Peñasquito open-pit polymetallic mine is Mexico’s biggest open pit mine and comprises of two open pits namely Peñasco and Chile Colorado. It is located in the north-eastern corner of the state of Zacatecas, Mexico. Goldcorp owns the mine through its indirectly wholly-owned subsidiaries, while Minera Peñasquito, a subsidiary of Goldcorp, operates the mine.
A major expansion was undertaken at the mine with pre-stripping starting in August 2007. The expansion was completed and officially inaugurated in March 2010. Full production was achieved by the end of 2011.
The expansion included the construction of two separate processing facilities, an oxide ore facility and a sulphide ore facility. The oxide plant commenced production in February 2008 and first gold was poured in May 2008.
The sulphide facility comprises of two process lines with a combined design capacity of 50,000tpd. The first lead and zinc concentrate was produced in October 2009 and the first concentrate was shipped in November 2009.
Geology and mineralisation of Peñasquito mine
The project lies within the Mexico Geosyncline, a 2.5km-thick series of marine sediments deposited during the Jurassic and Cretaceous periods and consisting of a 2,000m-thick sequence of carbonaceous, calcareous turbidic siltstones and interbedded sandstones underlain by a 1,200m-thick limestone sequence.
The two sierras in the area are separated in the western half of the district by the Mazapil Valley, a synclinal valley underlain by the Upper Cretaceous Caracol Formation. The Caracol siltstone-sandstone section is generally flat-lying in the valley with occasional small parasitic anticlines and drag folds along faults. A large granodiorite stock is believed to underlie the entire area and the sediments are cut by numerous intrusive dykes, sills and stocks of intermediate to felsic composition.
Peñasquito mine reserves and resources
Total proven and probable reserves at Peñasquito are estimated to be 15.69Moz of gold, 911.8Moz of silver, 2.63Mt of lead (Pb) and 6.3Mt of zinc (Zn).
Mining and processing activity at Peñasquito mine
Run-of-mine (RoM) oxide ore is delivered onto a heap leach pile using haul trucks. It is added with lime before being placed on the pad, and leached with cyanide solution. The leached solution is then clarified, filtered and de-aerated, treated with zinc dust to precipitate the precious metals. The precipitated metal is then pressure filtered and the resulting filter cake smelted to doré.
RoM sulphide ore is processed using a conventional crushing, milling and flotation facility. Haul trucks deliver the ore to a primary, gyratory type crusher, and the crushed ore is conveyed to a SAG mill, dual-ball mill set-up, and pebble crusher facility. Ground and classified sulphide ore is piped to the flotation circuit where the ore is processed to produce lead and zinc concentrates.
The concentrate slurries are first thickened and then dewatered using pressure filters. The dewatered concentrates are stockpiled before loading onto road vehicles for transport to in-country smelters or to the ports for export to foreign smelters..
Infrastructure facilities at the Peñasquito mine
Power supply for the mine is currently provided from the Mexican central grid by the Mexican Federal Electricity Commission. Goldcorp also signed a power supply agreement with a subsidiary of InterGen for a minimum term of 20 years. Under the agreement, InterGen will construct a gas-fired combined cycle power plant, which is expected to be completed in 2014.
Process water is sourced from the water field located 6km from the mine site. The mine received necessary permissions to pump up to 35 million cubic metres of water.
The tailings impoundment is a zero-discharge facility which stores excess water temporarily from mill operations and expected climatic events including the design storm. Water will be reclaimed as needed from the tailings facility for use in the mill.
Sale of silver produced at Peñasquito mine
Goldcorp entered into an agreement with Silver Wheaton in July 2007 for sale of 25% of the life-of-mine silver produced at Peñasquito mine.
Contractors involved with the expansion of Peñasquito mine
M3 Engineering and Technology, of Tucson in the US, was the EPCM contractor. MARC was awarded the contract for maintenance of mine equipment.