TY - JOUR

T1 - Chemical composition and origin of platinum-group minerals from placers of the Aunik River, Buryatia, Russia

AU - Airiyants, Evgeniya V.

AU - Belyanin, Dmitriy K.

AU - Zhmodik, Sergei M.

AU - Agafonov, Leonid V.

AU - Romashkin, Pavel A.

N1 - Publisher Copyright: © 2020 Elsevier B.V. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/5

Y1 - 2020/5

N2 - Platinum group minerals (PGMs) are occasionally encountered in gold placers around the world. Most research related to the gold placer deposits focuses on the origin, migration and concentration of gold, the primary commercial mineral in the placers. Both origin and fate of PGM are rarely studied. The present study of PGM grains reveals complex relationships between the mineral phases within the grains, conforms to the published results on immiscibility within certain PGM solid solutions, presents evidence of alteration of PGMs, and shows the presence of unusual secondary minerals within the grains. The studied PGM grains are Os-Ir-Ru alloys and can be divided into two types based on their chemical composition. The first type is solid solutions enriched in Os and Ru bearing inclusions of silicates such as olivine, pyroxene and amphibole. The second type is enriched in Ir and Pt, with inclusions of sulfides, tellurides and selenides such as cuproiridsite, iridisite, malanite, cooperite, laurite, erlichmanite and tolovkite. These two types of PGM have been described in other regions and the first type was attributed to ophiolitic origin of the mineralization. The authors confirm this theory, and find that the PGM of the Aunik River placers likely originated from ophiolites of the Shamanskaya spreading zone, with a possible contribution from ultrabasic rocks of Ural-Alaskan type. The secondary mineralization of the PGM, especially prominent in the peripheral parts of many studied samples, is most likely the result of post-magmatic metasomatic alteration. Interestingly, an unnamed, new mineral phase (Ir,Os)Se2 was detected in a hydrothermally altered grain.

AB - Platinum group minerals (PGMs) are occasionally encountered in gold placers around the world. Most research related to the gold placer deposits focuses on the origin, migration and concentration of gold, the primary commercial mineral in the placers. Both origin and fate of PGM are rarely studied. The present study of PGM grains reveals complex relationships between the mineral phases within the grains, conforms to the published results on immiscibility within certain PGM solid solutions, presents evidence of alteration of PGMs, and shows the presence of unusual secondary minerals within the grains. The studied PGM grains are Os-Ir-Ru alloys and can be divided into two types based on their chemical composition. The first type is solid solutions enriched in Os and Ru bearing inclusions of silicates such as olivine, pyroxene and amphibole. The second type is enriched in Ir and Pt, with inclusions of sulfides, tellurides and selenides such as cuproiridsite, iridisite, malanite, cooperite, laurite, erlichmanite and tolovkite. These two types of PGM have been described in other regions and the first type was attributed to ophiolitic origin of the mineralization. The authors confirm this theory, and find that the PGM of the Aunik River placers likely originated from ophiolites of the Shamanskaya spreading zone, with a possible contribution from ultrabasic rocks of Ural-Alaskan type. The secondary mineralization of the PGM, especially prominent in the peripheral parts of many studied samples, is most likely the result of post-magmatic metasomatic alteration. Interestingly, an unnamed, new mineral phase (Ir,Os)Se2 was detected in a hydrothermally altered grain.

KW - Cumulate gabbro

KW - Iridium selenides

KW - Ophiolite

KW - PGM alteration

KW - PGM origin

KW - Placer deposits

KW - Platinum-group minerals

KW - Ruthenium trend

KW - Transbaikalia

KW - IKAT-BAGDARIN ZONE

KW - GOLD

KW - PEGUERA

KW - CHROMITITES

KW - LOMA CARIBE PERIDOTITE

KW - DEPOSITS

KW - INDICATORS

KW - PGM

KW - MINERALIZATION

KW - NI

UR - http://www.scopus.com/inward/record.url?scp=85081638924&partnerID=8YFLogxK

U2 - 10.1016/j.oregeorev.2020.103453

DO - 10.1016/j.oregeorev.2020.103453

M3 - Article

AN - SCOPUS:85081638924

VL - 120

JO - Ore Geology Reviews

JF - Ore Geology Reviews

SN - 0169-1368

M1 - 103453

ER -