Los Filos Gold Mine

Mining and Processing

Open-pit mining is owner-operated with conventional load, haul, drill and blast methods. Mining methods for the underground deposits vary depending on the ore geometry and ground conditions. In the Los Filos Underground, mining methods include overhand cut and fill in narrow areas, overhand drift and fill in wider areas, and longhole open stoping in areas with vertical ore body continuity and good rock conditions. In the Bermejal Underground, oxide ore has been mined using overhand drift and fill, which constitutes the majority of the deposit, and underhand drift and fill is used to mine ore in intrusive host rock. Bermejal Underground was suspended in February 2023 while the Company advances plans to improve productivity and reduce costs, with the objective of restarting Bermejal in the future

Mined ore is allocated to either run-of-mine or crushed ore heap leach facilities, as appropriate. Two heap leach pads are in operation, one for crushed ore and the other for run-of-mine ore. Crushed ore is fully leached after 120 days and run-of-mine ore after 180 days. Pregnant leach solution from the heap leach pads is processed in a conventional adsorption, desorption and recovery (ADR) process plant that also includes an elution circuit, carbon regeneration circuit and gold refinery that produces a gold-silver doré product.

Exploration and Geology

The Los Filos Mine Complex is in the Guerrero Gold Belt near the centre of a large, approximately 200 km diameter circular feature known as the Morelos-Guerrero sedimentary basin. The basin consists of a thick sequence of Mesozoic platform carbonate and argillaceous rocks. Mineralization identified within the Los Filos property is typical of intrusion-related gold-silver skarn deposits. Mineralization is geologically controlled either by being hosted by, or spatially associated with, skarn development during contact metamorphism of the carbonates by the intruding granitoid rocks.

The Los Filos stocks form two circular deposits, each approximately 1.5 km in diameter, with mineralization focused along the contacts with the host rocks. The Bermejal-Guadalupe stock forms an oblong shape over 5 km long, with the Bermejal deposit on the northern end and the Guadalupe deposit approximately 2 km southeast of Bermejal; the stock continues further southeast to the San Pablo deposit. Extensive, deep oxidation of the deposits (that occurred at the time of mineralization) has altered the mineralization to be amenable to cyanidation recovery techniques without the need of pre-treatment by roasting or other methods.

In the Los Filos area, known mineralization is associated with early-Tertiary Los Filos and Bermejal-Guadalupe granodiorite stocks that were emplaced into the host carbonate rocks. Mineralization in the Bermejal-Guadalupe area occurs along the contact of the Bermejal-Guadalupe stock with the carbonate rocks of the Morelos Formation. The Bermejal Open Pit mineralization is typically at the top or on the flanks of the upper portion of the intrusive. On the northern end of the stock, mineralization extends below the Bermejal Open Pit and down the steeply dipping to vertical flanks of the intrusion and is referred to as the Bermejal Underground deposit.

The total circumference of the Los Filos stocks is approximately 8 km, with at least half of this circumference tested by drilling or with mining development. The Bermejal-Guadalupe stock has a circumference of approximately 16 km, and although the contacts along the upper portion of the intrusion have been mined by open pit, only a few kilometres of this contact have been explored at depth.

Mineralization extends from surface to over 700 m deep and is variable in grade and width. Gold mineralization at Los Filos extends beyond the drilled area, and it is expected that additional drilling along the contact between the intrusives and carbonate host rock could identify further skarn mineralization. With exploration success and conversion of Mineral Resources to Mineral Reserves, considerable potential exists to extend the Los Filos mine life.