The Terronera project is a high-grade silver-gold project being developed in San Sebastian mining district in the Jalisco state of Mexico. Endeavour Silver is the developer, which acquired the project in 2010.
Mexican environmental permitting authority SEMARNAT approved the environmental impact statement (EIS) of the project in the first quarter of 2017. The mine and plant permits of Terronera were granted in the third quarter of 2017.
Endeavour announced the results of the updated preliminary feasibility study (PFS) report and the mineral resource and reserve estimates of Terronera in September 2018.
The underground project is expected to produce an average of 2.9 million ounces (Moz) of silver and 28,000oz of gold (5.1 million silver equivalents approximately) a year through its anticipated mine life of 9.5 years.
Terronera silver-gold project location, geology and mineralisation
The Terronera project is situated on the north-west side of Jalisco State near the town of San Sebastian, approximately 40km north-east of Puerto Vallarta. The property comprises 21 mineral concessions spread over 16,691ha. It is located within the Sierra Madre volcanic belt, which hosts the majority of Mexico’s gold and silver deposits.
The underground mine consists of two deposits namely Terronera and La Luz. It comprises a low-sulphidation epithermal vein system, which is further divided into four mineralised vein sub-districts with an average thickness of 2m-8m.
Silver-gold mineralisation at Terronera is categorised as low-sulphidation, epithermal, bonanza style, and is hosted in Cretaceous andesite volcanics. The vein minerals are classified as quartz-adulariacalcite-barite (sericite), and most of the ore minerals are found as argentite-pyrite (galena-sphalerite-pyrargyrite) in ginguro bands.
Terronera silver-gold mine reserves
The Terronera project is estimated to contain probable ore reserves of 4.7Mt of ore containing 34Moz of silver and 342,000oz of gold, totalling 60Moz of silver equivalent.
Mining at Terronera
The Terronera and La Luz deposits will be accessed by ramps and cut-and-fill mining method will be used to mine the ore. Trackless equipment will be used for primary ore production. Longhole mining method will be applied at both the deposits for recovery of sill pillars.
Drift-and-fill mining method will be used at the Terronera deposit for primary production, while resue mining method will be applied at the La Luz deposit. The Terronera deposit is divided into five mining blocks, namely M1 to M5, while the La Luz deposit comprises a single mining block divided into upper and lower areas.
Processing at Terronera
The Terronera processing plant will operate at 750 tonnes per day (tpd) for the initial two years and at a rate of 1,500tpd from the third year. It will use ore from the Terronera deposit for the first two years, and a blend of ore from the Terronera and La Luz deposits from the third year until the end of mine life.
The ore will be crushed in a two-stage crushing circuit and then ground in a closed circuit to achieve a flotation feed grind size of 80%. The crushing circuit can process 1,500 dry tonnes per day in 18 hours of operation, while the grinding circuit will comprise two lines (A and B) with a single stage of grinding in primary ball mills.
A flash flotation unit will be an integral part of the grinding circuit, and the resultant flotation concentrate will be pumped directly to the final concentrate thickener.
The flotation circuit is categorised into rougher and scavenger cells to achieve maximum precious metal recovery. Cyclone overflow from the regrind circuit will be directed to a two-stage cleaning circuit to produce high-grade gold and silver in the final concentrate.
The final concentrate is then filtered, stored and air-dried in a warehouse, prior to shipment.
Infrastructure facilities at Terronera silver-gold project
The Terronera silver-gold project site can be reached through a public access road connecting Puerto Vallarta.
Power supply for the initial two years of operation will be provided through leased generators. Commission Federal de Electricidad (CFE), the national grid operator of Mexico, has agreed to supply power to the project through a new 115kV transmission line under an arrangement with Endeavour Silver.
Freshwater will be pumped from the underground mining operations to a freshwater tank and fed by gravity to the processing plant, fire water system, potable water system, and water trucks.
Workers will be accommodated at the construction camp to be established near the site.
Endeavour Silver engaged Smith Foster & Associates for the preparation of the PEA and PFS for the Terronera silver-gold project, while P&E Mining Consultants were engaged for preparing the mineral resource and reserve estimates.
Knight Piésold conducted mine geotechnical and water inflow tests as part of the PFS, while Wood (formerly AmecFW) is the designer of the tailings and water management facilities.
Resource Development was contracted to conduct metallurgical test works, while ALS Metallurgy was contracted to prepare flotation studies.