Chromian Spinel Composition and the Platinum-Group Minerals of the Pge-Rich Loma Peguera Chromitites, Loma Caribe Peridotite, Dominican Republic

Proenza, Joaquín A.; Zaccarini, Federica; Lewis, John F.; Longo, Francisco; Garuti, Giorgio

doi:10.2113/gscanmin.45.3.631

Cited by 101 publications

(48 citation statements)

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“…On the basis of their textural relationships, occurrence and composition, the PGM have been divided into (1) primary, formed in the magmatic stage, before and during the precipitation of chromite and (2) secondary, formed by the alteration of primary PGM at a relatively low temperature [2][3][4][5][6][7][8][9][10][11][12]. Paragenetic considerations indicate that in the Cedrolina chromitite only irarsite and laurite could represent relicts of the original igneous assemblage [54][55][56][57][58][59].…”

Section: The Accessory Minerals In the Cedrolina Chromitite And Theirmentioning

confidence: 99%

“…The platinum group minerals (PGM), with few exceptions, are grouped among accessory phases, being rare and occurring as tiny particles dispersed in their host rocks. Recent investigations have shown that the primary/magmatic PGM may be altered to secondary PGM during metamorphism, as well as weathering and lateritization [2][3][4][5][6][7][8][9][10][11][12]. It has also been demonstrated that hydrothermal solutions and metamorphic fluids are capable of introducing incompatible elements in the alteration system of a chromitite, giving rise to the formation of exotic accessory minerals, such as monazite, galena, bismuthinite, and antimony that normally do not occur in unaltered chromitites [13,14].…”

Section: Introductionmentioning

confidence: 99%

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The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle

et al. 2016

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Abstract:The Cedrolina chromitite body (Goiás-Brazil) is concordantly emplaced within talc-chlorite schists that correspond to the poly-metamorphic product of ultramafic rocks inserted in the Pilar de Goiás Greenstone Belt (Central Brazil). The chromite ore displays a nodular structure consisting of rounded and ellipsoidal orbs (up to 1.5 cm in size), often strongly deformed and fractured, immersed in a matrix of silicates (mainly chlorite and talc). Chromite is characterized by high Cr# (0.80-0.86), high Fe 2+ # (0.70-0.94), and low TiO 2 (av. = 0.18 wt %) consistent with variation trends of spinels from metamorphic rocks. The chromitite contains a large suite of accessory phases, but only irarsite and laurite are believed to be relicts of the original igneous assemblage, whereas most accessory minerals are thought to be related to hydrothermal fluids that emanated from a nearby felsic intrusion, metamorphism and weathering. Rutile is one of the most abundant accessory minerals described, showing an unusually high Cr 2 O 3 content (up to 39,200 ppm of Cr) and commonly forming large anhedral grains (>100 µm) that fill fractures (within chromite nodules and in the matrix) or contain micro-inclusions of chromite. Using a trace element geothermometer, the rutile crystallization temperature is estimated at 550-600 • C (at 0.4-0.6 GPa), which is in agreement with P and T conditions proposed for the regional greenschist to low amphibolite facies metamorphic peak of the area. Textural, morphological, and compositional evidence confirm that rutile did not crystallize at high temperatures simultaneously with the host chromitite, but as a secondary metamorphic mineral. Rutile may have been formed as a metamorphic overgrowth product following deformation and regional metamorphic events, filling fractures and incorporating chromite fragments. High Cr contents in rutile very likely are due to Cr remobilization from Cr-spinel during metamorphism and suggest that Ti was remobilized to form rutile. This would imply that the magmatic composition of chromite had originally higher Ti content, pointing to a stratiform origin. Another possible interpretation is that the Ti-enrichment was caused by external metasomatic fluids which lead to crystallization of rutile. If this was the case, the Cedrolina chromitites could be classified as podiform, possibly representing a sliver of tectonically dismembered Paleoproterozoic upper mantle. However, the strong metamorphic overprint that affected the studied chromitites makes it extremely difficult to establish which of the above processes were active, if not both (and to what extent), and, therefore, the chromitite's original geodynamic setting.

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Section: The Accessory Minerals In the Cedrolina Chromitite And Theirmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle

et al. 2016

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“…These authors have shown that secondary processes can cryptically modify the composition of primary PGM, which leads to the formation of new PGM phases. Alloys and oxides rich in Ru, Os and Ir are the most common secondary PGM encountered in podiform chromitites (e.g., Garuti & Zaccarini 1997, Ahmed & Arai 2003, Gervilla et al 2005, Proenza et al 2007, 2008.…”

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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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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“…1B). Draper et al (1996) suggested that the Loma Caribe peridotite, a serpentinized harzburgite with minor dunites, lherzolites and pyroxenites forming part of a dismembered ophiolite complex (Lewis et al, 2006;Proenza et al, 2007), was tectonically emplaced over the Maimón Formation during the late Albian along a northward thrust; obduction resulted in deformation and metamorphism of the Maimón Formation, particularly in the Ozama shear zone. The Loma Caribe peridotite belt is separated from the Maimón Formation at their southern contact by the Peralvillo Sur Formation, a thin sequence of arc-related volcanic and volcanosedimentary rocks of Late Cretaceous (?)…”

Section: Accepted M Manuscriptmentioning

confidence: 99%