Geochemistry and mineralogy of PPGE rich Middle Arm Brook chromitites (Newfoundland, Canada)

M. ESCAYOLA; J. A. PROENZA; F. ZACCARINI; G. GARUTI; J. BÉDARD; C. VAN STAAL

Sudbury

Simposio; 11th International Platinum Symposium; 2010

Laurentian University

ABSTRACT. The Middle Arm Brook (MAB) ophiolitic chromitites are located in the Baie Verte Peninsula of Newfoundland (Canada). The composition of chromite is homogeneous, with Cr# varying from 0.77 to 0.81, Mg# from 0.51 to 0.59, and TiO2 < 0.28 wt%. These values are very similar to those reported for a great number of mantle hosted chromitites, related with supra-subduction ophiolites. CI-chondrite normalized PGE patterns are variable, with relatively high total PGE (up to 1028 ppm). PGE richer chromitites show enrichment in PPGE relative to IPGE. The PGM assemblages consist of laurite, osmium and ruthenium accompanied by a great number of unknown PGM such as Ir-S, Ir-Cu-S, Pt-Ni-Fe-Cu, Cu-Os-Ni-Pt, Rh-Pd-Sb and Pd-Rh-Sb. Only laurite and an unknown Ir sulphide occur in fresh chromite as euhedral cystals, suggesting a primary origin. In contrast, Os, Pt, Rh and Pd bearing minerals always occur along cracks or in the silicate matrix. Most of these PGM are characterized by an irregular shape and some of them display a strong zonation. These PGM are interpreted to represent the product of alteration of primary PGM and redistribution of PGE at low temperature. Magmatic precipitation of PPGE was possibly related with the segregation of an immiscible sulphide liquid precursor, that does not exist anymore, having been totally altered and desolphurized during serpentinization. EL TRABAJO COMPLETO CON FIGURAS SE ENCUENTRA ADJUNTO