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.

Over the life of mine (LOM) of Adumbi, a total of 49.77 Mt grading 2.17 g/t Au is expected to be mined from the open pit and delivered to the processing plant.

The scheduling process consists of developing a mine plan that is economically optimal using the inventory included in the practical pit designs and pit shell. The production schedule was based on a methodology of block selections from the block model inside the designed pits.

The mining production schedule sequence is planned to mine the Cut 1 and Cut 2 pit designs from the beginning of Year 1 to get rapid access to the ore and manage the strip ratio. Mining of the Cut 3 pit shell starts from the beginning of Year 2. The Adumbi deposit is planned to be to provide a throughput of 5.0 Mt/a of ore to the processing plant. Adumbi has an average stripping ratio of 11:1.

A conventional open-pit shovel-and-truck method will be used for the mining of sufficient ore to supply a 5.0 Mt/a of oxide, transition and fresh ore throughput. The mining functions of the operation will be carried out by a mining contractor.

The practical pit design incorporates the ramps together with the appropriate inter-ramp slope angles.

The open-pit design criteria were as follows:
• A nominal bench height of 8 m;
• The inclusion of the ramping systems, resulting in the recommended overall slope angles of approximately 40° to 45° being achieved;
• Haul road widths of 25 m, including safety berms, providing sufficient room for twoway traffic for the planned 140 t capacity truck fleet;
• Haul road grades at a 10 % continuous gradient.

Principal haul roads shall be designed and constructed to connect the pit working areas to the primary crusher and the waste dumps.

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The plant design has been based on a nominal capacity of 5 Mt/a for all ore types (oxide, transition and sulphide). The plant design is based on the initial separate treatment of the oxide ore, followed by the introduction of a pebble crushing facility into the comminution circuit as the transition and sulphide ores are introduced into the plant feed.

The process flowsheet includes the following:
• Single-stage crushing facility, utilising a primary crusher to produce a crushed product size suitable for SAG milling;
• A crushed ore surge bin which, when full, allows crushed ore to be diverted to an emergency stockpile from which ore can be reclaimed by front-end loader (FEL) to feed the mill during the periods when the crushing circuit is offline;
• Two-stage SAG and ball mill combination, operating in closed circuit with the cyclone cluster to produce the required size;
• Additional pebble crushing system to crush pebbles from the SAG mill when treating ........