KGHM developed the Sierra Gorda copper-molybdenum-gold mine in the Atacama Desert of Chile. It processes copper / molybdenum / gold ores and produces copper and molybdenum concentrates separately, recovering gold from the copper concentrate.
Construction of the Gorda mine began in 2011 and pre-stripping works completed in April 2014. The project became one of the world’s biggest molybdenum producers upon its official inauguration in October 2014. It employs more than 2,000 permanent staff.
The production at Sierra Gorda commenced in July 2014. The mine is expected to produce 220,000t of copper, 11,000t of molybdenum and 2t of gold annually during its 23-year mine life, based on the current reserves.
Acquired from Quadra FNX, the mine is a joint venture between KGHM (55%), Sumitomo Metal Mining (31.5%), and Sumitomo (13.5%).
Sierra Gorda mine location, geology, mineralisation and reserves
The Sierra Gorda mine is located in the northern Region II of Chile, approximately 4km from the town of Sierra Gorda. It consists of low grade copper-molybdenum-gold mineralisation in four zones namely Catalina, Isabela, 281 and 285.
The mine is a typical porphyry deposit located within the Late Eocene to Early Oligocene Metallogentic Belt. The deposit is hosted by andesites, rhyolites and sedimentary rocks.
Mineralisation can be classified into three types: hypogene sulphides or primary mineralisation, leached oxides or secondary mineralisation, and supergene or secondary enriched mineralisation.
As of October 2014, the mine is estimated to contain reserves of 1.5Bt of ore at an average grade of 0.40% Cu, 0.020% Mo, and 0.065g/t Au.
Mining and processing of ore at Sierra Gorda
Conventional truck and shovel method of mining is applied at the open pit mine. The mining fleet comprises haul trucks, shovels, drills, Le Tourneau loader, track dozers, rubber tire dozers, water trucks and road graders.
The processing plant initially processes 110,000tpd, which is expected to increase to 190,000tpd from the fourth year. The run-of-mine ore is delivered to the dump pocket of the primary crusher station by mine haul trucks. The process facilities incorporate crushing, grinding, flotation, concentrate filtering and tailings dewatering and disposal for recycling.
Filtered copper concentrates are stored and loaded into rail cars for shipment to the port. Molybdenum concentrates are filtered, dried and bagged for shipment off-site by truck to the markets.
Dewatered and dried concentrates are discharged by gravity to a 6,400t capacity covered storage area below the filters. The stored concentrate is loaded by front-end loader into sealed tipper railway cars or road trucks for shipment to the port or a local smelter. Each container is sampled, and the tare and loaded weight for each container and the overall weight is recorded.
The first shipment from Sierra Gorda mine was delivered to Sumitomo’s Toyo smelter in December 2014.
Infrastructure facilities at the Sierra Gorda mine
The copper / molybdenum mine is accessible by both railroad and highway, which are 2km north-west of the village of Sierra Gorda. The highway and railroad connects Antofagasta to Calama and the port cities of Michilla and Mejillones.
Power supply to the mine is provided from the near-by coal fired power in the port of Mejillones. An 80km transmission line built between the Sierra Gorda and Encuentro substations transfers the power.
Potable water for the mine, camp and processing plant is provided by Ferrocarriles de Antofagasta y Bolivia (FCAB). Seawater is sourced from a thermal electricity generating plant located on the coast of Mejillones via a 142.6km pipeline, for non-potable requirements.
The engineering, procurement, and construction management (EPCM) services contract for installing the processing plant at the copper-molybdenum mine was awarded to Fluor in 2011.
Metso was awarded the contract to provide control and on/off valves. ABB was awarded a contract for supplying the electrical equipment. Salfa Montajes was awarded a $350m contract for the construction and installation of wet and dry areas of the processing plant.
FCAB was responsible for the handling and transportation of copper concentrates from the mine to the port.