Microprobe study of olivine chromitites of the Goodnews Bay ultramafic complex, Alaska, and the occurrence of platinum

Electron-microprobe analyses of the dunite and olivine chromitite of the ultramaflc complex at Goodnews Bay, Alaska, show that the chromite contains more ferrous and ferric iron than is found in chromite from alpine or stratiform complexes. The iron-magnesium distribution coefficients between chromite and olivine demonstrate that more ferrous iron is partitioned to the chromite in the Goodnews Bay complex than to the chromite in stratiform chromitite but that the distribution is similar to that for alpine chromitite. The high iron content of the chromite and olivine at Goodnews Bay and the general geology of the complex indicate that it is a concentric-type ultramaflc complex similar to the platinum-bearing concentric complexes of southeastern Alaska. A platinum-alloy inclusion in the chromite found in the ultramaflc section at Goodnews Bay demonstrates that the olivine chromitite is the source of at least some of the platinum.