Ballarat Goldfields this morning pleaded guilty in Ballarat Magistrates Court to one count of failing to provide a safe system of work.

The company was charged after a rock fall at its Woolshed Gully operation on November 19, 2007.

The incident occurred at 3.30am when the upper section of the mine's access tunnel collapsed about 700m from the main entrance.

One of the trapped miners called 000 on his mobile phone and alerted emergency services to the cave-in.

The first group of miners were brought to the surface in a large bucket, via a ventilation shaft in Elsworth St, at 7.20am.

Less than an hour later, the final group was rescued through the shaft, ending the five-hour ordeal.

The court was told the company had stripped back the walls of the mine about a month before the collapse in response to a phenomenon known as ''wall convergence''.

Wall convergence is a universal feature of underground works where the walls of the mine move inwards to fill the void created by the mining works due to natural forces.

The court was told Ballarat Goldfields failed to review and revise its safety management system when it conducted the wall stripping on October 11, 2007.

Magistrate Lionel Winton-Smith said while ''substantial penalties'' could be imposed, Ballarat Goldfields did not have any prior convictions.

''It was a technical breach,'' he said.

The company was fined $20,000 without conviction.