Abstract

The close association of platinum-group elements with chromite in the upper critical zone calls for the appraisal of structures, textures, and composition of chromitites in the development of genetic models. Cryptic variations in successive chromitite layers of the UG-1 unit are consistent with fractionation of limited melt volumes. Individual chromitite bands within the composite UG-2 chromitite layer exhibit distinctive compositions, but all display long-range compositional trends, with height, superimposed on short-range homogeneity. Accessory chromites are substantially different from massive chromitites in composition; reaction with residual liquids and subsolidus reactions were significant. Recrystallization of chromitites was ubiquitous, but the importance of in situ growth is shown by relict textures. Long-range settling, adcumulus growth, or deposition from density currents are processes that find little support in the data presented.

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