About 70 kilometres north of the ancient Chinese capital Xi'an lies a coal belt underneath the rolling mountains. Criss-crossed by a honeycomb of tunnels, the belt has helped fuel China's economic engine for many years and filled the coffers of Tongchuan, known as one of the country's ‘coal cities'. Covering the northern valley of the Weihe River, the largest tributary of the Yellow River, the Weibei coal belt recently achieved national attention not for the quality of its coal,