The Buenavista open-pit copper mine in Sonora, Mexico is one of the biggest porphyry copper deposits in the world. Southern Copper Corporation, a subsidiary of Grupo Mexico, is the 100% owner and operator of the project.
Producing since 1899, it is the oldest operating copper mine in North America. The deposit was mined exclusively through underground methods until the Anaconda Company started open-pit operations in the early 1940s.
Grupo Mexico has continuously expanded the Buenavista operation since it acquired the property for £290m ($475m) in 1990.
The Buenavista mine produced 965 million pounds (Mlbs) of copper in 2019 which accounted for approximately 44% of Southern Copper’s total copper production during the year. The mine also produces silver and molybdenum as by-products.
The company is also implementing a zinc project at Buenavista with an estimated investment of £315m ($413m). Scheduled for commissioning in the second half of 2022, the Buenavista zinc project is expected to produce 80,000 tonnes (t) of zinc a year and increase the annual copper production capacity of the mine by 20,000t.
Location, geology, and mineralisation
The Buenavista copper mine is located in the outskirts of Cananea, in the Mexican state of Sonora, approximately 100km north-west of La Caridad and approximately 40km south of the Arizona-Mexico border.
The mining concessions for the Buenavista project spread over 93,706ha at an altitude of 1.9km above sea level.
The Buenavista mining district is situated on the southern part of the Cordilleran Orogenic Belt that stretches from southern Mexico to the north-western US. The geology of the Buenavista mining district is characterised by large, disseminated, porphyry copper deposits.
The mineralised ore body at Buenavista measures 5km-long, 3km-wide, and extends more than 1km deep.
The Buenavista zinc project is located in the north-western part of the Buenavista ore body. It is a skarn deposit hosting zinc, copper, silver, and lead sulphide mineralisation.
Mineral reserves at Buenavista
The Buenavista copper mine is estimated to hold 4.46 billion tonnes of proven and probable sulphide ore reserves grading 0.421% copper and 0.008% molybdenum. The contained copper at the mine is estimated to be 22.1Mt.
The Buenavista zinc deposit is estimated to contain approximately 102.6Mt of ore grading 1.88% zinc, 0.47% copper and 17g/t silver.
Production from the Buenavista copper mine
The Buenavista mine produced 337,960t of copper in concentrate, 100,113t of cathode, 5.75 million ounces (Moz) of silver, and 13.48 million pounds (Mlbs) of molybdenum, by milling a total of 70.3Mt of ore in 2019.
Mining and ore processing
Buenavista is a conventional open-pit mining operation utilising trucks, shovels, and loaders for ore extraction.
The extracted ore material is trucked to the nearby processing complex that houses two copper concentrators with a total milling capacity of 182,000 tonnes per day (tpd), two molybdenum plants with a combined daily processing capacity of 4,600t, a leaching facility, and three solvent extraction-electrowinning (SX-EW) plants with a total cathode production capacity of 174,470 tonnes per year.
The ore material with a copper grade over 0.38% is sent to the 82,000tpd first concentrator facility where it undergoes crushing, grinding, and froth flotation for the production of concentrate with an average copper content of approximately 24%.
The ore material with a copper grade over 0.555% is sent to the 100,000tpd second concentrator plant that was commissioned in 2015.
The first molybdenum plant capable of processing 1,500t of copper-molybdenum concentrates a day was commissioned in 2013, while the second molybdenum plant capable of processing 3,040t copper-molybdenum concentrates per day commenced operation in 2016.
Copper concentrates from Buenavista are transported by rail and truck either to the Guaymas Port for export or to the La Caridad smelter for the production of copper anodes of 99.2% purity. The anodes produced at the smelter are further sent to the La Caridad copper refinery.
SX-EW facilities for the Buenavista copper mine
The ore material with a copper grade between 0.25% and 0.38% is delivered to the leach dumps for processing at the SX-EW facilities.
The pregnant leach solution (PLS) is processed at one of the three SX-EW plants at the facility for the production of copper cathodes with 99.9% purity.
The SX-EW plant with four solvent extraction tanks and 54 electrowinning cells has the capacity to produce 30t copper cathodes a day, while the second plant has five solvent extraction trains and 220 to produce 120t of copper cathodes a day.
The third SX-EW plant at Buenavista was commissioned in June 2014. With three solvent extraction trains and 270 electrowinning cells, it is designed to produce 328t of copper cathodes a day.
Buenavista zinc project
The on-going zinc project includes the construction of a new concentrator within the Buenavista facility which will be capable of producing 80,000t of zinc and 20,000t of copper a year.
The basic engineering for the new concentrator was completed in 2019 while the detailed engineering and site preparation was underway by the beginning of 2020.
When completed in 2022, the new plant will double the zinc production capacity of Southern Copper Corporation.
The Buenavista mine site is connected to the nearest towns Agua Prieta, Nacozari, and Imuris by paved highways. It is also connected to Agua Prieta and Nogales through rail, while a municipal airport is located approximately 20km northeast of the mine site.
The electricity for the mine is bought from Mexico Generadora de Energia (MGE), a subsidiary of Group Mexico that operates two gas-fired combined-cycle power plants with a total installed capacity of 516MW for supplying electricity to both the Buenavista and the La Caridad mines.
The water requirement for the mining operation is met through bore wells in the vicinity.
Outotec provided the copper SX-EW technology package for the third and the biggest SX-EW plant at Buenavista under a contract awarded in April 2012.
Metso was awarded a £6m ($8m) contract to deliver 38 belt-type feeders for the Buenavista copper mine expansion in July 2013.