Summary:
The Kabanga nickel deposit is located within the East African Nickel Belt, which extends approximately 1,500 km along a northeast trend that extends from Zambia in the southwest to Uganda in the northeast. In the northern and central sections of the East African Nickel Belt, a thick package of Paleoproterozoic to Mesoproterozoic metasedimentary rocks, known as the Karagwe-Ankole Belt (KAB), overlies this boundary, within which occurs a suite of broadly coeval, bimodal intrusions that correspond to the Mesoproterozoic Kibaran tectonothermal event between 1,350 Ma and 1,400 Ma.
The Kibaran igneous rocks comprise mafic-ultramafic intrusions, including well-differentiated lopolithic layered intrusions and small, narrow, tube-like sills, often concentrically zoned, called chonoliths. The nickel mineralization zones discovered to date have exclusively been found associated with the maficultramafic intrusions, in particular, along the Kabanga-Musongati Alignment.
The Project comprises six distinct mineralized zones, namely (from southwest to northeast) Main, MNB, Kima, North, Tembo, and Safari, which occur over a strike length exceeding 7.5 km. The five mineralized zones that contribute to the Mineral Resource estimate (Main, MNB, Kima, North, and Tembo) extend over a total strike length of 6 km and for up to 1.7 km below the surface.
Property Geology
The intrusions that host the potentially economic nickel-bearing massive sulfide zones known to occur in the Project area, namely Main, MNB, Kima, North, Tembo, and Safari, are hosted within steeplydipping overturned metasediments (dipping 70° to 80° to the west), with a north–northeast strike orientation (025°) from Main to North Zone, changing to a northeast strike orientation (055°) (dipping northwest) from North to Tembo. The zones are located within and at the bottom margin of the maficultramafic chonoliths. The chonoliths are concentrically zoned with a gabbronorite margin and an ultramafic cumulate core zone that ranges in composition from sulfidic dunite, plagioclase-peridotite, orthopyroxenite, to olivine melanorite (Evans et al., 2000).
The metasediments comprise approximately 90% metapelites and metasandstones, with the remainder comprising clean arenitic metasandstones or quartzites (Evans et al., 2016). Lenses and bands of iron sulfides (up to 5% modal of pyrrhotite) and graphite are common in the more-pelitic rocks, and it has been demonstrated that the sulfur within the different zones has similar isotopic signatures, indicating significant assimilation of external sulfur from the KAB sediments (Maier and Barnes, 2010).
Mineralization Style
Kabanga sulfide mineralization occurs both as:
- Disseminated to net-textured interstitial sulfides located within the cumulate core of the Kabanga chonoliths, as well as externally.
- Massive and semi-massive sulfide bodies along the lower and side margins of the chonolith, that being the contact with the stratigraphic host.
The massive sulfides, defined as having > 80% modal sulfide, comprise dominantly pyrrhotite, with trace to 15% pentlandite. These account for the majority of the Mineral Resource estimates reported for the Project. Pentlandite exhibits distinct recrystallization textures expressed as globules up to 5 cm in diameter. Accessory sulfides include chalcopyrite and trace pyrite, galena, arsenopyrite, cubanite, niccolite, cobaltite, and mackinawite. Remobilized, generally pyrrhotite-rich, massive sulfides also occur as cross-cutting and conformable veins within the ultramafic units.
The tenor composition of the sulfides (as represented by the percentage of nickel in 100% sulfide) ranges from 5% to 6% near the basal margins to 0.5% to 1% in the upper cumulates (Evans et al., 1999; Maier and Barnes, 2010). Tenor also varies between mineralized zones, generally the smaller intrusive bodies (by cross-sectional area) that occur lower in the stratigraphy, such as North and Tembo zones, are more richly endowed.
Alteration and Weathering
At the surface, the ultramafic bodies are completely weathered to saprolite. The depth of oxidation ranges from 40–100m in the Project area. At North Zone, massive sulfides are weathered to depths of 80–100m. The Tembo Zone massive sulfides horizon is located 98% in fresh, unoxidized material. In general, nickel laterite formation over the associated ultramafic is weakly developed with minor nickel-bearing serpentine and rare garnierite.