RT Journal Article
T1 Distribution of platinum-group and chalcophile elements in the Aguablanca Ni–Cusulfide deposit (SW Spain): Evidence from a LA-ICP-MS study
A1 Piña García, Rubén
A1 Gervilla, Fernando
A1 Barnes, Sarah-Jane
A1 Ortega Menor, Lorena
A1 Lunar Hernández, María Del Rosario
AB The concentrations of platinum-group elements (PGE) and chalcophile elements Ni, Co, Au, Ag, Se, Re, Cd, Bi,Te and As have been determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICPMS)in base metal sulfide minerals (BMS) from the Aguablanca Ni–Cu deposit, SW Spain. The main aim was toconstrain the role played by the BMS as hosts of PGE as this reveals important information regarding theprocesses controlling the distribution of these elements in the deposit. The BMS (pyrrhotite, pentlandite,chalcopyrite and minor pyrite) occur as semi-massive, disseminated and minor chalcopyrite-veined ores. Onthe basis of whole rock metal abundances and BMS mineralogy, these ore types have been interpreted to bethe result of the fractionation and crystallization of an immiscible sulfide liquid.Platinum-group and chalcophile element concentrations vary as a function of the BMS and ore types. Thepartitioning behavior of some of these metals during the fractional crystallization of the sulfide liquid largelygoverned their distribution in the ore. Rhenium, Os, Ir, Ru, and Rh occur mostly in solid solution in pyrrhotiteand pentlandite from the semi-massive ore which has been interpreted to represent monosulfide solidsolution (mss) cumulates. The mss crystallization gave rise to minor Cu-rich sulfide liquid in the form ofchalcopyrite veinlets with relatively Pd-, Au- and Ag-enriched chalcopyrite, and minor Re-, IPGE- and Rhdepletedpyrrhotite and pentlandite. Platinum-group element contents in the BMS from the disseminated ore,interpreted to represent an original unfractionated sulfide melt, are approximately intermediate to the semimassiveand chalcopyrite-veined ores.Palladium and Pt occur mostly associated with Bi, Te, and As forming platinum-group minerals (PGM, Pd–Ptbismuthotellurides and Pt arsenides) within individual BMS grains. This preferential location along with thetextures adopted (usually rounded grains and laths) and the temperatures of crystallization (inferred below500 °C) suggests that Pd and Pt, initially dissolved in the BMS, were exsolved along with Bi, Te and As to formthe PGM assemblage present in the ore. Some Pd (approximately 30% of the bulk) remains in solid solution inpentlandite for the three ore types. The presence of Pd in pentlandite is likely a combined effect of limitedsulfide fractionation with some of Pd remaining in mss and Pd diffusion into pentlandite from the mss and Curichportions on cooling.Two textural types of pyrite hosting distinct PGE concentrations have been described: (1) large idiomorphicpyrite and (2) ribbon-like pyrite. Idiomorphic pyrite is the unique BMS hosting Pt (with contents as high as15 ppm) and also contains relatively high Rh concentrations (4–31 ppm). By contrast, ribbon-like pyrite hasno Pt and hosts similar Os, Ir, Ru and Rh concentrations (30–360 ppb) to those of the host pyrrhotite to that itreplaces. The origin of the idiomorphic grains, whether exsolution products from mss or alteration products ofpyrrhotite, is not well known and further work will be necessary to constrain this point. Nevertheless, thepresence of PGE hosted by pyrite reveals that this sulfide should not be overlooked as a potential carrier of PGEin Ni–Cu–(PGE) ore deposits.
PB Elsevier Science B.V., Amsterdam.
SN 0009-2541
YR 2012
FD 2012
LK https://hdl.handle.net/20.500.14352/42391
UL https://hdl.handle.net/20.500.14352/42391
LA eng
DS Docta Complutense
RD 25 ago 2024