Abstract
The Munali Ni deposit and mine, southern Zambia, is an example of an economic magmatic Ni-Cu-PGE sulphide breccia deposit. Deposits such as Munali are typically hosted by mafic-ultramafic intrusions whose magmas have undergone sulphide saturation, forming in deep crustal conduits (Begg et al. 2010), which are temporal with intracontinental rift events and are spatially distributed among many of the world's craton margins. In the case of Munali, this is the southern margin of the Congo Craton along the Munali Fault (Evans 2011). These settings host some of the world's largest and well studied Ni-Cu-PGE deposits for example, Noril'sk, Siberia and Voisey's Bay, Canada. Munali, however, is relatively poorly documented, with very little academic research performed on the deposit.
Munali is a magnetite-rich deposit, comprised of a barren gabbro core with a marginal zone of sulphide-matrix, ultramafic breccias. The intrusion displays a distinct magnetic anomaly. A number of potentially similar mafic-ultramafic intrusions have been identified as magnetic anomalies with similar anomalies to the main Munali intrusion, including the Chibuku and T1B prospects, which immediately surround the main Munali intrusion along the Munali Fault. These intrusions remain untested for mineralisation but represent potentially prospective exploration targets.
Petrological and field studies have identified eight different igneous phases at Munali, all containing variable proportions of pentlandite, pyrrhotite, chalcopyrite and pyrite in addition to magnetite and ilmenite. Underground mapping revealed a multistage emplacement of the ultramafic units which are either structurally and/or genetically associated with mineralisation.
Initial analysis of drill hole geochemical data and subsequent down hole trace element plots from Chibuku, reveal four distinct igneous units, which display variably elevated concentrations of Ni, Cu and PGE in accordance with S. Petrologically, Chibuku contains magnetite-bearing rocks including, gabbro, poikilitic gabbro and a highly serpentinised ultramafic phases that are directly comparable to those at Munali. Subsequently, Ni-Cu-PGE mineralisation may be present at the Chibuku prospect. The T1B intrusion, however, is comprised of only one igneous phase with minor magnetite, and no elevated Ni, Cu or PGE concentrations.