Composition and textures of chromite and platinum-group minerals in chromitites of the western ophiolitic belt from Pampean Ranges of Córdoba, Argentina

Proenza, Joaquín A.; Zaccarini, Federica; Escayola, Mónica Patricia; Cábana, C.; Schalamuk, A.; Garuti, Giorgio

doi:10.1016/j.oregeorev.2006.05.009

Cited by 77 publications

(44 citation statements)

References 39 publications

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“…Ternary Cr-Al-Fe 3+ diagrams exhibiting >500 analyses of chromite from Cedrolina. (A) Modified after [11], with the fields of different metamorphic facies from [39][40][41]; (B) Stability limits of spinels defined for chromite and magnetite (calculated in equilibrium with Fo90 olivine). Modified after [42,43].…”

Section: Rutilementioning

confidence: 99%

“…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: Rutilementioning

confidence: 99%

Section: The Accessory Minerals In the Cedrolina Chromitite And Theirmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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“…Alchromite suggest that the Cr-spinel crystallized through high degrees of partial melting at the shallowest levels of an upper mantle source (within the Moho Transition Zone), i.e., close to the layered gabbro sequence (e.g. [60][61][62][63][64][65]). Trace element enrichment of Cs, Rb, Pb, Sb, Sr are caused due serpentinization process, tremolite and/or carbonate precipitation also caused Pb, Sb enrichment and produces in serpentinites (cf.…”

Section: Discussionmentioning

confidence: 99%

Petrology and geochemistry of meta-ultramafic rocks in the Paleozoic Granjeno Schist, northeastern Mexico: Remnants of Pangaea ocean floor

et al. 2017

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Abstract:The Granjeno Schist is a meta-volcanosedimentary upper Paleozoic complex in northeastern Mexico. We suggest different tectonic settings for metamorphism of its serpentinite and talc-bearing rocks based on petrographic and geochemical compositions. According to the REE ratios (La N /Yb N = 0.51-20.0 and La N /Sm N = 0.72-9.1) and the enrichment in the highly incompatible elements Cs (0.1 ppm), U (2.8 ppm), and Zr (60 ppm) as well as depletion in Ba (1 -15 ppm), Sr (1 -184 ppm), Pb (0.1 -14 ppm), and Ce (0.1 -1.9 ppm) the rocks have mid-ocean ridge and subduction zones characteristics. The serpentinite contains Al-chromite, ferrian chromite and magnetite. The Al-chromite is characterized by Cr# of 0.48 to 0.55 suggesting a MORB origin, and Cr# of 0.93 to 1.00 for the ferrian chromite indicates a prograde metamorphism. We propose at least two serpentinization stages of lithospheric mantle for the ultramafic rock of the Granjeno Schist, (1) a first in an ocean-floor environment at sub-greenschist to greenschist facies conditions and (2) later a serpentinization phase related to the progressive replacement of spinel by ferrian chromite and magnetite at greenschist to low amphibolite facies conditions during regional metamorphism. The second serpentinization phase took place in an active continental margin during the Pennsylvanian. We propose that the origin of the ultramafic rocks is related to an obduction and accretional event at the western margin of Pangea.

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“…PGM are susceptible to alteration during serpentinisation of their host chromitites and peridotites (e.g., [28,41,42]). We interpret the desulphurised phases of laurite and erlichmanite, as well as the associated IPGE-Ni alloys, occurring in Agios Stefanos, as products of such an episode.…”

Section: Petrogenetic Implicationsmentioning

confidence: 99%

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

et al. 2016

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Platinum-group minerals were concentrated using superpanning from two composite chromitite samples, which were collected from two old mines within the Othrys ophiolite. This method allows for the recovery of a broad spectrum of these rare and fine-grained minerals, and helps to better identify them and interpret their origin. Major differences between the east and west Othrys ophiolites were determined, probably as a result of their different origin and evolution. Primary Os-, Ir-, and Ru-bearing platinum-group minerals (IPGM)-alloys and the Rh-, Pt-and Pd-bearing platinum-group minerals (PPGM) occur only in the east Othrys chromitite, indicating an evolution from initially low f S2 conditions at shallower mantle levels with the subsequent implication of a S-saturated ascending fluid. In contrast, the absence of primary IPGM-alloys in west Othrys chromitite indicates that S saturation had been attained. The presence of erlichmanite suggests that sulphur fugacity eventually increased significantly in both suites. Substantial fluctuations of a fluid phase, likely related to serpentinising fluids, modified the platinum-group minerals (PGM) assemblage of west Othrys, and resulted in a large diversity of secondary PGM minerals. The limited number of secondary species developed in the east Othrys indicate that secondary processes were also different in the two suites.

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Composition and textures of chromite and platinum-group minerals in chromitites of the western ophiolitic belt from Pampean Ranges of Córdoba, Argentina

Cited by 77 publications

References 39 publications

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

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

Petrology and geochemistry of meta-ultramafic rocks in the Paleozoic Granjeno Schist, northeastern Mexico: Remnants of Pangaea ocean floor

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

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