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Damang mine, Ghana - Mining Weekly

Friday, 11 November 2016

Name: Damang mine.

Location: The mine is located in south-western Ghana and to the north of and joining the Tarkwa concession, which is located near the town of Tarkwa.

Controlling Company: Gold Fields.
Brief Description: The Damang mine is an openpit mine, which comprises four openpits and one carbon-in-leach plant with a current capacity of 4.5-million tonnes a year. It is estimated that the current mineral reserve will be depleted in 2020.

Brief History: Gold Fields and Repadre signed an agreement in 2001 to buy Ranger Exploration’s 90% interest in Damang. IAMGold and Repadre merged to give IAMGold an 18.9% interest in Damang and Gold Fields a 71.1% interest. In 2011, Gold Fields bought out IAMGold’s remaining interest in Damang and the company now owns a 90% stake, with the government of Ghana owining the remaining 10%.

The Damang expansion project was initiated in 2004 to identify additional sources of ore from areas around the main pit. Following further drilling, a feasibility study was initiated to test the feasibility of a cutback to extend the life of the main pit. In July 2005, the Damang pit cutback and waste mining project started.

Products: Gold.

Geology/Mineralisation: The Damang orebody is hosted by a north to north-easterly plunging antiform, developed within Tarkwaian sediments. The main Damang pit is located close to the closure of the antiform, while all other known mineralisation is located on the east and west limbs of the Damang anticline. The mine exploits fresh hydrothermal and oxide mineralisation, in addition to Witwatersrand-style, palaeoplacer mineralisation.

Reserves: Proven and probable mineral reserves as at December 31, 2015, were 21.12-million tonnes, grading 1.43 g/t gold. The new reinvestment plan will lead to a 72% increase in proven and probable reserves to 1.68-million ounces.

Resources: Mineral resources as at December 31, 2015, were estimated at 79.61-million tonnes, grading 2.2 g/t gold.

Mining Method: Mining at Damang is undertaken by conventional openpit methods using Gold Fields personnel and equipment. Owner mining includes all load-and-haul, blasting, construction and dewatering activities, while contractors are responsible for production drilling, blast-hole charging, stockpile rehandling and grade-control drilling. However, from 2016, load-and-haul, blasting, construction and dewatering activities have become the responsibility of a contractor. From 2017 onwards, two contractors will be used to conduct the mining of the Damang pit and the satellite pits now that the Damang reinvestment plan has been approved (see ‘prospects’ below).

Major Infrastructure and Equipment: The Damang plant processes mainly fresh ore, with about 5% oxides, which is sourced from four openpit mining operations and existing surface stockpiles, located on the Damang mine lease.

The plant has been upgraded from four-million tonnes a year to 4.5-million tonnes a year and is a conventional two-stage grinding circuit using a semiautogenous and ball mill combination, with pebble crusher and gravity concentration, followed by a carbon-in-leach recovery process. Gravity gold is collected and treated by a gravity concentrator and an in-line leach reactor.

The East Tailings Storage Facility, with additional lifts, supports the life-of-mine (LoM) plan to December, with the Far East Tailings Storage Facility (FETSF), for which permitting is already in place, extending the LoM from 2017 to 2024. Permitting is in place for a partial lift, with the full permitting being sought from the regulator.

Load-and-haul is undertaken using a standard truck-shovel operation, with excavators in backhoe configuration.

The haulage fleet consists of 26 dump trucks, with an average payload capacity of 91 t each. Off-highway trucks haul ore to the run-of-mine pad, stockpiles and waste dumps. A fleet of tipper trucks reclaims stockpiled ore and transports it to the treatment plant. Ancillary equipment supporting the drill-and-blast and haulage operations through road and bench maintenance, dust and erosion control, and equipment maintenance includes bulldozers, graders, water and service trucks.

Prospects: Gold Fields will invest $1.4-billion to extend the life of its Damang mine from 2017 to 2024.

Over the life of the mine, 165-million tons will be mined, with 32-million tons processed at a grade of 1.65 g/t, resulting in gold production of 1.56-million ounces.

The Damang mine is expected to produce, on average, about 225 000 oz/y of gold.

The reinvestment plan for the mine is based on mineral resource models that were updated earlier this year and extensively reviewed internally and by external consultants SRK Consulting, Optiro and Rowley Geological Services.

The reinvestment plan entails a major cutback to the eastern and western walls of the Damang pit cutback. This will result in a 72% increase in proven and probable reserves to 1.68-million ounces.
Mining will be undertaken by two mining contractors, with negotiations currently at an advanced stage. The contractors are expected to be mobilised early next year.

The reinvestment will also include the construction of the FETSF, as the existing tailings storage facility is approaching full capacity.

Stage 1 of the new FETSF is planned for completion by the end of 2017 and will provide 20-million tons of capacity. Further lifts of the FETSF will cater for all tailings for the new LoM.

Only minor capital work will be required on the Damang processing plant, which will mainly entail replacing the semi- autogenous grinding mill shell in 2018.

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