The Ni-Cu-(PGE) Aguablanca Ore Deposit (SW Spain) by Rubén Piña

Author:Rubén Piña
Language: eng
Format: epub, pdf
Publisher: Springer International Publishing, Cham

The ore assemblage is typical of magmatic Ni–Cu–Fe sulfide mineralizations, consisting of pyrrhotite (Fe1−xS), pentlandite [(Fe, Ni)9S8], chalcopyrite (FeCuS2) and minor pyrite (FeS2). Magnetite (Fe3O4), minor amounts of violarite (FeNi2S4) and marcasite (FeS2) replacing pentlandite and pyrrhotite, respectively, and a complex assemblage of platinum-group minerals (PGM), mostly Pd–Pt–Ni bismuthotellurides, complete the ore assemblage. Pyrrhotite is, by far, the most abundant sulfide in the semi-massive ore, occurring as large (1–2 mm) anhedral twinned crystals in proportions higher than 55 modal % (Fig. 4.7a–d). Pentlandite (10–35 modal %) occurs as polycrystalline, chain-like aggregates surrounding pyrrhotite (Fig. 4.7b, c), formed by relative high-temperature grain boundary exsolution, and as small exsolution flames along grain boundaries and fractures within pyrrhotite (Fig. 4.7d). Chalcopyrite (<10 modal %) forms anhedral grains of variable size randomly distributed between pyrrhotite and pentlandite. Magnetite (up to 2 modal %) occurs as individual euhedral crystals within sulfides (mostly, pyrrhotite) and in the contact between sulfides and silicates (Fig. 4.7a–c). The euhedral morphology of magnetite suggests early crystallization. In the most altered samples, chalcopyrite and, at a lesser extent, pyrrhotite, are located along cleavage planes of actinolite and chlorite (Fig. 4.7e, f), suggesting some sulfide remobilization during alteration.

Fig. 4.7Reflected-light photomicrographs of sulfide textures in the semi-massive ore of the Aguablanca Ni–Cu ore deposit. a–c Typical sulfide assemblage formed by pyrrhotite, pentlandite and chalcopyrite with minor amounts of magnetite. d Pentlandite flames within pyrrhotite. e, f Chalcopyrite occurring along cleavage planes of actinolite (e, transmitted light). Abbreviations: Po pyrrhotite, Pn pentlandite, Ccp chalcopyrite, Amp amphibole

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