Yanacocha is the largest gold producer in South America. Yanacocha is a complex of five open pit mines, four leach pads, two gold recovery plants and a crushing and agglomeration facility.
The claim was staked by a joint venture between France's BRGM and Peru's Buenaventura group, Newmont Mining joined exploration agreement in 1984. Minera Yanacocha was established by BRGM Peru, Cia de Minas Buenaventura, Newmont Gold Co and the International Finance Corp.
Newmont manages the project
The mine is located high in the Andes Mountains, 28 miles north of Cajamarca and 375 miles north of Lima. The property encompasses 607 square miles (1,572 square kilometers).
Geology and Mineralization
The Yanacocha mine operation is spread across 600 square miles at altitudes as high as 14,000 feet. Actual operations cover approximately 60 square miles. The highest operational area is at 13,812 feet. The concession granted by the Peruvian government has a term of 20 years, renewable for another 20 years.
The Yanacocha gold deposits are high sulfidation epithermal gold deposits, with varying amounts of silver, that occur within a mid to late Miocene flow dome field with associated volcaniclastic rocks and minor lacustrine sediments. The gold is associated with silver bearing enargite and arsenian pyrite. Copper mineralization occurs at depth below the gold deposits.
The Yanacocha gold district is a 10 x 4 km zone of altered rocks within a belt of tertiary volcanics that extends the whole length of Peru. Andesitic domes and dome complexes have been silicified and leached by epithermal gold-bearing solutions in at least nine distinct deposits. The mineralised sequences, which can also contain significant amounts of silver, are flanked by extensive argillitic alteration, and subsequent events have created siliceous breccia pipes with localised high gold grades.
Deposits on the property include Cerro Quillish, La Quinua, Chaquicocha, Corimayo, and El Tapado deposits, Maqui Maqui, Encajon, Carachugo, San Jose, Yanacocha Norte, La Quena deposits as well as the Cerro Yanacocha deposit and other prospects. It is estimated that the gold reserves ensure a minimum exploitation life of fifteen to twenty years more.
The La Quena deposit consists of a gold bearing glacial moraine in a gravel covered terrain. This deposit has an areal extent of 4-5 X 1.5-2 kilometres and is a NW trending deposit that has a thickness of 100 to 200 m. The deposit is derived from the adjacent Yanacocha deposits and is estimated to contain between 5 and 7 million ounces of gold and 256 million ounces of silver.
Mining & Operations
There are five separate open-pit mines on the property: Carachugo, Maqui Maqui, Yanacocha, San José and La Quinua. Yanacocha and La Quinua are in current operation. There is a 410 million ton-capacity leach pad at the Carachugo pit, a 60 million ton-capacity leach pad at the Maqui Maqui pit, a 460 million ton-capacity leach pad at the Yanacocha pit, a 400 million ton-capacity leach pad at the La Quinua pit, and two solution ponds and a storm water pond at the base of each leach pad.
The Carachugo pit was mined first, followed by Maqui Maqui in 1994 and the San José pit in 1996. These are now being reclaimed. The mines current production comes from Yanacocha, beginning in 1997, and La Quinua, beginning in 2001.
Wheeled loaders load ore into 85t-capacity trucks which transports it 2.5km or more to the leach pads. The ore is heaped by stackers. The Carachugo ore is porous and run-of-mine ore can be heap-leached without crushing. The initial heap is cyanide leached at a rate of 10 litres/h/m2 into a 16,000 m3 pond before the solution is treated by the Merrill Crowe plant.
Drilling is done using Ingersoll-Rand DM45E and Atlas Copco machines. Ore is transported 2.5 km or more to the leach pads using wheeled loaders and 85 ton trucks, and is heaped by stackers.
Companies that supply standard mining equipment include Ferreyros (trucks, front-end loaders, compressors and drill rigs) and subsidiaries of foreign companies such as Ingersoll Rand, Atlas Copco, and Baker Hughes. The mining rate is 600,000ton/d.
Low grade solution is sent to carbon columns to enrich the solution, then sent to Merrill Crowe process equipment. High grade solution is sent directly to Merrill Crowe. In the refining process mercury is removed, bottled, and shipped. Doré bars containing 47% gold and 52% silver are shipped overseas by the refiner, Johnson Matthey.
There are four excess water treatment plants, each with a capacity to treat 500 cubic meters of water per hour. The most recent plant began operation in 2001. Chemical controls ensure that discharged water meets environmental standards. Sampling and analysis are performed continuously by computerized equipment.
The ore leaching process takes place in a closed circuit with a solution recirculation system and within a waterproof environment that prevents leaks. Water comes mostly from the partial storage of rainwater in the wells. Excess water is the result of constant rain and exceeds the storage capacity and for this reason it must be eliminated. Water that has been in contact with the leaching system has a low concentration of cyanide and other elements. It is treated and returned to the environment.
Key equipment contractors were Kilborn Engineering for plant and Water Management Consultants for water supply equipment.
FIMA is manufacturing a zinc ferrite flotation plant, with a production capacity of 1,500 TPD. The primary equipment consists of attrition cells, mixers, thickeners, flotation cells, and pumping systems.
An oxide mill will be operating by the end of 2006. The 5-6Mt/y plant will cost US$250 million and will treat more complex mineralization than is being heap-leached at the open-pit mine. This will be a transition to treating sulfide as oxide reserves are depleted.