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- Aiglsperger, Thomas, et al.
(författare)
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Platinum group minerals (PGM) in the Falcondo Ni-laterite deposit, Loma Caribe peridotite (Dominican Republic)
- 2015
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Ingår i: Mineralium Deposita. - : Springer Science and Business Media LLC. - 0026-4598 .- 1432-1866. ; 50:1, s. 105-123
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Tidskriftsartikel (refereegranskat)abstract
- Two Ni-laterite profiles from the Loma Caribe peridotite (Dominican Republic) have been investigated for their platinum group element (PGE) geochemistry and mineralogy. One profile (Loma Peguera) is characterized by PGE-enriched (up to 3.5 ppm total PGE) chromitite bodies incorporated within the saprolite, whereas the second profile is chromitite-free (Loma Caribe). Total PGE contents of both profiles slightly increase from parent rocks (36 and 30 ppb, respectively) to saprolite (∼50 ppb) and reach highest levels within the limonite zone (640 and 264 ppb, respectively). Chondrite-normalized PGE patterns of saprolite and limonite reveal rather flat shapes with positive peaks of Ru and Pd. Three types of platinum group minerals (PGM) were found by using an innovative hydroseparation technique: (i) primary PGM inclusions in fresh Cr-spinel (laurite and bowieite), (ii) secondary PGM (e.g., Ru-Fe-Os-Ir compounds) from weathering of preexisting PGM (e.g., serpentinization and/or laterization), and (iii) PGM precipitated after PGE mobilization within the laterite (neoformation). Our results provide evidence that (i) PGM occurrence and PGE enrichment in the laterite profiles is independent of chromitite incorporation; (ii) PGE enrichment is residual on the profile scale; and (iii) PGE are mobile on a local scale leading to in situ growth of PGM within limonite, probably by bioreduction and/or electrochemical metal accretion.
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| 2. |
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| 3. |
- Pašava, Jan, et al.
(författare)
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Platinum-group elements (PGE) and their principal carriers in metal-rich black shales : An overview with a new data from Mo-Ni-PGE black shales (Zunyi region, Guizhou Province, south China)
- 2013
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Ingår i: Journal of Geosciences. - : Czech Geological Society. - 1802-6222 .- 1803-1943. ; 58:3, s. 213-220
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Tidskriftsartikel (refereegranskat)abstract
- Lower Cambrian Mo–Ni sulfidic black shales from the Huangjiawan mine (Guizhou Province, south China) have anomalousplatinum-group elements (PGE) concentrations (up to ~1 ppm in total). In order to identify principal PGE carriers,we used heavy mineral separates which were produced by innovative hydroseparation techniques. Subsequent detailedmineralogical study using electron microprobe did not result in the identification of discrete platinum-group minerals.Pyrite (grainy, not framboidal), millerite and gersdorffite that were found in our heavy concentrate were analyzed forPGE and Re. We found that they contain the following concentrations of PGE and Re: pyrite (up to 490 ppm Pt, 390ppm Pd and 220 ppm Rh), millerite (up to 530 ppm Pt, 430 ppm Pd and 190 ppm Rh) and gersdorffite (up to 410 ppmPt and 320 ppm Pd; no Rh detected). Rhenium was detected only in grainy pyrite (up to 1060 ppm). It was found thatdespite anomalous PGE concentrations, the Mo–Ni black shales do not contain any platinum-group minerals and thatthe PGE are bound to pyrite and Ni-sulfides (millerite and gersdorffite).
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| 4. |
- Zaccarini, Frederica, et al.
(författare)
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Chromite and platinum group elements mineralization in the Santa Elena Ultramafic Nappe (Costa Rica) : Geodynamic implications
- 2011
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Ingår i: Geologica Acta. - 1695-6133 .- 1696-5728. ; 9:3-4, s. 407-423
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Tidskriftsartikel (refereegranskat)abstract
- Chromitites associated with strongly altered peridotite from six distinct localities in the Santa Elena ultramaficnappe (Costa Rica) have been investigated for the first time. Santa Elena chromitites commonly display acompositional variation from extremely chromiferous (Cr/(Cr+Al)=0.81) to intermediate and aluminous(Cr/(Cr+Al)=0.54). This composition varies along a continuous trend, corresponding to calculated parental liquidswhich may have been derived from the differentiation of a single batch of boninitic magma with Cr-rich and(Al, Ti)-poor initial composition. Fractional precipitation of chromite probably occurred during differentiation ofthe boninitic melt and progressive metasomatic reaction with mantle peridotite. The distribution of platinum groupelements (PGE) displays the high (Os+Ir+Ru)/(Rh+Pt+Pd) ratio typical of ophiolitic chromitites and, consistently,the platinum group minerals (PGM) encountered are mainly Ru-Os-Ir sulfides and arsenides. Textural relations ofmost of the platinum group elements suggest crystallization at magmatic temperatures, possibly under relativelyhigh sulfur fugacity as indicated by the apparent lack of primary Os-Ir-Ru alloys.The chemical and mineralogical characteristics of chromitites from the Santa Elena ultramafic nappe have astrong affinity to podiform chromitites in the mantle section of supra-subduction-zone ophiolites. Calculatedparental melts of the chromitites are consistent with the differentiation of arc-related magmas, and do not supportthe oceanic spreading center geodynamic setting previously proposed by some authors.
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| 5. |
- Zaccarini, Frederica, et al.
(författare)
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The occurrence of platinum-group element and gold minerals in the Bon Accord Ni-oxide body, South Africa
- 2014
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 99:8-9, s. 1774-1782
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Tidskriftsartikel (refereegranskat)abstract
- Two samples from the enigmatic Ni-oxide body of Bon Accord (Barberton greenstone belt, South Africa) have been investigated with the hydroseparation technique to obtain heavy mineral concentrates. The concentrates contain abundant Pt, Pd, and gold minerals never reported before from the Bon Accord Ni-oxide body. The grains occur as: (1) minute inclusions (<3 μm) in trevorite (ideally NiFe3+O4) and (2) larger (5–70 μm) free aggregates liberated from the host phase. The first group comprises several PGM compounds of Pd-Sb, Pd-Sb-As, Pd-Cu-Sb, Pt-Sb, Pt-As-S, Ru-As-S, Ru-S, along with free grains of Ni-Fe-As. The second consists of sperrylite (PtAs2), members of the sobolevskite-kotulskite series, and electrum. These results are in good agreement with previous analyses of PGE-Au in bulk rock. Paragenetic relationships indicate that the PGM and electrum are of secondary origin, probably generated during low-temperature metamorphism of the Ni-rich mineralization. They have a terrestrial origin and are related with a low-sulfidation regime that usually accompanies hydrothermally driven serpentinization of mafic-ultramafic bodies. The ligands in the newly formed PGM (As, Sb, Bi, Te, and O) probably proceed from the same source of the hydrothermal solutions. In this model, the metals Ni-PGE-Au were original components of the primary mineral assemblage of the Bon Accord precursor, whereas As, Sb, Bi, Te, and O might have been contributed by the metasomatizing fluids, during near-surface evolution of the ore body. The data on the high-grade heavy mineral concentrates, obtained by hydroseparation, have provided new knowledge about the mineral deportment of Pd, Pt, and Au.
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