An industrial revolution in the Bronze Age
The Tonglushan Ancient Copper Mine is an industrial complex that operated for over 1,000 years, beginning in the Shang Dynasty around the 13th century BCE. Modern archaeologists, alerted to the site by local miners in 1973, have uncovered a sprawling network of hundreds of shafts and tunnels, some reaching depths of 60 meters. The engineering is remarkably advanced, using sturdy mortise-and-tenon timber frames to prevent collapse and sophisticated drainage channels to manage groundwater. This was not a small-scale operation. Over its lifetime, the mine produced an estimated 80,000 to 120,000 metric tons of raw copper. This immense output was the result of a complete production chain, from ore extraction to smelting, all located on-site.
The physical evidence of this production is a staggering 400,000 metric tons of accumulated slag, the glassy byproduct of smelting ore to extract metal. Analysis of this slag reveals the technical skill of the ancient metallurgists. They used stone-built shaft furnaces that could be reused, unlike many contemporary furnaces in other parts of the world. The process was so efficient that the slag left behind contains only 0.7% copper, a level close to modern smelting standards. The resulting copper ingots were over 93% pure, ready to be alloyed into bronze.