Platinum-group minerals from the Paleoproterozoic chromitite, Outokumpu ophiolite complex, eastern Finland

This paper describes the presence of platinum-group minerals in the Vasarakangas chromitite from the 1.97 Ga Outokumpu ophiolite complex in eastern Finland. The platinum-group mineral assemblages as well as the compositions of laurite, irarsite and orarsite, and also the chondrite-normalized platinum-group element patterns are compatible with those described in younger Mesozoic ophiolitic chromitites. In contrast to these younger chromitites, where Ir-group minerals occur mainly as inclusions in chromite, the platinum-group minerals at Vasarakangas are principally found as enclosed minor grains in euhedral matrix gersdorffites. The PGE distribution between separated chromite and gersdorffite fractions is in accordance with the observed exceptional mode of PGM occurrence.