Abstract

A UG-2 chromitite sample contains two sequences in which the concentrations of Cu, Ni, S, Pt, Pd, Rh, Ru, and Ir conform to a process of fractionation according to the Rayleigh law. Both of these sequences are followed by others in which the trends are almost horizontal.From the sequences that conform to the Rayleigh law one can calculate the relations between the possible thicknesses of the magma column that gave rise to the UG-2 layer, the bulk distribution coefficients, and the original concentrations of the elements involved. It appears that the elements were withdrawn from a surprisingly thin layer of magma. Between the first and the second cycles certain elements have been depleted and others enriched, which indicates a heave of new magma rather than the recirculation of old partly depleted magma by a process like convective overturn.The fact that S and the chalcophile elements Cu and Ni were concentrated in the same way and at the same time as the platinum-group elements shows that the same collector was probably involved. Therefore sulfide could not have acted as a collector for the platinum-group elements. It is thought that chromite, or a precursor of chromite, was involved in some way with the collection process.

First Page Preview

First page PDF preview
You do not currently have access to this article.