Conveyor belts in Andes an option
Mining copper at Los Bronces high in the Andes entails removing an entire bronze-coloured mountain peak. Anglo American is looking for smarter, more efficient and environmentally friendly ways to do it.
Mining copper at Los Bronces high in the Andes entails removing an entire bronze-coloured mountain peak. Anglo American is looking for smarter, more efficient and environmentally friendly ways to do it.
Anglo could do away with haul trucks entirely, replacing them with conveyor belts, which, as they move ore down the mountain to a primary crusher, could generate electricity, says Patricio Chacana, GM of Los Bronces.
Los Bronces in Chile produces 370,000 tons of copper a year, placing it at the lower end of the world’s top 15 copper miners. “We are on one of the world’s best copper bodies and we must have a business case to reflect that. We must use our creativity to transform this huge asset into a beautiful business,” says Chacana, pointing out that Los Bronces is in an area that hosts 10% of the world’s known copper resources.
About 40% of Anglo’s carbon emissions come from trucks at its South American copper mines. “You don’t only need to evaluate fuel trucks against electric trucks, but you need to evaluate if you can get rid of trucks. You can do that with conveyor belts. We are analysing alternatives to moving ore and waste with trucks,” he says.
“Probably the future of the mine will be a mix of trucks and conveyors, getting rid of some trucks in some parts of the mine. The distances for trucks to travel are growing and there comes a point where the economics of having trucks is too complex,” says Chacana.
On a 5km conveyor dropping 300m, Anglo is generating 1MW of electricity. It is trying to find a way to capture the 50MW it estimates could be generated from 150,000 tons a day of ore, which has been turned into a liquid mud, sliding down a pipe to the mills. The mine draws 200MW from the national grid.
If it could be passed through a turbine, it would generate enough electricity to pump water removed from mud back up the mountain to be used again in a closed circuit, Chacana says.
Anglo recycles 75% of its water, using 25 large pumps to return it to the mining area to liquefy the ore again. Tests showed the liquefied ore is far too abrasive for the turbine systems they tried.
The price of grid electricity rose fivefold in recent years to 10 US cents per kilowatt hour, making it all the more important to come up with a solution to make a quarter of the mine’s energy consumption free.
Anglo concluded agreements with electricity providers to source all its energy needs from renewable sources from 2021.
TAILINGS DUMP
The barren snow-capped mountains, with streaks of ice down their steep, ravined sides tower over the mine, which is 3,500m above sea level.
Mounds of broken rock are impressive, reflecting more than five decades of mining to extract the ore for copper used in electrical applications.
Anglo planned for a 1.9-billion tons tailings dump and has so far filled it with 600Mt of discard from the back of its processing plant. Through its mining, Anglo reduced the peak’s height by 600m to 3,600m.
Los Bronces and stateowned Codelco’s Andina mine on the other side of the mountain will eventually join and become one vast pit, removing entirely one of the Andes peaks. To extend the mine’s life and keep the grade at a steady 0.75% copper content in each ton of ore processed, Anglo had two options: start another open-pit mine or go underground, a more expensive, difficult choice.
Anglo chose the underground option as it makes its mine “invisible” and enables it to extract ore under politically sensitive and environmentally important glaciers.
Anglo would need to go underground only in about a decade, with preliminary project cost estimates at $2.5bn.
It must implement the project because of the sharp fall in grade from the pit. Grade has fallen more than 25% since 2010. If nothing is done to find highgrade resources, it will fall to 0.5% by the mid-2030s.
Until it starts the underground mine, Anglo is carving out 200Mt of waste rock from the northern face of its enormous open pit to prepare for when the eastern side reaches the bottom of the mine in about five years.