Platinum group minerals from chromitites of northern part of the Voykar-Synya massif (Polar Ural): new data

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Дәйексөз келтіру

Толық мәтін

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Аннотация

In chromitites of northern part of the Voikar-Synya ultramafic massif, which is part of the Khadatinsky ophiolite belt of the Polar Urals, native osmium, Ir-containing native osmium, native iridium, hongshiite, As-containing laurite, Ru-Os-containing pentlandite, kuvaevite, unnamed PGE sulfide with non-ferrous metals, close in stoichiometry to formula Me2S3 (Me = Os, Ru, Cu, Pt, Ir, Fe, Pd, Ni, Rh), high-temperature metallic solid solution (Pd, Pt, Fe), stibiopalladinite, geversite, genkinite, unnamed PGM close in stoichiometry of formula (Pd, Ni, Rh)5AsSb, Pd3Sb and (Ni, Rh, Pt)Sb were the first time discovered and characterized along with previously known platinum group minerals (PGMs). The set of PGMs of massif has been expanded from 10 to 25 mineral spicies and varieties. PGMs from high-alumina chromitites are characterized by wider variety than those from high-chromium chromitites (15 and 9 mineral species, respectively). PGMs of both Os–Ir–Ru and Pt–Pd specializations were found in high-alumina chromitites. High-chromium chromitites are characterized mainly by Os–Ir–Ru specialization. Such feature of PGMs distribution is explained by low degree of partial melting of mantle source of high-alumina chromitites, compared to high-chromium chromitites, which experienced high-temperature partial melting with removal of easily mobile Pd group of PGMs in composition of melted basaltic melt. New data have been obtained on noble metal minerals in the composition of primary and secondary chromitite assemlages.

Толық мәтін

Рұқсат жабық

Авторлар туралы

A. Yurichev

Tomsk State University

Хат алмасуға жауапты Автор.
Email: juratur@yandex.ru
Ресей, Tomsk

A. Chernyshov

Tomsk State University

Email: juratur@yandex.ru
Ресей, Tomsk

E. Korbovyak

Tomsk State University

Email: juratur@yandex.ru
Ресей, Tomsk

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2. Fig. 1. Schematic geological map of the Voykar-Syninsky massif (Nikolskaya et al., 2021), with additions by the authors: 1 — Quaternary deposits; 2 — Paleozoic volcanic-sedimentary complexes, undivided; 3 — Proterozoic metamorphic complexes, undivided; 4—16 — Voykar-Rai-Iz ophiolite complex: 4 — dolerite dikes; 5 — quartz diorites; 6—9 — dunite-wehrlite-clinopyroxenite structural-material complex (SMC): 6 — gabbro, metagabbro; 7 — undivided dunites, wehrlites, clinopyroxenites; 8 — undivided wehrlites and dunites; 9 — dunites; 10—12 — dunite-harzburgite SMC: 10 — depleted harzburgites with dunite component; 11 — depleted harzburgites with dunite component of 10—30 %; 12 — dunites with chromium chromospinelides; 13—15 — harzburgite SMC: 13 — undepleted harzburgites with dunite component <10 %; 14 — undepleted harzburgites with dunite component of 10—30 %; 15 — dunites with aluminous chromospinelides; 16 — serpentinites; 17 — geological boundaries; 18 — discontinuities; 19 — thrusts; 20 — ore occurrences of chrome ores: a — identified within boundaries of massif, b — studied in this work (1 — Paitovskoe, 2 — No. 118, 3 — Morkovkinskoe). The inset shows diagram of the location of the Voykar-Synya massif in structure of the Polar Urals. Ultramafic massifs: I — Syum-Keu, II — Kharcheruzsky, III — Rai-Iz, IV — Voykar-Synya.

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3. Fig. 2. Samples of high-alumina chromitites from the Morkovkinskoe (a, б) and No. 118 (в) ore occurrences and high-chromium chromitites from the Paitovskoe ore occurrence (г) of the Voykar-Synya massif.

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4. Fig. 3. Composition of ore chrome-spinels from chromitites of northern part of the Voikar-Synya massif: a — on triple classification diagram of N. V. Pavlov (Pavlov, 1949): 1 — chromite, 2 — subferrichromite, 3 — aluminochromite, 4 — subferrialuminochromite, 5 — ferrialuminochromite, 6 — subalumoferrichromite, 7 — ferrichromite, 8 — chrompicotite, 9 — subferrichromepicotite, 10 — subalumochromemagnetite, 11 — chromomagnetite, 12 — picotite, 13 — magnetite. Geodynamic settings of formation according to data of (Barnes, Roeder, 2001) are plotted; б — on binary diagram reflecting origin of ore chrome-spinels and their type (Ghazi et al., 2011).

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5. Fig. 4. Micrographs of native elements, sulfides and sulfoarsenides in studied high-alumina chromitites of northern part of the Voikar-Synya massif (BSE mode): a — association of laurite, As-bearing laurite (Table 4, an. 11) and Ir-bearing osmium (Table 3, an. 7) in serpentine interstitium; б — polyphase inclusion of osmium (Table 3, an. 1) and erlichmanite (Table 4, an. 5) in serpentine interstitium; в-hypidiomorphic grain of laurite (Table 4, an. 3) at boundary of chromospinelide and serpentine aggregate; г — hypidiomorphic zoned grain of laurite (Table 4, an. 6) at boundary of chromospinel and serpentine aggregate; д — euhedral polyphase inclusion of zonal laurite (Table 4, an. 7) and irarsite (Table 6, an. 2) in serpentine interstitium; е — euhedral zoned grain of laurite (Table 4, an. 8) with inclusion of Ru–Os-bearing heazlewoodite (Table 4, an. 20) in marginal part of chromospinel grain; ж–и — zonal As-bearing laurite (Table 4, an. 17—19, respectively) and irarsite (Table 6, an. 3, 9) in silicate interstitium; к — hypidiomorphic polyphase inclusion of arsenic-bearing laurite (Table 4, an. 15) and irarsite (Table 6, an. 6) in chromospinel grain; л — polyphase inclusion of As-bearing laurite (Table 4, an. 9), irarsite (Table 6, an. 1) and Pt-Sb-bearing irarsite (Table 6, an. 12) at boundary of heazlewoodite and serpentine aggregate; м — isolated irregular inclusion of irarsite (Table 6, an. 10) in serpentine interstitium. Hereinafter: CrSp — chromospinelide; Hzl — heazlewoodite; Srp — serpentine; RuS2(I) — laurite of composition (Ru0.72—0.76Os0.15—0.18Ir0.03—0.07) S2; RuS2(II) — laurite of composition (Ru0.96—0.97Os0.00—0.03Ir0.01—0.02) S2.

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6. Fig. 5. Ternary diagrams for PGMs from chromitites of the Voykar-Synya massif: a — composition of native osmium, iridium and ruthenium. Immiscibility field according to (Harris, Cabri, 1991); б, в-composition of minerals of laurite—erlichmanite series, including arsenic-containing varieties. The highlighted areas of sulfides correspond to zonal grains: I — central part, II — marginal part; г, д — composition of intermetallics and antimonides of Pt and Pd in high-alumina chromitites of ore occurrence № 118.

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7. Fig. 6. Micrographs of native elements, sulfides and sulfoarsenides in high-chromium chromitites of the Paitovsky ore occurrence of the Voikar-Synya massif (BSE mode): а–е — euhedral laurite grains (Table 5, an. 10, 7, 4, 3, 9, respectively, except for b) encapsulated in chromospinelide, including those with inclusion of Ir-bearing osmium (Table 3, an. 14, 16, respectively), native iridium (Table 3, an. 18) and irarsite; ж — nanoaggregate of mixture of isoferroplatinum and Os-Ir alloy (Table 3, an. 20—21) in chromospinel grain; з — euhedral grain of Ru–Os-bearing pentlandite (Table 5, an. 14) with inclusion of irarsite (Table 6, an. 16); и — hypidiomorphic grain of pyrite (Table 2, an. 21—22) with inclusion of irarsite at boundary of chromospinel grain and serpentine interstitium; к — euhedral grain of millerite (Table 2, an. 17) with inclusion of Rh-bearing irarsite (Table 6, an. 18); л — euhedral grain of chalcocite (Table 2, an. 19) with inclusion of hollingworthite (Table 6, an. 20); м — polyphase grain of kuvaevite (Table 5, an. 17), PGE sulfide with non-ferrous metals, close in stoichiometry to formula Me2S3 (Table 5, an. 20), and undiagnosed mineral phase. Mlr — millerite; Py — pyrite; Pn(Ru-Os) — Ru–Os-containing pentlandite.

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8. Fig. 7. Microphotographs of intermetallides and antimonides of Pt and Pd in high-alumina chromitites of ore occurrence No. 118 of the Voykar-Synya massif (BSE mode): a — polyphase inclusion of geversite (Table 7, an. 14), irarsite (Table 6, an. 4) and unnamed phase (Ni, Rh, Pt)Sb (Table 7, an. 20) in serpentine interstitium; б — microinclusions of Pt and Pd antimonides and irarsite at boundary of transformed marginal zone of chromospinelide and serpentine aggregate; в-polyphase grains of genkinite (Table 7, an. 18) and Rh-bearing irarsite (Table 6, an. 13) in serpentine interstitium; г, д — microinclusions of stibiopalladinite (Table 7, an. 2) in association with heazlewoodite (Table 2, an. 4, 5) at boundary of transformed marginal zone of chromospinelide and serpentine aggregate; е — stibiopalladinite (Table 7, an. 8) with inclusion of sperrylite (Table 6, an. 15) and high-temperature Fe-containing Pd-Pt solid solution (Table 3, an. 11) in crack in chromospinelide grain “healed” with serpentine; ж, з — stibiopalladinite (Table 7, an. 7—9), geversite (Table 7, an. 16—17) and hongshiite (Table 3, an. 9) in association with heazlewoodite (Table 2, an. 6—7) at boundary of transformed marginal zone of chromospinelide and serpentine aggregate; и — unnamed phase Pd3Sb (Table 7, an. 12) at boundary of transformed marginal zone of chromospinelide and serpentine aggregate. Cr-Mgt — chromium magnetite; Opx — orthopyroxene.

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