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Tellurium-bearing mineralization occurs in unusually well-preserved, mineralogically zoned hydrothermal vent chimney fragments from the Silurian and Devonian massive sulfide deposit of Yaman-Kasy, Spahyanovka, Valentorka and Alexandrinks at the Urals and Artemyevskoe, Nikolayevskoe at Rudniy Altay. Three main types of chimneys are identified by the composition: 1 chalcopyrite-pyrite; 2 pyrite-(marcasite)-chalcopyrite-sphalerite, and 3 ? sphalerite-pyrite-chalcopyrite. The mineralogical zonation shown by various chimneys is broadly comparable with those studied in modern black smoker chimneys, with the exception of the lack of evidence for the former initial chimney shell of anhydrite or silica. However, some chimneys show abundant tellurium-bearing phases, which are common for the Uralian and less for Kuroko types of massive sulphide deposits. In type 1 chimneys, tellurides are absent or rare, with occasional frohbergite, tellurobismuthite and altaite forming thin rims in the outermost part of the chalcopyrite zone. In type 2 chimneys, complex tellurium mineralization includes sylvanite, hessite-stuetzite (so-called γ-phase), petzite, empressite, coloradoite, tellurobismuthite, volynskite, altaite, goldfieldite, tellurium-rich cobaltite, Co-rich tellurian löllingite, native tellurium, unresolved tellurium oxides, goldfieldite, (Cu, Ag, Hg, Pb) (Fe, Te, Sb, As)-sulphosalts, and rare native gold. The mineralogical association of tellurides in 2 and 3 chimney types is quite different however. The gold, galena and tellurium-rich sulphosalts assemblages are more common for chimney type 3, but visible tellurides are rare. The broad sulfide zonation and specific site of tellurium-bearing phases can then be interpreted in terms of the extreme gradients of oxygen and sulfur fugacities as well as temperature across the vent chimney walls. The absence of tellurides in most chimneys of type 1 may be explained by the stability of HTe‾ in equilibrium with pyrrhotite whilst telluride phases are unstable. On the contrary, in chimney type 3, the inferred high-sulphidation and oxidation state inhibited the formation of tellurides. The intermediate conditions of type 2 chimneys were conducive to the deposition of tellurides. The development of sulphosalts, galena, native tellurium, tellurium oxides, and native gold in the various chimney types may be explained by contemporaneous sulphidation and oxidation, occurring during the interaction of reduced hydrothermal fluids and oxidized seawater. This data explains why Uralian type of massive sulfide deposits was enriched in tellurides and why there are rare in Cyprus and Kuroko types.
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