TY - JOUR

T1 - Multi-Stage Magmatic-Hydrothermal Sulfide-PGE Mineralization of the Khudolaz Complex (South Urals)

AU - Rakhimov, I. R.

AU - Vishnevskiy, A. V.

AU - Saveliev, D. E.

AU - Salikhov, D. N.

AU - Vladimirov, A. G.

N1 - Funding Information: The research was carried out with the financial support of the Russian Foundation for Basic Research (project no. 18-35-00391) and the state task of IG UFRC RAS (topic no. 0246-2019-0080). Publisher Copyright: © 2021, Pleiades Publishing, Ltd.

PY - 2021/7

Y1 - 2021/7

N2 - For the first time, from the standpoint of magmatism and subsequent hydrothermal–metasomatic alteration, sulfide and platinum-metal mineral assemblages of rocks of ore-bearing intrusions of the Khudolaz Complex have been characterized. Four types of assemblages have been identified: (1) pentlandite–chalcopyrite–pyrrhotite in the form of drop-shaped and interstitial disseminations with inclusions of sperrylite, moncheite, michenerite, merenskyite, froodite; (2) complex amoebalike inclusions with the composition pyrite ± pyrrhotite–chalcopyrite–violarite ± pentlandite with inclusions of Sb–michenerite, sudburyite, and borovskite; (3) newly formed pyrite–chalcopyrite veins and patches in intensely metasomatized rocks; (4) additionally-formed euhedral pyrite disseminations in metasomatites along zones intersected by dolerite dikes. The formation of these sulfide–platinum-metal assemblages occurred in three stages: (1) magmatic and late magmatic (type 1), 2) hydrothermal–early medium temperature and late low-temperature (types 2, 3), (3) repeated hydrothermal–low–medium temperature (type 4). It is shown that the crystallization of sulfide minerals occurred in a wide temperature range (about 1000–200°C). PGE minerals separated at the late magmatic stage during cooling of a highly fractionated sulfide or immiscible chalcogenide melt and during decomposition of sulfide solid solutions (T ~ 650–300°C). At the early hydrothermal stage (T ~ 300–250°C), pyrrhotite was replaced by pyrite; pentlandite, by violarite; a significant amount of Ni and Co from primary sulfides was inherited by secondary sulfides. Primary chalcopyrite was mainly replaced by silicates (chlorite, amphibole, etc.). It is suggested that the antimony minerals of Pd (including high-antimony michenerite with Sb up to 0.46 apfu) could have crystallized from an Sb-enriched hydrothermal fluid. Host rocks could have been an additional source of antimony in the fluid. At the late hydrothermal stage (T < 200°C), significant dissolution of primary sulfide and platinum-metal phases occurred with redeposition in the upper parts of massifs and in host rocks. The recurring hydrothermal process (T ≤ 200°C) was associated with emplacement of dikes of the Ulugurtau complex and new redeposition of sulfides along zones of fluid action.

AB - For the first time, from the standpoint of magmatism and subsequent hydrothermal–metasomatic alteration, sulfide and platinum-metal mineral assemblages of rocks of ore-bearing intrusions of the Khudolaz Complex have been characterized. Four types of assemblages have been identified: (1) pentlandite–chalcopyrite–pyrrhotite in the form of drop-shaped and interstitial disseminations with inclusions of sperrylite, moncheite, michenerite, merenskyite, froodite; (2) complex amoebalike inclusions with the composition pyrite ± pyrrhotite–chalcopyrite–violarite ± pentlandite with inclusions of Sb–michenerite, sudburyite, and borovskite; (3) newly formed pyrite–chalcopyrite veins and patches in intensely metasomatized rocks; (4) additionally-formed euhedral pyrite disseminations in metasomatites along zones intersected by dolerite dikes. The formation of these sulfide–platinum-metal assemblages occurred in three stages: (1) magmatic and late magmatic (type 1), 2) hydrothermal–early medium temperature and late low-temperature (types 2, 3), (3) repeated hydrothermal–low–medium temperature (type 4). It is shown that the crystallization of sulfide minerals occurred in a wide temperature range (about 1000–200°C). PGE minerals separated at the late magmatic stage during cooling of a highly fractionated sulfide or immiscible chalcogenide melt and during decomposition of sulfide solid solutions (T ~ 650–300°C). At the early hydrothermal stage (T ~ 300–250°C), pyrrhotite was replaced by pyrite; pentlandite, by violarite; a significant amount of Ni and Co from primary sulfides was inherited by secondary sulfides. Primary chalcopyrite was mainly replaced by silicates (chlorite, amphibole, etc.). It is suggested that the antimony minerals of Pd (including high-antimony michenerite with Sb up to 0.46 apfu) could have crystallized from an Sb-enriched hydrothermal fluid. Host rocks could have been an additional source of antimony in the fluid. At the late hydrothermal stage (T < 200°C), significant dissolution of primary sulfide and platinum-metal phases occurred with redeposition in the upper parts of massifs and in host rocks. The recurring hydrothermal process (T ≤ 200°C) was associated with emplacement of dikes of the Ulugurtau complex and new redeposition of sulfides along zones of fluid action.

KW - hydrothermal fluid

KW - Khudolaz Complex

KW - mafic–ultramafic magmatism

KW - michenerite

KW - platinum-metal mineralization

KW - sulfide melt

UR - http://www.scopus.com/inward/record.url?scp=85113370815&partnerID=8YFLogxK

U2 - 10.1134/S1075701521040061

DO - 10.1134/S1075701521040061

M3 - Article

AN - SCOPUS:85113370815

VL - 63

SP - 341

EP - 367

JO - Geology of Ore Deposits

JF - Geology of Ore Deposits

SN - 1075-7015

IS - 4

M1 - 4

ER -