Sources of basinal and Mississippi Valley-type mineralizing brines: mixing of evaporated seawater and halite-dissolution brine

Origins of basinal brines and Mississippi Valley-type (MVT) mineralizing fluids have been separately attributed to evaporation of seawater or dissolution of halite, although brines originating from the two processes are not mutually exclusive in basins. This study shows that the Na/Br-Cl/Br diagram cannot distinguish between evaporated seawater and halite-dissolution fluid. Using the Na-deficit-Ca-excess diagram which was previously proposed to characterize fluid-rock interactions of basinal brines, it is shown that most basinal brines including MVT mineralizing fluids of the Viburnum Trend deposits were probably initially a mixture of halite-dissolution fluid and evaporated seawater. Using the same diagram, we suggest that the mineralizing brines of the Gays River MVT deposit were derived from an aquifer of clastics underlying a thick succession of evaporites, where halite-dissolution fluid and evaporated seawater could have mixed. (C) 1997 Elsevier Science B.V.