Summary:
The Central African Copperbelt is a world-class metallogenic province which stretches from the Copperbelt Province in Zambia, through the Katangan Province of the Democratic Republic of Congo and into the North- Western Province of Zambia.
The Lumwana Project lies within the North-Western Province of Zambia and contains two major copper deposits, Malundwe and Chimiwungo, which are structurally controlled shear zone hosted deposits considered to be an end member of Central African Copperbelt class of deposits.
The Lumwana Project consists of two major copper deposits, Malundwe and Chimiwungo. Malundwe is the smaller deposit but has a higher copper grade and contains discrete zones of uranium and gold mineralization with occasional sporadic high cobalt (>0.1%). Chimiwungo is a much larger deposit that is lower in copper grade and contains a number of significant high grade (>0.1%) cobalt zones in addition to some uranium mineralization. Chimiwungo can be sub-divided into the Chimiwungo Main, Chimiwungo South, Chimiwungo North and Chimiwungo East mineralized zones.
The copper mineralization at Malundwe (including Kanga) and Chimiwungo is hosted almost entirely within high grade metamorphosed, intensely mylonitized, recrystallized muscovite–phlogopite–quartz–kyanite schists with disseminated sulphides (typically <5%) dominated by chalcopyrite and bornite which is locally referred to as Mineralized Ore Schist.
The ore host, Mineralized Ore Schist, has an intensely transposed foliation defined by layer-parallel alignment of both mica and quartz. The mineralized zones, as interpreted, comprise a series of interbanded Mineralized Ore Schist and gneissic units which are structurally derived. This fabric is the result of regional layer parallel shearing and subsequently thrusting and possible Nappe folding that has caused the overturning of the sequence. The internal structure of the mineralized package is attenuated and boudinaged in part, causing lensing along strike and down dip. Within the mineralized zone, gneissic units are typically low grade to barren with respect to copper, gold, cobalt and uranium grades.
The distribution of copper mineralization is controlled by visibly identifiable strata-bound geology, within which copper grades are consistent. Optimal grade continuity is aligned to an observed north– south stretching lineation.
The copper mineralization at Lumwana is almost entirely disseminated sulphides (typically <5%) dominated by chalcopyrite and bornite with a minor amount of the resource classified as oxide or transition.
The overall strike length of mineralization at Malundwe is approximately 6 km north-south, and up to 1.5 km wide (east-west), predominantly as a single Mineralized Ore Schist horizon. The mineralization outcrops in the east, has an overall gentle dip to the west and plunges to the south. It extends to maximum depth of approximately 380 m below surface in the southwest is closed off in all directions.
The Chimiwungo deposit is partitioned into three bodies by two steep west-northwest trending dip-slip fault zones. From south to north these mineralized zones are referred to as Chimiwungo South, Chimiwungo Main (includes the recently discovered Chimiwungo East mineralized shoot) and Chimiwungo North. Each is described as a discrete structural entity below, but the reality is that they represent the same mineralized package which has been dismembered by late, steep dip slip faults which will be collectively referred to hereafter as the Chimiwungo deposit.
Chimiwungo South mineralized zone is located south of the Chimiwungo South Fault. The mineralization consists of a package of three Mineralized Ore Schist horizons:
- Upper Ore Schist;
- Main Ore Schist; and
- Lower Ore Schist.
The horizons are separated by two near continuous barren gneiss zones, the Middle Gneiss and the Lower Gneiss. In the thickest and best grade portion of the mineralization, two thicker, higher grade copper mineralized shoot have formed where the barren Lower Gneiss unit is replaced by Mineralized Ore Schist resulting in the merger of the Main and Lower Ore Schists. The mineralized package and the individual Mineralized Ore Schist and gneiss zones have a gentle southerly dip and plunge. The mineralization currently extends up to 5.5 km north-south and 2.8 km in the east-west orientation and remains open to the east and south. The deepest drill intersections of the mineralization currently are approximately 680 m below surface. The northern limit of Chimiwungo South is defined by the Chimiwungo South Fault which has caused the mineralized package to drop down approximately 300 m on the north side of this major structure.
Chimiwungo Main mineralization is the down thrown continuation of Chimiwungo South mineralization on the north side of the Chimiwungo South Fault and is bound between this fault and the Chimiwungo North Fault. It consists of the same mineralized package and gneiss units that have a similar average dip and plunge to Chimiwungo South. It also hosts the northern continuation of the ore shoot observed in the Chimiwungo South area which extends approximately 1.4 km north of the Chimiwungo South fault. Drill definition of the mineralization extends approximately 2.7 km north-south, and 4.2 km in the east-west orientation. The deepest mineralization is located at approximately 495 m below surface at the southeastern limit of the Chimiwungo Main deposit adjacent to the Chimiwungo South Fault zone.
Chimiwungo North is located immediately north of the Chimiwungo North Fault which is a steep dip slip fault zone similar in style to the Chimiwungo South Fault. This fault has dropped the mineralization on the northern side of the fault approximately 100 m, preserving it from erosion. In the area drilled, the mineralization consists of one Mineralized Ore Schist unit which appears to have formed by the merging of the three Mineralized Ore Schist units seen in Chimiwungo Main. The mineralized zone dips and plunges gently to the south and currently extends over an area of 700 m (north-south) by 450 m (east-west). The southern boundary is constrained by the Chimiwungo North fault. Recent drilling indicates the eastern edge of the ore zone is an erosional boundary defined by the current topographical surface. However, a gentle north-south trending antiform has been interpreted to the east of this position which folds the mineralization back below surface in the north eastern portion of Chimiwungo. The Chimiwungo North ore body has a maximum depth of approximately 110 m.