Deep in the tunnel of the Collum mine, coal dust swirls thickly, and it's stifling for workers such as Chengo Nguni. He describes his $2-a-day job with a sigh: His supervisor yells incomprehensibly in Chinese. His rubber boots leak. The buttons to control the flow of ore out of the mine often deliver an electric shock. But the worst thing about life in the Chinese-owned mine in southern Zambia is that there is no such thing as a day off. Ever.