Faustin Matiya, a farmer turned miner, emerged from Congo's forest covered in mud and carrying more than his own weight in tin ore.

Matiya abandoned his fields to dig for cassiterite, the main ore of tin. After a two-day trek from the crude mines, he sold his 110-pound sack of red rock for 30 cents a kilogram (2.2 pounds) to a middleman. Government soldiers who carry Kalashnikov assault rifles and supplement their $10 monthly salaries with tips from the freelance middlemen then herded Matiya and other miners away.

Moments later, the middleman sold Matiya's sack for five times what he paid the miner. Thousands of miles from Mayuwano, in the world metal markets, a kilogram of tin sells for about $8. The price of tin nearly doubled in 2004 because of soaring demand.

Still, 18-year-old Matiya blessed his lot.

"At least I earn something. If there were no cassiterite, I would have no job," he said, spitting on the dusty ground as he removed his knee-high rubber boots.

Tin, used in humble kitchen appliances and the circuit boards of high-tech electronics, has shaped the lives of people around Mayuwano, an eastern region where some of the highest quality tin ore in the world is found, according to a report by Global Witness, the Washington-based resource and conflict reporting group.

The mineral-rich eastern provinces were at the heart of Congo's five-year civil war, which sucked in armies from six countries and ended in 2002 after nearly 4 million people had perished, mostly from hunger and disease.

Revenue from taxes and the sale of precious minerals financed the several warring factions that rushed across Congo to capture the mines.

Until last December, remnants of Rwandan-backed armies from the civil war still controlled the cassiterite trade in this region. Government troops who threw them out now rule the mines by the law of the gun, supervising the inhumane conditions in which tin ore is collected and exported.

"I sometimes pay the soldiers half of what I earn; other times they take everything I have," said Richard Mumfano, 34, a bald miner who wore a torn white undershirt and black shorts. "It depends on their mood. They have guns."

Matiya said nothing changed when the Rwandans left and the government forces arrived. "We are still exploited," he said.

It begins deep in the forests. Miners say they tie flashlights to their helmets and crawl into caves dug by hand and with primitive metal implements. The caves are supported by wooden posts, but collapses are common, they say.

The principal mine, at a place called Bisiye, is a two-day walk from Mayuwano and has been worked for more than a decade, initially by prospectors and later by militias that have waged wars to control it.

From the mines, the ore is trekked to the markets of Mayuwano. A thin, tarred airstrip nearby is one of Congo's busiest. Cargo planes take off every half-hour, transporting between $1 million and $2 million worth of cassiterite a week to the eastern provincial capital, Goma.

In Goma, the rocks of ore are smashed, cleaned and sorted at warehouses.

The owner of one such warehouse, Fidel Muhinda, said he had paid several thousand dollars to various branches of government for export permits.

Muhinda said the government did not monitor the quantities of cassiterite he exported.

"Why should they? I have my license," he said.

Corrupt government officials rarely bother with the details of mineral exploitation in their rich country, preferring to cash in on large, one-time payments for long-term licenses and mining concessions instead.

Though the Rwandan-backed fighters who had controlled the cassiterite trade have withdrawn, Rwandans still appear to be exploiting their neighbor's wealth. Much of Congo's cassiterite reportedly traverses its porous borders to Rwanda, which exports five times the amount of cassiterite it produces without recording any legal imports, according to Global Witness.

Global Witness said that from Rwanda, the tin ore is sent to Europe and the Far East, to countries such as Britain, Belgium, South Africa and Malaysia.

Congo contains other highly sought minerals, over which endless battles have been fought. An estimated two-thirds of the world's coltan, used in cell phones and video game consoles, is found mostly in the eastern provinces bordering Rwanda, Burundi and Uganda.

Vast open-pit gold mines have also been exploited by warring militias. The ore, bought by middlemen near Congo's border with Uganda, is transported in barges across Lake Edward to Uganda to be purified and exported.

A report in June by the New York-based group Human Rights Watch accused Uganda of doing little to control the illegal trade.

The group said Uganda exported $60 million worth of gold last year, mostly to Switzerland, though it produced only $25,000 worth of gold itself and recorded no legal imports. The miners make about $100 a month.

Matiya does not expect to become rich. He just wants to earn enough to keep his two younger brothers in school. After his trip to the market, he prepared to return to the forest to gather more cassiterite.

"As long as my body is strong, my family will not suffer," Matiya said. "My brothers should not be forced to work like me."

A miner hangs a sack of tin ore on a scale in Mayuwano, Congo. Middlemen, with the cooperation of soldiers, make far more money in the growing trade.