HYDROTHERMAL ORIGIN OF BI- AND LREE-ENRICHED MINERALIZING FLUIDS, KONKOLA NORTH, ZAMBIAN COPPERBELT

The origin of Copperbelt mineralization has long been disputed and most recent workers have divided over early diagenetic, late diagenetic, or hydrothermal origins for the mineralizing fluid. Detailed study of trace element distributions in cores taken at the Konkola North prospect demonstrate a hydrothermal origin. Based on basement topography, the cores can be divided into deep basin, topographic high, and local low locations. Cores sampling the deep basin display moderate Cu mineralization, moderate Bi enrichment (to 18 ppm), strong Co enrichment, and all mineralization as sulfides. In contrast the topographic highs, where footwall fluids were forced upward into the ore shale, show strong Cu mineralization, strong Bi enrichment (to 52 ppm), but weak Co enrichment, and a mix of sulfide and oxide mineralization. Within mineralized Ore Shale 1, the correlation coefficients for Bi and Cu and for Bi and S are 0.94 and 0.95. There is also an intimate association observed in some ore samples between Cu-sulfides, allanite, and hydrothermal biotite. Barite deposited immediately above or below the mineralized ore shale was probably transported in a separate fluid. Barite-rich samples are characterized by positive Eu-anomalies, suggesting a feldspar-rich fluid source. In contrast mineralization is generally associated with weak negative Eu/Eu*. K enrichment, extreme in many samples, is associated with a variety of REE patterns, and K may have been transported in multiple fluid events. Trace element and REE data indicate the mineralizing fluid or fluids at Konkola North and other Zambian Copperbelt deposits was hydrothermal in origin, oxidizing, and probably transported both Bi and LREE. Ba in barite spatially associated with Cu mineralization was transported separately. Fluid movement, and hence mineralization, was controlled by basement topography.