Sulfur and lead isotope constraints on the genesis of a southern Zambian massive sulfide deposit

The Nampundwe deposit is situated 45 km west of Lusaka in the southern province of Zambia. The ores typically consist of massive, bedded, fine-grained pyritic "sulfidite' horizons (i.e., >30% sulfide) up to 1.5 m thick and laterally extensive. Variable amounts of pyrrhotite, chalcopyrite, and sphalerite are present, typically forming veinlets or blebs, although massive pyrrhotite occurs in orebody 1. Analysis of acid-leached bulkrock samples by ICP-AES indicates three episodes of base metal mineralization with maximum Cu and Co concentrations reaching 8% and 3400 ppm, respectively. Sulfur isotope determinations on pyrite, pyrrhotite, chalcopyrite, and sphalerite show δ³⁴S values ranging from -10 to +9.8‰. Opposing trends in δ³⁴S values through the same stratigraphy are thought to be to mixing processes being dominant to the south, and to changes in fractionation between the fluid and precipitated mineral being dominant to the north. -from Authors