Loncor holds 84.68 % interest in the Imbo Project through its subsidiary Adumbi Mining S.A., with the minority shareholders holding 15.32 % (including the 10 % free-carried interest held by the Government of the DRC).
- subscription is required.
Summary:
Gold deposits within the Imbo Project are associated with the globally important Neo-Archean orogenic gold deposits. Gold mineralisation is associated with the epigenetic mesothermal style of mineralisation. This style of mineralisation is typical of gold deposits in Neo-Archean greenstone terranes and is generally associated with regionally metamorphosed rocks that have experienced a long history of thermal and deformational events. These deposits are invariably structurally controlled.
The Adumbi gold deposit is found within the Ngayu Archean greenstone belt, one of a number of Archean-aged, granite-greenstone belts that extend from northern Tanzania into northeastern DRC and then into the Central African Republic. The greenstone belt terrain in northeastern DRC has a number of major gold belts including Moto (Kibali), Kilo, Mambasa, Ngayu and Isiro.
The Adumbi deposit displays five distinct geological domains with the BIF unit attaining a thickness of up to 130 m in the central part. There is a higher-grade zone of gold mineralisation termed the “replaced rock zone” (RP zone) associated with alteration and structural deformation that has completely destroyed the primary host lithological fabric. The RP zone occurs in the lower part of the Upper BIF package and in the Lower BIF package, and transgresses the Carbonaceous Marker, located between the Upper and Lower BIF packages, both along strike and down dip. The geological interpretation from the Loncor drill intersections demonstrates that the mineralised BIF increases in thickness with depth and thus confirms the existence of significant underground potential at Adumbi below the mineral resources within the open-pit shell.
The detailed logging of the mineralised cores indicated a direct relationship between gold values and the percentage of sulphide mineralisation and intensity of silicification. In general, pyrite is the dominant sulphide followed by pyrrhotite, then arsenopyrite. When pyrite and pyrrhotite are associated with arsenopyrite, the gold values are very significant, compared to when pyrite is associated with pyrrhotite only. Silica is associated with the highest degree of hydrothermal alteration within the zones and serves as a marker of mineralisation; however, without sulphides, the gold values are insignificant. Specks of visible gold are occasionally found, generally within fractures and are present in white to grey, glassy, weak to moderately brecciated quartz veins.
Mineralisation in this environment is commonly of the fracture and vein type in brittle fracture to ductile dislocation zones. At the Adumbi deposit, the gold mineralisation is generally associated with quartz and quartz-carbonate-pyrite ± pyrrhotite ± arsenopyrite veins in a BIF horizon.
Most of the existing structural data for Adumbi is from underground mapping with some additional data from regional mapping.
Stereonet plots for bedding show two major planes oriented 315°/81° and 137°/84° defining a shallow northwesterly plunging fold (316°/07°).
It is observed that foliations are generally parallel to bedding, with average orientations of 314°/79° and 315°/81°, respectively, while the quartz veins have a general relatively less northerly orientation of 309°/79°.
Stereonet plot for the Adumbi quartz veins have two major planes oriented 309°/79° and 125°/83° defining a linear structure that is shallowly plunging to the southeast. It is not known if the intersection of these quartz vein major planes is associated with the mineralising event, but it is doubtful as it is known from previous interpretation that mineralisation at Adumbi is characterised by steep plunging shoots.
Gold mineralisation at Adumbi is generally associated with quartz and quartz-carbonate pyrite ± pyrrhotite ± arsenopyrite veins in a BIF horizon.
In the central part of the Adumbi deposit, three main zones of gold mineralisation are present:
1. Within the Lower BIF Sequence;
2. In the lower part of the Upper BIF Sequence (Zones 1 and 2 are separated by the Carbonaceous Marker, which is essentially unmineralised);
3. A weaker zone in the upper part of the Upper BIF Sequence.