Summary:
Lubambe Mine copper deposits are located at the northeast wing of the Kafue anticline and the northeast of the secondary Chililabombwe syncline (Konkola Dome). The Chililabombwe syncline has a length of 40 - 50km, a width of 12 - 15km and a presumable depth of 10km.
The Konkola North deposit is developed on a south-west trending dome/anticline controlled by basement topography a short distance to the north of the Konkola Mine. The general stratigraphy consists of thick successions of Lower Roan Formation clastic units comprising conglomerates, upward fining arenites and quartzites. Repeated upward fining cycles indicate unstable tectonic conditions triggering periodic influx of sediments into half-graben basins.
The Nchanga Formation commences with the Ore Shale (OS) 1 Member, which indicates the first major marine transgression of the area. The Nchanga Formation on project comprises six sedimentary upward-fining cycles of which the siltstone/shale units comprise the top of each cycle and are termed the OS 1-6 Members.
The Upper Roan Formation unconformably overlies the Nchanga Formation. This unconformity is marked by the Konkola Conglomerate Member, followed by interbedded siltstones, arkose, grit and dolomite units. The lower most dolomite unit, locally known as the Chingola Dolomite, is the main aquifer in this area.
The Mwashia Formation unconformably overlies the Nchanga Formation and comprises dolomitic siltstones, carbonaceous shale, intercalated limestones and dolomitic units.
Lubambe Mine Orebody
Copper mineralisation is largely hosted within the OS1 Member. The true thickness of the OS1 Member varies from 2 m to 10m. Typically, the lowermost 1.5 m of the OS1 is massive in structure and contains very little copper (Barren Shale). The transition to > 1% total Cu is extremely abrupt and takes place over centimetres, above a thin red iron oxide-rich marker layer, which probably acted as a redox boundary. A barren zone, with thickness varying between 1 m to 3m and characterised by a pink feldspathic sandstone marker bed, often occurs between the OS1 and OS2. The upper contact of the > 1% total Cu zone (assay hanging wall) is also well defined in the assay profile but is not as sharp as the assay footwall contact.
Mineralisation occurs as finely disseminated sulphides assuming the grain size of the host rock, as coarser grains along bedding planes and cleavage, in thin veinlets and in lenticles and stringers. These minerals comprise chalcocite, chalcopyrite and bornite in approximate order of abundance. Vertical zonation of the copper minerals is observed, with an increase in copper content and a decrease in iron and sulphur content with depth. An idealized Lubambe Mine orebody profile has chalcocite enrichment in the middle part, followed by bornite and then chalcopyrite and pyrite. Lateral zonation from bornite-chalcopyrite on the East Limb through chalcopyrite-dominated mineralisation on the South Limb to pyrite near the western boundary is also observed.
A large proportion of the non-sulphide copper minerals occur along fractures and veins. The main non-sulphide copper minerals are, in order of abundance, malachite, pseudomalachite, chrysocolla, cuprite, azurite and native copper. Leaching is typically concentrated at the base of the OS1 where the contact between the siltstone and conglomerate/arkose represents a permeability channel way. Development of iron oxide after weathering of chalcopyrite and bornite is common in leached zones.