Stratiform platinum-group element mineralizations in the ultramafic cumulates of the Leka ophiolite complex, central Norway

Pedersen, R. B.; Johannesen, Geir Mossige; Boyd, Rognvald

doi:10.2113/gsecongeo.88.4.782

Cited by 68 publications

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“…4). It fits the pattern of highly altered podiform chromitites from the mantle section and/or stratiform chromitites from the crustal section of ophiolites (Prichard et al 1986;Thalhammer et al 1990;Lord 1991;Pedersen et al 1993;Yang and Seccombe 1994;Auge´et al 1998;Malitch et al 2001a). On the contrary, the podiform chromitite (K 142) shows a negatively sloped PGE pattern (Fig.…”

Section: Pge Concentrations In Whole-rock Samplessupporting

confidence: 70%

Diversity of platinum-group mineral assemblages in banded and podiform chromitite from the Kraubath ultramafic massif, Austria: evidence for an ophiolitic transition zone?

Malitch

Thalhammer

Knauf³

et al. 2003

Miner Deposita

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We report highly unusual platinum-group mineral (PGM) assemblages from geologically distinct chromitites (banded and podiform) of the Kraubath massif, the largest dismembered mantle relict in the Eastern Alps. The banded chromitite has a pronounced enrichment of Pt and Pd relative to the more refractory platinum-group elements (PGEs) of the IPGE group (Os, Ir, Ru), similar to crustal sections of ophiolites. On the contrary, the podiform chromitite displays a negatively sloping chondrite-normalised PGE pattern typical of ophiolitic podiform chromitite. The chemical composition of chromite varies from Cr# 73-77 in the banded type to 81-86 in the podiform chromitite. Thirteen different PGMs and one gold-rich mineral are first observed in the banded chromitite. The dominant PGM is sperrylite (53% of all PGMs), which occurs in polyphase assemblages with an unnamed Pt-base metal (BM) alloy and Pd-rich minerals such as stibiopalladinite, mayakite, mertieite II, unnamed Pd-Rh-As and Pd(Pt)-(As,Sb) minerals. This banded type also contains PGE sulphides (about 7%) represented by a wide compositional range of the laurite-erlichmanite series and irarsite (8%). Os-Ir alloy, geversite, an unnamed Pt-PdBi-Cu phase and tetrauricupride are present in minor amounts. By contrast, the podiform chromitite, which yielded 21 different PGMs, is dominated by laurite (43% of all PGMs) which occurs in complex polyphase assemblages with PGE alloys (Ir-Os, Os-Ir, Pt-Fe), PGE sulphides (kashinite, bowieite, cuproiridsite, cuprorhodsite, unnamed (Fe,Cu)(Ir,Rh) 2 S 4 , braggite, unnamed BM-Ir and BM-Rh sulphides) and Pd telluride (keithconnite). A variety of PGE sulpharsenides (33%) including irarsite, hollingworthite, platarsite, ruarsite and a number of intermediate species have been identified, whereas sperrylite and stibiopalladinite are subordinate (2%). The occurrence of such a wide variety of PGMs from only two, 2.5-kg chromitite samples is highly unusual for an ophiolitic environment. Our novel sample treatment allowed to identify primary PGM assemblages containing all six PGEs in both laurite-dominated podiform chromitite as well as in uncommon sperrylite-dominated banded chromitite. We suggest that the geologically, geochemically and mineralogically distinct banded chromitite from Kraubath characterises the transition zone of an ophiolite, closely above the mantle section hosting podiform chromitite, rather than being representative of the crustal cumulate pile.

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Section: Pge Concentrations In Whole-rock Samplessupporting

confidence: 70%

Diversity of platinum-group mineral assemblages in banded and podiform chromitite from the Kraubath ultramafic massif, Austria: evidence for an ophiolitic transition zone?

Malitch

Thalhammer

Knauf³

et al. 2003

Miner Deposita

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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%

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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“…The fractionation of the PGE in the mantle during partial melting was considered for the Leka (Pedersen et al 1993), Newfoundland (Page & Talkington 1984), Shetland (Prichard et al 1986), Kempirsay (Distler et al 2003) and other ophiolite localities.…”

Section: Discussionmentioning

confidence: 99%

Platinum-Group Minerals From the Olkhovaya-1 Placers Related to the Karaginsky Ophiolite Complex, Kamchatskiy Mys Peninsula, Russia

Tolstykh¹,

Sidorov²,

Kozlov³

2009

The Canadian Mineralogist

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Mineral assemblages from the Olkhovaya-1 River placers, in Kamchatka, Far-Eastern Russia, provide genetic information on their evolution. The minerals are dominated by Os-Ir-Ru alloys (80%), consisting of all possible mineral species, and Pt-Fe alloys consisting of native platinum, Fe-rich platinum and isoferroplatinum. The following features of the mineral assemblage are characteristic of mineralization associated with an ophiolitic complex: (1) in the Os-Ru-Ir diagram, the compositions of the hexagonal alloy form a ruthenium trend; (2) there are two typical equilibrium magmatic parageneses of alloys: early osmiumiridium, and later isoferroplatinum-ruthenium, which both are associated with laurite and the solid solution laurite-irarsite (Ru,Ir) (S,As) 2 . The cooperite, sperrylite and Pd minerals formed at the postmagmatic stage. Tetraferroplatinum-tulameenite, replacing the Pt-Fe alloys, as well as the multicomponent compounds of Ru, Os, Ir, Rh, Pt with Fe replacing the Os-Ir-Ru alloys and PGE sulfides, result from serpentinization of PGM-bearing rocks. The PGM assemblage in the Ol'khovaya-1 River placers is related to the Karaginsky ophiolite complex of the Kamchatskiy Mys Peninsula.Keywords: platinum-group minerals, ophiolitic rocks, iridium-osmium paragenesis, isoferroplatinum-ruthenium paragenesis, Kamchatskiy Mys Peninsula, Russia. SOmmaiReLes assemblages de minéraux prélevés dans les placers de la rivière Olkhovaya-1, au Kamchatka, en Russie orientale, contiennent de l'information génétique concernant leur évolution. Les alliages Os-Ir-Ru sont les minéraux prédominants (80%); nous reconnaissons toutes les espèces connues. Parmi les alliages Pt-Fe, nous trouvons le platine natif, le platine riche en fer, et l'isoferroplatine. Les caractéristiques suivantes indiquent une minéralisation associée à un complexe ophiolitique: (1) dans le diagramme Os-Ru-Ir, les compositions de l'alliage hexagonal définissent un tracé d'enrichissement en ruthénium; (2) nous trouvons deux paragenèses magmatiques typiques parmi les alliages, osmium-iridium précoce et isoferroplatine-ruthénium tardif, les deux étant associés à la laurite et à la solution solide laurite-irarsite (Ru,Ir)(S,As) 2 . La cooperite, la sperrylite et les minéraux de Pd se sont formés à un stade postmagmatique. L'association tétraferroplatine-tulameenite, qui remplace les alliages Pt-Fe, ainsi que les composés à multi-composantes Ru, Os, Ir, Rh, Pt avec Fe, qui remplacent les alliages Os-Ir-Ru et les sulfures des éléments du groupe du platine, résulteraient de la serpentinisation des roches porteuses des minéraux du groupe du platine. Ces minéraux dans les placers de la rivière Ol'khovaya-1 proviendraient du massif ophiolitique de Karaginsky, qui affleure sur la péninsule de Kamchatskiy Mys.(Traduit par la Rédaction) Mots-clés: minéraux du groupe du platine, roches ophiolitiques, paragenèse iridium-osmium, paragenèse isoferroplatine-ruthé-nium, péninsule Kamchatskiy Mys, Russie. §

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Stratiform platinum-group element mineralizations in the ultramafic cumulates of the Leka ophiolite complex, central Norway

Cited by 68 publications

References 0 publications

Diversity of platinum-group mineral assemblages in banded and podiform chromitite from the Kraubath ultramafic massif, Austria: evidence for an ophiolitic transition zone?

Diversity of platinum-group mineral assemblages in banded and podiform chromitite from the Kraubath ultramafic massif, Austria: evidence for an ophiolitic transition zone?

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

Platinum-Group Minerals From the Olkhovaya-1 Placers Related to the Karaginsky Ophiolite Complex, Kamchatskiy Mys Peninsula, Russia

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