South Deep skip plunges 1.6 km

An investigation is underway at the South Deep underground gold mine in South Africa, after a loaded skip broke free of its winder drum and plunged some 1.6 km down one of the mine’s twin shafts.

The incident occurred during regular maintenance on 4 May. The skip and winder are inspected and maintained every four weeks. An initial assessment indicates that the rope detached from clamping devices on the drum while the skip was around mid-shaft.With a shaft depth exceeding 3 km, South Deep employs one of the largest winding systems in the world.

There were no injuries and all workers were safely removed to the surface.

The full extent of damage to the shaft has yet to be determined, and South DeepGeneral manager Gordon Thompson expects that a detailed investigation will not begin until some 6.7 km worth of rope has been removed. That alone is expected to take around 2 weeks.

“Teams of highly trained staff have been deployed in round-the-clock shifts to address the task ahead,” he said. “While remedial work is under way, production, albeit at a reduced capacity, will continue through the South shaft.

Significant shaft repairs are anticipated before normal hoisting can resume. There was no estimate of the impact on production.

Harmony Gold Mining (HMY-N) recently grabbed a 29.2% stake in Western Areas (WARSF-O, WARA-J), co-owner of South Deep, for around US$320 million.

Harmony picked up a 14.6% interest in the mine via the deal. Likewise, Barrick Gold (ABX-T, ABX-N) inherited a half-interest in the mine through its takeover of half-owner and operator Placer Dome.

Earlier this year, Western Areas and Placer halved South Deep’s reserves following a year-and-a-half review. Proven and probable reserves now total 147 million tonnes running 6.2 grams gold per tonne, for 29.3 million contained ounces.

The reduction in reserves is mostly attributed to a new geological model, an enlargement of regional pillars aimed at improving ground stability, and the inclusion of more low-grade material owing to a change in the mining method in certain parts of the mine.

Many of the trimmed ounces were shifted to the measured and indicated resource category, which now amounts to 109.9 million tonnes averaging 7.3 grams gold per tonne, for 25.9 million contained ounces. The estimates are based on a gold price of US$400 per oz.

In 2005, South Deep produced was 461,119 oz. gold at a cash cost of US$387 per oz., up from the 428,585 oz. poured at US$383 apiece a year earlier.

The South Deep twin-shaft expansion, which was commissioned in late 2004 after years of delay, is expected to boost total annual production to 750,000 oz. over 70 years.

In all, South Deep comprises the South shaft complex and newer Twin shaft complex. The South complex includes the Main shaft and sub-vertical shafts 1, 2 and 3, which service mining down to a depth of 2,692 metres below surface. The Twin shafts stretch to 2,590 metres and 2,890 metres below surface.