The La Arena gold-copper project, which is being developed by Rio Alto Mining, is located approximately 480km north-northwest of Lima in La Libertad region, northern Peru.
It is a two-staged development project comprising the development of an oxide gold project in the first phase and a copper-gold sulphide project in the second phase.
Rio Alto Mining acquired the La Arena project from IAMGOLD in February 2011 and produced its first gold in May 2011. The feasibility study for the second phase is expected to be completed in the first quarter of 2015.
La Arena mine geology and mineralisation
The La Arena project is located within the eastern flank of the Andean Western Cordillera in northern Peru. The project area is underlain by sedimentary rocks of the Mesozoic West Peruvian Basin, which are believed to be formed during the Cenozoic deformation.
Sedimentary rocks are intruded by intermediate to felsic porphyritic stocks, which tend to occupy the cores of anticlinal structures.
The oxide deposit hosts low grade gold-oxide mineralisation, while the sulphide deposit contains primary and secondary copper mineralisation along with gold.
Epithermal style gold mineralisation in sandstone-hosted oxidised fractures and breccia is found at the mine. The deposit also hosts porphyry Cu-Au (Mo) mineralisation.
The mineralisation extends over a strike length of 2.2km from south to north and is approximately 1.1km wide.
La Arena gold-copper project reserves
As of January 2015, the La Arena project is estimated to contain proven and probable oxide gold reserves of 103.3 million tonnes (Mt) grading 0.39g/t Au. The contained gold is estimated to be 1.28 million ounces (Moz).
The proven and probable sulphide reserves at La Arena (Phase II) are estimated to be 63.1Mt grading 0.31g/t Au, containing 579 million pounds (Mlb) of copper.
Mining and processing of ore at La Arena
Annual copper production from the mine is expected to be 160,000 tonnes in concentrate form.
Conventional drill and blast method of mining, using shovel and dump trucks, is applied at the Calaorco and Ethel open pits. The major mining fleet being used include CAT 777 haul trucks and Bucyrus RH90 excavators.
Ore collected from Calaorco and Ethel pits is dumped by trucks onto leach pads before treating with cyanide-leach solution. The project comprises an adsorption, desorption and refining (ADR) plant with capacity to treat 36,000 tonnes per day (tpd) of ore.
The impregnated solution containing gold is collected in a gold enriched solution pond and transferred to the ADR circuit where gold is recovered onto activated carbon.
Carbon is stripped off and gold is extracted by an electrowinning process to form a precipitate, which is dried and mercury evaporated. It is later mixed with fluxes and smelted to produce doré bars.
The run-of-mine sulphide ore will be delivered to the primary crusher to separate copper / gold flotation concentrate from tailings. The material undergoes crushing, grinding and flotation to produce a concentrate, which is dewatered onsite prior to being trucked to the port for shipping to third-party smelters.
Gold production from La Arena Au-Cu project
The La Arena mine produced 51,398oz of gold in 2011, 201,113oz in 2012, 214,742oz in 2013, and 222,255oz in 2014. It is forecasted to produce approximately 210,000-220,000oz of gold in 2015.
Infrastructure facilities at La Arena mine
Access to the project is provided through a 165km-long paved roadway from the coastal city of Trujillo.
The mine was connected to the Peru power grid in October 2014. The internal 22.9kV power network at the site allows for transmission of power from the national grid. The project also uses generators for power backup.
Water supply for the mine, processing plant, camp, workshop and other facilities is being provided by two bores, an 80m-deep bore located approximately one kilometre from the site and the other located to the north of Calaorco pit.
Key players involved with the La Arena project
A consortium of GyM and STRACON was awarded the civil works contract for building the leach pad, waste dump and related infrastructure for the project.
Ausenco conducted metallurgical testing of the sulphide mineralisation at La Arena. Coffey Mining prepared the technical report for the gold-copper project, while Hatch was engaged as the lead engineer for the sulphide feasibility study.
Heap Leaching Consulting SAC was awarded the processing plant construction contract.