Journal of Geochemical Exploration vol:118 pages:38-46
An assessment is presented of existing data on the most important copper and cobalt complexes and sulphides
applied to reactive transport modelling. The most important complexes in ore-forming hydrothermal solutions at 150 °C are CoCl(H2O)5+, CoCl4 −2 and CoCl2(H2O)2(aq) for cobalt, and CuCl2 − and CuCl3−2 for copper.
Reactive transport modelling was carried out to simulate the transport and precipitation of copper and cobalt sulphides in sediment-hosted stratiform ore deposits, such as the Central African Copperbelt. A limitation
is the lack of thermodynamic data for carrollite (CuCo2S4). Initially chalcopyrite (CuFeS2) and cattierite (CoS2) precipitate in a reducing host rock. Pyrite dissolves in the horizon where both minerals form and it precipitates in adjacent rocks. The continuous supply of copper and cobalt causes formation of the metalrich sulphides bornite (Cu5FeS4) and linnaeite (Co3S4). Chalcopyrite and cattierite precipitate further in the flow direction. In this model, the dissociation reaction of chalcopyrite and bornite are:
However, if the dissociation reactions only include Cu+ and Fe3+, simulations show the precipitation of only
chalcocite (Cu2S), which is explained by the low concentration of trivalent iron in solution. The dissociation