KIM HARRISBERG  FOUR nights a week, Given Zuli packs some food, meets his colleagues at the entrance of an abandoned coal mine in South Africa's eastern Mpumalanga province, and descends into the earth for up to 12 hours, chipping away at the black rock. Zuli is one of thousands of small-scale, illegal miners across South Africa - a number believed to be on the rise as unemployment spikes in a brittle economy - who make a living selling coal collected in abandoned, derelict mine shafts. But Zuli is also part of a growing environmental movement in the coal-rich province, campaigning for…