Chuquicamata, one of the largest open pit copper mines and the second deepest open-pit mine in the world, is located 1,650km north of Santiago, Chile. The mine, popularly known as Chuqui, has been operating since 1910.
The century-old copper mine is owned and operated by Codelco and forms part of the company’s Codelco Norte division, which includes the Radomiro Tomic (RT) mine found on the same mineralised system.
A new underground mine is being developed to access the ore body situated beneath the present open pit mine. The conceptual engineering for the underground Chuquicamata mine began in 2007 and was finalised in March 2009. The project obtained the environmental authorisation in September 2010.
Underground mining at Chuquicamata
The new underground mine, scheduled begin operations in 2019, will comprise of four production levels, a 7.5km main access tunnel, five clean air injection ramps, and two air-extraction shafts..
The tunnels will deepen the mine by nearly 787m by the end of production in 2060. The underground mine will be developed at an estimated cost of $4.2bn and will produce an estimated 140,000 tonnes of ore per day. It mine is expected to produce 366,000t of copper and 18,000t of fine molybdenum per year.
Sinclair Knight Merz undertook the conceptual engineering of the mine, including identification, option studying and analysis for ore excavation and handling. For ore extraction, panel caving and macro blocks were studied. Three extraction panels were identified at different depths for both options. Excavation panels identified for panel cavings were at 1,841m, 1,697m and 1,409m above sea level and 1,841m, 1,625m and 1,409m for macro blocks.
The copper ore reserves of the Chuquicamata underground mine are estimated to be 1,700mt grading 0.7% copper and with an average molybdenum content of 502ppm.
Chuqui porphyry complex geology
The Chuquicamata mine lies on the Chuqui porphyry complex, a north-north east trending, elongated, tabular, intrusive complex that measures 14kmx1.5km. The west-dipping, steep and sub-vertical complex extends from Chuquicamata to the RT mine. It also includes the east porphyry, west porphyry, banco porphyry and fine texture porphyry.
The zone’s porphyries are largely affected by potassic alteration. Composed partially of alkali feldspar polymorphs and albite replacement of plagioclase, the alteration is dominated by a more widespread biotite replacement of hornblende with highly preserved igneous texture. Granular quartz apart from quartz-K feldspar veinlets also exist along with the alteration.
A significant proportion of the mine’s copper is contained in veins, veinlet filling faults and fault-related shatter areas. Orebodies of the mine are controlled by west fault system, a regional sub-vertical fault trending north-south.
The fault demonstrates post-mineral displacement that separates the largely mineralised Chuqui Porphyry in the east and the barren Fortuna complex in the west. The fault, belonging to the Cenozoic period, bears an usually complex kinematic past including transverse and reverse movements. The west zone is also characterised by superposition of pyritic main-stage veins with widespread quartz-sericite.
Main-stage veins running adjacent to the west fault are concentrated along a structural zone that represents a younger, breakable and shallower environment. The main-stage veins, comprising quartz, pyrite, chalcopyrite and bornite, opened up during the dextral shear of the west fault system. When the sense of shear on the west fault system changed to sinistral, north-west enargite veins also emerged.
Mining and processing
Coldec uses conventional open pit mining methods at Chuquicamata. A conventional truck-and-shovel operation constitutes the mining activity. Large quantities of the ore are crushed within the pit. Underground conveyors transport the crushed ore to the mill bins.
An Outokumpu flash smelter is installed for smelting the concentrate. The concentrate is then passed through a converter with electric furnace. After the slag is cleaned, the concentrate passes through four Pierce Smith converters. Blister copper is then sent to six anode furnaces. The electrolytic refinery has a capacity of 855,000t per annum. Three anode casting wheels were installed and are fed by the furnaces.
Contractors involved with the Chuquicamata copper mine
The feasibility study for the underground mine was awarded to Hatch in November 2009. Hatch will oversee the basic engineering required for the development of access works, environmental studies, minerals handling, management models, infrastructure and ventilation works.
Codelco signed a contract with Aker Wirth at the end of 2012 for the delivery and testing of a Mobile Tunnel Miner (MTM) to be used for developing the Chuquicamata underground mine.
SNC LAVALIN was awarded the Engineering, Procurement, Construction and Management (EPCM) contract for the technology modernisation at the Chuquicamata refinery. The works involved changing the copper cathodes production technology, process capacity expansion and a new system of material handling.
VSL Chile constructed a rock crusher in the middle of the open pit mine, which involved erecting a 4,000m2 and 36m high wall to enable the transport of crushed rock by a conveyor belt through a tunnel rather than by truck.
Metso was awarded an 18-month services contract for the mine’s grinding process improvement in May 2014.