Paragenesis and composition of laurite from chromitites of Othrys (Greece): implications for Os-Ru fractionation in ophiolitic upper mantle of the Balkan peninsula

Garuti, Giorgio; Zaccarini, Federica; Economou-Eliopoulos, Maria

doi:10.1007/s001260050206

Cited by 101 publications

(85 citation statements)

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“…The authors recovered the PGM in concentrates and showed that the PGM assemblage inTrodUcTion The role of chromian spinel as an important collector of platinum-group elements (PGE) has been confirmed in investigations of the PGE content of different types of chromitites worldwide (e.g., Augé 1985, Ferrario & Garuti 1990, Pedersen et al 1993, Garuti et al 1999, Ahmed & Arai 2003. However, there is now convincing evidence that the PGE are not carried in solid solution in the chromian spinel, as had been proposed from experimental studies (e.g., Capobianco & Drake 1990, Capobianco et al 1994, Righter et al 2004, Pagé et al 2009), but form discrete platinumgroup minerals (PGM).…”

Section: Previous Work On the Pgm Of Milia Chromititesmentioning

confidence: 94%

“…On the basis of in situ textural observations, it has been confirmed that the PGM inclusions in unaltered chromian spinel are near-liquidus phases precipitated from the magma at a very early stage of its differentiation. The type of PGM assemblage hosted in chromitite is also considered a useful indicator of the physicochemical conditions prevailing in the early magmatic system (e.g., Augé & Johan 1988, Nakagawa & Franco 1997, Garuti et al 1999. In particular, the paragenesis and composition of the PGM are used to estimate the conditions of sulfur fugacity f(S 2 ) and temperature in the magma during formation of the chromitites.…”

Section: Previous Work On the Pgm Of Milia Chromititesmentioning

confidence: 99%

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Chromian Spinel Composition and Platinum-Group Element Mineralogy of Chromitites From the Milia Area, Pindos Ophiolite Complex, Greece

Kapsiotis

Grammatikopoulos

Tsikouras

et al. 2009

The Canadian Mineralogist

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The chromitites of the Milia area in the Pindos ophiolite complex, in Greece, were investigated for their platinum-group mineral (PGM) content. The chromitites are massive, more rarely disseminated in texture and occur as small pods. They are composed of magnesiochromite crystals with Cr# [Cr/(Cr + Al)] between 0.80 and 0.84, and Mg# [Mg/(Mg + Fe 2+ )] between 0.54 and 0.72. The total platinum-group-element (PGE) contents in chromitites are relatively low (≤170 ppb), although they may locally be higher (up to 1059 ppb). The IPGE (Os, Ir and Ru) predominate over the PPGE (Rh, Pt and Pd). The PGM assemblage, consistent with the geochemical data, is dominated by laurite and Os-Ir-Ru alloys that occur both as single and composite grains, generally less than 15 mm in size. Laurite has a wide range of Os-for-Ru substitution [Ru/(Ru + Os): 0.42-0.99], whereas primary alloys are enriched in Ru (up to 73.80 wt.%). Some laurite crystals exhibit an anomalous pattern of zoning. Such zoning requires an inversion of the normal T-f(S 2 ) trend in magmatic systems, and is herein considered to be due to postmagmatic processes. Some Ru-rich alloy grains contain relatively high Rh and Pt abundances, similar to those of residual sulfides in mantle peridotites. This feature suggests that these alloys may represent residual PGM phases from earlier episodes of melt extraction from the severely depleted mantle unit of the Pindos ophiolite complex. Combined compositional data indicate that the Milia chromitites formed from a hydrous boninitic melt in a suprasubduction-zone environment.Keywords: chromitites, platinum-group minerals (PGM), laurite, alloys, ophiolites, Pindos, Greece. Certains grains d'alliages riches en Ru contiennent des teneurs relativement élevées en Rh et Pt, tout comme les sulfures résiduels de péridotites du manteau. Ces grains d'alliage pourraient donc représenter des MGP résiduels après l'extraction antérieure de liquide silicaté, laissant un manteau très stérile dans le complexe ophiolitique de Pinde. Les données combinées sur la composition indiquent que les chromitites de Milia se sont formées à partir d'une magma hydraté boninitique dans un milieu au dessus de la zone de subduction.(Traduit par la Rédaction)

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Section: Previous Work On the Pgm Of Milia Chromititesmentioning

confidence: 94%

Section: Previous Work On the Pgm Of Milia Chromititesmentioning

confidence: 99%

Chromian Spinel Composition and Platinum-Group Element Mineralogy of Chromitites From the Milia Area, Pindos Ophiolite Complex, Greece

Kapsiotis

Grammatikopoulos

Tsikouras

et al. 2009

The Canadian Mineralogist

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“…Although the stability relationships between various phases can be studied using the experimental method, thermodynamics may give us an approach to the calculation of the Gibbs free energy and phase diagrams [28]. However, the requirements for the PGM stability and re-deposition remain still unclear, since the activity-composition models and relevant phase diagrams for PGM are very limited, and the PGM forming processes in natural systems are complicated [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]28].…”

Section: Application Of (∆ F G) Values To the Origin Of Pgmmentioning

confidence: 99%

“…On the basis of the calculated Gibbs free energy of formation for the RuS 2 (´204.1 kJ/mol), which is lower compared to that for the OsS 2 (´135.1 kJ/mol) (Table 1, Figure 2A), the reaction Os + RuS 2 ØRu + OsS 2 is not favorable thermodynamically (positive ∆ f G˝), although the substitution reaction of Ru by Os has been recorded in nature: laurite in chromitites associated with ophiolite complexes is commonly characterized by the general formula (Ru > Os > Ir)S 2 , but in the Othrys complex and other ophiolites of the Balkan Peninsula, it is Os-rich (Os > Ru > Ir)S 2 , reaching the composition of erlichmanite [4]. Such a composition has been interpreted as Os-Ru substitution during crystal fractionation, while the metal-sulfide equilibrium curves for PGE indicate that at given T, the formation of RuS 2 requires fS 2 lower than that for OsS 2 [56].…”

Section: Application Of (∆ F G) Values To the Origin Of Pgmmentioning

confidence: 99%

“…Platinum groupelements (PGE) can be classified into two subgroups: the Os-, Ir-, Ru-rich or IPGE (more refractory) and PPGE (low-melting and more soluble) (Ir group), interpreted to reflect compatible behavior (partition or distribution coefficient between solid and magma, D ě 1) during large-degree mantle melting and (Pt, Pd)-rich or PPGE assemblages, reflecting the incompatible behavior (D ď 1) of the PPGE, showing enrichment as a function of the differentiation degree [1]. The behavior of PGE during partial melting and crystal fractionation and which minerals are collectors of PGEs have been investigated and reviewed extensively [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

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Gibbs Free Energy of Formation for Selected Platinum Group Minerals (PGM)

Olivotos

Economou-Eliopoulos

2016

Geosciences

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Thermodynamic data for platinum group (Os, Ir, Ru, Rh, Pd and Pt) minerals are very limited. The present study is focused on the calculation of the Gibbs free energy of formation (∆ f G˝) for selected PGM occurring in layered intrusions and ophiolite complexes worldwide, applying available experimental data on their constituent elements at their standard state (∆G = G (species)´∆ G (elements) ), using the computer program HSC Chemistry software 6.0. The evaluation of the accuracy of the calculation method was made by the calculation of (∆G f ) of rhodium sulfide phases. The calculated values were found to be in good agreement with those measured in the binary system (Rh + S) as a function of temperature by previous authors (Jacob and Gupta (2014). The calculated Gibbs free energy (∆ f G˝) followed the order RuS 2 < (Ir,Os)S 2 < (Pt, Pd)S < (Pd, Pt)Te 2 , increasing from compatible to incompatible noble metals and from sulfides to tellurides.

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Seepage in Serpentinised Peridotites and on Mars

Etiope

2015

Natural Gas Seepage

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Thus far, this book has mainly addressed the classical seepage of natural gas of biotic (microbial and thermogenic) origin in sedimentary rocks. However, it is also known that methane and other light hydrocarbons can be abiotically produced (i.e., by chemical reactions that do not directly involve organic matter). Abiotic production may occur over a wide range of temperatures and pressures and within a variety of geological systems. Two main classes of abiotic CH 4 generation processes can be distinguished, magmatic and gas-water-rock interactions. For details, the reader is referred to the review of Etiope and Sherwood Lollar (2013). Here, it is important to keep in mind that while magmatic or mantle-derived CH 4 is abiotic, not all abiotic CH 4 is mantle derived. Magmatic and high temperature hydrothermal processes in volcanic and geothermal systems produce a gas mixture that is mainly composed of carbon dioxide (CO 2 ), while abiotic methane is a very minor component. Indeed, field observations suggest that the majority of abiotic gas on Earth's surface is produced by low-temperature, gas-water-rock reactions. Of particular interest are the Fischer-Tropsch Type (FTT) reactions, the mechanism most widely invoked for explaining large quantities of abiotic CH 4 seeping to the surface. In the sub-chapters that follow, only CH 4 -rich abiotic gas seeping to the surface is considered. Such seepage generally occurs in serpentinised ultramafic rocks (peridotites). Serpentinisation (the hydration of olivine and pyroxene minerals, which leads to the formation of H 2 and the subsequent production of CH 4 through FTT synthesis) is considered a fundamental step in the origin of life, representing the primordial passage from inorganic to organic chemistry (Russell et al. 2010). Serpentinisation can also be a source of methane in atypical petroleum systems where hydrocarbon reservoirs are formed by or are adjacent to igneous rocks (Sect. 7.1.2), and a potential source of methane on other planets, such as Mars (Sect. 7.2).

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Paragenesis and composition of laurite from chromitites of Othrys (Greece): implications for Os-Ru fractionation in ophiolitic upper mantle of the Balkan peninsula

Cited by 101 publications

References 16 publications

Chromian Spinel Composition and Platinum-Group Element Mineralogy of Chromitites From the Milia Area, Pindos Ophiolite Complex, Greece

Chromian Spinel Composition and Platinum-Group Element Mineralogy of Chromitites From the Milia Area, Pindos Ophiolite Complex, Greece

Gibbs Free Energy of Formation for Selected Platinum Group Minerals (PGM)

Seepage in Serpentinised Peridotites and on Mars

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