Target Gold Mine, South Africa

The newest deep gold mine to be developed in South Africa, Target first hit its scheduled mining rate of 17,500t/d in late 2001, and has since been ramping up to its scheduled production rate of 350,000oz/y of gold. The mine has been under development since 1995, with the aim of accessing previously unknown gold resources that lie to the north of the existing Welkom goldfield, some 200km southwest of Johannesburg. The total capital cost of bringing the mine into production has been R2.01 billion ($215 million).

The corporate rearrangement that has taken place between Avmin, Harmony Gold Mining Co. and African Rainbow Minerals has resulted in Target being transferred from its original owner, Avgold, to Harmony, which now has 100% ownership.

GEOLOGY AND RESOURCES

The Welkom goldfield lies at the southwestern end of the major Witwatersrand basin. The Welkom section was discovered in the late 1940s, leading to the development of several mines, including Anglovaal's Loraine operation.

The Eldorado Reef mineralisation is contained in a series of ancient alluvial fans, stacked sequentially within the rocks of the Central Rand Group of the Witwatersrand Supergroup. Avgold's recognition of the periodicity of these sequences led the company to explore the area to the north of its Loraine mine, where it has discovered substantial gold resources contained in the Basal, ‘B' and Elsburg Reefs, which occur throughout the Welkom area, and the previously uneconomic Big Pebble and Dreyerskuil Reefs.

At the end of 2006, the company estimated proven and probable gold reserves at Target to total 18.1Mt grading 6.55g/t gold. In addition, 6.8Mt grading 4.47g/t lie within the old Loraine mine, with minor low-grade surface stockpiled material available as well. In total, the operation has a resource of 25.1Mt containing 4.8Moz of gold. Exploration carried out over the past few years has identified substantial indicated and inferred resources in the Northern Free State area, north of Target itself, totalling some 325Mt containing around 74Moz that could form the basis for a separate new mine, and for which a prefeasibility study has been completed.

MINE DEVELOPMENT

The Target orebodies, which lie at depths of between 2,200m and 2,500m below surface, have been accessed by declines sunk from the existing underground infrastructure at Loraine, where production ended in mid-1999. This has substantially reduced the cost of bringing Target into production. Drilling equipment used included Sandvik (Tamrock) twin-boom jumbos.

The declines are equipped with roof-slung Walter-Becker monorails for transporting materials from the Loraine shaft to the Target production areas. The declines also handle crushed ore from the main underground primary crushers to the hoisting skips in Loraine's No.1 shaft, using belt conveyors that are also used for transporting personnel.

MINING METHODS

From the outset, Avgold planned Target to be highly mechanised, using long-hole stoping where reef widths allow this, and either cut-and-fill or long-hole stoping in narrow reef areas. Broken ore is handled using remote-controlled Sandvik load-haul-dump machines. Drift-and-fill mining is used in flat-lying reef areas. The depth of the orebodies means that all the stoping areas must first be de-stressed by developing conventional narrow-reef stopes above them, and once extracted, all stopes are backfilled using cemented mill tailings.

In order to monitor the mine, Avgold installed a fully integrated information system - Prostar (Production Systems for Target) - that provides real-time information on all aspects of the operation, including geological data, mine operations, maintenance, materials management, production control and other parameters. The network is run from a centralised surface control room. The mine is also equipped with a leaky-feeder radio system for improved communications between surface and the entire underground operation.

The mine has 24MW of refrigeration capacity for underground ventilation air, helping to maintain the operations at temperatures of below 27.5°C.

Progress in the massive stope areas of the mine has been hampered by high stresses that caused large low-grade rocks to block the drawpoints. This has been handled by reducing the size of the stopes, by increasing the drawpoint spacing and by mining new destressing slots, giving increased mining flexibility.

ORE PROCESSING

While the initial development material containing ore was treated in the old Loraine concentrator, this has now been partly demolished and a new, highly automated metallurgical plant is scheduled for commissioning in late 2001.

The new concentrator process will feature semi-autogenous grinding (SAG) of the crushed ore from underground. Following thickening, centrifugal gravity concentration of the slurry from the SAG mills produces feed for continuous cyanide leaching. Carbon-in-pulp systems are used to retrieve the gold from the leach fluids, with Anglo American Research Laboratories' proprietary elution and electrowinning technology used for final gold recovery.

PRODUCTION

Since coming into Harmony’s portfolio in April 2004, Target’s focus has been on reducing its production costs. In the 2005–2006 fiscal year, the mine hoisted 813,000t of ore grading 6.3g/t gold and recovered 150,196oz at a cash cost of production of US$346/oz. It also recovered 1,350oz from surface stockpiled material at a cash cost of US$346/oz. Its 2005–06 production was significantly lower than that achieved the previous financial year, when it hoisted 1,178,000t of ore and recovered 209,847oz of gold at a cash cost of US$273/oz.

Poor vehicle availability underground led to a shortfall in development, which in turn created a shortage of broken ore. As a result, the mill treated an average of 67,500t/month compared to its 105,000t/month capacity. While the mine has extensive reserves, falling ore grades continue to present a problem, with the head-grade reducing over calendar 2006 from 6.36g/t in the first quarter to 5.18g/t in the fourth quarter. Harmony spent some US$9.6m at Target during 2005–06, mainly on underground development and the replacement of the underground fleet.

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