JOHANNESBURG (Reuters) - Bullion producer Gold Fields said on Wednesday an illegal strike at some of its Beatrix shafts in South Africa had ended but the majority of its operations are still being hit by wildcat strikes that have halted production.

The world's fourth largest gold producer on Tuesday issued striking employees an ultimatum to return to work by Thursday or be sacked.

By Wednesday morning, 6,200 employees returned to work at Beatrix shafts 1, 2 and 3 but the fourth shaft at the mine remained closed due to the strike.

About 2,800 employees at the Beatrix 4 Shaft, 11,000 at KDC West and 8,500 at KDC East are on illegal strikes, it said.

The company has lost 65,000 ounces of gold production, or 1.2 billion rand ($137.5 million) in revenue so far and the longer workers stay away, the greater the risk the company will shut struggling shafts, chief executive Nick Holland said.

($1 = 8.7284 South African rand)

(Reporting by Sherilee Lakmidas; Editing by Ed Cropley and Jon Herskovitz)