6 december 2015
Chile’s great Chuquicamata open pit mine is looking ahead to a new and prosperous future – underground.
After more than 100 years of production in what is now the world’s largest copper open pit, Chuquicamata is paving the way for a complete transition from surface to underground excavation. The decision is due to depleting, profitable reserves and the increasing cost of additional waste removal as mining goes deeper. Added to this is the high energy cost of mining and transportation at this giant site which has grown to 5 km long, 3 km wide and 1 km deep.
Instead, Codelco Norte, the stateowned mining company, is going undeground where the “red metal” can not only be extracted from the rich orebody at lower cost but will also prolong the life of the Chuquicamata mine to 2060. The project aims to ramp up to full scale production by 2020 and development of the undground structure is making good headway. This first phase involves the construction of four tunnels, two for ventilation, one for access and one for transport. These total 20 km in length and are being driven by contractors Astaldi and Acciona Ossa, both using equipment from Atlas Copco.
For this phase, which started in 2012 and aims to be complete by year-end 2015, Atlas Copco has provided a fleet of Boomer XE3C and Boomer E2C drill rigs, Scooptram ST14 and Scooptram ST1030 LHD loaders as well Minetruck MT6020 trucks. In addition, Atlas Copco has established a Customer Center branch office in the town of Calama, about half an hour’s drive from Chuquicamata, in order to be as close as possible to the site, to provide technical, logistical and service support as well as training for equipment operators.
The second and main phase of the project, which starts in 2016, will involve the construction of no less than 100 km of tunnels and drifts. These will be used for production, material transport, ventilation levels and auxiliary facilities such as crusher stations.
Astaldi and Acciona Ossa say they are therefore well equipped and confident to take on this second phase alongside the two other contractors bidding for the project, Züblin and Geovita.
Astaldi’s current assignment is divided into three contracts: mine development, ventilation drifts and drifts for access and transport, all of which are on a huge scale. Using its fleet of two Boomer XE3 C, one Boomer E2 C and two Boltec LC bolting rigs, the company is currently developing an access tunnel and a transport tunnel in parallel with 180 m between them. The access drift has a cross section of 8.7 m wide x 5.9 m high, a gradient of 8% and will ultimately be 7.6 km in length. The transport drift is 9.3 m x 6.2 m, has a gradient of 15% and will be 6.3 km long. In time, this will be equipped with a giant conveyor belt that will carry the excavated ore and waste to the surface. At the 4.5 km point, the tunnels will also be connected by a 2.5 m diameter escape shaft installed at an inclination of 70 degrees from the horizontal. Average advance in the access tunnel is 272 m per month, while the average advance in the transport drift is 245 m/month. Both 48 mm and 51 mm holes are drilled for blasting and 38 mm holes are used for the installation of rock bolts.