Experimental Constraints on the Chromite-melt Partitioning Behaviour of Rhenium and Platinum-group Elements PDF Download

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Languages : en
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Author: Parisa Sattari
Publisher: National Library of Canada = Bibliothèque nationale du Canada
ISBN: 9780612534650
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Languages : en
Pages :

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Author: Parisa Sattari
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Abundant geochemical and petrological data exists to suggest that chromite may be an important phase in concentrating and fractionating the PGEs in mafic/ultramafic systems. To investigate this possibility, chromite/silicate- and sulphide-melt partitioning experiments have been conducted at conditions of pressure, temperature and fO2 appropriate for basalt genesis. Trace elements in run products were determined 'in situ' using laser ablation ICP-MS, which allowed us to discern both phase homogeneity and detect the presence of sulphide or alloy contaminants. Experiments yielded absolute chromite/silicate melt partition coefficients (Ds) for Re (0.15) and maximum values for the PGEs (Ru

Author: Craig Stewart Finnigan
Publisher:
ISBN: 9780494218693
Category :
Languages : en
Pages : 306

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Experiments were performed to document the role of chromite in affecting the behaviour of the platinum group elements (PGEs) during melting and crystallization. Initial experiments involving diffusive exchange of natural chromite with PGE-saturated basaltic melt revealed platinum group minerals (PGMs; including metal alloys and laurite) as precipitates along the chromite-melt interface. X-ray photoelectron spectroscopy of the glass near the chromite showed lower Fe3+/Fe2+ relative to measurements far removed from the interface, indicating a local zone of reduction The reduction is likely caused by preferential uptake of Fe3+ and Cr 3+ by the chromite relative to the melt. The effect causes the precipitation of PGMs due to their locally lowered solubility. PGM precipitation was also found to occur during spinel growth experiments, which we attribute to the same effect. This process could explain the commonly observed inclusion of PGM in chromite in ophiolites and layered intrusions, and may contribute to the fractionation of the PGEs due to their differential solubilities in silicate melt. Chromite may therefore concentrate and fractionate the PGEs by two different mechansims, one involving physical entrapment of PGMs following local reduction, and the other involving direct solid solution into the chromite lattice. The diffusive exchange technique was also used to measure chromite-melt partitioning of the PGEs, which avoids the problem of PGE contamination during heterogeneous nucleation of chromite in metal-saturated experiments. Run product chromite crystals and glass were analysed by laser ablation---inductively coupled plasma---mass spectrometry (LA-ICP-MS). Partition coefficients were calculated using the composition of chromite margins and coexisting glass. In sulfur-free experiments, chromite-melt partition coefficients (D) for Rh and Ru are large (> 10), and show a progressive decrease with lower fO 2, but still remain> 1. Partition coefficients for Pt are & sim;2 or less, whereas values for Pd are “1 under all conditions studied. Partition coefficients for Os range from 9 to 213, and minimum partition coefficients for Ir are all> 1. Partition coefficients for Ru, Rh and Pt measured at log fS2 of -0.23 are all lower than those measured in S-free experiments at the same or similar fO2. Of Significance, Os and Ru retain their compatibility in chromite in S-bearing experiments at FMQ. Measured partition coefficients confirm that chromite can fractionate Os, Ir, Ru and Rh from Pt and Pd during crystallization, provided the system is sulfur-poor.

Author: Federica Zaccarini
Publisher: MDPI
ISBN: 3039365975
Category : Science
Languages : en
Pages : 270

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This book (Special Issue) presents the geological environment, physical/chemical properties, and crystallographic data for two new minerals associated with chromitites from the Othrys ophiolite complex: Eliopoulosite, V7S8/IMA2019-96, and Grammatikopoulosite, NiVP/IMA2019-090. The distribution, mineralogy, and field relationships of PGE-enriched ores, which are important for our understanding of the metallogenic controls on the concentration of PGE and their exploration, are addressed in papers, providing (a) the first detailed data on the chromitites and platinum-group elements (PGE) mineralization from Ulan-Sar’dag ophiolite, Central Asian Fold Belt/East Sayan, Russia, (b) peculiarities on the distribution of PGE in arsenopyrites and pyrites from the Natalkinskoe gold ore deposit, NE Russia, and (c) the occurrence of zoned laurite found in the Merensky Reef of the Bushveld layered intrusion, South Africa, characterized by textural/compositional features suggesting “hydrothermal” origin. Two papers deal with (a) the rare earth element (REE) distribution in various mineral deposits of Sweden, obtained during the EURARE project, and their application to the exploration of REE and (b) the optimization of the beneficiation process for the REE recovery from black sands. Five papers provide new data of genetic and exploration significance on trace elements, including REE and PGE in various ore-types, and factors controlling the Cr stable isotope (δ53Cr values) in chromitites from the Balkan peninsula.

Author: Anthony J. Naldrett
Publisher: Springer Science & Business Media
ISBN: 3662084449
Category : Science
Languages : en
Pages : 744

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This book is written by a leading authority on the subject of magmatic sulfide deposits. An overview of deposit types, accompanied by a summary of the resources of nickel, copper and platinum-group elements in the world’s principal known deposits, is followed by a summary of the relevant physical chemistry. The core of the book comprises a discussion about the geology and geochemistry of each of the deposit types in turn, accompanied by the implications of this data to the origin of the deposits in the light of our understanding of the chemical processes involved. A final chapter focuses on the use of the genetic concepts in exploration.

Author: Sanjib Chandra Sarkar
Publisher: Cambridge University Press
ISBN: 1107079977
Category : Science
Languages : en
Pages : 1137

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Crustal evolution means the resultant changes that the Earth's crust has gone through in its geologic past affected by changes in the mantle-crust system, the atmosphere, the hydrosphere and the biosphere. Metallogeny is the genesis of metallic mineral deposits. Both the terms are used in the book in their conventional sense, but keeping in mind an Indian context. This book is the first of its kind to document in detail the nature, origin and evolution of mineral deposits in India and is contextualized in local, regional and global geology. The book is unique in that it combines both metallogeny and crustal evolution that were hitherto treated as stand-alone topics. The exhaustive chapters in the book carry detailed case studies of the distribution and occurrence of ores. The book would be useful to students of advanced geology, researchers, teachers, planners and global metallogeneticists around the world.

Author: Roberto Moretti
Publisher: John Wiley & Sons
ISBN: 111947325X
Category : Science
Languages : en
Pages : 436

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Explores the many facets of redox exchanges that drive magma's behavior and evolution, from the origin of the Earth until today The redox state is one of the master variables behind the Earth's forming processes, which at depth concern magma as the major transport agent. Understanding redox exchanges in magmas is pivotal for reconstructing the history and compositional make-up of our planet, for exploring its mineral resources, and for monitoring and forecasting volcanic activity. Magma Redox Geochemistry describes the multiple facets of redox reactions in the magmatic realm and presents experimental results, theoretical approaches, and unconventional and novel techniques. Volume highlights include: Redox state and oxygen fugacity: so close, so far Redox processes from Earth’s accretion to global geodynamics Redox evolution from the magma source to volcanic emissions Redox characterization of elements and their isotopes The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals.

Author: Yanan Liu
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Languages : en
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Abstract A more quantitative understanding of how highly siderophile elements (HSEs: Os, Ir, Ru, Rh, Pt, Pd, Au, Re), Ag, Pb and chalcogens (As, Se, Sb, Te and Bi) behave during magmatic sulfide solidification in nature builds on several important aspects: 1) accurate measurements of their concentrations in natural samples; 2) quantitative constraints on their partitioning behaviors; 3) a crystallization model that can reasonably simulate the ore deposits of interest. In order to better measure the concentrations of these elements during the solidification of sulfide melts, we have developed a new Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) standard (Ge-Sb-S glass; Ge6) for improving the trace level measurements of these elements in both sulfide and silicate glass matrices. The Ge6 composition has excellent glass forming capability and can incorporate a variety of dopants up to the 100 ppm level, except for Ru, Os, Re, W and Mo, which can be doped to 5-10 ppm without sacrificing homogeneity. Reference materials (JBSulfide, NiS4, JGb-1, JG-1a, JB-2, BIR-1, BHVO-1) were tested using Ge6 as the standard, and the results agree with accepted values. To better understand and simulate the partitioning behaviors of these elements, a series of experiments to measure partition coefficients (D values) between monosulfide solid solution (MSS) and sulfide melt, as well as MSS and intermediate solid solution (ISS) were also conducted, at 0.1 MPa and 860-926 °C (where these phases can be stabilized), log fS2 -3.0 to -2.2 (similar to the Pt-PtS buffer), with fO2 controlled at the fayalite-magnetite-quartz (FMQ) buffer. The IPGEs (Os, Ir, Ru), Rh and Re are found to be compatible in MSS relative to sulfide melt with D values ranging from ~20 to ~5, and DRe/DOs of ~0.5. Pd, Pt, Au, Ag, Zn, Pb, as well as the chalcogens, are incompatible in MSS, with D values ranging from ~0.1 to ~1 x 10-3. For the same metal/sulfur ratio, D values for the IPGEs, Rh and Re are systematically larger than most previous studies and correlate with higher oxygen content in the sulfide liquid, reflecting the significant effect of oxygen on increasing the activity coefficients for these elements in the melt phase. MSS/ISS partitioning experiments reveal that Ru, Os, Ir, Rh and Re are partitioned into MSS by a factor of >50, whereas Pd, Pt, Ag, Au and the chalcogens partition from weakly (Se, As) to strongly (Ag, Au) into ISS. Uniformly low MSS- and ISS- melt partition coefficients for the chalcogens, Pt, Pd, Ag and Au will lead to enrichment in the residual sulfide liquid, but D values are generally too large to reach early saturation in Pt-Pd-chalcogen-rich accessory minerals, based on current solubility estimates. Instead, these phases likely precipitate at the last dregs of crystallization. Modeled evolution curves for the PGEs and chalcogens are in reasonably good agreement with whole-rock sulfide compositions for the McCreedy East deposit (Sudbury, Ontario), consistent with an origin by crystallization of MSS, then MSS + ISS from sulfide magma.

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Category : Geology, Economic
Languages : en
Pages : 916

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