Modern Mining September 2019

outcrops and gold workings, undertaken both ground and airborne geophysics pro- grammes, and completed a huge amount of drilling totalling around 500 000 m (including 168 000 m of core drilling). The proven and probable mineral reserve defined in the 2019 FS totals approximately 70 Mt at 0,81 g/t Au for 1,83 Moz of gold. Some 52 Mt of this is oxide material at a grade of 0,81 g/t Au with the balance being sulphides at 1,19 g/t Au. In all, the oxide and sulphide mining opera- tion will extract ore from over 60 separate pits of variable size and depth across a mineralised zone approximately 12,2 km long and 3 km wide, with the overall strip

apron feeder, the ore is transferred to a conveyor that feeds directly to a ball mill. The plant is designed with two ore transfer points and one conveyor, thereby minimising issues associated with wet sticky ore in the rainy season. The ball mill is equipped with a variable speed drive sized to accommodate a wide range of ore types and hardness. Ball mill discharge is pumped to a cyclone cluster with the oversize reporting back to the mill and the undersize fed to a pre-leach tank and seven-stage CIL circuit. The CIL tails are thickened to recover process water and then pumped to a lined tailings facility. The tailings facility is designed to be zero discharge, with water recovered in a decant tower and returned to the process water tank at the plant. Gold is recovered in a standard 10-t carbon desorp- tion plant, finishing with electrowinning and smelting to produce gold doré bars. The sulphide circuit will consist of a primary jaw crusher followed by a SAG mill in closed circuit with hydrocyclones and a recirculation pebble conveyor system. The cyclone overflow will be thickened and transferred to the pre-oxidation and leaching circuit. After 24 hours leaching, the leached sulphide prod- uct will be combined with the oxide mill product and fed to the CIL circuit for an additional 24 hours of

ratio being 2,34. While the grade of the oxides is on the low side, this is offset by the free-dig nature of the oxide material (which also requires minimal grinding before leaching). The 2019 FS mine plan is based on an annual feed rate to the plant of 5,2 Mt/a of ore, delivering higher-grade ore in the early years of the project, by stockpiling of lower-grade material and sub- sequent drawdowns in the later years. The first 2,5 years of production will be free-dig oxide ore only. In year 3 the sulphide circuit will be commis- sioned and as it ramps up to 2,2 Mt/a capacity, the throughput of the oxide circuit will be correspond- ingly reduced to 3,0 Mt/a to maintain the combined capacity at 5,2 Mt/a. The LT and sulphide ore, which require conven- tional drill and blast mining methods, will be mined using a separate equipment fleet to account for the increased density, abrasion and hardness. Mining of the oxides will be by a local contractor using a conventional diesel-hydraulic excavator fleet, and small 30-t and 50-t road-type rear-dump trucks. Ore and waste are all ‘free-dig’ material with little or no oversize material, eliminating the need for drill and blast. This type of load-and-haul fleet is common in Burkina Faso and West Africa for similar free-dig material and will provide the needed versatility for a mine plan having a large number of shallow pits of varying tonnage. Mining of the sulphides in the first three years of Phase II will incorporate the high grade P17S ore blended with higher-grade material from the other sulphide zones to maximise the value of the project. Mining of the LT and sulphides will be by contractor with trucks suited to the more abrasive and denser rock types. The LT material requires a less dense drill hole pattern and lower powder factor than needed for sulphides. The flowsheet and plant designed for the oxides have been designed to process the soft fine-grained ore which does not require crushing. The ore is direct dumped across a static grizzly into a large hopper and onto a variable speed apron feeder. From the

A sulphide circuit will be added to the processing plant in year 3 of production.

Orezone’s Senior VP Exploration, Pascal Marquis, at the high-grade P17S zone.

September 2019  MODERN MINING  35