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Article

Ferrotorryweiserite, Rh5Fe10S16, a New Mineral Species from the Sisim Placer Zone, Eastern Sayans, Russia, and the Torryweiserite–Ferrotorryweiserite Series

1
Research Laboratory of Industrial and Ore Mineralogy, Cherepovets State University, 5 Lunacharsky Avenue, 162600 Cherepovets, Russia
2
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Science, 3 Avenue Prospekt Koptyuga, 630090 Novosibirsk, Russia
3
Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720-8229, USA
4
Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC H3A 0E8, Canada
5
Harquail School of Earth Sciences, Laurentian University, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6, Canada
6
Cabri Consulting Inc., 514 Queen Elizabeth Drive, Ottawa, ON K1S 3N4, Canada
*
Author to whom correspondence should be addressed.
Minerals 2021, 11(12), 1420; https://doi.org/10.3390/min11121420
Submission received: 29 October 2021 / Revised: 8 December 2021 / Accepted: 10 December 2021 / Published: 15 December 2021

Abstract

:
Ferrotorryweiserite, Rh5Fe10S16, occurs as small grains (≤20 µm) among droplet-like inclusions (up to 50 μm in diameter) of platinum-group minerals (PGM), in association with oberthürite or Rh-bearing pentlandite, laurite, and a Pt-Pd-Fe alloy (likely isoferroplatinum and Fe-Pd-enriched platinum), hosted by placer grains of Os-Ir alloy (≤0.5 mm) in the River Ko deposit. The latter is a part of the Sisim placer zone, which is likely derived from ultramafic units of the Lysanskiy layered complex, southern Krasnoyarskiy kray, Russia. The mineral is opaque, gray to brownish gray in reflected light, very weakly bireflectant, not pleochroic to weakly pleochroic (grayish to light brown tints), and weakly anisotropic. The calculated density is 5.93 g·cm–3. Mean results (and ranges) of four WDS analyses are: Ir 18.68 (15.55–21.96), Rh 18.34 (16.32–20.32), Pt 0.64 (0.19–1.14), Ru 0.03 (0.00–0.13), Os 0.07 (0.02–0.17), Fe 14.14 (13.63–14.64), Ni 13.63 (12.58–14.66), Cu 4.97 (3.42–6.41), Co 0.09 (0.07–0.11), S 29.06 (28.48–29.44), and total 99.66 wt.%. They correspond to the following formula calculated for a total of 31 atoms per formula unit: (Rh3.16Ir1.72Pt0.06Ru0.01Os0.01)Σ4.95(Fe4.48Ni4.11Cu1.38Co0.03)Σ10.00S16.05. The results of synchrotron micro-Laue diffraction studies indicate that ferrotorryweiserite is trigonal; its probable space group is R 3 ¯ m (#166) based on its Ni-analog, torryweiserite. The unit-cell parameters refined from 177 reflections are a = 7.069 (2) Å, c = 34.286 (11) Å, V = 1484 (1) Å3, and Z = 3. The c:a ratio is 4.8502. The strongest eight peaks in the X-ray diffraction pattern derived from results of micro-Laue diffraction study [d in Å(hkil)(I)] are 2.7950 (20 2 ¯ 5) (100); 5.7143 (0006) (60); 1.7671 (22 4 ¯ 0) (44.4); 3.0486 (20 2 ¯ 1) (39.4); 5.7650 (10 1 ¯ 2) (38.6); 2.5956 (20 2 ¯ 7) (37.8); 3.0058 (11 2 ¯ 6) (36.5); and 1.5029 (4 2 ¯   2 ¯ 12) (35.3). Ferrotorryweiserite and the associated PGM crystallized from microvolumes of residual melt at late stages of crystallization of grains of Os- and Ir-dominant alloys occurred in lode zones of chromitites of the Lysanskiy layered complex. In a particular case, the residual melt is disposed peripherally around a core containing a disequilibrium association of magnesian olivine (Fo72.9–75.6) and albite (Ab81.6–86.4), with the development of skeletal crystals of titaniferous augite: Wo40.8–43.2En26.5–29.3Fs20.3–22.6Aeg6.9–9.5 (2.82–3.12 wt.% TiO2). Ferrotorryweiserite represents the Fe-dominant analog of torryweiserite. We also report occurrences of ferrotorryweiserite in the Marathon deposit, Coldwell Complex, Ontario, Canada, and infer the existence of the torryweiserite–ferrotorryweiserite solid solution in other deposits and complexes.

1. Introduction

Ferrotorryweiserite, Rh5Fe10S16, is a new mineral species discovered in the River Ko suite, which represents part of the Sisim placer zone, south of Krasnoyarsk, Krasnoyarskiy kray, Russia (approximate location 54°45′ N, 93°09′ E). The mineral and its name were approved (IMA 2021-055) by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association [1]. Our aims are to describe its properties and to report, with reference to literature sources, on the probable existence of a complete solid-solution series between ferrotorryweiserite and torryweiserite, Rh5Ni10S16, discovered in the Marathon Cu-Pd deposit, Coldwell complex, Ontario, Canada [2,3,4]. Ferrotorryweiserite is also related to tamuraite, Ir5Fe10S16, and kuvaevite, Ir5Ni10S16 [5,6], which are other members of the torryweiserite family that also occur as inclusions in grains of Os-Ir alloy in heavy-mineral fractions of platinum-group minerals (PGM) in the placer zone of the Sisim river and its tributaries, rivers Ko and Seyba [7,8]. An evaluation of the economic potential of these placers had not yet been completed. The placer grains of PGM were likely derived from ultramafic units of the Lysanskiy layered complex, Eastern Sayans, south-central Siberia [9]. In relation to the series of ferrotorryweiserite–torryweiserite, we document an unusual occurrence of the association olivine-albite (Fo73–76 and Ab82–86) developed in the core of a globular inclusion hosted by a grain of iridium from the River Ko. Additional occurrences of members of the ferrotorryweiserite-torryweiserite series are expected in a variety of ore deposits associated with ultramafic-mafic complexes that are known to contain Rh- and Ir-based species of PGM, cf. [10,11].

2. Materials and Methods

Hundreds of grains of Os-Ir alloy minerals and inclusions were examined from placer suites in the Sisim zone. In some of these grains from the River Ko, ferrotorryweiserite occurs as composite inclusions in other PGM hosted by osmium enriched in Ir or, less commonly and inversely, by iridium enriched in Os.
Electron-microprobe analyses of ferrotorryweiserite and iridium were done at McGill University by means of wavelength spectrometry (WDS) using a JEOL JXA 8900L facility operated at 20 kV, 20 nA, with a beam diameter set at 3 μm. The following X-ray lines were used: CuKα, NiKα, FeKα, CoKα, IrLα, RhLα, PtLα, PdLβ, OsMα, RuLα, and SKα. Counting times were 20 s on the peak. The Phi-Rho-Z method of corrections was applied. The peak-overlap corrections included Fe → Co, Os → Ir, Ru → Pd, Ir → Pt, and Ru → Rh corrections. The standards used are pure metals for the platinum-group elements (PGE), Fe, Cu, Co, and pentlandite for Ni and S. Values of standard deviations (σ) are ≤0.2 wt.% for Ir, Pt, and Cu, ≤0.1 wt.% for Ru, Os, Fe, and Ni, and ≤0.05 wt.% for Rh, Co, and S.
The minerals were also analyzed via quantitative energy-dispersive spectrometry (EDS), at 20 kV and 1.6 nA, using a MIRA 3 LMU (Tescan Orsay Holding, Brno, Czech Republic) scanning electron microscope with an attached INCA Energy 450 XMax 80 (Oxford Instruments Nanoanalysis, Wycombe, UK) system at the Analytical Center for multi-elemental and isotope studies, SB RAS, Novosibirsk, Russia. The following X-ray lines were used: SiKα, TiKα, AlKα, CrKα, MgKα, FeKα, NaKα, KKα, CuKα, NiKα, CoKα, IrLα, RhLα, PtLα, and SKα. Minimum detection limits (2σ level) are ≤0.2 wt.% for S, Fe, Co, Ni, Cu; ≤0.4 wt.% for Rh; and ≤0.5–0.7 wt.% for Ir. Certified standards were used, such as pure metals, SiO2, TiO2, Al2O3, Cr2O3, and FeS2, along with diopside, albite, and orthoclase. The analytical error for the main components did not exceed 1–2 relative %.
Synchrotron micro-Laue diffraction studies, followed by monochromator energy scans, were performed on the holotype specimens of ferrotorryweiserite at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory, Berkeley, CA, USA. The Laue diffraction patterns were collected using a PILATUS 1M area detector operated in reflection geometry. The patterns were analyzed and indexed using the software package XMAS v.6 after Tamura, 2014 [12].

3. Results and Observations

3.1. Appearance, Properties, and Morphology

Ferrotorryweiserite occurs as small grains (≤20 µm), which are portions of composite, droplet-like inclusions (up to 50–70 μm in diameter) of PGM, mainly oberthürite or pentlandite enriched in Rh, laurite, Pt-(Pd)-Fe alloy (isoferroplatinum or Fe-Pd-rich platinum), braggite-vysotskite, vasilite, and chalcopyrite, hosted by placer grains of Os- or Ir-dominant Os-Ir alloys (≤0.5 mm across) (Figure 1 and Figure 2a,b). In general, the PGM assemblage is dominated by Os-Ir-Ru alloys, where osmium is a major species, and iridium is subordinate. Rutheniridosmine is rare. The compositional field is limited to the Ru-poor portion of the system Os–Ir–Ru by the line Ru:Ir = 1 in the entire Sisim–Ko–Seyba placer area [9]. In addition, ferrotorryweiserite has also been observed in the Marathon deposit, Coldwell Complex, Ontario, Canada, in association with torryweiserite and oberthürite, Rh3(Ni,Fe)32S32 [3].
Ferrotorryweiserite develops as anhedral grains; no evidence of twinning was observed. The c:a ratio calculated from the unit-cell parameters is 4.8502.
In reflected light, ferrotorryweiserite is gray to brownish gray. Bireflectance is very weak to absent. The mineral is not pleochroic or weakly pleochroic (gray to light brown tints). It is weakly anisotropic (gray to light yellow tints). Internal reflections were not observed; neither reflectance values nor streak could be examined because of the small grain sizes. The mineral is opaque; its luster is metallic. Fluorescence and tenacity were not determined, and hardness values (Mohs or micro-indentation) could not be measured owing to the small grain size. No cleavage or fracture were observed. The density also could not be measured. The calculated value of density, 5.93 g·cm−3, is based on the unit-cell volume (1484 Å3) derived from diffraction measurements by means of synchrotron radiation and the empirical formula.

3.2. Mineral Association and Compositions

The silicate core, mantled by the rim-like aggregate of grains of ferrotorryweiserite–torryweiserite and other PGM (Figure 1 and Figure 2b,c), is composed mainly of microgranular olivine, Fo73–76, with a subordinate quantity of sodic plagioclase enriched in albite: Ab82–86 (Table 1). The skeletal texture (Figure 1 and Figure 2b–d) is formed by lamellar grains of titaniferous augite (2.82–3.12 wt.% TiO2) enriched in the aegirine component: Wo41–43En27–29Fs20–23Aeg7–10, which is less magnesian (Mg# 53.8–59.3; Mg# = 100 Mg/(Mg + Fe2+ + Mn) than the olivine.
Various species of PGM and base-metal sulfides were recognized in association with ferrotorryweiserite: braggite-vysotskite, vasilite, laurite, oberthürite, or Rh-rich pentlandite, Pt-(Pd)-Fe alloys, and chalcopyrite (Table 2). Our compositions are consistent with pentlandite, corresponding to the general formula Rh(Ni4Fe4)S8 or (Rh, Co, Pd)(Ni4Fe4)S8, in which one atom per formula unit of Rh + Pd + Co likely enters a distinct site.

3.3. Chemical Composition and Formula of Ferrotorryweiserite

Mean results of electron-microprobe analyses (WDS) of four grains of ferrotorryweiserite, each based on four data-points (n = 4; Table 3), correspond to the following formula based on a total of 31 atoms per formula unit (apfu) by analogy and according to the structure of the Ni-dominant analog, i.e., torryweiserite [3]: (Rh3.16Ir1.72Pt0.06Ru0.01Os0.01)Σ4.95(Fe4.48Ni4.11Cu1.38Co0.03)Σ10.00S16.05.
Results of quantitative SEM/EDS analyses performed on additional grains of ferrotorryweiserite (n = 5; Table 3) are also in agreement, leading to (Rh3.31Ir1.64Pt0.03)Σ4.98(Fe4.33Ni3.79Cu1.74)Σ9.86S16.16. The simplified formula is (Rh,Ir)5(Fe,Ni,Cu)10S16. Consequently, the ideal formula, Rh5Fe10S16, based on the assumption that other elements are not essential, requires Rh 32.44, Fe 35.21, and S 32.34, total 100 wt.%.
The average of four WDS data points, carried out on specimens of ferrotorryweiserite from the Marathon deposit, Coldwell complex, Ontario, Canada, gives the formula (Rh4.59Ir0.11Pt0.06)Σ4.76(Fe4.62Ni3.58Cu1.66Co0.39)Σ10.24S15.99. A total value of all metals is notably stoichiometric (15 apfu) in this formula. Thus, a minor amount of a Fe-site cation is presumably present at the Rh site.
Compositional variations documented in the ferrotorryweiserite–torryweiserite series in the River Ko placer area are presented in Table 4. Compositions of grains of ferrotorryweiserite from other complexes and ore deposits are listed in Table 5.

3.4. Crystallography and Results of Synchrotron Micro-Laue Diffraction Study

A standard single-crystal study could not be conducted because of the small size of the grains. Thus, we have performed a synchrotron X-ray study, which also is a single-crystal diffraction technique, of ferrotorryweiserite grains analyzed by Laue microdiffraction at the 12.3.2 beam line of the Advanced Light Source (ALS). The Laue diffraction patterns were collected using a PILATUS 1M area detector operated in reflection geometry. The patterns were indexed and analyzed using XMAS v.6 (Tamura, 2014) [12]. Monochromator energy scans were used to determine the unit-cell parameters and to evaluate the basic symmetry features of ferrotorryweiserite.
Our results indicate that the mineral is trigonal, and the probable space group, R 3 ¯ m (#166), is inferred by analogy with the Ni-dominant analog, i.e., torryweiserite from the Marathon deposit, Coldwell complex, Ontario, Canada [2,3]. The unit-cell parameters obtained are a = 7.069 (2) Å, c = 34.286 (11) Å, V = 1484 (1) Å3, and Z = 3.
The X-ray powder-diffraction pattern derived for ferrotorryweiserite from results of synchrotron micro-Laue diffraction study (based on principles described in [12]) is listed in Table 6 together with the observed pattern for torryweiserite (IMA2020-048) from the Marathon deposit, Coldwell complex, Ontario, Canada [3]. The characteristics of ferrotorryweiserite are compared with those of related species in Table 7. Based on these results, it is inferred that ferrotorryweiserite is isostructural with torryweiserite. By analogy with the structural motif and assignments presented for torryweiserite by McDonald et al., 2021 [3], the crystal structure of ferrotorryweiserite is composed of three distinct layers of poly-hedra stacked along [001]. The first is a layer of Rh1S6 octahedra sharing edges; it has octahedral voids, such as are found in dioctahedral micas. The second is a mixed layer composed of Rh2S6 octahedra, Fe1S4, and Fe2S4 tetrahedra arranged in a pinwheel fashion, with Rh2S6 at the center. The third layer consists of a double sheet of Fe3S4 tetrahedra that share edges along [001] to form six-membered Fe3S4 rings. Thus, the structure is related to that of synthetic Cu4Sn7S16 [16]. It is described in detail and illustrated in the article on torryweiserite [3].

3.5. Name and Type Material

The name ferrotorryweiserite reflects its Fe-dominant composition as an analog of torryweiserite.
The holotype specimen of ferrotorryweiserite is deposited (catalog number: III-105/1) at the Central Siberian Geological Museum, Sobolev Institute of Geology and Mineralogy, Akademik Koptyug Avenue, no. 3, 630090 Novosibirsk, Russia.

4. Discussion

4.1. Relation to Other Species

As noted, ferrotorryweiserite Rh5Fe10S16 is isostructural with torryweiserite Rh5Ni10S16 [3] found at its type locality, the Marathon deposit, Coldwell complex, Ontario, Canada. Ferrotorryweiserite is the Fe-dominant analog of torryweiserite and is considered to form a complete series of solid solution with torryweiserite (Figure 3a,b; Table 4 and Table 5). Therefore, ferrotorryweiserite belongs to the torryweiserite family of sulfide minerals, which includes tamuraite Ir5Fe10S16 [5] and kuvaevite Ir5Ni10S16 [6] (Table 7), all of which crystallize in space group R 3 ¯ m (#166).
Ferrotorryweiserite is distinct from oberthürite (Rh3Ni32S32), both compositionally and structurally; the latter is a member of the pentlandite group (with a = 10.066(5) Å) first described from the Marathon deposit, Canada [3]. Ferrotorryweiserite also differs from ferhodsite [(Fe,Rh,Ir,Ni,Cu,Co,Pt)9−xS8] described from Nizhniy Tagil, Urals. The latter mineral has a tetragonal unit-cell (P42/n or P4/nmm) with parameters a = 10.009(5) and c = 9.840(8) Å [17]; in addition, note the critical comments in [18].

4.2. Genetic Implications and the Ferrotorryweiserite–Torryweiserite Series

The inferred terrane affinities and mineral associations indicate that the placer PGM grains with inclusions of the ferrotorryweiserite–torryweiserite solid solution are related to zones of chromitite within ultramafic units of the Lysanskiy layered complex of dunite–peridotite–gabbro. Indeed, detrital grains of chromian spinel (up to 16.6 wt.% MgO in magnesiochromite) are associated with PGM grains in the Sisim placer zone.
This complex is the likely primary source for the PGM-bearing placers for the entire Sisim placer zone. The direct intergrowths of PGM with an REE mineral, monazite-(Ce), documented at Sisim [9], resemble examples of atypical mineralization reported from the Oktyabrsky deposit, Norilsk complex, Russia [19]. Heterogeneous micro-inclusions rich in Ti, documented in the placer grains of PGM, are consistent with the inferred provenance related to the Lysanskiy complex, which is known to contain reserves of titanium [9]. The Ti-enriched composition of augite (Table 1) is notably consistent.
Members of the ferrotorryweiserite–torryweiserite series associated with the tamuraite-kuvaevite solid solution likely formed at an advanced stage of crystallization because of the buildup in sulfur in droplets of incompatible residual melt enriched in Ni, Fe, Cu, Rh, and lithophile elements during the formation of the alloys in lode zones of chromitites in the Lysanskiy layered complex, Eastern Sayans.
The extent of Fe-for-Ni substitution is determinative for members of the inferred ferrotorryweiserite–torryweiserite series (Figure 3a,b), as is reflected in data for related PGM from the River Ko placer, Eastern Sayans, Russia (this study), the Marathon deposit, Coldwell complex, Ontario, Canada [3], the Tulameen Alaskan-type complex, British Columbia, Canada [13], the Yubdo placer deposit in Ethiopia [14,20], and the Miass placer zone, southern Urals, Russia [15].
A plot of Fe vs. Ni (Figure 3a) shows a negative correlation (R = −0.73), calculated for Fe vs. Ni and based on a total of 39 data points available for members of the series, which contain substantial Cu. The Rh vs. Ir correlation is inverse (R = −0.97 for n = 39: Figure 3b). Note that correlations of Fe vs. Rh, Fe vs. Ir, Ni vs. Rh, and Ni vs. Ir all are statistically insignificant. Thus, the observed substitutions of Fe vs. Ni and Rh vs. Ir operate independently in the structure, and the PGE occupy crystallographic sites different from those of Ni+Fe. This is corroborated by crystal-chemical considerations reported for the type specimen of torryweiserite from the Marathon deposit, Coldwell complex, Ontario, Canada [3].

4.3. The Olivine-Plagioclase Inclusion and Its Significance

We describe the occurrence of a highly unusual core in a globular inclusion hosted by the Ir-Os alloy (Figure 1 and Figure 2b–d). It is composed of microgranular olivine, subordinate amounts of sodic plagioclase, and skeletal or lamellar grains of titaniferous augite. These silicates are rimmed by an intermediate member of the ferrotorryweiserite–torryweiserite solid solution, oberthürite or Rh-enriched pentlandite, laurite, vasilite, braggite-vysotskite, and other species.
There is a remote similarity with parageneses of olivine and plagioclase known in inclusions in carbonaceous chondrites, i.e., POIs [21] or, e.g., with the olivine-anorthite melt inclusions present in allivalite of the low-K tholeiitic island-arc series of the Kuril-Kamchatka island, Russia [22]. On the other hand, note that the association in the globule hosted by iridium differs drastically by its high enrichment in Na (Ab82–86), which clearly cannot have resulted from an equilibrium crystallization with olivine of the Fo73–76 composition. Thus, we infer metastable conditions of crystallization with effects of overcooling, which are consistent with the development of skeletal crystals of titaniferous augite in the core (Figure 2d).
Interestingly, the sulfide phases were deposited along the periphery and around the silicate core, thus indicating a highly efficient differentiation and fractionation of sulfur and ore components, PGE, Cu-Ni-Fe, in the late portion of residual melt crystallizing after the silicate globule. Laurite, inferred to be a result of magmatic crystallization, e.g., [23], occurs in the intimate association with palladium species, such as braggite-vysotskite (Figure 2b), which formed under submagmatic conditions, cf. [24]. These observations are consistent with the hydrothermal origin of laurite, as inferred in the Imandra complex, Russia [25], and could well imply a similarly low-temperature crystallization of laurite, ferrotorryweiserite, and associated species in the ore assemblage deposited in the rim assemblage.
The overall variations in compositions of the ferrotorryweiserite–torryweiserite series (Figure 3a,b) can reflect Ni/Fe and Rh/Ir ratios that vary importantly among droplets of fractionated melt or portions of fluid in various ore deposits. In addition, sulfur fugacities can also be important to control the Ni/Fe ratio, as is known in pentlandite, e.g., [26]. In the Marathon deposit, an increase in oxygen fugacity likely played a major role in the formation of torryweiserite-ferrotorryweiserite via the progressive oxidation of precursor grains of pentlandite and intermediate oberthürite [3].

Author Contributions

The authors wrote the article together. A.Y.B., R.F.M.: data analysis, conclusions, writing; N.D.T.: investigations, discussions, writing; N.T.: synchrotron X-ray micro-Laue diffraction study, writing; A.M.M., L.J.C.: discussions, conclusions, writing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported in part by the Russian Science Foundation (grant #22-27-00419).

Data Availability Statement

The data are available upon a reasonable request (from A.Y.B.).

Acknowledgments

This research used beamline 12.3.2 at the Advanced Light Source. A.Y.B. acknowledges that this study was supported in part by the Russian Foundation for Basic Research (project # RFBR 19-05-00181). A support from the Cherepovets State University is gratefully acknowledged (A.Y.B.). N.D.T. also acknowledges that this study was carried out within the framework of the state assignment of the Sobolev Institute of Geology and Mineralogy of the SB of the RAS, financed by the Ministry of Science and Higher Education of the Russian Federation. We appreciate the help of Lang Shi with the electron–microprobe analyses at McGill University. We thank the editorial board members and six anonymous reviewers for their constructive comments.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. A backscattered electron image (BSE) showing a rounded, subhedral grain of iridium enriched in Os (labeled Ir-Os) which hosts globular or elongate inclusions of PGE- and base-metal sulfides (gray in the BSE) from the River Ko placer. An intermediate member of the ferrotorryweiserite–torryweiserite series (labeled Ftyw) occurs as a portion of a composite and partial rim deposited around an olivine-plagioclase core (dark gray in the BSE), which includes skeletal forms of titaniferous augite. The host is epoxy. See Figure 2b–d for greater magnification and details.
Figure 1. A backscattered electron image (BSE) showing a rounded, subhedral grain of iridium enriched in Os (labeled Ir-Os) which hosts globular or elongate inclusions of PGE- and base-metal sulfides (gray in the BSE) from the River Ko placer. An intermediate member of the ferrotorryweiserite–torryweiserite series (labeled Ftyw) occurs as a portion of a composite and partial rim deposited around an olivine-plagioclase core (dark gray in the BSE), which includes skeletal forms of titaniferous augite. The host is epoxy. See Figure 2b–d for greater magnification and details.
Minerals 11 01420 g001
Figure 2. BSE images showing characteristic examples of droplet-like inclusions of platinum-group minerals (a,b) hosted by placer grains of Os-Ir alloys, which correspond to osmium or iridium (labeled Os-Ir and Ir-Os, respectively). Grains of ferrotorryweiserite (Ftyw), shown in (a), and inclusions of an intermediate member of the ferrotorryweiserite–torryweiserite series (b) are associated with oberthürite or Rh-rich pentlandite (Pn), a Pt-Fe alloy (possibly isoferroplatinum, Ifpt) or with related alloys of Pt-Fe and Pt-(Pd)-Fe compositions (labeled Pt-Fe and Pt-Pd-Fe), braggite-vysotskite (Bg), vasilite (Vs), and laurite (Lrt). Note the presence of an unusual intergrowth of silicate minerals (black in the BSE), which is composed of olivine (Ol; Fo73–76) and subordinate amounts of sodic plagioclase, Pl (Ab82–86), developed in the core of the globular inclusion shown in Figure 1 and Figure 2b. Forms with a skeletal texture (ST) are observed locally in the silicate core (bd), which is composed of titaniferous augite (Wo40.8–43.2En26.5–29.3Fs20.3–22.6Aeg6.9–9.5). The scale bar and symbols, relevant to (c), are shown in (b).
Figure 2. BSE images showing characteristic examples of droplet-like inclusions of platinum-group minerals (a,b) hosted by placer grains of Os-Ir alloys, which correspond to osmium or iridium (labeled Os-Ir and Ir-Os, respectively). Grains of ferrotorryweiserite (Ftyw), shown in (a), and inclusions of an intermediate member of the ferrotorryweiserite–torryweiserite series (b) are associated with oberthürite or Rh-rich pentlandite (Pn), a Pt-Fe alloy (possibly isoferroplatinum, Ifpt) or with related alloys of Pt-Fe and Pt-(Pd)-Fe compositions (labeled Pt-Fe and Pt-Pd-Fe), braggite-vysotskite (Bg), vasilite (Vs), and laurite (Lrt). Note the presence of an unusual intergrowth of silicate minerals (black in the BSE), which is composed of olivine (Ol; Fo73–76) and subordinate amounts of sodic plagioclase, Pl (Ab82–86), developed in the core of the globular inclusion shown in Figure 1 and Figure 2b. Forms with a skeletal texture (ST) are observed locally in the silicate core (bd), which is composed of titaniferous augite (Wo40.8–43.2En26.5–29.3Fs20.3–22.6Aeg6.9–9.5). The scale bar and symbols, relevant to (c), are shown in (b).
Minerals 11 01420 g002aMinerals 11 01420 g002b
Figure 3. Correlations of Fe vs. Ni (a) and Rh vs. Ir (b) (plotted in values of atoms per formula unit, apfu, calculated for a total of 31 apfu) that are observed in compositions of members of the ferrotorryweiserite (Ftyw)–torryweiserite (Tyw) series at River Ko, Eastern Sayans, Russia (this study), the Marathon deposit, Coldwell complex, Ontario, Canada [2,3,4], the Tulameen Alaskan-type complex, British Columbia, Canada [13], the Yubdo placer deposit in Ethiopia [14], and the Miass placer zone, southern Urals, Russia [15].
Figure 3. Correlations of Fe vs. Ni (a) and Rh vs. Ir (b) (plotted in values of atoms per formula unit, apfu, calculated for a total of 31 apfu) that are observed in compositions of members of the ferrotorryweiserite (Ftyw)–torryweiserite (Tyw) series at River Ko, Eastern Sayans, Russia (this study), the Marathon deposit, Coldwell complex, Ontario, Canada [2,3,4], the Tulameen Alaskan-type complex, British Columbia, Canada [13], the Yubdo placer deposit in Ethiopia [14], and the Miass placer zone, southern Urals, Russia [15].
Minerals 11 01420 g003
Table 1. Compositions of olivine, clinopyroxene, and plagioclase in the core of globular inclusion hosted by the grain of Ir-Os alloy in the River Ko area.
Table 1. Compositions of olivine, clinopyroxene, and plagioclase in the core of globular inclusion hosted by the grain of Ir-Os alloy in the River Ko area.
wt.%Ol-1Ol-2Ol-3Ol-4CpxPl-1Pl-2ApfuOl-1Ol-2Ol-3Ol-4CpxPl-1Pl-2
SiO237.9338.2138.7438.6847.2466.1767.71Si1.001.011.001.011.722.962.95
TiO200003.1200Ti00000.0900
Al2O3000013.1719.9920.39Al00000.571.051.05
FeO20.8023.0221.2322.6210.8100.40Fe0.460.510.460.500.3300.01
MnO0.370.3200.30000Mn0.010.0100.01000
MgO38.5936.8539.1937.018.740.220Mg1.511.451.511.440.4800
CaO0.380.430.560.5517.912.102.32Ca0.010.010.020.020.700.100.11
NiO0.620.560.600.61000Ni0.010.010.010.01000
Na2O00001.589.159.07Na00000.110.790.77
K2O00000.110.430.57K00000.010.020.03
Total98.6999.39100.3299.77102.6898.06100.46Fo (An)75.672.975.673.2-11.012.0
Fa (Ab)22.825.523.025.1-86.484.6
Tep (Or)0.40.400.3-2.73.5
Note: Results of quantitative energy-dispersive X-ray spectrometry (EDS) obtained in conjunction with scanning electron microscopy (SEM) are listed in weight %. Zero means “below detection”. Values of atoms per formula unit (apfu) are based on four oxygen atoms for olivine (Ol), six atoms for clinopyroxene (Cpx), and eight atoms for plagioclase (Pl). Values of end-member components are expressed in mol %, i.e., forsterite (Fo), fayalite (Fa), and tephroite (Tep) in olivine, and anorthite (An), albite (Ab), and orthoclase (Or) in plagioclase.
Table 2. Compositions of ore minerals associated with ferrotorryweiserite in the River Ko placer area.
Table 2. Compositions of ore minerals associated with ferrotorryweiserite in the River Ko placer area.
#MineralSFeCoNiCuRuRhIrOsPtPdTotal, wt.%
1Bg-122.600.3203.84000007.6864.4498.88
2Bg-222.500.3303.74000008.1364.4699.16
3Vs11.681.62003.620000082.1999.11
4Lrt-133.180.5100.50035.8904.0127.3800101.47
5Lrt-237.160.3500.46053.0404.884.030099.92
6Lrt-336.750.3800.44055.1301.903.340097.94
7Lrt-437.140.4800.73052.5106.414.7900102.06
8Pn-130.9325.10028.370011.72000096.12
9Pn-231.3625.25028.260011.7801.280097.93
10Pn-331.7130.310.9325.96007.210001.6597.77
11Ccp34.4829.1900.3732.9100000096.95
12Pt-Fe alloy-1012.3300.840000061.7221.1396.02
13Pt-Fe alloy-2011.7800.670000062.5222.6297.59
14Pt-Fe alloy-3010.0500.520000087.142.29100.00
15Pt-Fe alloy-4012.1202.230006.34072.980.9996.00
16Pt-Fe alloy-5011.8801.000.85000068.7713.9196.41
17Ir-dominant alloy00.3300.0201.190.7459.9735.122.000.1499.50
18Os-Ir alloy-10000.4208.95035.4256.1100100.90
19Os-Ir alloy-2000006.88042.6351.4800100.99
Atoms per formula unit (apfu)
# SFeCoNiCuRuRhIrOsPtPd
1 0.990.0100.09000000.060.85
2 0.990.0100.09000000.060.85
3 6.850.55001.070000014.53
4 1.970.0200.0200.6800.040.2700
5 1.990.0100.0100.9000.040.0400
6 1.980.0100.0100.9400.020.0300
7 1.980.0100.0200.8900.060.0400
8 8.153.8004.08000.960000
9 8.183.7804.03000.9600.0600
10 8.104.450.133.62000.570000.13
11 2.030.9900.010.98000000
12 029.4401.910000042.1826.47
13 027.9201.510000042.4328.14
14 027.3801.360000067.983.28
15 032.3205.660004.91055.721.39
16 029.2902.351.84000.00048.5318.00
17 01.1200.0502.201.3458.4934.621.920.25
18 0001.24015.40032.0551.3000
19 0000012.15039.5748.2800
Note: Results of quantitative SEM-EDS analyses (#1–16, 18, 19) and wavelength-dispersive X-ray spectrometry (WDS; #17) are listed in weight %. Zero means “below detection”. The atomic proportions are based on a total of 2 apfu for braggite-vysotskite, Bg (#1, 2), 23 apfu for vasilite, Vs (#3), 3 apfu for laurite, Lrt (#4–7), 17 apfu for oberthürite or Rh-rich pentlandite, Pn (#8–10), and 4 apfu for chalcopyrite, Ccp (#11). Compositions of Pt-(Pd)-Fe alloys (#12–16), iridium rich in Os (#17), and osmium rich in Ir (#18, 19) were recalculated based on a total of 100 at %. A minor amount of S (1.34 wt.%), present in analysis #15, is ascribed to interference from the associated sulfide. The slightly lower totals observed in some of the analyses are attributed to an insufficient volume of the grains.
Table 3. Chemical data for ferrotorryweiserite from the River Ko placer deposit.
Table 3. Chemical data for ferrotorryweiserite from the River Ko placer deposit.
ConstituentMean (wt.%) WDS *Range (wt.%)Mean (wt.%) EDS **Range (wt.%)
Cu4.973.42–6.416.186.01–6.43
Ni13.6312.58–14.6612.4611.18–12.90
Fe14.1413.63–14.6413.5213.24–14.18
Co0.090.07–0.1100
Ir18.6815.55–21.9617.6715.39–25.05
Rh18.3416.32–20.3219.0613.46–20.95
Pt0.640.19–1.140.340–1.72
Os0.070.02–0.1700
Ru0.030–0.1300
S29.0628.48–29.4429.0027.82–29.45
Total99.66 98.23
Note: * Results of WDS analyses; ** Results of quantitative SEM/EDS analyses. The mean values of WDS and EDS analyses are based on four and five data points, respectively. Zero means “not detected”.
Table 4. Compositions of members of the ferrotorryweiserite–torryweiserite series from the River Ko placer area.
Table 4. Compositions of members of the ferrotorryweiserite–torryweiserite series from the River Ko placer area.
#SFeCoNiCuRuRhIrOsPtTotal, wt.%
228.4814.640.0914.663.650.0016.3221.960.020.19100.02
328.9614.330.1114.543.420.0016.7821.460.020.3099.91
429.4413.630.0712.586.410.0019.9615.550.171.1498.96
529.3813.970.0712.746.400.1320.3215.750.070.9499.77
631.2013.580.1218.742.620.0129.324.240.000.1199.95
730.8113.430.1418.742.530.0429.404.500.000.2499.83
830.6913.330.1218.952.180.0328.994.300.030.3498.95
931.0013.230.1218.491.900.3230.994.000.000.04100.09
1031.0613.400.1118.882.290.0429.654.450.000.35100.23
1128.7812.310.0915.664.040.0716.7620.830.030.8899.45
1228.3112.450.0916.203.770.0616.6120.650.070.7999.00
1327.9512.090.0816.083.800.0516.4920.930.061.0998.63
1430.6813.200.1318.462.150.4430.144.1910.000.1599.53
1528.809.700.0516.377.150.0317.9317.940.041.9199.92
1628.599.560.0516.366.800.0217.5817.890.082.0498.95
1729.9713.630.0414.606.430.0523.9710.580.010.75100.03
1830.0013.090.0514.856.300.0123.9310.570.000.6299.42
Apfu(based on a total of 31 apfu)
#SFeCoNiCuRuRhIrOsPtΣPGEΣ(Fe,Ni,Cu,Co)ΣMe
115.994.550.034.530.990.002.852.040.000.024.9110.1015.01
215.894.690.034.471.030.002.842.040.000.024.9010.2115.11
316.104.570.034.410.960.002.911.990.000.034.929.9814.90
416.174.300.023.771.780.003.421.420.020.104.969.8714.83
516.044.380.023.801.760.023.461.430.010.085.009.9614.96
615.994.000.035.250.680.004.680.360.000.015.069.9515.01
715.903.980.045.280.660.014.730.390.000.025.149.9615.10
815.943.970.045.380.570.014.690.370.000.035.109.9615.06
915.983.910.035.200.490.054.980.340.000.005.389.6515.02
1015.963.950.035.300.590.014.750.380.000.035.169.8815.04
1116.123.960.034.791.140.012.921.950.000.084.979.9214.88
1215.954.020.034.981.070.012.921.940.010.074.9510.1115.05
1315.913.950.035.001.090.012.921.990.010.105.0310.0715.09
1415.923.930.045.230.560.074.870.360.000.015.329.7615.08
1515.993.090.024.962.000.013.101.660.000.174.9410.0715.01
1616.033.080.015.011.920.003.071.670.010.194.9410.0214.97
1715.914.150.014.231.720.013.960.940.000.074.9710.1215.09
1815.994.000.014.321.690.003.970.940.000.054.9710.0315.01
Note: These results of WDS analyses are listed in weight %, and values of atoms per formula unit (apfu) are based on a total of thirty-one atoms per formula unit (apfu). Zero means “not detected”. Analyses #1–5 pertain to ferrotorryweiserite, and #6–18 correspond to torryweiserite.
Table 5. Compositions of grains of ferrotorryweiserite from other localities.
Table 5. Compositions of grains of ferrotorryweiserite from other localities.
LocalityMarathonTulameenYubdoMiass
wt.%12345678910Mean
S32.6331.3830.4931.8230.0731.9032.1031.8031.9028.2231.23
Fe21.0514.0014.5513.9016.8316.3015.8015.6017.8014.9416.08
Co0.752.200.662.100.001.011.091.110.800.001.22
Ni10.1714.5712.5114.459.9611.5011.6011.6010.1012.5211.90
Cu5.756.447.126.645.784.714.344.054.713.325.29
Ru0.000.000.000.000.040.000.000.000.000.000.04
Rh28.7730.3925.5931.6520.9527.2027.4028.2026.5017.1422.07
Ag0.030.000.000.000.000.000.000.000.000.000.03
Ir0.000.005.340.0618.206.816.706.547.2122.969.23
Os0.000.000.000.050.150.000.000.000.000.000.10
Pt0.210.192.130.331.240.961.201.050.700.000.89
Total, wt.%99.3699.1798.39101.00103.22100.39100.2399.9599.7299.10100.05
apfu
S16.1615.8616.0615.8816.1016.4216.5516.4916.4816.0616.20
Fe5.994.064.403.985.174.824.684.645.284.884.79
Co0.200.610.190.570.000.280.310.310.230.000.34
Ni2.754.023.603.942.913.233.273.292.853.893.38
Cu1.441.641.891.671.561.221.131.061.230.951.38
Ru0.000.000.000.000.010.000.000.000.000.000.01
Rh4.444.794.204.923.504.364.404.564.263.044.25
Ag0.000.000.000.000.000.000.000.000.000.000.00
Ir0.000.000.47<0.011.630.590.580.570.622.180.83
Os0.000.000.00<0.010.010.000.000.000.000.000.01
Pt0.020.020.180.030.000.000.000.000.000.000.06
Total apfu31.0031.0031.0031.0030.8930.9230.9030.9130.9431.0031.24
ΣPGE (+Ag)4.464.804.804.805.144.954.985.124.895.224.88
ΣPGE/ΣMe14.8415.1414.8914.9714.7914.5014.3514.4314.4714.9414.71
Ni/Fe0.460.990.990.990.560.670.700.710.540.800.74
Fe/Ni2.181.011.221.011.781.491.431.411.851.251.51
Note: Minerals of ferrotorryweiserite composition are from the Marathon deposit, Coldwell complex, Ontario, Canada [2,3,4], the Tulameen Alaskan-type complex, British Columbia, Canada, after Aubut, 1979 [13], the Yubdo placer deposit in Ethiopia after Evstigneeva, 1992 [14], and the Miass placer zone, southern Urals, Russia, after Barkov et al., 2018 [15].
Table 6. X-ray powder-diffraction data (d in Å) for ferrotorryweiserite.
Table 6. X-ray powder-diffraction data (d in Å) for ferrotorryweiserite.
IndicesFerrotorryweiserite *Torryweiserite **
hkild (Å)Idobs (Å)dcalc (Å)IobsIcalc
000311.428710.0
10 1 ¯ 25.765038.6 5.758 6
00065.714360.8 5.712 12
11 2 ¯ 03.534310.73.5663.5301714
2 1 ¯ 1 ¯ 33.376520.2
20 2 ¯ 13.048639.43.0803.0453337
11 2 ¯ 63.005836.53.0293.00358100
10 1 ¯ 102.991421.3 2.990 51
20 2 ¯ 52.79501002.8172.7922360
20 2 ¯ 72.595637.8
2 1 ¯ 1 ¯ 92.59106.3
20 2 ¯ 82.490921.52.5082.4881714
3 1 ¯ 2 ¯ 12.292912.3
000152.28578.6 2.282 5
20 2 ¯ 102.283322.4
10 1 ¯ 142.27388.3
20 2 ¯ 112.183915.62.1992.1822123
3 1 ¯ 2 ¯ 72.092012.6
30 3 ¯ 32.00879.8
30 3 ¯ 61.92176.21.93291.91953025
000181.90486.2 1.9039 7
22 4 ¯ 01.767144.41.77971.765010077
20 2 ¯ 161.75549.1 1.7542 70
3 1 ¯ 2 ¯ 131.73937.2
4 2 ¯ 2 ¯ 61.68827.5
20 2 ¯ 171.684128.31.69291.683099
3 1 ¯ 2 ¯ 141.681820.3
40 4 ¯ 11.55451.31.53801.5270125
02 2 ¯ 191.52905.0
13 4 ¯ 101.52438.9 1.5199 12
30 3 ¯ 151.52232.2
4 2 ¯ 2 ¯ 121.502935.3
40 4 ¯ 51.493611.3 1.4920 10
31 4 ¯ 111.49102.7
4 2 ¯ 2 ¯ 151.39808.0
23 5 ¯ 51.37501.5
40 4 ¯ 111.37385.1 1.3723 5
20 2 ¯ 231.34028.3
41 5 ¯ 61.30084.81.30721.29922318
32 5 ¯ 101.29971.7
4 2 ¯ 2 ¯ 181.29557.4
40 4 ¯ 161.245423.81.25121.24424921
40 4 ¯ 171.21915.6
22 4 ¯ 211.19927.5 1.1982 12
11 2 ¯ 271.19512.2
42 6 ¯ 11.15631.31.15981.15171717
33 6 ¯ 61.15391.5
13 4 ¯ 221.14813.50
Note: Only reflections with I ≥ 5 are listed. * The PXRD pattern of ferrotorryweiserite derived from results of synchrotron micro-Laue diffraction study. ** The PXRD pattern of torryweiserite after McDonald et al. [3].
Table 7. Comparison of ferrotorryweiserite to related species.
Table 7. Comparison of ferrotorryweiserite to related species.
#SpeciesType LocalityIdeal FormulaUnit-Cell ParametersReference
1FerrotorryweiseriteRiver Ko deposit, Sisim placer zone, southwestern Eastern Sayans, RussiaRh5Fe10S16a = 7.069 (2) Å
c = 34.286 (11) Å
V = 1484 (1) Å3
and Z = 3
(This study)
2TorryweiseriteMarathon deposit, Coldwell complex, Ontario, CanadaRh5Ni10S16a = 7.060 (1) Å,
c = 34.271 (7) Å,
V = 1479.3 (1) Å3,
and Z = 3
McDonald et al., 2021 [3]
3TamuraiteRiver Ko depositIr5Fe10S16a = 7.073 (1) Å
c = 34.277 (8) Å
V = 1485 (1) Å3
and Z = 3
Barkov et al., 2021 [5]
4KuvaeviteRiver Ko depositIr5Ni10S16a = 7.079 (5) Å
c = 34.344 (12) Å
V = 1490 (2) Å3
and Z = 3
IMA2020-043 [6]
Note: Unit-cell parameters refined from 177 reflections indexed for the ferrotorryweiserite grain (Rh3.46Ir1.43Pt0.08Ru0.02Os0.01)Σ5.00(Fe4.38Ni3.80Cu1.76Co0.02)Σ9.96S16.04 studied by synchrotron micro-Laue diffraction. The space group R 3 ¯ m (#166) is inferred for these compounds by analogy with torryweiserite [3].
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Barkov, A.Y.; Tolstykh, N.D.; Tamura, N.; Martin, R.F.; McDonald, A.M.; Cabri, L.J. Ferrotorryweiserite, Rh5Fe10S16, a New Mineral Species from the Sisim Placer Zone, Eastern Sayans, Russia, and the Torryweiserite–Ferrotorryweiserite Series. Minerals 2021, 11, 1420. https://doi.org/10.3390/min11121420

AMA Style

Barkov AY, Tolstykh ND, Tamura N, Martin RF, McDonald AM, Cabri LJ. Ferrotorryweiserite, Rh5Fe10S16, a New Mineral Species from the Sisim Placer Zone, Eastern Sayans, Russia, and the Torryweiserite–Ferrotorryweiserite Series. Minerals. 2021; 11(12):1420. https://doi.org/10.3390/min11121420

Chicago/Turabian Style

Barkov, Andrei Y., Nadezhda D. Tolstykh, Nobumichi Tamura, Robert F. Martin, Andrew M. McDonald, and Louis J. Cabri. 2021. "Ferrotorryweiserite, Rh5Fe10S16, a New Mineral Species from the Sisim Placer Zone, Eastern Sayans, Russia, and the Torryweiserite–Ferrotorryweiserite Series" Minerals 11, no. 12: 1420. https://doi.org/10.3390/min11121420

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