A New Copper Belt in the DRC
In the western portion of the DRC, within 70 kilometers of Kinshasa is an interesting geological feature that runs from the northern part of Angola and even has showings in the southern part of Congo. During the formation of Pangea (Pan African), the two sides of the Macaúbas basin amalgamated, resulting in the Araçuai-West Congo Orogen (AWCO). The AWCO split again during the early Cretaceous and the formation of the Atlantic Ocean. This break-up resulted in the Macaúbas basin with its three aulocogens. This system saw bi-modal magmatism followed by passive margin sedimentation and development of platform carbonates, now making up the West Congo Supergroup. The WCB presently extends along 1 400 km over Angola, DRC, ROC and Gabon.
The Inkisi Formation is an alluvial-deltaic sequence, that, according to Pedroso-Soares et al (2008), is borne out by the presence of a basal conglomerate followed by upward fining sequences of coarse to fine sand with increasing clay intercalations the higher you go in the sequence. Historical interpretation indicated that he Mpioka subgroup was largely, if not totally, eroded along the Mbamba-Kilenda fault, on its northern side. This gap was subsequently filled with Inkisi group sediments. The project scale mineralisation is structurally and stratigraphically localised in, and adjacent to, the contact between fluvial deltaic to intertidal sandstones in the hanging wall and fine laminated to thin bedded, micritic silty carbonate rocks in the footwall. Dorling (2014) describes the contact of the carbonate rocks with the overlying clastic sediments (matrix-supported conglomerate) as an angular unconformity. The overlying sediments are laterally variable in thickness but can reach thicknesses of 25m. The structural setting of the northern limit of the aulocogen is characterised by strike-slip faults, relays and folding.The structural setting of Mbamba-Kilenda could possibly be similar (though somehow symetrical) to the structure that borders the north of the aulocogen. These structures host the base metal deposits. According to (Dorling, 2014) the base metal and precious metal mineralisation is enveloped by a halo of hypogene haematite alteration which extends beyond the mineralisation itself.
Mineralisation is always associated with alteration. Weathering has overprinted the hypogene mineralisation and led to secondary mineral formation.
Massive copper minerals include (in order of significance):
- Chalcocite: copper sulphate, CuS. A secondary mineral in or near the oxidized zone of copper sulfide deposits. According to Dorling’s (2014) compilation of historic and Phase 1 diamond drilling results, the chalcocite is the only sulphide mineral observed at the deposit; no other sulphide mineral were observed.
- Malachite: copper carbonate hydroxide, Cu₂CO₃3(OH) 2. Very common secondary copper mineral with a widely variable habit
- Chrysocolla: hydrated copper phyllosilicate, (Cu,Al)2H2Si2O5(OH)4·nH2O. A mineral of secondary origin, commonly associated with other secondary copper minerals
- Azurite: carbonate mineral formed as result of weathering, Cu3(CO3).2(OH) 2. Found largely in the oxidized portions of copper deposits, it is a secondary mineral formed by the action of carbonated water acting on copper-containing minerals, or from Cu-containing solutions, such as CuSO^4 or CuCl^2 reacting with limestones.
Zinc, lead and silver minerals occur as fine disseminated phase that are not recognised macroscopically. These minerals may be silicates, carbonates, arsenides or phosphates. At its most intense near the centre of the main conduit, the alteration system has led to the complete replacement of the host rocks, which allowed the precipitation of specular haematite (Figure 6, A). The haematite alteration forms a predominantly hangingwall halo; possibly due to the greater permeability that is provided by the siliciclastic rocks.
There is only a minor overlap of mineralisation with carbonate rocks in the footwall. It appears that alteration has migrated upwards and outwards.
Historic exploration by the Belgians defined the mineralisation during the 1950’s and 1960’s.
Based on the exploration, sampling and assay work that has been undertaken, JORC compliant mineral resources have been provided for the MK deposit by COMILU, a DRC based subsidiary company of Central Copper Resources. The resource estimation has been undertaken by Simon Dorling of CSA Global for COMILU. The mineral resources provided were compiled and issued during March 2017, the table below shows a summary of the mineral resources estimated to date. Exploration work is ongoing.
|SUMMARY OF JORC COMPLIANT MINERAL RESOURCES FOR MK DEPOSIT AT 0.5% Cu CUT OFF|
|Resource Category (JORC)||Tonnes (Mt)||Cu (%)||Cu metal (kt)|
The concept level geotechnical analysis of the MK deposit indicates that the rock mass in close proximity to the ore zone is of a poor quality. This has a major influence on the parameters used to determine the stope design for mining. The strike length and vertical height of mining is restricted as a result and this warranted the contemplation of both rib and sill pillars. In a Preliminary Economic Assessment (PEA) conducted by Bara Consulting in 2017, cut and fill mining and long hole open stoping were considered as potential solutions to the mining.
Following on from this, management of Central Copper has re-evaluated the prospectivity of the 85 km strike length within their contiguous Exploration Permit packages, resulting in a changed strategy of exploration. As the existing resource is developed on the eastern end of the strike length, the first 15 km of this strike has been deemed as project 1, known as Mbamba Kilenda (MK), and exploration will focus on resource extension to the existing resource and addition of additional phases of development within the first project. Since drilling stopped in mineralised areas, the extension of this resource would be logical via step out and then infill campaigns to upgrade the confidence and thus the JORC classification. The 15 km limit is the notional logistical limit defined by high level modelling before it becomes economic to start a separate project.
Regional exploration would thus follow the historic showings given by the Belgian exploration results coupled with the entire strike length geophysical survey results. Given that the regional exploration is behind the resource extension drilling in the MK area, the development of new drill targets in the central portion and the western extent, where historic showings have shown similar mineralisation to the MK deposit in the central portion, while the western portion has shown high levels (>10%) vanadium combined with zinc and lead at also high levels.
Commenting on this, Central Copper Resources’ CEO, Kevin van Wouw, says that the development of our first project on the eastern end as we go through the development steps of pre-feasibility to final feasibility is the company’s no. 1 priority. But that does not recuse our responsibility of continuing the exploration and development of new project targets in the remainder of the strike length identified by the geophysical investigations and historic information. Accordingly, it is the company’s strategy in execution to complete the pre-feasibility in progress by October 2020, while at the same time seeking either partnerships or funding to continue the regional exploration.
During the course of 2020 Central Copper management requested a review of the business case for Project Mbamba Kilenda in order to determine the feasibility of the project. A scoping level assessment was performed of the various Options presented in the PEA, with option 1 being developed to maximise the ROM treatment rate, coupled with an envisaged extension in the resource to the west of the current resource. The larger project was then broken down into 5 phases, namely;
Phase A – Trial Mining via a single decline and DSO material generation
Phase 1 – 1.2 m.t.p.a ROM, producing 27 k.t.p.a Cu in Conc within the current resource
Phase 2 – Doubling ROM, resource extension within PR1297
Phase 3 – Doubling ROM to 4 m.t.p.a, Resource extension limited to 15km
Phase 4 – Establishing a Smelter – Refiner for upgrading Concentrate to Cu Metal. This phase is independent of the other phases, and modularity to be investigated for early implementation.
It was decided that the Phase 1 Project was to be moved to a Pre-Feasibility status and that the technical aspects of the study be revisited. This would include Phase A, allowing the development of a detailed implementation schedule for the commencement of Trial Mining. Central Copper management approved a project budget for the project to commence with the required Pre-Feasibility activities.
The problem statement and purpose for the MK Project is therefore to:
- Investigate all pre-feasibility study areas and re-determine if there is an economically mineable reserve within the confined geological zones of the historically defined MK project resource. (firstname.lastname@example.org %Cu)
- Compile Design Criteria documentation for later physical testwork validation, using all available information and interpretation with respect, geotechnical, hydro-geological, and metallurgical criteria. These design criteria will then form the basis of the pre-feasibility design.
- Compile a best practise project topography map, using all available methods including resource information, Landsat imagery and other available digital information. It is envisaged that as the project moves forward to feasibility, a lidar type survey will be completed. A logistical limit of 15 km has been used to approximate the likely resource contained within the first mining and processing project. Within this, using the resource statistics of the known mineralization, perform a phase 1 pre-feasibility study. The majority of this would therefore exist on PR 1297.
- Performing a Pre-Feasibility Study on the 1st phase development, including all steps required to the eventual development. This will include a trial mining scenario, and development based on a phased exploitation plan.
- Based on the outline defined above, update the Competent Persons Report in terms of JORC 2012 compliance once physical works are completed on site
From a metallurgical perspective, four characterisation testwork campaigns have been conducted on the samples generated in drilling the resource. These testwork campaigns have identified the use of Dense Medium Separation and Flotation in combination, generating two discrete concentrate products: a Direct Shippable Ore (DSO) from the gravity circuit, and a cleaner, higher grade flotation concentrate. Given the metallurgical complexity of treating both carbonaceous and sandstone hosted minalisation, the two different technologies result in a reasonable recovery, as evidenced in the tabulation below.
Scoping level economic assessment of this approach has been conducted internally by Central copper, with the following outcomes.