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Minerals 2018, 8(6), 247; https://doi.org/10.3390/min8060247

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

1
Research Laboratory of Industrial and Ore Mineralogy, Cherepovets State University, 5 Lunacharsky Avenue, 162600 Cherepovets, Russia
2
Institute of Mining, Geology and Geotechnology, Siberian Federal University, 95 Avenue Prospekt im. gazety “Krasnoyarskiy Rabochiy”, 660025 Krasnoyarsk, Russia
3
Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC H3A 0E8, Canada
*
Author to whom correspondence should be addressed.
Received: 21 May 2018 / Revised: 4 June 2018 / Accepted: 5 June 2018 / Published: 12 June 2018
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Abstract

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 ~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+ + □ → 3Fe2+]. 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. View Full-Text
Keywords: platinum-group elements; gold; platinum-group minerals; placer deposits; ophiolite complexes; western Sayans; Russia platinum-group elements; gold; platinum-group minerals; placer deposits; ophiolite complexes; western Sayans; Russia
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Barkov, A.Y.; Shvedov, G.I.; Silyanov, S.A.; Martin, R.F. Mineralogy of Platinum-Group Elements and Gold in the Ophiolite-Related Placer of the River Bolshoy Khailyk, Western Sayans, Russia. Minerals 2018, 8, 247.

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