With his Hulk cartoon T-shirt and his solemn face, Stephane Kapenda looks even younger and smaller than his 12 years. He knows he shouldn't be here. But for years he has hauled tainted soil from this toxic waste pit into dirty pools of water so that he can search for bits of copper.

"It's bad," he says quietly. "I would like to leave it and go to school."

Asked what is the worst thing about the work, he thinks for a moment and then whispers: "The sickness."

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Twice, the effects of heavy-metal contamination have been so severe that he needed hospital treatment. Yet he keeps at it, alongside his siblings, to scrounge a tiny income for his parents – impoverished farmers who could not otherwise survive.

About 200 to 300 children toil daily in this vast open pit, a bleak wasteland outside a copper and zinc mine at Kipushi in the southeastern corner of the Democratic Republic of the Congo, near the Zambian border.

"It's poisoning them," says a South African engineer, shaking his head in dismay, as he pumps out water from the mine. The site was abandoned two decades ago by state mining company Gécamines, but now it is being prepared to go back into production by the Canadian-controlled consortium that recently acquired it. The new owners say they are deeply worried by the child labour and are assessing what to do.

Stephane and Kipushi are just the tip of a widespread phenomenon. More than 40,000 children, according to one survey, are working in informal mines and quarries in three provinces of southern and central Congo.

Across the country, about 800,000 children are estimated to be working in the hundreds of state-owned mines that were abandoned as Congo fell into corruption and chaos under kleptocratic dictator Mobutu Sese Seko and his successors.

Women and children are not legally permitted to work in small mining here. But a government official admits it happens "clandestinely," often "with the complicity of the police."

I've been stumbling across similar scenes in my travels in Africa and Asia for many years. I've seen children dressed in rags in Mongolia, competing with bulldozers for a tiny share of the gold in giant pits. I've watched villagers digging deep hazardous shafts for gold in the remote hills of northern Tanzania. I've seen adolescent girls scraping for flecks of gold in small pits under the burning sun of Burkina Faso.

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Globally, the number of child miners is probably more than a million. Hazardous underage labour is banned in most countries, yet groups such as the International Labour Organization have struggled in vain to prohibit it. That United Nations agency launched a campaign against children working in mining in 2005, calling it one of the world's worst forms of labour.

"There is no justification – poverty included – for children to work in this sector," the ILO said. "It is literally back-breaking work."

Clawing out a living

This is the "artisanal mining" sector – a bureaucratic euphemism for the job of scavenging, digging and clawing a living from the harsh earth with bare hands and crude tools.

Its constant dangers were illustrated tragically this week when at least 60 artisanal miners were killed in an accident in a rebel-controlled region of northeastern Congo. They had reportedly rushed to be the first to the bottom of an abandoned gold pit, about 100 metres underground – far deeper than safety rules permitted – and the shaft collapsed, burying them.

Yet today artisanal mining is one of the world's fastest-growing industries. As mineral prices soar to record levels, a tattered army of unemployed workers and farmers trudges to the mines, willing to accept the frightening risks. About 15 million to 20 million people labour in artisanal gold mining alone in 60 countries worldwide. Their incomes range from perhaps a dollar a day to much higher payoffs for bigger teams on luckier days.

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Big mining companies often prosecute the artisanal miners or evict them from their land. But other times they use them as an unofficial exploration team, tipping them off to new deposits. And their yield finds its way to commercial jewellery stores, accounting for 15 per cent of global gold production, according to the Artisanal Gold Council, a Canadian-based non-profit organization that tries to help the workers.

The toll of death and injury is shockingly high. The routine use of mercury to extract gold from crushed ore, in particular, can cause permanent damage to the central nervous system. In Colombia, where more than half the gold is produced by about 200,000 small-scale miners, thousands of children suffer intoxication from the dangerously high levels of mercury gas in mining towns.

In a bid to make the occupation safer, University of Victoria earth sciences professor Kevin Telmer, who heads the Artisanal Gold Council, is pushing for mining methods that would use far less mercury.

But mercury is not the only hazard. In the Zamfara region of northern Nigeria, about 400 children have died of lead poisoning from the lead-laden rock that they pulverize in search of gold, and thousands of other children need urgent medical care, according to reports by Human Rights Watch and Médecins sans frontières (Doctors Without Borders).

In Mali, an estimated 20,000 children toil in artisanal gold mines, and injury is common. Of 33 child workers interviewed by Human Rights Watch last year, 21 suffered from regular pain in their limbs, back, head or neck, while others were plagued by coughing and respiratory disease.

"Local officials often benefit from artisanal gold mining and have little interest in addressing child labour," says Juliane Kippenberg, a Human Rights Watch researcher.

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In eastern Congo, mine sites are usually controlled by government soldiers or rebel militias, and the women and children who work there are also vulnerable to sexual violence and abuse.

'The diggers stay poor and the companies get rich'

As demonstrated by the disaster in Congo this week, hundreds of miners across Africa, including many children, have lost their lives to falls, cave-ins and collapsed tunnels. If they make it through childhood, their odds don't get much better.

"The work is seriously dangerous," Felicien Tshilay says as he climbs up a narrow mine shaft at the Karajipopo cobalt mine in Congo, abandoned by a Chinese company last year. "It's very difficult work," he says. "Look how hard I'm breathing, and I went down for only a few minutes."

The rudimentary tunnels can extend for up to 40 metres underground, running the risk of collapsed walls and oxygen shortages. To ventilate the shafts, the miners use improvised generators and plastic tubes, sometimes connected to bicycle wheels.

And it's not only the conditions of labour that are risky – the compensation can be too. In the village of Kawama, to the south, about 100 men smash rocks with sledgehammers, collecting low-grade copper from an abandoned state mine. Many are the sons of ex-employees of the state mining company, Gécamines, which is now in disarray. They wear ragged clothes, cheap sandals or tattered sneakers, and no safety equipment. Some are barefoot.

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Working from dawn to dusk, they can earn up to $10 a day – a considerable sum in Congo. But it should be much more. They are at the mercy of a local buyer, a foreign company that tests the copper grade and sets the price on a take-it-or-leave-it basis.

"They cheat us," says miner Sakila Mav. "So the diggers stay poor and the companies get rich."

These diggers have a much harder life than did their parents, who had free access to the schools and hospitals of the state mining company.

"We cough from the dust, and our bones are in pain," says 59-year-old Arnold Kyoni, a miner at the Kawama pit for 13 years. "We're working in these bad conditions because we have nothing else. We're fighting for our life."

Eyes fixed on a fatal glint

Nevertheless, the lure of the potential profit can be irresistible. Relief agencies and private charities try to remove the children from the mines, but it's frequently a losing battle.

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"The ones from the mines are easily distracted – they're still thinking about the gold," says Ouidi Naaba, a vocational teacher for school dropouts in Burkina Faso. "Often they don't show up for class."

In southern Congo, activists such as Helene Mwaluke try to persuade the children to quit the mining pits. She gently places a hand on Stephane Kapenda's head. "You have to leave," she tells him. "Working here is not good for you. You'll be suffering and coughing. You'll be smoking marijuana and drinking beer."

Many of the diggers in Congo smoke marijuana as a crude way of easing the pain and discomfort of their work.

At Kipushi, the police and security guards mostly ignore the illegal labour, making only token efforts to enforce the law. My visit there was interrupted by two green-uniformed guards who rushed toward the child labourers, chasing them away from the edge of the mine buildings, using slingshots to hurl stones at them. (The guards claim that they are careful not to hit the children.)

But just a few metres away, where hundreds of people are working in the pit, the guards do not dare enter. They say they would be attacked by a furious mob if they got too close.

In one corner of the pit, Mbuyi Kazadi and her children are digging up rocks and breaking them into gravel to sell to construction companies. Her skinny five-year-old son, Trija, toddles around the pit and tries to help his mother by gathering rocks in a pot that he can barely lift.

Ms. Kazadi has been working here for 10 years now, from dawn to dusk, taking just two weeks off work when one of her babies is born. She earns the equivalent of a dollar a day. "I pray to God that I will leave the quarries," she says. "If I could do anything else, I would do it. I would like the children to go to school and not get sick."

She and her children often fall ill from the dust and pollution at the pit, but she cannot afford hospital care. Instead she begs for free pills at a pharmacy. "All of my children cough at night," she says. "It's very hard work. We work in the sun and the rain."

Her five children are barefoot and grimy. They have never been to school. Her 16-month-old daughter is slung on her back, while her other children are collecting rocks in tattered old buckets and pounding them into smaller rocks with crude homemade hammers.

Sometimes the police raid the pit, forcing her to flee. Once, a policeman grabbed one of her children and took him to a police station. She had to pay a bribe to get her child back.

At the end of each day, she sells her buckets of gravel to truckers from construction and mining companies. If she can sell five buckets, she earns a dollar for the day's labour.

"If there are no trucks, we go home without eating."

The Canadian connection

The Kipushi mine, which operated from 1924 to 1993, is today owned by a joint-venture company, KICO, in which Vancouver-based mining company Ivanplats Ltd. purchased a 68-per-cent stake last year, seeking the mine's untapped zinc resources.

Ivanplats is headed by Robert Friedland, the controversial Canadian entrepreneur who made a fortune from the Voisey's Bay nickel deposit in Labrador and has many other mining interests in Africa and Asia.

In a statement sent to The Globe and Mail, Ivanplats acknowledged that KICO has the mining rights to the waste-rock heaps and tailings piles where the children dig. But it said it does not yet control their daily use – surface rights are still held by Gecamines. Ivanplats is likely to gain those rights by 2015, when the underground mine is expected to return to production.

The company said the child labourers are "a serious concern" and "symptomatic, in part, of wider social and economic conditions." It added that its plans to reopen the mine would create many new jobs, and that the company is assessing the "extent, impact and hazards of unregulated artisanal mining" on its site.

In the meanwhile, UNICEF child-protection specialist Maxime Germain is trying to persuade families to quit the mines in exchange for start-up business subsidies. "It breaks my heart," he says. "They are no better or worse than any other children – they are just unlucky to be here."

Mr. Germain and his UNICEF colleagues have helped hundreds of children and parents escape the mines with small grants to use, for example, for welding equipment or sewing machines.

Father of six Kazadi Kalala worked for 10 years in the gravel pits, crushing rocks into sand, working with two of his children and watching them become ill. UNICEF and its local partners gave him $350 so he could set up a small shop in his house. Now, his modest income is enough to send his children to school.

Similar programs have been tried in Latin America, Nepal and Tanzania, often using a combination of education, grassroots campaigning and small loans. They are innovative, but make only a tiny dent in the problem.

Mr. Germain admits that the UNICEF program might even have the self-defeating effect of luring more people to the mines in hopes of getting grants. "For every 400 kids you take out of the mining site, there are 400 more to replace them," he says. "We need to go deeper to fight the structure of the problem."

The solution, he believes, will have to come from broader economic and income-disparity reforms.

"The real problem," he says, "is the poverty."