Mercedes Mine, Mexico

As of December 2021, the Mercedes mine is estimated to contain (including mineral reserves) 3.8 million tonnes in measured and indicated categories grading 4.73 grams per tonne (gpt) gold and 42.4gpt silver, containing approximately 575 thousand ounces (oz) of gold and 5.1 million oz of silver.

Mercedes Location and Site Details

Mercedes Project is located within the Cucurpe Municipality in the Mexican state of Sonora. The site is around 250km northeast of Hermosillo, the capital of Sonora.

The project has a total of 43 mineral concessions spread across approximately 69,284 hectares.

All these concessions are owned by Minera Meridian Minerales (MMM), a wholly owned subsidiary of Bear Creek.

The mine can be accessed via highway and then through the Cucurpe community to the entrance of the Rancho Los Pinos. A 10km improved and gravel road then leads to the site.

Site elevation ranges from 950masl to 1,400masl.

Ownership History of Mercedes Mine

Since 1900s, exploration work and mining activities have been conducted around the Mercedes mine. In 1936, the Mercedes vein was discovered.

FMC Gold Company, a predecessor of Meridian Gold, explored the Mercedes Mine in 1993. Meridian Gold entered a joint venture with Fischer-Watt in 2002 to continue exploration at the site.

The joint venture was terminated in 2004 and Mercedes again went back to Meridian.

In October 2007, Yamana Gold acquired the property and owned it until September 2016 when Premier Gold Mines purchased the mine. In between, commercial production started in 2011.

Between 2016 and 2021, drilling activity focused on underground delineation of the various zones.

Equinox Gold purchased Mercedes mine by purchasing all outstanding shares of Premier Gold in April 2021.

In April 2022, Bear Creek Mining completed the acquisition of the gold-silver mine. The consideration included a cash payment of $75m, 24.7 million Bear Creek common shares, a deferred payment of $25m and 2% net smelter return on metal production.

Geology and Mineralisation

The Mercedes Mine is located on the north-western edge of the epithermal (Au-Ag) deposits belt of Mexico besides Cananea and Nacozari deposits.

Two northwest trending arches dominate the gold-silver property exposing old marine sediments, overlying interbedded volcaniclastic sediments, and lithic, quartz crystal lithic tuff units.

Andesitic flows and flow breccias were preserved on the northwest-trending arches in a minimum of three west-northwest thickening basins.

Gold-silver bearing epithermal low sulphidation veins totalling 16.5km were identified within or along the margins of the andesite-filled basins. These veins form the primary exploration target.

Mineral Resources and Reserves

According to the technical report, the Mercedes Mine’s total (measured and indicated) mineral resource estimate excluding reserves is 2.5 million tonnes containing 312,000oz gold at a grading of 3.81gpt and 3 million oz silver at a grading of 37.47gpt.

The Inferred mineral resources stand at 884,000 tonnes containing 128,000oz gold at a grading of 4.50gpt and 1,167,000oz silver at a grading of 41.02gpt.

The project is estimated to host total (proven and probable) mineral reserves of 2.2 million tonnes containing 267,000oz gold at a grading of 3.75gpt and 2 million oz silver at a grading of 29gpt.

Mining and Ore Processing

The Mercedes Mine is completely mechanised with ramp access and five underground areas: Mercedes, Lupita, Barrancas, Diluvio, and Rey de Oro.

After the Covid-19-related shutdown, operations resumed at the Diluvio and Lupita zones.

Through the main ramps, the ore is brought to the surface and is stockpiled near the individual portals. From the Barrancas, Lupita, Diluvio, and Rey de Oro, the ore is stockpiled in a common stockpile area near the jaw crusher.

Most of the areas have been mined using mechanised cut-and-fill methods. Long hole stoping is being used in Diluvio and Diluvio West as the volume of ore and ground conditions allow better economics.

Previously, the Rey de Oro Superior deposit was mined using open pit methods. Now, it is being mined as an underground operation and it is producing from Q4 2023.

The ore is processed by a plant with a capacity of approximately 2,000tpd. It uses conventional milling with Merrill-Crowe recovery of gold and silver.

The Run-of-Mine (ROM) is transferred to and crushed by a primary jaw crusher dump hopper. From here, it is discharged onto a vibrating grizzly feeder and into the primary jaw crusher.

The crushed ore enters the fine crushing and reclaim conveyor circuit for further crushing and subsequent grinding.

Key components of the processing include gravity concentration; counter current decantation; Merrill-Crowe zinc precipitation; smelting; cyanide detoxification of tailings; and disposal of tailings.

The precious metal recovery circuit can process around 155,000 ounces of gold and 595,000 ounces of silver per year.

Infrastructure Details

The infrastructure of the Mercedes Mine consists of surface and underground facilities.

The infrastructure facilities include a processing plant, three-stage crushing plant, tailings management facilities, a paste plant for underground backfill, water supply, water treatment plant, two batch plants, electricity supply, ore and waste stockpiles areas.

Associated facilities include administrative offices, core storage and exploration offices, change room for personnel, safety room, and two camp facilities for personnel of mine and exploration.

The mine receives power from Magdalena de Kino located 65km away.

During an emergency, the 2kVA backup diesel generators deliver power to the mine and site. A diesel generator is used during maintenance shutdowns.

Contractors Involved

Breton, Banville and Associates (BBA) Engineering, a technological and engineering company, prepared an updated independent technical report and conducted independent audit of its mineral resources and reserves.

PLR Resources, a mineral resource estimates and exploration specialist, was also involved in the preparation of the independent technical report of the mine.

In September 2022, Bear Creek awarded Unison Mining Consulting a contract to design a 32-week performance improvement programme for the mine. Additionally, Renoir Management was selected to implement the programme.

JDS Energy and Mining led construction management team and supplied trained personnel for 240m of ground support and installed ladders in the boreholes at the mine.