Cryptic compositional variation in laurite and enclosing chromite from the Bird River Sill, Manitoba

Ohnenstetter, Daniel; Watkinson, David H.; Jones, Peter Tom; Talkington, Raymond W.

doi:10.2113/gsecongeo.81.5.1159

Cited by 26 publications

(9 citation statements)

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“…10). On the other hand, the laurite composition of the Oman ophiolite is quite different from those in some ophiolites and layered intrusions, i.e., New Caledonia (Augé & Maurizot 1995) and Vourinos (Augé 1988) ophiolites, Stillwater Complex, Montana (Talkington & Lipin 1986), and the Bird River Sill complex, Manitoba (Ohnenstetter et al 1986). The laurite in these complexes is usually Ru-rich and Osand Ir-poor relative to those of the first group (Fig.…”

Section: The Oman Ophiolite Among Others: a Comparisonmentioning

confidence: 89%

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Platinum-Group Minerals in Podiform Chromitites of the Oman Ophiolite

Ahmed¹,

Arai²

2003

The Canadian Mineralogist

101

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Chromitite lenses rich in the platinum-group elements (PGE) have recently been discovered in the deeper part of the mantle section of the northern part of the Oman ophiolite. In terms of stratigraphic level, there are two types of chromitite: Moho transition zone (MTZ) and mantle types. The mantle type can be further classified into two subtypes: PGE-poor and PGE-rich. Platinum-group minerals (PGM) have been mainly observed in the PGE-rich mantle chromitite and, to a lesser extent, in the PGEpoor mantle chromitite, although a few PGM grains have been detected from the MTZ chromitites. The PGM comprise four main categories in the following order of abundance: (1) sulfides [Os-rich laurite, erlichmanite and unnamed (Ir,Rh)(Ni,Cu,Fe) 2 S 3 ], (2) sulfarsenide and arsenide (irarsite-hollingworthite series, palladoarsenide), (3) alloys and native metals [Os-Ir alloy, (Cu-Pt-FeIr-Rh) alloy, Pt-Fe alloy, (Ni-Ru-Os-Ir) alloy, Ir-Pt alloy, Ir-Rh alloy and native Pd metal], and (4) PGE oxide (Ru-Os-Ir oxide). Base-metal sulfides (BMS) and base-metal alloys (BMA) also are found, as inclusions in chromian spinel and interstitial matrix, mainly in the MTZ and PGE-poor mantle chromitites. The common abundance of PGE sulfides, i.e., Os-rich laurite, in the Oman chromitites is ascribed to the sulfide-undersaturated nature of the magma involved in chromitite formation. However, the sulfur fugacity was sufficiently high to produce the Os-rich laurite and, to a lesser extent, erlichmanite and Ru-poor Os-Ir alloy. The sulfur fugacity was higher in the formation of the PGE-poor mantle chromitite relative to the PGE-rich chromitite, as indicated by the presence of the unnamed Ir-rich sulfides and, to a lesser extent, BMS. The presence of PGE oxide commonly associated with fractured chromian spinel indicates that the PGE distribution in rocks can easily be modified at an early stage of serpentinization.Keywords: laurite, chromitite, ophiolite, platinum-group elements, platinum-group minerals, sulfur fugacity, northern Oman. SOMMAIRENous avons récemment découvert des lentilles de chromitite enrichies en éléments du groupe du platine (EGP) dans la partie la plus profonde de la séquence mantellique de la partie nord de l'ophiolite d'Oman. Du point de vue niveau stratigraphique, nous distinguons deux sortes de chromitites, celles qui sont associées à la zone de transition du Moho (MTZ), et celles provenant du manteau sousjacent. Ces dernières comprennent à leur tour deux types, l'un pauvre en EGP et l'autre enrichi en EGP. Les minéraux du groupe du platine se trouvent surtout dans les chromitites mantelliques enrichies en EGP, quoique qu'on en trouve aussi, mais à un degré moindre, dans les chromitites mantelliques à faible teneur en EGP et dans les chromitites de type MTZ. Nous documentons quatre groupes de ces minéraux, présentés ici dans un ordre selon leur abondance: (1) (4) oxyde des EGP (oxyde Ru-Os-Ir). Nous avons aussi trouvé des sulfures et des alliages de métaux de base, en inclusion dans le spinelle chromifère et dans l...

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Section: The Oman Ophiolite Among Others: a Comparisonmentioning

confidence: 89%

“…3. Layered intrusions: Stillwater complex, Montana (Talkington & Lipin 1986), and Bird River Sill complex, Manitoba, Canada (Ohnenstetter et al 1986). Garuti et al 1999a, Brenan & Andrews 2001.…”

Section: Origin Of Primary Pgm Assemblagesmentioning

confidence: 99%

Platinum-Group Minerals in Podiform Chromitites of the Oman Ophiolite

Ahmed¹,

Arai²

2003

The Canadian Mineralogist

101

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“…Detailed point analyses showed that the large crystals of laurite in type-1 assemblages are not zoned, unlike laurite from the Bird River Sill, Manitoba (Ohnenstetter et al 1986). An Os-rich core was, however, observed in a large crystal of laurite from sample BN40.…”

Section: Moncheitementioning

confidence: 96%

Magmatic and Hydrothermal Platinum-Group Minerals and Base-Metal Sulfides in the Baula Complex, India

Augé

Salpeteur

Bailly

et al. 2002

The Canadian Mineralogist

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The 3 ϫ 0.5 km gabbro-hosted Precambrian Baula Complex, in Orissa, India, comprises a steeply dipping pyroxenite unit in tectonic contact to the east with a peridotite unit that contains three chromitite layers and that becomes pyroxene-rich eastward toward the top. The ultramafic formations are intruded by the Bangur Gabbro, the top of which entered a shear zone, forming a breccia zone. The breccia, 1 to 40 m thick and almost continuous along strike for 2000 m, shows extensive vertical and lateral variations. It is made up of ultramafic blocks of various sizes derived from the Baula Complex within a matrix of hydrothermally altered Bangur Gabbro. The brecciation process has affected one of the chromitite layers. Two categories of platinum-groupelement (PGE) mineralization have been observed in the Baula Complex, both associated with the Bangur Gabbro. The first (type 1) occurs within a sulfide-free magmatic environment within the Bangur Gabbro near its contact with the peridotite, and is clearly formed within a magmatic environment. The PGE-bearing rock contains relics of dunite and chromitite extracted mechanically from the ultramafic formations by the intrusive gabbro. This mineralization is dominated by Pt (Pt/Pd in the range 8-9), is anomalous in Rh, and the platinum-group-mineral (PGM) assemblage is dominated by isoferroplatinum, braggite and malanite, with sperrylite and laurite, included in pyroxene and plagioclase. The second category (types 2A and 2B) is restricted to the hydrothermally altered matrix of the breccia zone. Type 2A has PGE associated with base-metal mineralization; the PGE assemblages are characterized by Pd (Pt/Pd 0.5), and the PGM are mainly sudburyite, minerals of the system Pd-Bi-Te-Sb, and sperrylite. Type 2B is not associated with base metals, the PGE are characterized by Pt (Pt/Pd in the range 2-3), and PGM phases of the Pt-Sb-As system (geversite, sperrylite) coexist with Pd antimony (mertieite-II). The PGE minerals form discrete grains, a) in the hydrous silicate matrix (commonly as clusters) without base-metal sulfides (BMS) or in the silicate matrix accompanying BMS trails, where they are in some cases adjacent to disseminated BMS, b) within ferrian chromite, c) within BMS in silicates, and d) within or adjacent to BMS in ferrian chromite. We present the results of electron-microprobe analyses of the PGM and BMS phases, and propose a model in which type-1 mineralization results from an orthomagmatic episode, whereas the type-2 mineralization is a result of hydromagmatic processes affecting the gabbroic matrix of the complex breccia zone.

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“…For example, chromite deposits are predominant in the early to mid Archean greenstone belts (3500-2900 Ma) namely, the Shurugwi greenstone belt in the Zimbabwe craton (South Africa; Rollinson, 1997;Stowe, 1987), the Tomka-Daitari-Gorumahishani-Badampahar-JamdaKoira greenstone belts in the Singhbhum craton (eastern India; Mondal, 2009), the Nuggihalli-Krishnarajpet-Holenarsipur greenstone belts in the Western Dharwar craton (southern India; Mukherjee et al, 2010), and the Jamestown igneous complex in the Barberton greenstone belt (Kaapvaal craton, South Africa;. Slightly younger (≈2.7 Ga) chromite deposits within greenstone belt occur in the sill-like ultramafic complex of the Bird river sill deposit in the Superior craton, Canada (Ohnenstetter et al, 1986).…”

Section: Implications For Chromite Ni-sulfide and Pge Mineralizationmentioning

confidence: 99%

“…The greenstone belts are composed of interlayered volcanic-sedimentary rocks that are surrounded by the belt (Jamestown Igneous complex, Kaapvaal craton, South Africa;, the Bird River sill within the Bird River greenstone belt (Superior craton, Canada; Mungall and Staff, 2008;Ohnenstetter et al, 1986), and the Obanga greenstone belt (Superior craton, Canada; Tomlinson et al, 2002). These ultramafic-mafic bodies are genetically related to high-Mg magmas such as komatiite, boninite or high-Mg siliceous basalt (Mondal, 2000;Mondal et al, 2006Mondal et al, , 2007Prendergast, 2008;Rollinson, 1997).…”

Section: Introductionmentioning

confidence: 99%