Los Filos Area Mineralization
In the Los Filos area, mineralization is associated with two early Tertiary granodiorite stocks that were emplaced in carbonate rocks and resulted in development of high-temperature calc-silicate and oxide metasomatic alteration (skarn) assemblages that were followed by distinct meso to epithermal alteration. Hematite and magnetite are typical skarn minerals, but diopside, which is usually recognized in skarn assemblages, is not present.

The Nukay and Sur deposits formed along the north and southern margins of the West Stock . The Peninsular and Zona 70 deposits formed on the northern and southwest margins of the East Stock, respectively.

The Los Filos Open Pit mineralization is hosted primarily within or on the lower contact of a diorite sill that dips from 20° to 50° to the east, away from the East Stock. The diorite was emplaced into a large, moderately dipping active structure that parallels bedding in the marble. The sill has a sigmoidal shape that starts out roughly flat at the stock, extends east at a moderate dip for approximately 200 m, turns south, flattens out, and extends to the Bermejal Intrusion, located approximately 2 km to the south.

The diorite sill hosts approximately 75% of the mineralization at the Los Filos Open Pit deposit. Mineralization is structurally controlled by breccias and quartz-hematite-gold (± calcite) veins that occur relatively late in the paragenetic sequence and probably ........

The Los Filos Mine Complex comprises two active open pits (Los Filos Open Pit and Bermejal Open Pit), one active underground mine (Los Filos Underground Mine), one planned open pit mine (Guadalupe Open Pit), and one planned underground mine (Bermejal Underground Mine).

The Expansion Feasibility Study incorporates the potential for: development of the Bermejal underground mine, enlarging the Los Filos open pit mine, re-phasing of the Bermejal open pit into two distinct open pits (Bermejal and Guadalupe).

The site-wide LOM plan for the Los Filos mine complex has contributions from two high-grade underground mines and three large, lower-grade open pits.

Underground Mining

Bermejal Underground
The mining method selected for Bermejal Underground is underhand drift-and-fill (UHDAF). This is a highly selective, fully supported man-entry system that allows maximum flexibility and the ability to control mining recovery and dilution through good management and planning practices.

The mine design is based on trackless mobile equipment with ramp-access from one portal within the mined out portion of the north end of the Bermejal Open Pit. This portal is constructed and is currently in use. Ore and waste material will be trucked to the surface and re-handled by larger surface mobile equipment to its ultimate destination.

Lateral development sizes range from 5.0 m high x 5.0 m wide for main access ramps, levels, and ........

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Ore is currently processed by conventional heap leaching methods to recover the contained gold and silver. In addition, installation of carbon-in-leach (CIL) cyanidation processing facilities to recover gold and silver from higher grade ore sourced primarily from the future Bermejal Underground mine is being investigated.

Heap Leach Processing

Heap Leach Pad Operation
There are two large geosynthetic lined heap leach pads in operation, both of which have been divided in two sections: one for Crush ore and the other for Uncrush ore. Uncrush ore is currently stacked on Pad 1 and Crush ore on Pad 2. Pads 1 and 2 cover areas of 2,515,000 and 721,000 m², respectively, for a total of 3,236,000 m2.

After 60 days of leaching, the drip lines are removed from the surface of the Crush material and the top of the lift is ripped to a depth of 3.5 m using a CAT D11 dozer. Drip lines are reinstalled after ripping and leaching is resumed and continued for an add ........