By Lydia Polgreen

The people who toil in the tin ore mine here are links in a long, global chain that reaches all the way to the cellphones and digital music players so ubiquitous in modern life.

At the very bottom of that chain, hunched beneath the blasting sun in a deep red gash near the base of a mountain, a 15-year-old named Imani Mulumeo Derwa sifted through ochre-colored earth this summer with his slender fingers.

In a small plastic bag, he stowed tiny rocks he hoped were tin ore. If the day went well, he might find enough ore to buy a plate of rice and beans. If not, he would fall asleep hungry on a dirt floor.

Every Thursday, he must hand over a day’s wages to Col. Samy Matumo’s men, who control the mountain and illegally extract taxes from every enterprise here. Imani arrived in July, hoping to save enough money to return to school at the end of September. But by early August, he found himself trapped in a web of debt and despair.

“I am stuck here,” he said, his weary, almond-shaped eyes betraying traces of a war-tossed childhood otherwise invisible on his smooth, boyish face. “I want to go home but I can’t.”

On July 6, Imani arrived at the head of the winding 30-mile jungle trail leading to the mine at Bisie. He said he had joined a river of people streaming into the forest, men and women laden with crates of beer, sacks of rice and cartons of powdered milk, all destined for Bisie, a town in the middle of the jungle where, Imani had heard, a hardworking boy could earn a few hundred dollars by picking up bits of a certain heavy rock from the ground.

Like many children in this war-ravaged country, Imani looks younger than he is. He said he had spent much of his childhood in flight from the latest armed group swarming into his hometown, Walungu. The gnawing hunger of life on the run has left him stunted, a little more than four feet tall. His voice has not yet broken.

All that running meant he was far behind in school, having completed only the fourth grade. But he was determined to finish high school and go on to college. At the end of the school year, his mother, a widow, told him he would need to get a job and contribute something to the household, he said. So he left Walungu with friends on the back of a pickup truck, headed for the tin ore mine at Bisie.

Imani did not carry much with him on the journey. Everything fit in a small blue plastic bag: an extra pair of trousers, a notebook with the Unicef logo across its cover, a ballpoint pen and an empty wallet emblazoned with a fake Nike swoosh. At the entrance of the trail, he said, he took his last 200 francs, less than 50 cents, out of the wallet and handed them to the soldier watching the gate.

The walk to the mine was hard. Hills followed hills. Imani’s green plastic sandals struggled to grip the iridescent, mineral-rich mud. The mossy roots of soaring trees criss-crossed the path, creating a ropy web that battered his narrow ankles. He had brought no food and had to beg for leftovers from hungry porters, he said. To cool his parched throat he slurped water directly from the streams that bisect the trail. Many times he thought of turning back, of going home. But the lure of quick cash was strong.

“I didn’t want to give up,” he said. He could not face going home empty-handed.

Finally, after two days of walking, he arrived in Bisie, half-starved and exhausted.

The mine operates in a rigid hierarchy, and Imani struggled to find his place in it.

The highly skilled miners who work in tunnels sometimes 600 feet deep can make good money here, dividing the minerals they find 30-70 with the owner of the tunnel, usually a businessman or a soldier, with the owner getting the lion’s share.

These workers sometimes toil in 48-hour shifts in narrow, airless tunnels, with no safety gear beyond their dim headlamps. Because there is no industrial equipment or electricity here, the tunnels are built by hand and lined with wood. Cave-ins are common, and toxic gases fill the tunnels at times, sickening workers. It is impossible to say how many workers have been injured or killed because there are no authorities here to keep track.

A worker on a productive mine can make $200 on a good shift, but those days are few and far between. Moreover, those kinds of jobs are out of reach for boys like Imani, too young and weak to wield a steel mallet or clear heavy stones.

So Imani joined the other boys who sift earth discarded by bigger, stronger diggers, looking for bits of ore. He recorded the date of his arrival in his notebook and drew a makeshift calendar.

He recorded in his diary that he worked 2.1 hours the day he arrived and made 240 francs, less than 50 cents. That was the last entry.

“I wanted to keep track of what I earn,” Imani said. “But so far I really haven’t earned anything.”

Because he arrived penniless, he had to borrow money to buy food and rent a room. He happened upon Daniel Mubwirano, a friend of the family, who said he had space he could rent Imani. Imani joined three other boys sleeping on the floor of his room, scarcely six feet square.

Mr. Mubwirano, a stocky man with dark, deep-set eyes, was a new arrival, too. He had borrowed $200 from relatives to buy merchandise to sell here. Despite having a leg that is lame from an accident, he carried a sackload of salt, gin, cigarettes, powdered milk and soap through the forest into Bisie, determined to triple his money in a month and return home to his wife and three children.

But nothing had gone according to plan. He did not anticipate the inordinate expense of life here. Flooding in the tunnels meant fewer people had the cash to seek oblivion in his small plastic bottles of gin. Workers asked for credit, which he granted. He waited in vain to be paid.

“What choice do I have but to hope that someday they will pay?” he said.

And Mr. Mubwirano had not expected to have to fork over a good portion of his earnings to militiamen, who collect $20 in illegal taxes from him each week. That is in addition to the taxes he paid along the trail getting here: 10 percent of his merchandise and cash.

So when Imani showed up, he felt no compunction about asking the boy for $10 a month to sleep on a corner of the crowded $20-a-month room he already shared with two other boys. They also paid $10 each.

“We are all just trying to survive,” he said. “Everyone must look after himself.”

Imani said he had not known that Mr. Mubwirano was turning a profit on renting the floor of his squalid room, but he was not surprised. He has nowhere else to live.

Imani borrowed $10 worth of cassava flour from a merchant who also came from Walungu, imploring the man to take pity on him. But more than a month later the man was starting to harass him for payment. Imani keeps making excuses and promises.

“I am full of debt,” he said.

Back in Walungu, Imani and his friends would play soccer after school, slipping off rubber sandals to kick around a ball made of wadded-up plastic bags.

But in Bisie there is no flat surface on which to play soccer, just hills upon hills. To pass the evenings Imani and his friends prowl Bisie’s fetid alleyways. There is no room here for the pleasures of childhood. So the boys amuse themselves spying on prostitutes and sneaking pulls of rot-gut gin.

The worst is Thursday, when the soldiers come. For boys like Imani, the tax is 500 francs, about a dollar. But that is a whole day’s wages. When he does not have the money, he runs into the forest to hide.

“If you don’t pay they will kill you,” he said.

Although Imani wants to leave, he has no money to pay the taxes along the road. And his creditors would send soldiers to arrest him if he tried to escape.

“I can’t go home,” he said.