Barefoot with water up to his knees, seven-year-old Isaac sifts through sand to extract copper like hundreds of boys in southeast DR Congo, forced by poverty to quit school and work in the mines.

Isaac abandoned his maths and language classes in February, leaving the only school in Kamatanda, a small village in Katanga province, the main mining region in the Democratic Republic of Congo.

Since then, he has worked in a vast open copper mine in the area, helping some 2,000 "diggers" extract the mineral under a blistering sun, then to sell to businesses in Likasi, a nearby town.

There are about 400 children from Kamatanda and other surrounding villages who contribute to the effort by sorting, carrying, or cleaning the mineral.

Katanga province contains more than 30 percent of the world's reserves of cobalt and 10 percent of copper, in addition to tin, gold and uranium, but many illegal workers and children are involved in the extraction process.

Isaac says he earns less than four dollars (three euros) each day in the mine, "and with that I can buy clothes and contribute to the expenses at home," he explains, his face still full of childhood innocence.

He is the third child in a family of eight, and when his parents could not afford the 30 dollars needed to pay his yearly school fee he joined his brothers and sisters in the mine.