A geochemical model for sulfide paragenesis and zoning in the Cu---Fe---As---S system (Tsumeb, South West Africa/Namibia)

The Cu-bearing hypogene mineralization at Tsumeb, South West Africa/Namibia, is interpreted to have resulted from the interaction of hot circulating Cu-rich saline solutions and host dolomites. Fluids attending formation of the main sulfide stage were warm (210-280[deg]C) and moderately saline (6-12 wt.% NaCl equivalent).Phase relations within the Cu---Fe---As---S system suggest that the observed paragenetic sequence (chalcopyrite --> bornite --> chalcocite --> enargite --> tennantite) is consistent with a model calling for successive introduction of a single Cu-rich solution into a host dolomite. The Cu and As content of the solution decreased as it passed through the permeable dolomite precipitating Cu---As-sulfides and sulfosalts. A concomitant increase in pH created by the dissolution and buffering effect of dolomite produced sufficient changes in the fluid chemistry to shift the stable sulfide mineral assemblage.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24601/1/0000009.pd