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Compositions of the tolovkite-irarsite-hollingworthite solid solutions from the Bolshoy Khailyk deposit.
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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 all...
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Compositional variations of major and minor elements were examined in Pt–Fe alloys from various geological settings and types of deposits, both lode and placer occurrences. They included representatives of layered intrusions, Alaskan-Uralian-(Aldan)-type and alkaline gabbroic complexes, ophiolitic chromitites, and numerous placers from Canada, USA,...
Citations
... They were found in placers, including those formed due to erosion of gold ore deposits. Iridium selenides with Os-Te impurities were found out in gold pacers of the Aunik (Western Transbaikalia) (Ayriyants et al., 2020); Ir(As,Se,S) 2 compounds (Tolstykh et al, 1997) and (Pt,Rh)(As,Se,S), PtSe 2 (Barkov et al., 2018) in alluvial placers of the West Sayan (Kurtushibinsky ophiolite complex); in the alluvial placers of the East Sayan, Ir-PGE selenides and selenoarsenides were found (Kiseleva et al., 2021;Ayriyants et al., 2022). ...
... Magmatic laurite is nearly completely depleted in Se compared to magmatic Se-bearing sulfides (Hattori et al., 2004). The finds of natural Se and Ir-subgroup PGE compounds are rare, although due to the development of high-resolution electron microscopy, the number of such finds has increased (Tolstykh et al., 1997;Barkov et al., 2017Barkov et al., , 2018Airiyants et al., 2020;Kiseleva et al., 2021). The first information about the finding of Ru selenide in chromitites of the East Sayan appeared in 2016 (Kiseleva et al., 2016). ...
... These relationships suggest that Rh substitutes more readily for Fe for an indeterminate crystal-chemical reason. A related case may be seen in the substitution involving Rh and Co, documented in pentlandite at Bolshoy Khailyk, western Sayans, Russia: Rh 3þ þ Co 3þ þ h ? 3 Fe 2þ (Barkov et al. 2018c). In both these schemes, a possible involvement of Fe 3þ could explain the relationship observed between Rh and Fe. 8. (a, b) Torryweiserite, ferrotorryweiserite, tamuraite, and kuvaevite, which form an extensive series of mutual solid solutions (Barkov et al. 2022), are closely associated with the Rh-(Ru)-bearing pentlandite-related minerals (Figs. ...
The textures and chemical compositions (based on the results of over 1000 analyses) of a suite of platinum-group minerals obtained from concentrates collected along the River Ko watershed in the Sisim placer zone, Eastern Sayans, Russia, have been analyzed and described. Detrital grains of Ir–Os alloy, considered to have been derived from the Lysanskiy layered ultrabasic complex, are interpreted to be domains of melt in the interstices of olivine–chromian spinel cumulates. This melt fractionated before crystallization of the alloys; some domains show a core-to-rim enrichment in Ir. The incompatible behavior of lithophile elements, base metals, S, semimetals, and H2O in the melt now represented by the alloy led to the crystallization of a broad range of ore minerals in multicomponent globules of residual melt. In this way, laurite and cuproiridsite developed in the melt and now are in a symplectitic intergrowth with the alloy. A spherule of laurite with a core of anthophyllite-rich amphibole and a mantle of irarsite shows that H2O and lithophile components were also present in the PGE-rich melt. Rhodium-rich pentlandite-related minerals, likely including oberthürite, postdate the crystallization of laurite; these may be Ru-enriched and may contain lamellar grains of torryweiserite or ferrotorryweiserite, both of which may represent exsolution products. These two species, and the related kuvaevite, which locally replace the Rh-rich pentlandite-related minerals, appear to be paragenetically later. The new data provide valuable insight on the evolution of late, multicomponent melts in basic–ultrabasic complexes.
... The podiform chromitites and PGE mineralization of the ultrabasic massifs and ophiolite complexes within the Central Asian fold belt (Altai-Sayan region) have been investigated in some previous studies, including the ultrabasic massifs in ophiolite complexes of Tuva [20], Western Sayan (Kalna ultrabasic massif [21], Aktovrakskiy complex [22][23][24]), and Eastern Sayan (Ospa-Kitoy ultrabasic massif [25][26][27][28][29]). However, there are only a few records of PGE mineralization in alluvial sediments in the Eastern Sayan [30], and there are practically no detailed studies. ...
... The size of the oxide does not allow the calculation of the mineral formula, but according to the atomic ratio, it corresponds to the AO 2 stoichiometry. Oxides of the PGE are currently described in the platinum mineralization of ophiolite complexes of the Urals, Finland, and Oman [9,17,53], including in the alluvial deposits of Chukotka [53,54], Gornaya Shoria [55], Western Sayan [23], among others. ...
... Compounds of selenides and tellurides of the iridium subgroup of PGE (IPGE: Ir, Os, and Ru), as well as Se-rich phases of PGE, are exotic for ophiolite complexes. However, recently in the literature, there have been more and more references to findings of Se-enriched PGE compounds in ophiolite complexes and primitive ultrabasic rocks [22,23,46,56,57]. Barkov et al. [23] noted the predominance of stoichiometry of the AB 2 type for such compounds, with the formation of structures most optimal for the placement of Se under the given crystallization conditions. ...
The platinum-group minerals (PGM) in placer deposits provide important information on the types of their primary source rocks and ores and formation and alteration conditions. The article shows for the first time the results of a study of placer platinum mineralization found in the upper reaches of the Kitoy River (the southeastern part of the Eastern Sayan (SEPES)). Using modern methods of analysis (scanning electron microscopy), the authors studied the microtextural features of platinum-group minerals (PGM), their composition, texture, morphology and composition of microinclusions, rims, and other types of changes. The PGM are Os‑Ir‑Ru alloys with a pronounced ruthenium trend. Many of the Os‑Ir‑Ru grains have porous, fractured, or altered rims that contain secondary PGE sulfides, arsenides, sulfarsenides, Ir-Ni-Fe alloys, and rarer selenides, arsenoselenides, and tellurides of the PGE. The data obtained made it possible to identify the root sources of PGM in the placer and to make assumptions about the stages of transformation of primary igneous Os-Ir-Ru alloys from bedrock to placer. We assume that there are several stages of alteration of high-temperature Os-Ir-Ru alloys. The late magmatic stage is associated with the effect of fluid-saturated residual melt enriched with S, As. The post-magmatic hydrothermal stage (under conditions of changing reducing conditions to oxidative ones) is associated with the formation of telluro-selenides and oxide phases of PGE. The preservation of poorly rounded and unrounded PGM grains in the placer suggests a short transport from their primary source. The source of the platinum-group minerals from the Kitoy River placer is the rocks of the Southern ophiolite branch of SEPES and, in particular, the southern plate of the Ospa-Kitoy ophiolite complex, and primarily chromitites.
... The placer deposits of the River Bolshoy Khailyk, western Sayans, in the Ermakovskiy district, southern Krasnoyarskiy kray of Russia [1] are known for assemblages of platinumgroup minerals (PGM) and associated PGE-Au phases. The river drains the Aktovrakskiy ophiolitic complex, part of the Kurtushibinskiy belt. ...
... 19)Σ0.98S1.02, a bornite-like phase, (Cu4.06Fe1.47)Σ5.53S4.5, and a godlevskite-like phase, Ni9.5S7.5. Less common and rare minerals include sperrylite, a zoned oxide Ru6Fe 3+ 2O15, and an uncommon variety of seleniferous and rhodiferous sperrylite (Pt,Rh)(As,Se,S)2 [1,10]. ...
... The sulfide species observed in the placer are members of the laurite-erlichmanite series, cooperite, bowieite (Cu-rich), a monosulfide-type phase, (Fe 0.40 Ni 0.39 Cu 0.19 ) Σ0.98 S 1.02 , a bornite-like phase, (Cu 4.06 Fe 1.47 ) Σ5.53 S 4.5 , and a godlevskite-like phase, Ni 9.5 S 7.5 . Less common and rare minerals include sperrylite, a zoned oxide Ru 6 Fe 3+ 2 O 15 , and an uncommon variety of seleniferous and rhodiferous sperrylite (Pt,Rh)(As,Se,S) 2 [1,10]. ...
Citation: Barkov, A.Y.; Bindi, L.; Juárez-Arellano, E.A.; Tamura, N.; Shvedov, G.I.; Ma, C.; Martin, R.F. Unnamed Pt(Cu 0.67 Sn 0.33) from the Bolshoy Khailyk River, Western Sayans, Russia, and a Review of Related Compounds and Solid Solutions. Minerals 2021, 11, 1240. https://doi.org/10.3390/ min11111240 Academic Editors: Mark D. Welch and Sytle M. Antao Abstract: We describe a potentially new species of a platinum cupride-stannide mineral (PCSM) of composition Pt(Cu 0.67 Sn 0.33). It occurs in a placer deposit in the River Bolshoy Khailyk, southern Krasnoyarskiy kray, Russia. A synthetic equivalent of PCSM was obtained and characterized. The PCSM occurs as anhedral or subhedral grains up to 15 µm × 30 µm in association with various platinum-group minerals, Rh-Co-rich pentlandite and magnetite, all hosted by a placer grain of Cu-Au-Pt alloy. Synchrotron micro-Laue diffraction studies indicate that the PCSM mineral is tetragonal and belongs to the inferred space-group P4/mmm (#123). Its unit-cell parameters are a = 2.838 (3) Å, c = 3.650 (4) Å, and V = 29.40 (10) Å 3 , and Z = 1. The c:a ratio calculated from the unit-cell parameters is 1.286. These characteristics are in good agreement with those obtained for specimens of synthetic Pt(Cu 0.67 Sn 0.33). A review on related minerals and unnamed phases is provided to outline compositional variations and extents of solid solutions in the relevant systems PtNi-PtFe-PtCu, PdCu-PdHg-PdAu, PdHg-PtHg, and AuCu-PtCu. The PCSM-bearing mineralization appears to be related genetically with an ophiolitic source-rock of the Aktovrakskiy complex of the western Sayans. The unnamed phase likely crystallized from microvolumes of a highly fractionated melt rich in Cu and Sn.
... On the basis of a structural analogy with pentlandite, one can expect that levels of f S 2 play an important role in controlling the Ni:Fe ratio in argentopentlandite. Another example of coupled substution, involving Rh and Co, was reported for pentlandite at Bolshoy Khailyk, western Sayans, Russia: Rh 3+ + Co 3+ + → 3 Fe 2+ [39]. Related schemes of coupled substitution may well be common in pentlandite-type phases in other deposits. ...
Highly atypical mineralization involving Pd-Pt, Au-Ag, REE, Y, Zr, U, Th, and Cl-F-enriched minerals is found in zones with base metal sulfides (BMS; ~5 vol.% to 20 vol.%) in the eastern portion of the Oktyabrsky deposit in the Norilsk complex (Russia). The overall variations in Mg# index, 100 Mg/(Mg + Fe2+ + Mn), in host-rock minerals are 79.8 → 74.1 in olivine, 77.7 → 65.3 in orthopyroxene, 79.9 → 9.2 in clinopyroxene, and An79.0 → An3.7. The span of clinopyroxene and plagioclase compositions reflects their protracted crystallization from early magmatic to late interstitial associations. The magnesian chromite (Mg# 43.9) trends towards Cr-bearing magnetite with progressive buildups in oxygen fugacity; ilmenite varies from early Mg-rich to late Mn-rich variants. The main BMS are chalcopyrite, pyrrhotite, troilite, and Co-bearing pentlandite, with less abundant cubanite (or isocubanite), rare bornite, Co-bearing pyrite, Cd-bearing sphalerite (or wurtzite), altaite, members of the galena-clausthalite series and nickeline. A full series of Au-Ag alloy compositions is found with minor hessite, acanthite and argentopentlandite. The uncommon assemblage includes monazite-(Ce), thorite-coffinite, thorianite, uraninite, zirconolite, baddeleyite, zircon, bastnäsite-(La), and an unnamed metamict Y-dominant zirconolite-related mineral. About 20 species of PGM (platinum group minerals) were analyzed, including Pd-Pt tellurides, bismuthotellurides, bismuthides and stannides, Pd antimonides and plumbides, a Pd-Ag telluride, a Pt arsenide, a Pd-Ni arsenide, and unnamed Pd stannide-arsenide, Pd germanide-arsenide and Pt-Cu arseno-oxysulfide. The atypical assemblages are associated with Cl-rich annite with up to 7.54 wt.% Cl, Cl-rich hastingsite with up 4.06 wt.% Cl, ferro-hornblende (2.53 wt.% Cl), chlorapatite (>6 wt.% Cl) and extensive solid solutions of chlorapatite, fluorapatite and hydroxylapatite, Cl-bearing members of the chlorite group (chamosite; up to 0.96 wt.% Cl), and a Cl-bearing serpentine (up to 0.79 wt.% Cl). A decoupling of Cl and F in the geochemically evolved system is evident. The complex assemblages formed late from Cl-enriched fluids under subsolidus conditions of crystallization following extensive magmatic differentiation in the ore-bearing sequences.
... Thirdly, the co-occurrence of gold and PGM derived from ultrabasic lithologies in placer deposits has been reported in many districts worldwide but there is not always a genetic relationship. Compositional studies of both gold and PGMs can indicate an association (Fig. 5, and Zaykov et al. 2017;Barkov et al. 2018) or absence of an association (Svetlitskaya et al. 2018). Gold genetically related to PGM may show distinctive characteristics such as those illustrated in Figure 3k-m. ...
Detrital gold fulfils the criteria of chemical inertia and physical durability required by indicator minerals but it has not found wide application in this role because it may be formed in different deposit types. This problem is soluble, because the generic compositional features of hydrothermal gold differ according to mineralization environment. The wide distribution of gold as a minor component of mineralization where other commodities are the principle exploration target extends the potential of an indicator methodology based on detrital gold to beyond the search for gold itself. Here we highlight how distinctive gold compositional signatures derived from alloy composition and deposit- specific suites of mineral inclusions could contribute to exploration for Cu-Au porphyries, redox- controlled uranium mineralization and ultramafic-hosted PGE mineralization.
Future refinement this approach will focus on establishing the spatial distribution of elements at trace levels within gold particle sections using ToF-LA-ICP-MS and application of Exploratory Data Analysis to the resulting data sets. This approach is in its infancy, but aims to develop a classification algorithm useful to researchers irrespective of their previous experience. A pilot study has that random forests provide the best approach to establishing gold particle origins.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.5625450
... The presence of both PGE inclusions and elevated PGE concentrations, including Pt, in artefact gold relate to the exploitation of placer deposits where gold co-collects with PGMs (e.g. Meeks and Tite 1980;Junk and Pernicka 2003;Jansen et al. 2016;Borg et al. 2019); a scenario that is not uncommon worldwide (see also Nixon et al. 1990;Barkov et al. 2018). However, although the heavy mineral species may provide information on provenance in some cases, this is not always the case. ...
... (6) The mineralogical inventory of the heavy fraction of sediments is a consequence of the geology and mineralization within a river's drainage. Thus, heavy minerals from the host rocks of gold mineralization, such as cassiterite (e.g. in Cornwall, UK : Penhallurick 1986;Jackson et al. 1989), or from separate types of mineralization, such as PGMs (Nixon et al. 1990; Barkov et al. 2018), may be present in a gold placer, and their co-collection is inevitable. Incorporation into a smelting charge may result in either chemical modification of the alloy, e.g. with Sn (Raub 1995), or alteration of its physical characteristics, e.g. with PGM (Meeks and Tite 1980). ...
Compositional studies of natural gold usually have a geological focus, but are also important in archaeological provenancing. Both methodologies rely on compositional comparison of two sets of samples, one of which is geographically constrained. Here we describe how experiences in gold characterization resulting from geological studies are relevant to archaeology. Microchemical characterization of polished sections of natural gold identifies alloy compositions, alloy heterogeneity and mineral inclusions. Gold from all deposit types shows Cu and Sn values much lower than those recorded during numerous studies of artefacts. Inclusions in
artefact gold include various Cu- and Sn-bearing compounds which indicate specific high temperature reactions that could ultimately illuminate the conditions of (s)melting. The use of LA-ICP-MS to generate a wide range of elemental discriminants for provenance studies may be compromised by alloy adulteration and/or unrepresentative analysis of natural/artefact alloys, which are commonly highly heterogeneous at the micron scale. Geological studies normally characterize only the earliest-formed (hypogene) alloy, whereas archaeology-focused studies should entail analyses of bulk alloy compositions and impurities that may be incorporated during(s) melting. Isotopic-based provenancing alleviates many of these problems but, to date, generates regional rather than locality-specific targets. A dual isotopic�compositional approach is recommended.
... This feature is reminiscent of the synthesis of the pentlandite-type phase Rh(Ni 4 Fe 4 )S 8 at 700 • C, along with other Fe 4 Ni 4 MS 8 compounds (M = Ru, Pd) [8]. Rhodium is not associated with Co in compositions of the grains analyzed in the River Ko suite, in contrast to specimens of Rh-Co-bearing pentlandite from the River Bolshoy Khailyk deposit, in western Sayans, Russia, in which Rh and Co enter solid solution and substitute for Fe, not Ni, via a coupled mechanism of substitution: Rh 3+ + Co 3+ + → 3 Fe 2+ [9]. Several occurrences of PGE-rich pentlandite have been reported ( [10,11] and references therein). ...
Tamuraite, ideally Ir5Fe10S16, occurs as discrete phases (≤20 μm) in composite inclusions hosted by grains of osmium (≤0.5 mm across) rich in Ir, in association with other platinum-group minerals in the River Ko deposit of the Sisim Placer Zone, southern Krasnoyarskiy Kray, Russia. In droplet-like inclusions, tamuraite is typically intergrown with Rh-rich pentlandite and Ir-bearing members of the laurite–erlichmanite series (up to ~20 mol.% “IrS2”). Tamuraite is gray to brownish gray in reflected light. It is opaque, with a metallic luster. Its bireflectance is very weak to absent. It is nonpleochroic to slightly pleochroic (grayish to light brown tints). It appears to be very weakly anisotropic. The calculated density is 6.30 g·cm−3. The results of six WDS analyses are Ir 29.30 (27.75–30.68), Rh 9.57 (8.46–10.71), Pt 1.85 (1.43–2.10), Ru 0.05 (0.02–0.07), Os 0.06 (0.03–0.13), Fe 13.09 (12.38–13.74), Ni 12.18 (11.78–13.12), Cu 6.30 (6.06–6.56), Co 0.06 (0.04–0.07), S 27.23 (26.14–27.89), for a total of 99.69 wt %. This composition corresponds to (Ir2.87Rh1.75Pt0.18Ru0.01Os0.01)Σ4.82(Fe4.41Ni3.90Cu1.87Co0.02)Σ10.20S15.98, calculated based on a total of 31 atoms per formula unit. The general formula is (Ir,Rh)5(Fe,Ni,Cu)10S16. Results of synchrotron micro-Laue diffraction studies indicate that tamuraite is trigonal. Its probable space group is R–3m (#166), and the unit-cell parameters are a = 7.073(1) Å, c = 34.277(8) Å, V = 1485(1) Å3, and Z = 3. The c:a ratio is 4.8462. The strongest eight peaks in the X-ray diffraction pattern [d in Å(hkl)(I)] are: 3.0106(26)(100), 1.7699(40)(71), 1.7583(2016)(65), 2.7994(205)(56), 2.9963(1010)(50), 5.7740(10)(45), 3.0534(20)(43) and 2.4948(208)(38). The crystal structure is derivative of pentlandite and related to that of oberthürite and torryweiserite. Tamuraite crystallized from a residual melt enriched in S, Fe, Ni, Cu, and Rh; these elements were incompatible in the Os–Ir alloy that nucleated in lode zones of chromitites in the Lysanskiy layered complex, Eastern Sayans, Russia. The name honors Nobumichi Tamura, senior scientist at the Advanced Light Source of the Lawrence Berkeley National Laboratory, Berkeley, California.
... The Os plates in such grains form several distinct parallel systems, whose orientation is determined by the crystallographic properties of the mineral. Barkov et al. (2018) describe similar structures of exsolution of solid solutions in PGM from alluvial sediments of the Big Khailyk River, Western Sayan. They argue that the linear Os-Ir lamellae develop later and dissect the pre-existing Pt-Fe alloy; this Os-Ir alloy is thought to have appeared at the subsolidus stage. ...
... The presence of the various sulfide, arsenide, selenide and telluride inclusions suggests that the PGM had undergone a substantial metasomatic alteration. The metasomatic fluids of the post-magmatic stage were enriched in S, As, Te and Se (Barkov et al., 2018). The morphology and inter-relationship of these species in the inclusions indicates that metasomatism likely occurred in multiple stages, and the spatial relationship of the minerals in the inclusions (Fig. 6) helps understand the order of their formation. ...
... One of the last minerals to populate the cavities in the PGM is gold, which fills the remaining space between other minerals (Fig. 6a). Such metasomatic zones likely formed because of the increased levels of fS 2 and fAs 2 in the residual melt and congregation of insoluble components, such as Cu and Se, in the margins of PGM grains following or overlapping with the crystallization of the Pt-Fe alloy (Barkov et al., 2018). This resulted in the formation of a variety of low-temperature sulfide and arsenide minerals. ...
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.
... PGM and PGE-Au phases found in alluvium along the River Bolshoy Khailyk, in the western Sayans, Russia, have been described by Barkov et al [6]. Three groups of alloy are reported and an order of crystallization is suggested: 1) Os-Ir-Ru, 2) Pt 3 Fe, and 3) Pt-Au-Cu alloys, which likely crystallized in the sequence from Au-(Cu)-bearing platinum, Pt(Au,Cu), Pt(Cu,Au), and PtAuCu 2 , to PtAu 4 Cu 5 . ...
... Many of the Os-Ir-Ru and Pt-Fe grains have porous and altered rims that contain secondary PGM, gold, and rare Cu-rich bowieite and a Se-rich sulfarsenide of Pt. Barkov et al. [6] argued that the alloys precipitated in a highly reducing environment. Late assemblages indicate the presence of an oxygenated local environment leading to Fe-bearing Ru-Os oxide and seleniferous minerals. ...
The platinum-group minerals (PGM) consist of a group of accessory minerals that concentrate the six platinum-group elements (PGE): osmium (Os), iridium (Ir), ruthenium (Ru), rhodium (Rh), platinum (Pt), and palladium (Pd) [...]
