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 represent the last stage of hydrothermal activity in the deposit. The veins dip at moderate to steep angles (50 to 80 degrees), while the breccias dip more moderately (30 to 40 degrees). Both veins and breccias are developed preferentially within the intrusive rocks and their contacts with marble. The veins typically occur in clusters with spacings of 5 to 50 cm. The breccias tend to occur as isolated or bifurcating structures.

The 4P portion of the Los Filos area comprises the El Grande, Agüita, Zona 70, and Crestón Rojo zones.

Mineralization is hosted within Cretaceous-aged medium-bedded to massive fossiliferous limestone of the Morelos Formation. The carbonates were intruded by granodioritic plutons resulting in the formation of marble within the calcareous rocks and local development of calcsilicate endoskarn in the intrusive rocks. Pods of calc-silicate and iron-rich exoskarn in the marble formed along contacts. These deposits are at the contacts of the East Stock.

Bermejal Area Mineralization
The Bermejal area consists of mineralization along the contact of the Bermejal 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 intrusion. Mineralization extends below the Bermejal Open Pit and down the steeply dipping intrusion to vertical flanks of the intrusion and at the northern end of the intrusion the mineralization is referred to as the Bermejal Underground deposit.

Deposit geology consists of calcareous and argillaceous rocks of Cretaceous age formation that are intruded by a granodiorite stock of Tertiary age, forming metasomatic halos at the contacts. Iron-oxide skarn mineralization is best developed at the granodiorite-limestone contacts and within endoskarn. The Bermejal Stock is approximately 2 km in diameter, is roughly circular, and connects to a larger mass that extends for several kilometres to the southeast.

The major mineralized bodies at Bermejal consist of iron-oxide gold skarn with minor amounts of copper and silver at the intrusive-limestone contact. Mineralization also occurs within endoskarn and also disseminated within the hydrothermally altered intrusive rocks.

Quartz, iron-oxides, high-grade gold mineralized veins, stockwork, and disseminated mineralization are locally important. Both limestone and intrusive rocks host the quartz-iron-oxide and high-grade gold mineralization. Stockworks and disseminated mineralization are restricted to the intrusion.

The Guadalupe deposit is located on the eastern extension of the Bermejal Intrusion and is adjacent to the southeast wall of the planned Guadalupe Open Pit. Mineralization comprises iron-oxide gold skarn with minor amounts of copper and silver developed along the intrusion-limestone contact. Mineralization also occurs within exoskarn and can form disseminations within the hydrothermally altered intrusive rocks. Both limestones and intrusive rocks host the quartz-iron-oxide and high-grade gold veins. Stockworks and disseminated mineralization are restricted to the intrusion.

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 ancillary development, to more narrower headings up to 4.0 m high x 3.5 m wide in top-cut production stopes. Undercut production stopes are planned to be mined with 4.0 m high headings and widths varying from 4.0 m to 6.0 m, depending on local geotechnical conditions. The largest excavations are in the main shop area where several 6.0 m high x 6.0 m wide excavations and one 7.0 m wide x 8.0 m high excavation are planned. Ramp grades are kept to within +/- 15%, with some attack ramps being driven at a maximum of 18% where required. A minimum turning radius of 25 m is kept in the main ramps.

The mining method requires the placement of cemented rock fill (CRF) in volumes roughly equivalent to the extracted ore.

Los Filos Underground
The Los Filos Underground operations are focused on the mineralized skarn on the perimeter of the Los Filos intrusive and are accessed by multiple portals that are located outside of the current open pit operations. The main ramps are driven at a gradient of 12.5% and have a profile of 4.5 m x 4.5 m to accommodate 10-wheel, 14 m3 class highway dump trucks. The main ramps are located in the hanging wall, in competent limestone, at a distance of 60 to 100 m from the ore to minimize geotechnical issues. The main ramps provide access to ore zones that are separated by subeconomic material. The ore and the immediately adjacent waste zones have a poor rock quality and require increased ground support for stability.

The primary mining methods are OHCAF and OHDAF, with the latter being used in wide areas of the orebody. Ore drives typically have a profile of 3.5 m wide x 4.0 m high. Underground development waste rock is used for backfill. When adequate development waste rock is not available, rock from open pit waste dumps is dropped into the underground mine through 3 m diameter vertical borehole raises.

Open Pit Mining
Open pit mining is by conventional drilling and blasting with loading by excavator and haulage by trucks to a crusher (for Crush heap leach processing) or directly to a run-of-mine (Uncrush) leach pad. Leagold plans to construct a 4,000 t/d carbon-in-leach (CIL) processing plant.

Los Filos Open Pit
Production benches are designed to be 9 m in height and stacked in double benches of 18 m. The standard haul road width is 25 m to allow for two-way traffic, but is narrowed to allow only one way traffic when extracting the lowest benches of the pit. The maximum haul road gradient is 10% and the minimum mining width is 50 m.

Bermejal and Guadalupe Open Pits
Production benches are designed to be 9 m in height and stacked in double benches of 18 m. The standard haul road width is 25 m to allow for two-way traffic, but is narrowed to allow only one way traffic when extracting the lowest benches of the pit. The maximum haul road gradient is 10% and the minimum mining width is 50 m.

The Guadalupe Open Pit: Production benches are designed to be 9 m in height and stacked in double benches of 18 m. The standard haul road width is 25 m to allow for two-way traffic, but is narrowed to allow only one-way traffic when extracting the lowest benches of the pit. The maximum haul road gradient is 10% and the minimum mining width is 50 m.

Heap Leach
Ore that is classified as low-grade is stacked as Uncrush ore on Pad 1 for leaching. Medium and high-grade ore is crushed to 80% minus (P80) 19 mm, agglomerated with lime and cement, and transported by conveyors as Crush ore to Pad 2 for leaching. The Pad 2 ore is placed in 5-m lifts.

The crushing circuit has a maximum operating capacity of 1,500 t/h, but depending on ore supply, crusher feed size distribution and moisture content, the circuit normally operates between 830 to 875 t/h for 16 to 18 h/d based on 2016 to 2018 production rates. Medium and high-grade open pit ore is end-dumped from 136-t capacity mine haulage trucks near the primary crusher into a 200,000-tonne stockpile without significant blending of ore types.

Underground ore is end-dumped in a separate stockpile by 20-t capacity dump trucks. The ore is delivered to the jaw crusher feeder hopper, which is equipped with a 400 mm grizzly and fed by a dedicated CAT 992 front-end loader from the stockpile. The separately stockpiled underground ore is fed to the crusher as a weekly campaign, one day per week. Grizzly oversize material is broken down with a remotely operated stationary rock breaker on the grizzly or by a track-mounted rock breaker.
The major components of the crushing plant include a primary jaw crusher (Sandvik JM 311), which is set at a 100 mm opening, and two secondary cone crushers (Metso HP-800) operated in closed circuit with double-deck banana screens to produce a final P80 19 mm final crushed product.

Carbon-in-Leach
Ore will be transported to the plant by mine haul trucks of up to 136-t capacity (CAT 785C). The trucks will tip directly into the feed bin through a static grizzly. Any ore stockpiled on the ROM stockpile will be fed to the bin by front-end loader (FEL) when truck deliveries are interrupted. The FEL will also be used to clear any build-up of material from the grizzly should this occur. The ore stockpile will facilitate ore blending to ensure a uniform feedstock to the plant.

The feed ore bin will have a live capacity of approximately 270 t (equivalent to 2 truck loads). A static grizzly, mounted on top of the bin, will prevent the ingress of oversize material. Ore will be drawn from the bin, by a variable speed apron feeder, discharging into the jaw crusher via a vibrating grizzly. The primary crushing circuit will reduce the underground and open pit ores from a nominal top size of 500 mm to a product size of P80 of 82 mm. The jaw crusher is a C120 or equivalent with a 160 kW motor. Crush ore from the crusher and vibrating grizzly undersize will discharge directly onto the primary crusher discharge conveyor, which will convey the crusher product to the surge bin.

The surge bin will have a live capacity of 46 t (equivalent to approximately 15 minutes of mill feed rate). The surge bin includes an overflow facility, with excess crushed ore conveyed to the crushed ore stockpile. The crushed ore stockpile will have a capacity of approximately 4,400 tonnes (providing 24 hours of mill feed). Crush ore will be reclaimed from the stockpile, to the ore bin, via FEL. Crush ore will be withdrawn from the ore bin by a variable speed apron feeder. The feeder will discharge onto the SAG mill feed conveyor, which will convey the crushed ore to the SAG mill feed chute. The SAG mill feed conveyor will be fitted with a weightometer, used for controlling the speed of the apron feeder and hence the feed rate to the grinding circuit.

The grinding circuit consists of a single stage SAG mill with a 5 MW variable speed drive. The mill is 7.32 m in diameter and has a 5.55 m equivalent grinding length (EGL). The SAG mill will operate in closed circuit with hydrocyclones. Modelling predicts that pebble rejection by the grates and trommel will be minimal and will be recycled back to mill feed surge bin by FEL.

The mill has been designed to be capable of achieving the required grind size with a mill feed blend of 57% oxide, 34% intrusive and 9% carbonate ore, which is harder than the life of mine average blend feed. The installed variable speed drive will ensure that the mill can be controlled to draw the required power when treating softer blends to avoid grinding out the mill pebble charge. The mill will operate with a nominal 11.8% (maximum 15.0%) by volume ball charge.

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 ........