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The Vizcaino complex is characterized by tectonised harzburgites overlain by serpentinized dunite bodies and wherlites layers containing several cumulate chromitite deposits and by fractional crystallization sequences: cyclic repetititons of dunites, pyroxenites with pegmatoidal textures, and gabbros overlain by a succession of gabbronorites to diorites in which olivine is followed by pyroxene and by plagioclase. Enriched sulfide horizons generally associated with pegmatoidal rocks are lacking. The fractionation of platinum-group element (PGE) displays evidence of erratic dispersion throughout the intrusion. PGE patterns of chromitites show high Ir and Ru contents, relatively high Rh content and an unusual Pt–Pd depletion lower than in ophiolitic chromitites. These chromitites do not contain laurite-type sulfides, which are commonly observed in association with Os–Ir–Ru alloys. Dunites show relatively flat patterns and gabbros present typical trends with depletions in the Iridium-group (IPGE) relative to PPGE. Ru, Rh, and especially Ir are very low in these silicate rocks, indicating the precipitation of these elements during the earliest stages of fractional crystallization and their concentration in chromitites. Spilitized dolerite dykes from the metamorphic basement show significant PGE enrichments similar to those of gabbros. Based on our previous thermochemical data, an extremely low fS2 ( |
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