Iduapriem, the fourth mine, has a reasonable outlook, within the constraints of its 110 km2 mining lease where there is very little exploration upside. Iduapriem mines from two pits and has a projected mine life till 2018. It is carrying out a scoping study on its underground potential. Iduapriem together with Obuasi and the fading operation of Bibiani make Ghana AngloGold Ashanti’s second largest source of production, contributing some 680,000 ounces of gold a year, behind South Africa only.
Iduapriem, located 300 km from Accra and 85 km from the nearest coastal town of Takoradi, shares a mining lease boundary with Gold Fields’ Tarkwa mine and mines the same 40O to 50O dipping orebody to produce 210,000 ounces of gold a year at a cash cost of just over US$310/oz. Some 24 million tonnes of material is moved a year in the course of mining this open pit operation.
The operation used to mine from three reefs, A, B and C, but the A reef which was mined for the heap leach plant now forms the footwall, and only the B and C reefs are mined, the former ranging from five to 20 metres in thickness and the latter from five to 10 metres in thickness.
Iduapriem has a total resource of some 66.5 million tonnes at 1.66 g/t for 3.5 million ounces of gold. It has reserves of 45.9 million tonnes at 1.71 g/t for 2.5 million ounces of gold. The cut-off grade has decreased from 0.78 g/t at US$450/oz to 0.6 g/t at US$550/oz. The mine employs 648 people, of whom only two are expatriates and there are an additional 570 contractors.
Formerly Ghanaian Australian Goldfields, Iduapriem became part of Ashanti Goldfields in 1996. It used to be a combined CIL and heap leach operation, and was boosted by additional heap leachable reserves from the former Teberebie operation in 2000 (it and Tarkwa shared the spoils of Teberebie after Pioneer Goldfields gave up on that operation). A few years ago Iduapriem upgraded the capacity of its CIL plant and decommissioned its heap leach plant due to low recoveries and poor economics of the operation.
“The heap leach operation was no longer viable as the harder fresh rock material was being mined, and recoveries were down to 33%,” managing director of Iduapriem David Renner says. The recovery from the CIL plant at Iduapriem is on average 94.6%.
The mine is currently investing in an additional mill and a new crushing plant that will upgrade this plant’s capacity from 3.8 million tonnes a year to 4.3 million tonnes a year. The upgrade is being done at a cost of US$25 million and could see annual production increase up to 250,000 ounces of gold by the end of 2008. It will also reduce production costs by 10% to 15%. Currently the old crusher from the heap leach plant is used for 25% of the material and the main crusher processes 75% of the ore. With the upgrade, the new crushing facility will process all the ore from a single source. The main plant features a crushing circuit, two SAG mills and a ball mill, and the upgrade involves the addition of a second ball mill. The plant will then have the option of two processing streams. The plant includes four leach tanks and seven adsorption tanks.
“After the expansion the CIL plant will have the same capacity as the CIL plant at Tarkwa and will have a recovery rate of 95%,” Renner says.
Mining at Iduapriem is undertaken by contractor Taywood Mining. The mine’s fleet includes 14 Cat 777 haul trucks, two Liebherr 994 excavators and two Liebherr 984 excavators, as well as seven Atlas Copco L8 drill rigs and other ancillary fleet. Should the mine convert to owner mining, it has first option on buying the fleet. The current mining contract runs until February 2008, and fuel and other costs saw the cost of the contract increase from US$25 million in 2004 to US$30 million in 2005. The life of mine stripping ratio is 3.7:1 and the pit extends 4 km north to south and has an average width of 150 metres. Mining takes place using six metre benches. None of the material is free dig and the mine uses some four to five hundred tonnes of explosives a month, this supplied by Spanish contractor UEE. The average distance from the pit to the plant at Iduapriem is four to five kilometres.
Iduapriem uses some 7,000 MWh of electricity a month. It spent US$1.38 million on procurement from local suppliers and contractors in Ghana during 2005 as part of its bid to enhance sustainable socio-economic development in the region. The region where Iduapriem’s location is very lush, receiving 2,000 mm of rain a year, and some of the mine’s dumps revegetate themselves within a few years without the addition of topsoil.
Once the mill upgrade is complete Iduapriem will remain a steady state mine for the rest of its life, unless of course the gold price settles sustainably at over US$750/oz, in which case the mining plan will be revised to relocate existing infrastructure which could be affected by additional stripping. MRA