Tarkwa gold mine - Mining

The mine utilises selective surface mining methods to optimise the extraction of the mineralised conglomerate units. Short-term mine planning and forecasts are based on grade controlled models. During mining, fresh rock and transitional zones are drilled and blasted in six-metre lifts, with excavation in three-metre flitches.

The mine is owner-operated and has its own load and haul fleet of 13 excavators, which range from 120 to 400 tonnes. The haul fleet includes 67 dump trucks with a payload of 146 tonnes, eight dump trucks with a payload of 240 tonnes and nine dump trucks with a payload of 90 tonnes. The load and haul fleet are supported by an ancillary fleet consisting of dozers, graders, water carts and compactors. A total of 22 owner-operated drill rigs are used for blast hole drilling. Maintenance of the fleet is carried out by Tarkwa mine, while maintenance of the excavators is carried out by contractors.

Tarkwa is in the process of assessing and potentially changing its business model from owner to contractor mining. The current outlook for longer hauling distances and increased drilling costs due to rock hardness will drive further cost pressures at site. A transition from owner mining to contract mining provides an opportunity to abate cost increases and maximise cash-flow, and in conjunction with an accelerated exploration campaign assist in underpinning the mine's sustainable long-term future.

Mine planning and scheduling

The planning cycle commences with the ratification of key input parameters, before producing a compliant and updated Mineral Resource Estimate that is adjusted for all Mineral Resource depletions. This is followed by the planning process, which includes all technical inputs such as geotechnical, hydrogeological and detailed pit engineering and accommodates all modifying factors and fleet productivity rates.

Mine planning is based on 3D block models of in situ mineralisation, with allowances made for minimum mining widths, dilution and ore loss in line with the mining method being considered. Open pit optimisation software, in conjunction with economic parameters and physical constraints is used to generate a series of nested pits for open pit mining. An optimal shell is then selected and a detailed design used to confirm the mineability.

A cut-off grade strategy is used in the Mineral Reserve estimation process whereby the cut-off defines the ore/waste segregation. The optimal cut-off/cut-over is also derived, which can be applied to increase the grade and therefore the cash-flow in the initial years of the LoM plan without compromising long-term planning objectives. Material between the optimal cut-off/cut-over and the metallurgical process cut-off is stockpiled for treatment at the end of the LoM.

Historic productivity data and operating costs are utilised as the basis from which the operational budget is benchmarked. All capital projects are ranked and prioritised to maximise capital efficiency and return on investment. Importantly, maintenance of the capital waste strip to secure a steady flow of high-grade ore to deliver ongoing mining flexibility is strictly monitored.