Mineralogy of Platinum-Group Elements and Gold in the Ophiolite-Related Placer of the River Bolshoy Khailyk, Western Sayans, Russia : сборник научных трудов
Библиографическое описание:Mineralogy of Platinum-Group Elements and Gold in the Ophiolite-Related Placer of the River Bolshoy Khailyk, Western Sayans, Russia : сборник научных трудов / A. Y. Barkov [et al.]. - Текст : непосредственный // Minerals. - 2018. - Vol. 8, Is. 6. - P. 247. - Cited Reference Count: 58. - Гранты: We are grateful to Liana Pospelova (Novosibirsk) for her expert assistance with the WDS EMP data. We thank two anonymous reviewers and the Editorial Board members, for their comments and improvements. A.Y.B. gratefully acknowledges a partial support of this investigation by the Russian Foundation for Basic Research (project # RFBR 16-05-00884). - Финансирующая организация: Russian Foundation for Basic Research [RFBR 16-05-00884]. - JUN. - ISSN 2075-163X, DOI 10.3390/min8060247.
Аннотация:We describe assemblages of platinum-group minerals (PGM) and associated PGE-Au phases found in alluvium along the River Bolshoy Khailyk, in the western Sayans, Russia. The river drains the Aktovrakskiy ophiolitic complex, part of the Kurtushibinskiy belt, as does the Zolotaya River similar to 15 km away, the site of other placer deposits. Three groups of alloy minerals are described: (1) Os-Ir-Ru compositions, which predominate, (2) Pt-Fe compositions of a Pt3Fe stoichiometry, and (3) Pt-Au-Cu alloys, which likely crystallized in the sequence from Au-(Cu)-bearing platinum, Pt(Au,Cu), Pt(Cu,Au), and PtAuCu2, to PtAu4Cu5. The general trends of crystallization of PGM appear to be: [Os-Ir-Ru alloys] -> Pt3Fe-type alloy (with inclusions of Ru-dominant alloy formed by exsolution or via replacement of the host Pt-Fe phase) -> Pt-Au-Cu alloys. We infer that Rh and Co mutually substitute for Fe, not Ni, and are incorporated into the pentlandite structure via a coupled mechanism of substitution: [Rh3+ + Co3+ + rectangle -> 3Fe(2+)]. Many of the Os-Ir-Ru and Pt-Fe grains have porous, fractured or altered rims that contain secondary PGE sulfide, arsenide, sulfarsenide, sulfoantimonide, gold, Pt-Ir-Ni-rich alloys, and rarer phases like Cu-rich bowieite and a Se-rich sulfarsenide of Pt. The accompanying pyroxene, chromian spinel and serpentine are highly magnesian, consistent with a primitive ultramafic source-rock. Whereas the alloy phases indicate a highly reducing environment, late assemblages indicate an oxygenated local environment leading to Fe-bearing Ru-Os oxide (zoned) and seleniferous accessory phases.
