SYDNEY (REUTERS) - Prisoners in central Australia are being offered an unusual way to defray the costs of their incarceration and to build their savings and self-esteem - by working in a salt mine.

The mining project, in the inhospitable desert about 250 km south-west of Alice Springs, had been struggling to recruit staff and took advantage of a scheme offered by the Northern Territory government.

"I appreciate there is no small amount of humour in being the minister sending prisoners to a salt mine. The truth of the matter is that it has proven itself to be a worthwhile programme," said John Elferink, Northern Territory's minister for justice and correctional services.

"It's work aimed at normalisation and lifting people's self-esteem, giving them a chance to build a future for themselves."

In pre-industrial times, salt was such a valuable commodity that it was used as payment for Roman soldiers but mining of it was so dangerous that work was often undertaken by prisoners.

The convicts working at the Karinga Lakes Potash project, a joint venture between mining companies Rum Jungle Resources Ltd and Reward Minerals Ltd, earn award wages of around A$16 (S$18.70) an hour and are allowed to keep A$44 a week as spending money.

The government makes deductions, including jail costs and a 5 percent donation to a victims' assistance fund. The rest is placed into a trust that is paid when the prisoner is released.

Northern Territory prisoners have also worked as waiters, conveyancers, retailers and labourers since the programme's inception 12 months ago.

During the 18th and 19th centuries, the British government sent more than 165,000 convicts to Australia to settle in penal colonies, helping to ease pressure on overcrowded jails at home.