Palladium, platinum, rhodium, ruthenium and iridium in peridotites and chromitites from ophiolite complexes in Newfoundland

Abstract

Samples of spinel lherzolite, harzburgite, dunite and chromitite from the Bay of Islands, Lewis Hills, Table Mountain, Advocate, North Arm Mountain, White Hils Peridotite, Point Rousse, Great Bend and Betts Cove ophiolite somplexes in Newfoundland were analyzed for the platinum-group elements (PGE) Pd, Pt, Rh, Ru and Ir. The ranges of concentration (in ppb) observed for all rocks are: <0.5 to 77 (Pd), <l to 120 (Pt), <0.5 to 20 (Rh), <100.to 250 (Ru) and <20 to 83 (Ir). Chondritensrmalizsd PGE ratios suggest differences between rock tlpes and between complexes. Samples of chromitite and dunite show relative enrichment in Ru and Ir and relative depletion in Pt and Pd. These trends are similar to those from ophiolite complexes in Turkey, Iran, Oman, southwestern Oregon, northern California, New Caledonia, Greece, and the Polar Urals, USSR. Partial melting of mantle matedal, either by a single-stage or multistage process, and either in sulfur-saturated or unsaturated conditions, which produces a residue and melt with different pGE concentrations, coupled with the crystallization of the melt ro form the upper portions of the ophiolite, is invoked to explain the distribution of the PGE in the rocks.