Abstract

Platinum-group elements and Au have been analyzed from five Finnish Ni-Cu occurrences (Kotalahti, Vammala, Laukunkangas, Hitura, and Petolahti), from a layered mafic intrusion in northern Finland (Siika-Kaemae), and from several weakly mineralized ultramafic bodies in Lapland. Platinum-group element values recalculated to 100 percent sulfide are slightly higher for Rh, Pt, and Pd in the Kotalahti deposit (Pd, 72 ppb; Pd/Ir, 22.6) than in Laukunkangas (Pd, 29 ppb; Pd/Ir, 9.1), and in Vammala (Pd, 25 ppb; Pd/Ir, 9.7), which exhibits the lowest platinum-group element values of the Ni-Cu occurrences analyzed. The ultramafic-hosted Hitura deposit, with a flat chondrite-normalized distribution platinum-group element pattern, has a platinum-group element concentration 20 to 40 times higher than those in Laukunkangas and Vammala. The nickel deposit of Petolahti (Pd, 813 ppb) in a postsvecokarelian diabase dike has platinum-group element values close to those of Hitura (Pd, 750 ppb), but the Pd/Ir ratio of Hitura (4.66) is much lower than that of Petolahti (59.7). The slope of the platinum-group element distribution pattern for Siika-Kaemae is steep and the deposit has the highest concentrations analyzed in this study, Pt and Pd being up to 656 and 1,790 ppm, respectively, recalculated to 100 percent sulfides. The platinum-group element values of the weakly mineralized ultramafic bodies of Lapland are very low, all well below the values reported from Laukunkangas and Vammala.The Hitura-type ultramafic intrusion differs markedly from the other analyzed host rocks of the Svecokarelian Ni-Cu occurrences and its platinum-group element distribution pattern corresponds to the komatiitic character observed also in major and trace elements of the rocks. The fractionated platinum-group element pattern of the Kotalahti and Laukunkangas deposits match well with the observations of rock sequences and geochemistry of the host rocks.

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