Chihuahua State, Northern Mexico
Pinos Altos is located in the mountainous region of northern Mexico, 220 km west of Chihuahua. It is an open-pit and underground mining operation containing substantial reserves of gold and silver. The nearby Creston Mascota deposit is a satellite stand-alone pit and heap leach operation of Pinos Altos.
Open Pit and Underground
2015 production and costs
192,974 oz, $387/oz gold
54,703 oz, $430/oz gold
Pinos Altos has proven and probable reserves containing 1.5 million ounces of gold and 37.5 million ounces of silver (16 million tonnes grading 2.88 g/t gold and 74.18 g/t silver). Creston Mascota has proven and probable reserves containing 0.2 million ounces of gold and 1.6 million ounces of silver (4.2 million tonnes grading 1.30 g/t gold and 12.02 g/t silver). Pinos Altos is expected to produce 175,000 ounces of gold in 2016, and to average 178,000 ounces of gold per year from 2017 to 2018. Creston Mascota is expected to pour 45,000 ounces of gold in 2016 and to average 40,000 ounces of gold per year from 2017 and 2018.
Pinos Altos lies in the Sierra Madre gold belt, on the northeast margin of the Ocampo Caldera, which hosts many epithermal gold-silver occurrences. The property is underlain by volcanic and intrusive rocks disturbed by faulting. Its geological focus is a horst structure – which is an uplifted block of rocks – at least 10 km long by 3 km wide, defined by the Reyna de Plata Fault to the north and the Santo Niño Fault to the south.
The property’s mineral reserves are in four zones hosted by the Santo Niño Fault – the El Apache, Oberon de Weber, Santo Niño and Cerro Colorado lenses – as well as the San Eligio lens 600 metres north of the fault. More than 62% of the current Pinos Altos mineral reserve is located in the steeply dipping Santo Niño vein zone, which is up to 40 metres thick and 2.5 km long. Other promising zones include the Reyna de Plata and Sinter Zones, Creston Mascota, and the Cubiro deposit, which is 2 km west of Creston Mascota.
Pinos Altos is a series of open pits and an underground mine along the Santo Niño Fault. Surface mining is carried out at the Santo Niño and San Eligio pits, and, in future, the El Apache pit. Mining is by conventional open pit methods, using shovels and trucks to remove about 9 million tonnes of ore and waste in 2016, and about 2 million tonnes of ore and waste per year in subsequent years. The underground mining method is sub-level stoping (paste backfill) to extract ore from the Santo Niño and Cerro Colorado deposits. The shaft project for hoisting underground ore was completed in mid-June 2016, with ramp-up to the design capacity of 6,000 tonnes of ore per day completed in July.
Creston Mascota is an open-pit, heap-leach facility. It mines an average of 5,500 tonnes of ore/day and employs the same surface mining method as Pinos Altos.
Ore from the Pinos Altos mine is treated by two different processes – conventional processing, as well as the lower grade ore through heap-leaching. The conventional, 5,500-tonne/day process plant includes crushing, grinding, gravity concentration and agitated leaching followed by counter-current decantation. Gold and silver are recovered using the Merrill-Crowe method, and a refinery produces gold/silver doré bars on site. Metals recovery in the plant is estimated at 94% for gold and 44% for silver over the life of the mine. The lower grade Pinos Altos ore is treated in a heap-leach system designed to accommodate 5.6 million tonnes of material over the life of the mine, contributing about 4.3% of the total metal production.
All the Creston Mascota ore is processed using heap-leaching. Its 5,500-tonne- per-day heap leach facility is similar to the Pinos Altos facility, but the precious metals are recovered by a small carbon column circuit.
We continue to evaluate the sequencing of additional satellite zones, which could provide additional ore to the Pinos Altos complex. Drilling data is being incorporated into preliminary studies along with metallurgical testing and geotechnical data in order to better optimize the development potential of remaining satellite resources including Sinter and Bravo.
Agnico Eagle has undertaken a first campaign of drilling on the recently acquired Madrono prospect surrounded by the Pinos Altos mine property, and just 0.5 km from the Creston Mascota pit. Mapping and sampling of historical mine workings have quickly identified high-potential targets. The Madrono prospect includes at least three gold-silver veins: Madrono, Santa Martha and La Curva. Initial drilling confirms the potential to outline additional high-grade satellite zones close to the existing mines.
Previous mining in this area included small-scale bonanza production from underground mine development on three levels in the 1930s. Mapping, surface sampling, drilling and exploration planning for Madrono are underway.