Investigation of Platinum-Group Minerals (PGM) from Othrys Chromitites (Greece) Using Superpanning Concentrates

Tsikouras, Basilios; Ifandi, Elena; Karipi, Sofia; Grammatikopoulos, Tassos; Hatzipanagiotou, Konstantin

doi:10.3390/min6030094

Cited by 10 publications

(15 citation statements)

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“…Chromium, and other metal catalysts occurring in chromitites such as Ni and Fe, could also support the Sabatier reaction, but they need higher temperatures, generally above 200 °C 9 . It was observed that Ru-minerals, such as laurite and Ru-pentlandite, are frequently within or in contact with fractures and chlorite/serpentine-filled veins 25 and have been reported in both Othrys and Vourinos chromitites 26,27 . The Ru-minerals are often altered due to contact with percolating serpentinization fluids, H 2 in particular 28 .…”

Section: Resultsmentioning

confidence: 99%

Widespread abiotic methane in chromitites

Etiope

Ifandi

Nazzari

et al. 2018

Sci Rep

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Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of 13C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars.

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Section: Resultsmentioning

confidence: 99%

Widespread abiotic methane in chromitites

Etiope

Ifandi

Nazzari

et al. 2018

Sci Rep

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“…We tested the Alloy 1 used during the preparation of the studied concentrates and found that it was composed of Cr and Mo only. Previously, other chromitite samples, obtained with the same technique in the same laboratory, had been carefully studied, however, no phosphides had been recovered [22,32,33]. The finding, by X-ray examination of a very minor amount of a spinel-group mineral (e.g., magnesiochromite) finely intergrown with tsikourasite, represents strong proof against possible anthropogenic contamination.…”

Section: Discussionmentioning

confidence: 97%

“…Many studies rely on the investigation of only a few mineral grains found using in situ technique. On the contrary, the study of mineral concentrates provides a greater bulk and more extensive range of minerals than petrographic thin sections and, as consequently, a better characterization of the heavy-mineral assemblage and a better statistical basis for mineralogical and petrological conclusions can be achieved (e.g., [22,[31][32][33]). Using this technique, several new minerals have been discovered in recent years.…”

Section: Discussionmentioning

confidence: 99%

“…The chromitites were collected in the abandoned mine of Agios Stefanos located about 10 km south of Domokos village ( Figure 1B). The studied sample consists of massive chromitite, hosted in strongly serpentinized dunite from a mantle tectonite composed of harzburgite and minor intercalations of plagioclase-bearing lherzolite [19][20][21][22]. Mafic rocks, mainly gabbro of the crustal sequence and gabbro dykes, have also been recognized ( Figure 1B,C).…”

Section: Geological Background and Occurrence Of Tsikourasitementioning

confidence: 99%

“…Finally, the alkaline WPB are interpreted to have formed either in oceanic seamounts or in the ocean-continent transition zone adjacent to the rifted continental margin [23]. In addition to tsikourasite, previous mineralogical studies on specimens from the Agios Stefanos chromium mine revealed the presence of accessory minerals such as the platinum group minerals (PGM) [21,22], which are Ru-Os-Ir-Ni alloys, laurite, erlichmanite, Pd-Sb-Cu alloys, Pd-Cu-Pt alloys, irarsite, platarsite, hollingworthite, merenskyite, and cooperite-braggite.…”

Section: Geological Background and Occurrence Of Tsikourasitementioning

confidence: 99%

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Tsikourasite, Mo3Ni2P1+x (x < 0.25), a New Phosphide from the Chromitite of the Othrys Ophiolite, Greece

et al. 2019

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Tsikourasite, Mo3Ni2P1+x (x < 0.25), is a new phosphide discovered in a mantle-hosted podiform chromitite collected in the abandoned mine of Agios Stefanos (Othrys ophiolite), Central Greece. It forms tiny grains (from a few μm up to about 80 μm) and occurs as isolated grains or associated with other known minerals such as nickelphosphide and awaruite, and with undetermined minerals such as Ni-allabogdanite or Ni-barringerite and a V-sulphide. Tsikourasite is brittle and has a metallic luster. In plane-polarized light, tsikourasite is white yellow and it shows no bireflectance, anisotropism or pleochroism. Internal reflections were not observed, Reflectance values of tsikourasite in air (R in %) are: 55.7 at 470 nm, 56.8 at 546 nm, 57.5 at 589 nm and 58.5 at 650 nm. Five spot analyses of tsikourasite give the average composition: P 7.97, S 0.67, V 14.13, Fe 14.37, Co 7.59, Ni 23.9, and Mo 44.16, total 99.60 wt%, corresponding to the empirical formula (Mo1.778V1.071Fe0.082Co0.069)Σ3.000(Ni1.572Co0.428)Σ2.000(P0.981S0.079)Σ1.060, on the basis of Σ(Mo +V + Fe + Co + Ni) = 5 apfu and taking into account the structural results. The simplified formula is Mo3Ni2P1+x (x < 0.25). The density, which was calculated based on the empirical formula and single-crystal data, is 9.182 g/cm3. The mineral is cubic, space group F-43m, with a = 10.8215(5) Å and Z = 16. Although tsikourasite is similar in composition to those of monipite (MoNiP), polekhovskyite (MoNiP2), and the synthetic compound MoNiP2, all these phases are hexagonal and not cubic like tsikourasite. It exhibits the same structure as the cubic Mo3Ni2P1.18 compound [space group F-43m, a = 10.846(2) Å] synthesized at 1350 °C. The mineral and its name have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2018-156). The mineral honors Professor Basilios Tsikouras of the Universiti Brunei Darussalam.

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Arsenotučekite, Ni18Sb3AsS16, a new mineral from the Tsangli chromitites, Othrys ophiolite, Greece

et al. 2020

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Arsenotučekite, Ni18Sb3AsS16, is a new mineral discovered in the abandoned chromium mine of Tsangli, located in the eastern portion of the Othrys ophiolite complex, central Greece. Tsangli is one of the largest chromite deposit at which chromite was mined since 1870. The Tsangli chromitite occurs as lenticular and irregular bodies. The studied chromitites are hosted in a strongly serpentinized mantle peridotite. Arsenotučekite forms anhedral to subhedral grains that vary in size between 5 μm up to 100 μm, and occurs as single phase grains or is associated with pentlandite, breithauptite, gersdorffite and chlorite. It is brittle and has a metallic luster. In plane-polarized light, it is creamy-yellow, the bireflectance is barely perceptible and the pleochroism is weak. In crossed polarized reflected light, the anisotropic rotation tints vary from pale blue to brown. Internal reflections were not observed. Reflectance values of arsenotučekite in air (Ro, Re′ in %) are: 41.8–46.4 at 470 nm, 47.2–50.6 at 546 nm, 49.4–52.3 at 589 nm, and 51.3–53.2 at 650 nm. The empirical formula of arsenotučekite, based on 38 atoms per formula unit, and according to the structural results, is (Ni16.19Co1.01Fe0.83)Σ18.03Sb3(As0.67Sb0.32)Σ0.99S15.98. The mass density is 6.477 g·cm−3. The simplified chemical formula is (Ni,Co,Fe)18Sb3(As,Sb)S16. The mineral is tetragonal and belongs to space group I4/mmm, with a = 9.7856(3) Å, c = 10.7582(6) Å, V = 1030.2(6) Å3 and Z = 2. The structure is layered (stacking along the c-axis) and is dominated by three different Ni-coordination polyhedral, one octahedral and two cubic. The arsenotučekite structure can be considered as a superstructure of tučekite resulting from the ordering of Sb and As. The name of the new mineral species indicates the As-dominant of tučekite. Arsenotučekite occurs as rims partly replacing pentlandite and irregularly developed grains. Furthermore, it is locally associated with chlorite. These observations suggest that it was likely precipitated at relatively low temperatures during: 1) the late hydrothermal stages of the ore-forming process by reaction of Sb- and As-bearing solutions with magmatic sulfides such as pentlandite, or 2) during the serpentinization of the host peridotite. The mineral and its name have been approved by the Commission of New Minerals, Nomenclature, and Classification of the International Mineralogical Association (number 2019–135).

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Investigation of Platinum-Group Minerals (PGM) from Othrys Chromitites (Greece) Using Superpanning Concentrates

Cited by 10 publications

References 40 publications

Widespread abiotic methane in chromitites

Widespread abiotic methane in chromitites

Tsikourasite, Mo3Ni2P1+x (x < 0.25), a New Phosphide from the Chromitite of the Othrys Ophiolite, Greece

Arsenotučekite, Ni18Sb3AsS16, a new mineral from the Tsangli chromitites, Othrys ophiolite, Greece

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