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Precious metals in magmatic Fe-Ni-Cu sulfides from the Potosí chromitite deposit, eastern Cuba
Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada.
Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona.
Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona.
Division of Earth Sciences, School of Environmental and Rural Science, University of New England.
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2020 (English)In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 118, article id 103339Article in journal (Refereed) Published
Abstract [en]

The Moa-Baracoa ophiolite in eastern Cuba is one of the few known ophiolites that display sulfide mineralization attributable to a magmatic origin in association with podiform-chromite ores hosted in the mantle-crust transition. These sulfide ores chiefly consist of Fe-Ni-Cu sulfides, namely pyrrhotite, pentlandite, chalcopyrite and cubanite partly altered to valleriite. The sulfide mineralization is located along the contact between the podiform-like chromite ores and intruding pegmatitic gabroic dykes. The detailed mineralogical study of the sulfide mineralization coupled with the first ever laser ablation ICP-MS analysis reveals that this sulfide mineralization show contents of the precious metals (Os, Ir, Ru, Pt, Re, Au, Ag) and other (semi)-metals (Co, Ni, Cu, Se, Te, Bi, Pb, As Sb) comparable to those sulfides from the magmatic sulfide deposits associated with mafic complexes hosted in the continental crust. The results obtained from this study confirm that Fe-Ni-Cu sulfides at Potosí are magmatic in origin, and very likely derived from the solidification of droplets of sulfide melt segregated by immiscibility from the intruding mafic melts once they interacted with the pre-existing chromitite at the mantle-crust transition zone of the ophiolite. The immiscibility of sulfide melt was achieved as a result of a progressive increase of fS2, very likely triggered by a set of circumstances, including the progressive fractionation of the intruding mafic melt leading to increase of aSiO2 and accumulation of volatiles as well as the crystallization of oxides. Two main generations of pentlandite were observed. One generation is primary in origin and it was locally exsolved along with pyrrhotite from monosulfide solid solution (MSS) during low-temperature cooling. The second type of pentlandite resulted from the reaction of MSS with coexisting droplets of Cu-and Ni-rich sulfide melt. LA-ICP-MS analysis reveals that most precious metals (Ru, Os, Ir, Re, Au, Ag) were concentrated along with the base-metal sulfides (BMS), although their distribution among the different BMS (pyrrhotite, pentlandite, chalcopyrite and cubanite) does not strictly follow the expected distribution according to the known melt-solid and solid-solid partition coefficients. Unlike the other analyzed PGEs, Pt was not preferentially concentrated in BMS but as discrete micrometer-sized sperrylite grains. The crystallization of sperrylite took place before and contemporaneous to sulfide segregation, and Pt-As nanoparticles probably played an important role in the Pt uptake as nucleation seeds for the formation of micron-sized sperrylite grains. These observations highlight the open-system nature of the ore forming system as well as the important role of arsenic in concentrating PGE in high-temperature silicate and sulfide melts.

Place, publisher, year, edition, pages
Elsevier, 2020. Vol. 118, article id 103339
Keywords [en]
Sulfide mineralization, Platinum-group elements, Mantle-crust transition, Chromitite, LA-ICP-MS
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
URN: urn:nbn:se:ltu:diva-77780DOI: 10.1016/j.oregeorev.2020.103339ISI: 000518709000008Scopus ID: 2-s2.0-85078830019OAI: oai:DiVA.org:ltu-77780DiVA, id: diva2:1394683
Note

Validerad;2020;Nivå 2;2020-02-26 (alebob)

Available from: 2020-02-19 Created: 2020-02-19 Last updated: 2020-04-28Bibliographically approved

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Aiglsperger, Thomas

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