It is estimated that illegal mining is costing the mining industryabout R5-billion a year.
Known as Zama Zama, illegal mining is run by syndicates that target young men from Lesotho, Swaziland, Zimbabwe and Mozambique.
The syndicates depend largely on corrupt security officers and clerks who work at the mines to clear the way for new recruits.
Branch chairman of the National Union of Mineworkers at the Tshepong mine in Welkom, Free State, Gcinikhaya Silwanyana, said some mineworkers were willing to "lose" their access cards for a fee.
"The lost access cards get reported long after illegal miners have gone underground," he said.
Some syndicates who find it too expensive to bribe security guards and mine employees, prefer to smuggle workers through tunnels they have dug in old disused mines around Tshepong mine.
The syndicates also use retrenched and former mineworkers to train the new recruits.
Zama Zamas earn decent wages compared to official mineworkers, but the danger posed by rockfalls, police raids and syndicate turf wars are permanent threats to their lives.
A 23-year-old man from Lesotho, whose identity we have concealed because he still has to appear in court, related his story as an illegal miner at Tshepong mine.
Zama Motloung* is currently under police guard. He was shot in the early hours of last Saturday during a fight with Mozambican illegal miners, who allegedly wanted to monopolise a section identified for mining. The shootout left three people dead and several others wounded.
Motloung and another Lesotho national were arrested on Sunday after they were discovered by mine security officers.
Motloung said he came to South Africa in March last year with a group of about 20 men from his country. After going through the main gate, they were escorted to the mine shaft and down into the earth.
He said: "I was scared. I did not know what to expect. The group of men we joined looked stern and they appeared uneasy.
"At all times there are about 5000 people underground. The heat and hunger are the main problems."
Motloung claimed he was brought to the mine under the pretext that he would be formally employed, but once he was underground he realised that he was part of about 2000 illegal mineworkers.
Illegal miners also work in shifts.
"We have foremen we report to and get instructions from. We wash the gold after we have dug it and we deliver it to a different group.
"We have weekly targets to meet and we are paid according to what we produce. Once you stop being productive because of illness or something, they take you out and you will be arrested," he said.
Motloung said he and his countrymen spent a year underground and did not see the outside world at all.
He said there were many ways to evade the police and security.
"A message is relayed from outside each time a raid is about to take place. Those who get the information indicate to the rest by using flash lights. We retreat into dark enclaves called 'madala site'."
Illegal miners are also known to violently fight raids.
Food is a lucrative business underground. A lunch box containing meat, pap and gravy can cost anything between R200 and R300.
To try and sniff out illegal miners in June 2010, mine management banned workers from taking their lunch boxes and any food underground.
But Silwanyana said the company was forced to make an exception for miners who have diabetes because they must eat regularly.
"I suspect that some workers get forged documents that they present as proof that they are diabetics so that they can take food underground to sell," Silwanyana said.
"Despite continuous warnings that they should not associate with illegal miners, most workers continue to sell food to them."
Welkom police spokesman Captain Stephen Thakeng said police were making progress in squashing syndicates that trade in gold.
He said that a five-month police investigation resulted in the arrest of several members of a syndicate who were found in possession of gold worth R120000, four vehicles and R75000 in cash.
"The aim was to bust illegal gold buyers whom we suspect are the ones who are buying the gold from the illegal miners," Thakeng said.
Tshepiso mine is owned by Harmony Gold Mining and its chairman is Patrice Motsepe.
The company did not want to comment over illegal mining.
* Not his real name.