-rich gossany products of seafloor oxidation of clastic sulphides were depleted of chalcophile trace element. They contain only new elements as like Ni, V , Mn and Ba.
VHMS deposits of the South Urals generally show a continuum in degradation and reworking ranging from pristine steep-sided hydrothermal sulphide mounds to deposits dominated by layered strata of clastic sulphides. Four different deposits with varying degrees have been ranked in order of increased reworking: Yaman-Kasy (N.Sybay, Ozernoe, Komsomolskoe) Molodezhnoe (Uchaly, Chebachye, Yubileynoe, Blyava) Alexandrinskoe (Talgan, Barsuchiy Log, XIX parts fezda) Balta-Tau (Jusa, Babarik, Utrennee, Zvezdnoe, Uvaryazh). The influence of sulphide mound destruction and sea-floor alteration on the gold-silver-tellurium mineral assemblages was investigated. The mineral assemblages changed from Au, Ag, Hg, Co, Bi tellurides to Pb, Ag, Cu-sulphide+gold , then to Ag sulphosalts + electrum and kustelites wich were enriched by Hg, and Bi. The gold standard decreases from 930 in pyrite breccia to 450 and less in polymetallic barite-rich low temperature sea floor altered associations. We suggest that the mineralogy and siting of native gold, silver and tellurium are a consequence of cooling and/or oxidation of hydrothermal fluids and also of seafloor alteration of primary sulfides and tellurides. A geochemical classification of VHMS deposits using the degree of secondary enrichment of Ag and leaching of Te seems possible.