The distribution of nickel, cobalt, gallium, palladium and gold in iron meteorites

Abstract

The concentrations of nickel, cobalt, gallium, palladium and gold have been determined in 45 iron meteorites including representatives from all structural classes. Gallium was determined, in addition, in two specimens of troilite and in the metallic phase of two pallasites. The analytical procedures and the structural characteristics of the meteorites studied are described in detail.It is found that most meteorites fall into three distinct classes, each class possessing a fairly narrow range of gallium concentrations: Class I, 40–100 ppm Ga; Class II, 20 ppm Ga; and Class III, 2 ppm Ga. Analysis of the structures, nickel contents and palladium and gold distributions leads to the same divisions.All hexahedrites, nickel-poor ataxites and coarse and coarsest octahedrites possess gallium levels corresponding to Class I. Medium octahedrites are split between Classes I and II in the approximate ratio 1:2. All fine and finest octahedrites which posses nickel contents in the range 7·5% to 8·5% are in Class III.The conclusions which might be drawn from these observations are discussed.