Tracing seawater evaporation and evaporite dissolution in the Zambian Copperbelt: evidence from crush-leach analysis of fluid inclusions and stable isotopes

Fluids in the Zambian Copperbelt have been investigated by sampling different generations of vein material from numerous deposits across the classic mining district and currently explored Western Domes region. Veins were segregated into pre kinematic, pre-syn kinematic and post kinematic groups based on their relationship to host rock fabrics. Crush-leach halogen data indicates the presence of two main fluid types, one with Cl/Br < seawater, indicative of a fluid derived from residual evaporated seawater which dominate the pre and pre-syn kinematic samples, and one with Cl/Br > seawater, characteristic of a fluid containing a component derived from dissolved evaporites which dominated the post-kinematic vein generation. Halogen data suggests fluids were ultimately derived from strong evaporation of seawater beyond the carnalite saturation point. Cation data suggests significant water-rock interaction consistent with hydrothermal alteration assemblages. delta Cl-37 of fluid leachate is close to 0 for all samples, suggesting an ultimate seawater source of chlorine. delta O-18(fluid) is variable between similar to -3 and +11, probably reflecting different amounts of water-rock equilibration and different residence times. Isotopically light delta C-13 and delta D signatures reflect oxidation of organic matter. Vein material with delta C-13 similar to Neoproterozoic carbonates reflects buffering by host rock carbonate sequences