Overview
Zaldívar is an open-pit, heap-leach copper mine, located in the Atacama Desert in Chile. Pure cathode copper is produced by three stages of crushing and stacking, followed by heap leaching and bacterial activity to remove the copper from the ore. Run-of-mine dump leach material is placed on the old sulphide ore pad and leached.
In 2009, Zaldívar produced 302 million pounds of copper at total cash costs of US$1.17 per pound. Proven and probable copper reserves as of December 31, 2009 are estimated at 6.0 billion pounds.
Location
The property is composed of 247 patented claims covering 1,240 hectares, located in the Andean Precordillera in Region II of northern Chile, approximately 1,400 kilometres north of Santiago and 175 kilometres southeast of the port city of Antofagasta. The mine lies at an average elevation of 3,000 metres.
Geology
Located on the western margin of the Atacama Plateau, the Zaldivar porphyry system is at the intersection of a north-south fault system and a series of northwest and northeast striking faults . The deposit is generally centred on a northeast striking granodiorite porphyry body that intruded andesites and rhyolites.
Both the Main and the Pinta Verde deposits are near surface and are suitable to solvent extraction and electrowinning recovery.
Copper mineralization is contained within an area of 3 x 1.5 km and occurs in both oxide and sulphide secondary enrichment horizons. The mine is expected to produce 2 Mt cathode copper over the 20 year mine life. An additional 42 Kt will be produced by leaching. The deposit will be mined in 8 stages. The metallurgical processing plant is composed of a crushing plant, heap leach operation, and an SX-EW plant. Construction was completed during 1995. Capital costs were $600 million. Estimated additional expenditures of about $105M will be required.
Mining & Operation
Conventional methods of open pit mining are used. The open pit contemplates mining the remaining mineral reserves in eight stages, referred to as Stage 3 through to Stage 10.
Process water is being supplied from ground water at Negrillar, 120 kilometres east of Zaldívar. Water is drawn from six production wells and pumped along the 120-kilometre route to the fresh water pond, located near the tertiary crushing facility at the plant site.
Copper is recovered by heap leaching followed by solvent-extraction and electrowinning to produce high-grade cathode copper. In 2004, Zaldívar processed 18.17Mt of ore grading 1.0% Cu resulting in the production of 147,581 tonnes of copper.
Zaldívar receives power from SING, the regional electricity grid system, and purchases electricity from one of the electrical utilities operating on the SING system. A dual circuit, 220 kilovolt transmission line, which is 230 kilometres long, was constructed in conjunction with Minera Escondida Limitada between the Zaldívar and Escondida plant sites and the SING system substation at El Crucero. In addition, Gener constructed a link from their power line that crosses the Andes from Salta to the Zaldívar sub-station. The average power requirement of the mine is about 69 mega watts. Annual power consumption is 530 GWHr.
Process
The metallurgical processing plant is composed of a crushing plant, heap leach operation, and an SX- EW plant. Construction was completed during 1995. Capital costs were US$600 million. Estimated additional expenditures of about US$105M will be required.
Open-pit ore is hauled to the primary gyratory crusher and the discharge fed into two secondary cone crushers. Waterflush crushers are used to perform the tertiary crushing reduction of the ore to ?12mm to reduce dust production and to optimise leach recoveries . The ore is then screened to remove fines, which are subsequently treated by flotation to produce copper concentrate and accounts for 10,000-12,000t/y of additional copper.
Heap leaching of ore uses dynamic stacking in 6m lifts and chemical and bacteriological dissolution of copper through consecutive lifts from the top to the bottom of the heap.
Copper is recovered from the oxides by sulphuric acid in the circulating leach solutions, and from sulphides by bio-leaching using bacteria naturally present in the ore. The pregnant solution containing the dissolved copper flows by gravity to the solvent-extraction plant.
Solvent extraction mixer-settlers recover 90% of the copper from the pregnant leach solution. The remaining 10% is recycled to the heap leach.
Solvent extraction trains transfer copper to the tankhouse, which produces LME Grade A copper cathodes. The electrowinning tankhouse has a design capacity of 125,000t/y of cathode copper, a figure that has been exceeded in practice.
