Mineralogy of Platinum-Group Elements and Gold in the Ophiolite-Related Placer of the River Bolshoy Khailyk, Western Sayans, Russia

Autor: Andrei Y. Barkov, Robert F. Martin, Gennadiy I. Shvedov, Sergey A. Silyanov
Jazyk: angličtina
Rok vydání: 2018
Předmět:
Zdroj: Minerals, Vol 8, Iss 6, p 247 (2018)
Minerals
Volume 8
Issue 6
Popis: We describe assemblages of platinum-group minerals (PGM) and associated PGE&ndash
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 ~15 km away, the site of other placer deposits. Three groups of alloy minerals are described: (1) Os&ndash
Ir&ndash
Ru compositions, which predominate, (2) Pt&ndash
Fe compositions of a Pt3Fe stoichiometry, and (3) Pt&ndash
Au&ndash
Cu alloys, which likely crystallized in the sequence from Au&ndash
(Cu)-bearing platinum, Pt(Au,Cu), Pt(Cu,Au), and PtAuCu2, to PtAu4Cu5. The general trends of crystallization of PGM appear to be: [Os&ndash
Ru alloys] &rarr
Pt3Fe-type alloy (with inclusions of Ru-dominant alloy formed by exsolution or via replacement of the host Pt&ndash
Fe phase) &rarr
Pt&ndash
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+ + □ &rarr
3Fe2+]. Many of the Os&ndash
Ru and Pt&ndash
Fe grains have porous, fractured or altered rims that contain secondary PGE sulfide, arsenide, sulfarsenide, sulfoantimonide, gold, Pt&ndash
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&ndash
Os oxide (zoned) and seleniferous accessory phases.
Databáze: OpenAIRE
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