Terronera is a major underground silver and gold mine proposed to be developed by Endeavour Silver in San Sebastian mining district in the Jalisco state of Mexico.
The first pre-feasibility study (PFS) for the project was completed in August 2018, while an updated PFS was released in July 2020.
The latest PFS suggests a 1,600 tonnes per day (tpd) underground mining operation capable of producing up to three million ounces (Moz) of silver and 32,800 ounces (oz) of gold a year over an estimated mine life of 10 years.
The total investment for the Terronera project development is estimated to be £128m ($161.5m). A final development decision is expected after the completion of a definitive feasibility study (DFS) is in 2021, while the construction and commissioning is expected to take 18 months.
Location, geology, and mineralisation
The Terronera silver-gold deposit is situated approximately 50km northeast of the port city of Puerto Vallarta in the Jalisco state of Mexico. The town of San Sebastian del Oeste is about half an hour’s drive and the city of Guadalajara lies approximately 155km west of the project site.
The Terronera project consists of the Terronera as well as the La Luz Vein ore body which was discovered later in 2016. The project lies in the Sierra Madre Occidental Volcanic belt, volcano-sedimentary sequence predominantly comprising shale, sandstone, and narrow calcareous-clayey interbeds covered by volcanic breccias, tuffs and lava flows of andesitic composition.
Silver and gold reserves at Terronera
The Terronera project is estimated to hold 5.56 million tonnes (Mt) of probable ore reserves grading 205g/t silver and 2.29g/t gold and containing a total of 36Moz of silver and 410koz of gold.
The indicated and inferred mineral resources at the project are estimated to be 6.4Mt with silver grading 2.2g/t silver and 2.1g/t gold.
Mining and ore processing at Terronera mine project
Terronera will be an underground mining operation involving cut and fill, as well as long hole stoping method.
The principal mining method will be the cut and fill method utilising trackless underground equipment including scoop trams, haulage trucks, and electric-hydraulic drill jumbos. The long-hole stoping method will be implemented for mining approximately 41% of the mine.
The run of the mine (ROM) ore will be trucked to a nearby processing plant where it will be crushed to 3/8 inches in three stages before being ground to a size of 70 microns.
The ground ore will be fed into a flotation circuit for the recovery of silver and gold through flash floatation. The obtained concentrate will undergo cleaning, thickening, and filtering before being packaged for transport.
The Terronera project can be accessed through the public road from Puerto Vallarta, located approximately 55km away from the project site.
The electricity for the project will be sourced from Mexico’s national grid operator Commission Federal de Electricidad (CFE). The power during the construction phase will be sourced through the leased generators installed on the site.
The water will be sourced from the underground mining operation and stored in freshwater near the processing plant.
Ausenco Engineering worked with Endeavour on the re-conceptualisation and reengineering of the project to generate the enhanced PFS economics.
Knight Piesold provided the geomechanical and hydrogeological support services for the project in 2016.
P&E Mining Consultants and Smith Foster & Associates were the other major consultants engaged for the project.