MAYUWANO, Congo — Farmer-turned-miner Faustin Matiya emerges 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. Kalashnikov-toting government soldiers who 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 due to 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 the Washington-based resource and conflict reporting group Global Witness.

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

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

Until December last year, remnants of Rwandan-backed armies from the civil war still controlled the cassiterite trade in this region. Government troops that threw them out now rule the mines by gun-law, 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 white torn undershirt and black shorts. "It depends on their mood. They have guns."

Matiya said nothing changed when the Rwandans left and the government came.

"We are still exploited."

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

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

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.

Though 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.