Please use this identifier to cite or link to this item: https://hdl.handle.net/1959.11/30145
Title: Precious metals in magmatic Fe-Ni-Cu sulfides from the Potosí chromitite deposit, eastern Cuba
Contributor(s): González-Jiméneza, José M (author); Proenza, Joaquin A (author); Pastor-Oliete, Miriam (author); Saunders, James  (author)orcid ; Aiglsperger, Thomas (author); Pujol-Solà, Núria (author); Melgarejo, Joan Carles (author); Gervilla, Fernando (author); Garcia-Casco, Antonio (author)
Publication Date: 2020-03
Early Online Version: 2020-01-18
DOI: 10.1016/j.oregeorev.2020.103339
Handle Link: https://hdl.handle.net/1959.11/30145
Abstract: 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.
Publication Type: Journal Article
Source of Publication: Ore Geology Reviews, v.118, p. 1-15
Publisher: Elsevier BV
Place of Publication: Netherlands
ISSN: 1872-7360
0169-1368
Fields of Research (FoR) 2008: 040306 Mineralogy and Crystallography
040304 Igneous and Metamorphic Petrology
040299 Geochemistry not elsewhere classified
Fields of Research (FoR) 2020: 370505 Mineralogy and crystallography
370501 Biomineralisation
370503 Igneous and metamorphic petrology
Socio-Economic Objective (SEO) 2008: 840205 Mining and Extraction of Precious (Noble) Metal Ores
Socio-Economic Objective (SEO) 2020: 250405 Mining and extraction of precious (noble) metal ores
Peer Reviewed: Yes
HERDC Category Description: C1 Refereed Article in a Scholarly Journal
Appears in Collections:Journal Article
School of Environmental and Rural Science

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