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SummaryTo investigate the possible fractionation of sulphides in stratiform ore deposits, experimental work was carried out on two important processes in the mobilisation of sulphide minerals; i.e. the kinetics of the sulphide-volatile halide conversion, and the final deposition of the sulphide minerals from the vapour phase in the presence of H2S. The work was carried out on the assumption that transport was by means of the volatile halide, and that temperatures were of the order of 600 ° C. Minerals used were galena, sphalerite, covellite, and chalcocite. It was shown that the rate of attack of HC1 varied with different sulphides and this can be explained by differences in bond energies of the various minerals. From the results, two fundamental mechanisms for gas phase ore transport are postulated. In porous media, the rate of transport is determined by the rate of mobilisation at the site of reaction. In less porous media the rate of transport is determined by a Schafer mechanism, i.e. the rate is diffusioncontrolled.The relationship of the kinetics of the depositional process to paragenetic sequences and zoning is also discussed, and using these principles some mechanisms causing transport and segregation of sulphide minerals are postulated.

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