Innovation could range from better mine layouts to new technologies for lower energy use in smelting or crushing rocks.

Meanwhile, China's aluminium exports are increasing, in effect giving foreigners the benefits of the state-subsidised electricity used in smelting.

"And mercury was also used in smelting, to separate silver and gold from crushed ore."

There is plenty of mineral coal in the vicinity, but wood is so cheap and abundant that charcoal is principally used in smelting.