539
The Canadian Mineralogist
Vol. 42, pp. 539-544 (2004)

TARKIANITE, (Cu,Fe)(Re,Mo)4S8, A NEW MINERAL SPECIESFROM THE HITURA MINE, NIVALA, FINLANDKARI K. KOJONEN§
Geological Survey of Finland, FIN–02150 Espoo, Finland

ANDREW C. ROBERTS
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada

OLLI-PEKKA ISOMÄKI
Outokumpu Mining Oy, Hitura Mine, FIN–85560 Ainastalo, Finland

VLADIMIR V. KNAUF
NATI Research JSC, Otechestvennaya Street 3, Office 3a, RU–195030 St. Petersburg, Russia

BO JOHANSON AND LASSI PAKKANEN
Geological Survey of Finland, FIN–02150 Espoo, Finland

ABSTRACT
Tarkianite, a new mineral species of ideal composition (Cu,Fe)(Re,Mo)4S8, was recently discovered in sulfide concentratefrom the Hitura Ni–Cu–PGE mine, Nivala, western central Finland. It is associated with pyrrhotite, pentlandite, valleriite,
chalcopyrite, cubanite, mackinawite, chromite, and the PGE minerals sperrylite, michenerite, irarsite, froodite and hollingworthite.
It is black, opaque with a metallic luster, a black streak, and is brittle with an irregular fracture. VHN15 is in the range 537–584,
which corresponds to a Mohs hardness of 5½ to 6. Under reflected plane-polarized light, the mineral is light brown-gray andisotropic. The CIE color values (illuminant C) are: x 0.314 (air), 0.315 (oil); y 0.321 (air), 0.323 (oil) Y: 38.9 (air), 21.7 (oil); ␭d:575 (air), 573 (oil); Pe%: 2.1 (air), 3.2 (oil). The measured values of reflectance in air and oil for a single grain, respectively, are38.02, 20.91 (470 nm), 37.87, 21.76 (546 nm), 39.18, 21.84 (589 nm), 39.30, 22.12 (650 nm) and values for 400–700 nm aretabulated. Tarkianite is cubic, F4̄3m (by analogy with the synthetic equivalent), with unit-cell parameter refined from powder
data: a 9.563(1) Å, V 874.5(1) Å3, Z = 4. The strongest eight lines of the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are:5.531(100)(111), 2.885(90)(311), 2.389(90)(400), 2.194(70)(331), 1.952(60)(422), 1.841(90)(511), 1.690(80)(440) and1.246(50)(731). D (calc.) is 7.30 g/cm3 (for the empirical formula and unit-cell parameter). Averaged electron-microprobe data
yielded Re 53.61, Mo 12.32, Cu 5.48, Os 0.84, Fe 0.59, Ni 0.09, Co 0.08, S 26.77, total 99.78 wt.%, corresponding to(Cu0.83Fe0.10Ni0.02Co0.01)⌺0.96(Re2.79Mo1.22Os0.04)⌺4.03S8.01, based on a total of thirteen atoms. The mineral name honors Professor
Mahmud Tarkian, of the University of Hamburg, Germany, for his contributions to ore mineralogy.
Keywords: tarkianite, new mineral species, rhenium molybdenum copper sulfide, X-ray data, electron-microprobe data, reflectance data, Hitura mine, Nivala, Finland.

SOMMAIRE
Nous décrivons la tarkianite, nouvelle espèce minérale de composition idéale (Cu,Fe)(Re,Mo)4S8, découverte récemment
dans un concentré de sulfures provenant de la mine à Ni–Cu–EGP de Hitura, près de Nivala, dans le centre-ouest de la Finlande.
Lui sont associés pyrrhotite, pentlandite, vallériite, chalcopyrite, cubanite, mackinawite, chromite, et les minéraux des éléments
du groupe du platine (EGP) sperrylite, michenerite, irarsite, froodite et hollingworthite. Il s’agit d’un minéral noir, opaque avec
un éclat métallique, et une rayure noire. Elle est cassante avec une fracture irrégulière. La dureté mesurée (VHN15) est dansl’intervalle 537–584, ce qui correspond à 5½ ou 6 sur l’échelle de Mohs. En lumière réfléchie polarisée en plan, la tarkianite est§

E-mail address: kari.kojonen@gsf.fi

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THE CANADIAN MINERALOGIST

brun-gris pâle et isotrope. Les paramètres CIE décrivant la couleur pour l’illuminant C sont: x 0.314 (air), 0.315 (huile); y 0.321(air), 0.323 (huile) Y: 38.9 (air), 21.7 (huile); ␭d: 575 (air), 573 (huile); Pe%: 2.1 (air), 3.2 (huile). Les valeurs de sa réflectancedans l’air et dans l’huile (%), mesurées sur un seul grain, sont 38.02, 20.91 (470 nm), 37.87, 21.76 (546 nm), 39.18, 21.84 (589nm), 39.30, 22.12 (650 nm), respectivement, et les valeurs standards pour 400–700 nm sont présentées. La tarkianite est cubique,F4̄3m (par analogie avec l’équivalent synthétique), et son paramètre réticulaire a été affiné à partir du spectre de diffraction
obtenu sur poudre: a 9.563(1) Å, V 874.5(1) Å3, Z = 4. Les huit raies les plus intenses du spectre de diffraction [d en Å (I)(hkl)]
sont: 5.531(100)(111), 2.885(90)(311), 2.389(90)(400), 2.194(70)(331), 1.952(60)(422), 1.841(90)(511), 1.690(80)(440) et
1.246(50)(731). La densité, calculée à partir de la formule empirique et du paramètre réticulaire, est 7.30 g/cm3. Les analyses à lamicrosonde électronique ont donné, en moyenne, Re 53.61, Mo 12.32, Cu 5.48, Os 0.84, Fe 0.59, Ni 0.09, Co 0.08, S 26.77, pour
un total de 99.78% (poids), ce qui correspond à (Cu0.83Fe0.10Ni0.02Co0.01)⌺0.96(Re2.79Mo1.22Os0.04)⌺4.03S8.01, sur une base de treize
atomes. Le nom est choisi pour honorer le professeur Mahmud Tarkian, de l’Université de Hambourg, en Allemagne, et ainsisouligner des contributions aux études de la minéralogie des minerais.
(Traduit par la Rédaction)
Mots-clés: tarkianite, nouvelle espèce minérale, sulfure de rhénium, molybdène et cuivre, diffraction X, données de microsondeélectronique, données de réflectance, mine Hitura, Nivala, Finlande.

INTRODUCTION
The new mineral species described here, tarkianite,with a general formula (Cu,Fe,Co,Ni)(Re,Mo,Os)4S8,
was recently discovered in samples of sulfide concentrate obtained from the Hitura Ni–Cu–PGE mine,
Nivala, west-central Finland. The grains were found ina heavy-mineral concentrate containing pentlandite,chromite, pyrrhotite, and PGM (platinum-group minerals), consisting of sperrylite (81.1%), michenerite(6.6%), irarsite (1.9%), froodite (6.9%), hollingworthite(1.9%) and an undefined Rh–Ni–Co sulfarsenide. The
average contents of the PGE (platinum-group elements,
in ppb) in the sulfide concentrate are: Ir 51, Os 20, Pd
417, Pt 1125, Rh 123 and Ru 46. The average Re content is 20 ppb. The mineral is named tarkianite in honorof Professor Dr. Mahmud Tarkian (b. 1941), Universityof Hamburg, Germany, in recognition of his important
contributions to ore mineralogy. Tarkian et al. (1991)
previously described this phase from the StillwaterComplex, Sweetwater County, Montana, and resolved
the crystal structure of the synthetic equivalent. The
mineral and mineral name have been approved by theCommission on New Minerals and Mineral Names,
IMA (2003–004). A polished section containing
tarkianite grains is preserved in the collection of theFinnish Museum of Natural History, Geological Museum, University of Helsinki, Helsinki, Finland, undersample number C4001.

plex is 1877 ± 2 Ma, determined on zircon from a crosscutting dyke of granitic pegmatite. The ore (Häkli et al.
1976) consists of 1) fine-grained sulfides disseminatedin the serpentinite core, 2) medium-grained sulfides disseminated in the serpentinite and amphibole-dominantrock, and 3) high-grade interstitial disseminated sulfides
and massive accumulations in an amphibole-dominantrock at the contact zones. In the core of the intrusive
body, the main sulfides are pentlandite, mackinawite
and valleriite. In the marginal zones, the main ore lodes
consist of dense disseminations and net-textured primary intergrowths of pyrrhotite, pentlandite andmackinawite with secondary films of magnetite alongcleavage planes of the sulfides. Chalcopyrite and graphite are common, and less common ore minerals include
cobaltite, maucherite, nickeline, parkerite, native gold,
Au–Ag alloy, native bismuth, pilsenite, tellurobismuthite, galena, altaite, clausthalite, ilmenite,
chromite, cassiterite, monazite and uraninite. Tarkianite
occurs with the primary sulfides and PGM. The concentrates were investigated for a detailed PGM study,
as a follow-up to a previous study by Häkli et al. (1976).
This earlier study showed that sperrylite is the only Ptbearing mineral, and that the Pd-bearing minerals include michenerite, froodite, Pd-bearing irarsite and an
undefined Pd-bearing Bi–Ni telluride resembling
melonite. Iridarsenite, irarsite and hollingworthite werereported as Ir- and Rh-bearing minerals.
Other occurrences

THE TYPE LOCALITY AND OTHER OCCURRENCES
The type locality
The Hitura mine is located about 13 kilometers southof the town center of Nivala in western central Finland(lat. 63°51’N, long. 25°02’W). The Ni–Cu–PGE ore ishosted by serpentinized ultramafic intrusions and averages Ni 0.67, Cu 0.25, Co 0.03, S 3.0 %, Pt 0.1 and Pd
0.1 ppm. The minimum U–Pb age of the Hitura com-

The first discovery of a phase corresponding to theformula Cu(Mo2Re2)S8 was made at two localities in
Sweden (Ekström & Hålenius 1982), where it isintergrown with an undefined phase of composition(Ni,Pd)5(Te,Bi)8 in pyrrhotite and at the contact between
siegenite and chalcopyrite. At the Coldwell complex,
Ontario, a sulfide hosted by pyrrhotite and corresponding to the (approximate) formula (Re,Mo,Fe,Cu)2S3 wasdescribed by Mitchell et al. (1989). At Stillwater, Mon-TARKIANITE, A NEW MINERAL SPECIES FROM FINLAND

tana, a phase with an empirical formula (Cu0.84Fe0.20
Ni0.04)⌺1.08(Re2.72Mo1.16)⌺3.88S8.00 is enclosed in pentlandite and pyrrhotite in a high-temperature magmatic assemblage (Volborth & Housley 1984, Volborth et al.
1986, Tarkian et al. 1991). At Lukkulaisvaara, Karelia,
Russia (Barkov & Lednev 1993), a phase with an empirical formula (Cu0.88Fe0.21)⌺1.09(Re2.94Mo1.04)⌺3.98S8.00
occurs in association with chalcopyrite – bornite – millerite, millerite – bornite – pentlandite and various PGM.
At Ekojoki, southwestern Finland, a sulfide with a formula Cu1.02(Re3.11Os0.18Mo1.59)⌺4.88S9 is enclosed inintercumulus pentlandite with numerous worm-likegrains of mackinawite (Peltonen et al. 1995). At
Monchegorsk, Kola Peninsula, Russia, a sulfide withsimilar chemical composition was found within hexagonal pyrrhotite by one of us (VVK) after the discovery oftarkianite at Hitura.

MATERIAL AND METHODS OF INVESTIGATION
Tarkianite was identified in a polished specimen prepared from a PGM concentrate that was obtained usinga gravimetric hydroseparation method [developed by
one of us (VVK) (http://www.natires.com/)]. The grains
were located during routine back-scattered electron imaging with a Cameca SX–50 electron microprobe
equipped with a PGT energy-dispersion spectrometer(EDS) as detector. The micro-indentation hardness wasmeasured with a Leitz Durimet tester. The X-ray pow-541

der-diffraction data were obtained with a Debye–
Scherrer camera 114.6 mm in radius, employing CuK␣radiation. The reflectance values were measured using
a computerized Zeiss MPM microphotometer and Zeiss
standard WTiC (Nr 326). The measurements were madeevery 20 nm, both in air and using standard immersion
oil. For the light source of the Zeiss microscope, we used
a 100 W halogen lamp (diaphragm 0.15, measuring
objective 16⫻). The area of measurement was 5 ␮m indiameter.

GENERAL APPEARANCE AND PHYSICAL PROPERTIES
Tarkianite is black and opaque with a metallic luster. The color of the streak is black, and grains are brittle
with an irregular fracture. Some grains show an idiomorphic cubic morphology (Fig. 1); the grain size is<75 ␮m. Tarkianite grains are associated with pentlandite and sperrylite in the polished mounts made of theconcentrates.
Optical properties
Under plane-polarized reflected light in air,tarkianite is light grey and isotropic. Under oil immersion, the mineral has a light brown-gray color. Reflectance measurements were made every 20 nm in both air
and oil from 400 to 700 nm (Table 1, Fig. 2). The values for the standard wavelengths 470, 546, 589 and 650
nm were calculated.

FIG. 1. A euhedral grain of tarkianite associated with sperrylite (Sp) in heavy-mineral
concentrate. Plane-polarized light, oil immersion, sample 2_72_6. Scale bar: 50 ␮m.

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THE CANADIAN MINERALOGIST

Physical properties
The grains available, all less than 75 ␮m in size, were
mounted in epoxy. The grains are very fragile; we foundit difficult to measure hardness without breaking them.
Therefore, micro-indentations were made with a 15 gload, which still led to slight fracturing of the measured
grains. Only two successful micro-indentation hardness
measurements were made, and these gave values of
VHN 537 and 584, with a mean of 561 kg/mm2. This
corresponds to a Mohs hardness of 5½ to 6. The calculated density, 7.30 g/cm3, is based on the averaged empirical formula derived from the electron-microprobe
analyses and the unit-cell parameter refined from the
X-ray powder-diffraction data.

try (from Fd3̄m to F4̄3m) owing to vacancies at the tetrahedrally coordinated A sites and shifts of the B and S
atoms. The A-site atoms are predominantly Cu and Fe,
and the B-site atoms are predominantly Re and Mo.
Chemical composition
Quantitative electron-microprobe analyses (EPMA)of tarkianite were performed utilizing a Cameca SX–50
electron microprobe, with an operating voltage of

X-ray crystallography
The powder-diffraction data are presented inTable 2. The mineral is cubic, space group F4̄3m, andthe refined unit-cell parameter, a 9.563(1) Å, V 874.5(1)Å3, Z = 4, is refined from 17 powder-diffraction reflections (Table 2), representing d values between 5.531 and1.246 Å for which unambiguous indexing was possible
based on an analogy with the synthetic equivalent. Comparable powder-diffraction data for the synthetic equivalents are presented in the Powder Diffraction File:
84–2349 (calculated), 80–2304 (calculated), 47–1360(experimental), 44–149 (experimental) and 34–1384(experimental). Tarkian et al. (1991) and Kohlmann &Schulz (1993) reported crystal-structure data for thesynthetic equivalent. The structure is a cubic derivativeof spinel of the type IVA2VIB4S8, with reduced symme-

FIG. 2.

Reflectance spectra of tarkianite (Table 1), sample 2_72_6.

TARKIANITE, A NEW MINERAL SPECIES FROM FINLAND

25 kV, a beam current of 10 nA, and a beam-spot diameter of 1 ␮m. For standards, we used pentlandite (Fe,Ni, S), chalcopyrite (Cu), cobaltite (Co) and pure metals (Re, Mo, Os). A LiF analyzing crystal was used for
ReL␣, FeK␣, CuK␣, CoK␣, and NiK␣; a PET crystal
was used for MoL␤ and SK␣, and a TAP crystal for
OsM␤. Peak counting time was 20 seconds for all elements. Electron-microprobe data for tarkianite are presented in Table 3.
The average of 34 analytical points yielded Re 53.61,
Mo 12.32, Cu 5.48, Os 0.84, Fe 0.59, Ni 0.09, Co 0.08,
S 26.77, total 99.78 wt.%, corresponding to (Cu0.83Fe0.10
Ni0.02Co0.01)⌺0.96 (Re2.79Mo1.22Os0.04)⌺4.03S8.01 (Table 3),
based on a total of thirteen atoms.

DISCUSSION
Tarkianite is characterized as a new mineral species
with a cubic spinel-derivative structure with generalformula A1䡺1B4S8, space group F 4̄3m, and an ideal
chemical composition (Cu,Fe,Ni,Co)(Re,Mo,Os)4S8.

543

The tetrahedrally coordinated A sites are only half occupied by Cu, Fe, Ni and Co (Tarkian et al. 1991), andthe B-site atoms are statistically occupied by Mo, Re
and Os, and form tetrahedral clusters with metal–metalbonding distances of 2.81 Å (Perrin et al. 1975, 1976).
The apparent valences of the elements are 1+ for Cu, 2+
for Fe, Ni, Co, 3+ for Mo and 4+ for Re and Os (Umarji
et al. 1979), which leads to a general formula of [Cu1–x(Fe,Ni,Co)x䡺1][(Re,Os)3–xMo1+x)S8.
The chemical compositions of the Re–Mo–Cu sulfides found at various localities spatially cluster in the(Cu + Fe + Ni + Co) – (Re + Os + Mo) – S triangulardiagram and in the S – (Re + Mo + Os) binary diagram(Figs. 3a, b), and most probably represent the same mineral phase. However, without complete optical, physical and X-ray-diffraction data, the above hypothesis
cannot be tested, except in the case of the complete
description of (Cu 0.84 Fe 0.20 Ni 0.04 ) ⌺1.08 (Re 2.72
Mo1.16)⌺3.88S8.00 from Stillwater and its synthesized
equivalent (Tarkian et al. 1991).

ACKNOWLEDGEMENTS
Outokumpu Mining Oy is thanked for permission to
study the Hitura concentrates and to publish these results. Professor Mahmud Tarkian is gratefully acknowledged for providing the reflectance values and forproviding a constructive review of this paper. Drs.
Andrei Y. Barkov, Joseph A. Mandarino and Robert F.
Martin are acknowledged for their corrections, whichmuch improved this paper.

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THE CANADIAN MINERALOGISTREFERENCESBARKOV, A.Y. & LEDNEV, A.I. (1993): A rhenium – molybdenum – copper sulfide from the Lukkulaisvaara layered intrusion, northern Karelia, Russia. Eur. J. Mineral. 5, 12271233.
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FIG. 3. Average chemical composition (Table 4) of Re–Mo–
Cu sulfides plotted in terms of a) the triangular plot (Cu +Fe + Ni + Co) – (Re + Os + Mo) – S, and b) a binary plot of
S versus (Re + Mo + Os). Symbols used: H: Hitura,tarkianite; L: Lukkulaisvaara, St: Stillwater, C: Coldwell,
E: Ekojoki, and S: Sweden.

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Received January 9, 2004, revised manuscript February 29,
2004.