Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The distribution of PGM provides insights into the processes forming PGE deposits. PGM have been located in 8 chromitite layers from basal layer A to top layer Kin the ultramafic units below the economic PGE-rich JM reef in the Stillwater complex, USA. Within chromite grains most PGM are laurite, with rarer, smaller PPGM including malanite [CuPtRh(+/-lr)SJ and Pt-Pd-sulfides. Interstitial to chromite grains PPGM dominate including Pd-Pb, PtPdtellurides, sperrylite, platarsite, minor laurite and one grain of Pd-Ge. The laurite shape reflects formation and varies from mainly round in lower and upper layers, to euhedral in the thicker middle G layer. The Os content of laurite is lowest and silicate inclusions with laurites are most abundant in layer G. Rutile inclusions are most abundant in layer B. Trace Rh in laurite and PPGM with laurite are most abundant in the uppermost layer Kand laurite size increases upwards. Each layer has a distinct PGM assemblage. Within chromite grains IPGE- and PPGE-PGM are greatest in the upper layers suggesting increasing PGE content in the magma upwards whereas interstitial PGM associated with BMS indicate sulphur saturation occurred between chromite grains in the lower layers.