Abstract

The Mufulira copper deposits are in the Lower Roan, lowest subdivision of the Katanga Sequence, overlying an early Precambrian Basement Complex. The Lower Roan is described as a transgressive marine sequence; at Mufulira three essentially stratabound ore bodies are contained in identical phases of a cyclic succession. Large-scale cross-bedded units in the Footwall formation are interpreted as subaqueous dunes in a high-energy shallow marine environment, refuting their generally accepted eolian origin. Analysis of cross-bedding in the lower part of the Ore formation and in the Footwall formation throughout the mine reveals a bimodal distribution of paleocurrent directions with southerly offshore and northeasterly longshore directions. In the west, southerly directions with little variation around their mean vector indicate fluviatile channels.The typical host rock of the economic mineralization at Mufulira is a fine-grained carbonaceous wacke. This wacke was deposited in basin-like depressions of the near-shore seafloor, sheltered from the open sea by shoals. Stagnating bottom waters, resulting in anaerobic conditions, may have contributed to the exceptional conditions under which synsedimentary sulfides could form. These original sulfide deposits were probably of a low grade and were later enriched, possibly during diagenesis as is indicated by diagenetic mottling in sandstones, by mineral zoning, and by copper sulfide distribution in and around shale fragments enclosed in coarse sandstone. Clean arenites and conglomeratic sandstones in the lowest parts of the ore bodies and in their footwall beds were ideal channelways for laterally migrating copper-bearing fluids. The economic concentration of copper was principally dependent upon the presence of a reducing carbonaceous-sulfureous environment that was associated with the carbonaceous wacke and a mottled sandstone.A unique relationship of copper sulfides to a particular sedimentary facies is not observed, but sedimentological trends are consistent with the distribution pattern of the sulfides and can be used in exploration for this type of deposit.

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