The interesting thing about this axe blade is the material used: copper. There is evidence of mining in the Andean region since at least the fourth century AD. Usually the desired material - mostly gold - was collected near the surface of the earth or washed from the rivers. Copper was extracted by mining, but the galleries driven into the earth were not very deep. The ore was smelted in tower-shaped furnaces, the huayrachina. The Inca Empire operated several major mining centres, including one in northern Chile, where copper was mined. Today Chuquicamata in the north of Chile is the largest copper mine in the world.