UPDATE 2-Gold Fields says losing 20 kg a day at shut shaft

(Adds lost output, updates share price)

By James Macharia

JOHANNESBURG, June 26 (Reuters) - Gold Fields Ltd (GFIJ.J) said on Thursday it had lost 20 kg of gold after shutting one shaft at its Kloof mine in South Africa to allow investigations to take place after two miners were killed following a tremor.

The employees were killed in a fall of ground at Kloof's No.4 Shaft early on Thursday while cleaning some 3 km (1.8 miles) below the surface. No other injuries were reported.

The tremor rated 1.2 magnitude on the Richter scale.

"All production at the shaft has been stopped and an investigation by the Department of Minerals and Energy (DME) is being carried out," Gold Fields said in a statement.

"We have lost 20 kg (706 ounces) of gold after closing the shaft, and we could continue to lose the same amount per day if it remained shut," Gold Fields spokesman Andrew Davidson said.

The shut shaft is one five at the key Kloof mine, which produces a total of 95 kg of gold a day, he added.

The DME had issued an order to shut the shaft and take remedial action before the shaft could re-open, Davidson said.

"We shall report to the inspector on Friday and if he deems fit we shall re-open the mine," he said.

Kloof is a star among mines owned by the world's fourth biggest gold producer, and employs some 15,000 workers.

Kloof's total gold production fell by 24 per cent to 175,500 ounces in the quarter to end-March from 230,800 ounces in the preceding quarter to end-December.

The National Union of Mineworkers (NUM) said it would also take part in the probe at the shaft, and spokesman Lesiba Seshoka said: "(the NUM) calls on the mining industry to pull up its socks when coming to safety rather than lip service."

The latest deaths come in the wake of the mine having hit a safety milestone.

"We are deeply saddened and shocked by this accident which took place within 24 hours of Kloof achieving a million fatality-free shifts," Nick Holland, Chief Executive of Gold Fields said.

Holland, who has said the company will not mine if it cannot mine safely, reiterated that safety was the number one priority at Gold Fields.

Shares in Gold Fields rose 4.68 percent to 94 rand, underperforming the gold index .JGLDX, which added 6 percent after the metal's price rose 3.5 percent in London trading.

The deaths put a further spotlight on the treacherous nature of mines in South Africa, some of which are among the deepest in the world. Last year the NUM staged an unprecedented one-day strike across the mining sector to protest mine deaths, and force companies to spend more resources in curbing fatalities.

The DME says mineworker deaths rose 11 percent last year to 221, the first increase since 2002. (Reporting by James Macharia, Editing by Nigel Hunt)