C. A. Cousins and E. D. Kinloch
Some observations on textures and inclusions in alluvial platinoids
Economic Geology and the Bulletin of the Society of Economic Geologists (November 1976), 71(7):1377-1398

Abstract:
Studies of grains of recent alluvial platinoids from six localities indicate that they are predominantly alloys of the platinum-group elements, that they show both rounded and irregular outlines, and that they are much larger than known primary grains of platinoid minerals. These features are observable not only in alluvial grains but also in the eluvial grains from the Birbir deposit of Ethiopia.Zoning and inclusions are present. They are conspicuous in British Columbian particles.The authors consider the possibility that the particles originated largely from the weathering and accretion of platinoids in intimate association with base-metal sulfides contained in the mother rock and not altogether from the liberation of metallic platinoid particles contained in this rock.Subsequent leaching of platinoid particles during transportation may have occurred.