Factors controlling the precipitation of copper and cobalt minerals in sediment-hosted ore deposits: Advances and restrictions

• Published in: Journal of geochemical exploration Vol. 118; pp. 38 - 46
• Main Authors: Muchez, Ph, Corbella, M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-07-2012
• Subjects: Central African Copperbelt; Cobalt sulphides; Copper sulphides; Reactive transport modelling; Sediment-hosted stratiform deposits; Central African Copperbelt; Cobalt sulphides; Sediment-hosted stratiform deposits; Copper sulphides; Reactive transport modelling
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/j.gexplo.2012.04.006

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 metal-rich 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:
CuFeS2(s)+2H+=Cu2++Fe2++2HS−
Cu5FeS4(s)+2H+=4Cu++Cu2++Fe2++4HS−
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 reactions are:
CuFeS2(s)+2H+=Cu++Fe3++2HS−
Cu5FeS4(s)+2H+=5Cu++Fe3++4HS−
► Simulation of replacement reactions of chalcopyrite by bornite and chalcocite ► Importance of the valence of copper and iron in ore forming-processes ► Simulation of the evolution copper and cobalt sulphides through time ► Spatial distribution of Cu and Co ore minerals and the formation of an ore deposit