Originally I had wanted to go to Potosi, Bolivia to see the silver mines that fueled the Spanish Empire. Those plans were scrapped after considering eight hours on the bus and our motivations to get to Chile. Instead, we learned that a cousin of a friend lived in Calama and her husband worked as a geologist in Chuquicamata, the largest open pit copper mine in the world. A few emails later, we had reservations for a free tour and a futon to sleep on.
All the tour books describe Calama as drab and gritty. It’s a working town. Everyone who works in the mine lives in Calama, a small oasis in the middle of the Atacama Desert. There aren’t any signs for yoga or massage or spiritual healing like San Pedro (a tourist town) to the East. Instead, you will find red work trucks with wheel chocks and safety flags, everywhere. They are the symbol of Calama. They make me smile.
Our tour starts at 1 PM in Calama where we board a bus with a number of other interested foreigners. We briefly stop at the old town of Chuquicamata right next to the mine. The town was closed in 2007 when the unwanted mountains of rock excavated from the mine began to encroach on the town. I also understand that arsenic is present in the mine dust. All the residents were moved to Calama.
We continue past one of the largest copper refineries in the world and on to the hole. At 4.3 Km long, 3 Km wide and 900 m deep it’s the largest hole in the world by excavated volume.
We spend 45 minutes peering into the hole. We watch trucks get filled at the bottom and start their journey to the surface. When loaded they require one hour to drive to the top. Each filled with 320 to 360 tons of rock which contains 0.8% copper on average.
This ore is dumped at the surface and pulverized further until reaching 0.3 mm in size. The copper is then concentrated to about 30% by mixing the dust with water and aerating from underneath. The precious metals bind with the air and float to the surface where they are removed. A secondary step removes molybdenum from the copper concentrate.
The copper concentrate then goes through a smelting process that increases the purity to 99.7%. Impurities are essentially burnt off at high temperatures through multiple stages. The 99.7% pure copper is poured into rectangular molds approximately 3′ x 4′ and 3″ thick.
At this point the copper is sent to the refinery where it undergoes electrolysis. The large plates from the smelter (the anode) are put in a bath with a cathode and electricity is run between the plates. Copper moves through the bath from the anode and is deposited on the cathode with 99.99% purity. The copper is now ready for sale. The mud left at the bottom of the bath contains gold and silver concentrates that will also be sold.
Chile produces about 30% of the world’s copper followed by China with 10%. China is the world’s largest consumer of copper, consuming almost half of the world’s supply.
And so concludes the tour.
Check out this site for some photos of the process side.