SUPERGENE ALTERATION OF SULFIDES .4. LABORATORY STUDY OF WEATHERING OF NICKEL ORES

A laboratory study of gossan formation has been made by anodically weathering supergene Ni ores in a circulating flow tank specially devised to simulate natural processes. The main phases produced by the system are goethite and a Ni-rich phase that is similar to reevesite and suspected of being the precursor of Ni-rich pyroaurite minerals. It is shown that the composition of the ore influences the amount of base-metal coprecipitated with the goethite. With Ni and Co, coprecipitation is enhanced by high pH and high base-metal activity; Cu, on the other hand, acts differently due to a catalytic effect on the oxidation of Fe2+ and the few results for Pb and Zn show no clear trend. The propensity to form coprecipitates with Fe in goethite was found to be Cu > Pb > Co ∼ Ni > Zn. The geochemical usefulness of this data is discussed. © 1979.