Overview
Penasquito gold-silver-lead-zinc mine is situated in the western half of the Concepcion del Oro district in the northeast corner of Zacatecas State, Mexico, approximately 200 km northeast of the city of Zacatecas.
The region has a strong tradition of mining going back to the mid 1500's when silver mining first started in the region and the city of Zacatecas was founded.
At the Penasquito project, some limited exploration of the project area had taken place in the 1950's. In 1994, Kennecott initiated a comprehensive exploration program that revealed the real size and potential of the mineralized system.
Western Silver acquired 100% of the Penasquito project from Kennecott in March 1998. Glamis Gold Inc. acquired Western Silver on May 3, 2006. Goldcorp acquired Glamis in November 2006 and as a result owns 100% of the project.
On September 12,2010 Goldcorp announced the commencement of commercial production at the Penasquito mine.
Penasquito will be Mexico's largest open pit mine once built.
Penasquito is an open-pit mining operation where the ore is processed at an initial nominal rate of 50,000 tpd and then, after expansion, to 130,000 tpd rate through a conventional crushing, milling and flotation facility.
Over its 23-year mine life, the operation is expected to produce an annual average of 500,000 ounces of gold, 28 million ounces of silver, 450 million pounds of zinc, and 200 million pounds of lead at net negative by-product cash costs.
Location
The project is located in the state of Zacatecas, Mexico. The state of Zacatecas has a population of 1,441,734 inhabitants. Mexico's National Population Council estimates that 600,000 natives of Zacatecas now live in the United States, a figure that is equivalent to 40 percent of the state's resident population of 1.5 million.
In 1546, Juan de Tolosa, one of the early conquistadores, was guided by local Indians to a place located in the rough and arid mountains of the Zacatecas where he discovered silver ore. That triggered a real mining rush and some five thousand mines of the newly born silver camp sent a river of silver flowing down to the Spanish treasury; for centuries to come Zacatecas produced 20% of the colony's silver. In 1585, it was upgraded to the status of city with the name of "Muy Noble y Leal Ciudad de Nuestra Señora de Zacatecas" (Very Noble and Loyal City of Nuestra Señora de Zacatecas).
Nowadays, Zacatecas is a UNESCO World Heritage site and a major tourist attraction renowned for its colonial architecture, historic and mining monuments and places. The region's main economic activities are mining, agriculture and tourism.
The deposits occur in a wide valley bounded to the north by the Sierra El Mascaron and the south by the Sierra Las Bocas. Except for one small outcrop, the area is covered by up to 30 meters of alluvium. The terrain is generally flat, rolling hills; vegetation is mostly scrub, with cactus and coarse grasses. The prevailing elevation of the property is approximately 1,900 m above sea level.
Road access to the site is presently gained west out of Concepción del Oro approximately 15 km to the town of Mazapil and then a further 12 km west from Mazapil. Goldcorp has finished construction of a new road east from Mazapil to join Highway 54 approximately 25 km south of Concepción del Oro.
The climate is generally dry with precipitation being limited for the most part to a rainy season in the months of June and July. Annual precipitation for the area is approximately 700 mm, most of which falls in the rainy season. Temperatures range between 30 deg C and 20 deg C in the summer and 15 deg C to 0 deg C in the winter.
Geology
The project lies within the Mexico Geosyncline, a 2.5 km thick series of marine sediments deposited during the Jurassic and Cretaceous Periods and consisting of a 2,000 meter thick sequence of carbonaceous, calcareous turbidic siltstones and interbedded sandstones underlain by a 1,200 meter thick limestone sequence.
Goldcorp geologists have interpreted the presence of mineralization to be associated with hydrothermal breccias, small-scale veining and narrow fracture-filling stockwork structures cross-cutting lithological boundaries.
Economic mineralization is also divided into an oxide domain and a stockwork sulphide domain.
The mineralization domains have been further separated into northern (Penasco) and southern (Chile Colorado/Azul) components by a sub-vertical fault associated with an east-west trending arroyo cutting through the property.
The northern Penasco sulphide domain is centered on the Peñasco Diatreme Breccia, and the southern Chile Colorado sulphide domain is centered on the Azul Diatreme Breccia.
Additional domains are formed by a complex porphyritic intrusive cross-cutting the Penasco Diatreme Breccia, as well as deep skarn mineralization.
The economically important styles of mineralization are:
- Sedimentary-rock-hosted sulphide veinlet/stockwork deposits typified by Chile Colorado;
- Breccia-hosted disseminated and veinlet sulphide deposits typified by Penasco-Azul; and
- Secondary oxide deposits.
Proven and probable reserves were estimated at 1,191.4 Mt for 17.8 Moz gold, 1,070 Moz silver, 7.2 Mlb lead and 15.9 Mlb zinc.
Operation
The Peñasquito Project is being developed by constructing a modern, world class open pit mine and metals extraction facility.
Access roads to the site have been improved and bypass routes around affected municipalities have been constructed.
Power has been brought in from the 400kV power line national grid and is transmitted at 400kV from the 400kV/400kV switchyard tap-in via a new overhead power line to the mine site main 400kV/69kV substation.
Process water is being obtained from groundwater wells developed on-site and supplemented from pit dewatering wells. The aquifers in the Cedros Basin (the groundwater basin containing Penasquito) have enough available water to provide 40 million m³ per year. The Penasquito project has received permits to pump up to 35 million m³ of this water per year.
Ore and waste is being mined using open pit mining utilizing four electric shovels, three large front end loaders, and a fleet of up to 57 diesel/electric haul trucks.
The major mining equipment currently on-site consists of four (4) Bucyrus 495HR electric shovels equipped with 55 cubic meter buckets, three (3) Komatsu WA 1200 loaders equipped with 26 cubic meter buckets, eight (8) Atlas Copco PV351 diesel blast hole drills and forty-four (57) Komatsu 930E (290 tonne rated load) haul trucks.
Support equipment including track dozers, rubber tire dozers, excavator, and graders are also on site.
The open pits (Penasco and Chile Colorado) will be mined in a series of 11 phases.
The mine will operate a total of 700 shifts per year with four mining crews working on a 4 on and 4 off rotation.
Process
The sulphide ore will be processed at an initial nominal rate of 50,000 tpd and then, after expansion, to 130,000 tpd rate through a conventional crushing, milling and flotation facility.
Haul trucks deliver ore to a primary crusher; crushed ore is conveyed to a SAG mill, dual ball mill setup, and a pebble crusher facility.
In 2012, an in-pit crushing and conveying system is planned to be operational. This requires the installation and use of two similar size 10,000 tph nominal throughput in-pit crushers and associated conveyers. The crushing facility will initially consist of a single FFE 1524 x 2870 mm (60 x 113 in) gyratory crusher capable of operating at 92% utilization on a 24-hour-per-day, 365-days-per-year basis. A parallel in-pit crushing circuit will be designed and adapted to the current system as the pit develops and higher throughput scenarios are achieved.
A single 1.52m wide conveyor transports the reclaimed crushed ore from the stockpile and discharges directly into the SAG mill. A "wet spray" system and ventilation equipment will be installed in the reclaim tunnel to suppress dust in ore feed streams.
The two grinding circuits will operate in parallel at forecast 92% availability on a 24-hour-per-day, 365-days-per-year basis. Each grinding circuit will be designed to reduce the crushed ore from 80% passing 159 mm to 80% passing 125 microns. The FFE SAG mills operate in closed circuit with/without pebble crushers.
Two Sandvik CH880 crushers are installed for Line One, with provision to install up to four pebble crushers in total when Line Two is brought into production. The crushers will be choke fed with variable speed belt feeders. The 600 kW pebble crushers will be set to produce a P80 28mm product. The SAG pebble crusher product will be directed to Polysius 2.4m x 1.7m High Pressure Grinding Rolls (HPGR).
Ground and classified sulphide ore are being piped to the flotation circuit where the ore will be processed to produce a lead concentrate and zinc concentrate. Both concentrates will have gold and silver credits.
Dorr Oliver Eimco flotation machines have been selected for the lead flotation circuit. All rougher and cleaner cells are mechanically agitated (i.e. no flotation columns are used). Tailings from the lead circuit will flow by gravity to zinc rougher conditioner tanks. Tailings from all rows of zinc rougher cells will be combined in a tailings box and will then flow by gravity to a tailings pond.
The concentrate slurries are thickened and then dewatered using pressure filters.
The dewatered concentrates is being stockpiled before being loaded onto highway road vehicles for transport to in-country smelters and to ports for export to foreign smelters.
A stockpile will allow the mill to operate a scheduled 360 days per year.
