Silver, lead and zinc oxide and sulphide mineralization at La Encantada occurs in vein, manto, chimney, breccia pipe, and irregular replacement and stockwork deposits. In general, shallower veins, mantos and breccias are oxidized whereas deeper mantos, skarn dissemination and stockworks contain primary sulphides. Most mining at La Encantada has been done in the oxidized mineral deposits and only some drilling and limited underground access has been done in the deposits with primary sulphides. Drilling indicates potential for deep seated disseminated or massive sulphide replacement mineralization.

Structural controls on mineralization include intrusive contacts, faults, fold axes, fractures, fissures, and cavern zones. Intrusive contacts and intrusion-related faults are the most important controls in the skarn, whereas regional faults, folds, and fracture systems are dominant controls on mantos, chimneys and veins.

Mineral deposition at La Encantada is recognized across a vertical extent of at least 500 metres. Primary sulphides generally occur 400 metres below surface at the skarn dome area (La Prieta) and Milagros area. Sulphide mineralization consists primarily of sphalerite, galena, pyrite and acanthite.

In terms of volume, the mostimportant mineral depositsthat occur at La Encantada are mineralized tectonic breccias and breccia pipes. Skarn, hornfels and marble are developed at depth at the contact with the main stocks (Skarn dome and Milagros areas) and often contain sulphide mineralization.

The La Encantada deposit is a typical example of a high temperature carbonate replacement deposit.

The La Encantada property is located in the northern part of Coahuila within the Sierra Madre Oriental fold and thrust belt. The Sierra Madre Oriental extends in a south-southeasterly direction about 1,500 km, from the U.S.- Mexican border to approximately latitude 20°N in the south. The geologic history initiated in the Permian-Triassic with the Ouachita-Marathon orogenic event, followed by Late Triassic to Middle Jurassic rifting of Pangaea, subsequent opening of the Gulf of México and the formation of the Sabinas basin, passive-margin development through the Late Cretaceous, and Laramide foreland deformation and emplacement of intrusions through the early to mid-Tertiary

La Encantada lies on the southwestern flank of the NW-trending Sierra de La Encantada anticlinorium. The mines occur along a series of NE-trending faults and fractures that cut obliquely across the regional N-NW-trending anticlinorium. The most important ore-controlling structures appear to be the NE-trending faults and fractures that seem to control the localization of chimneys and vein shoots at the intersection with the NW trending structures. Major NW-NNW trending faults such as the main La Encantada front range fault do not appear to be mineralized

Mining the Veins System and other minor deposits at La Encantada is undertaken using primarily the conventional overhand cut-and fill mining method. Ramps are driven into the orebodies, and stopes are developed from sill drifts driven in the ore zones and slashed out the full width of the ore.

Mining operations at La Encantada mine are partially mechanized. Drilling of access drifts and ramps is carried out using hydraulic jumbos, and most of the headings and cut-and fill stoping is accomplished using pneumatic hand-held jackleg machines.

The cut-and-fill stoping cycle is started with blast holes drilled using hand-held jackleg drills, followed by blasting using conventional mining explosives. After blasting, LHD’s are used to muck the blasted ore. The cut and fill stopes range between 50 to 150 m in length along strike, and extend between levels which are typically spaced 15 to 30 m apart vertically. Each cut is 2.5 to 3.0 m in height. Depending on ground conditions, the blast holes are drilled either upward or horizontally. Waste and mineralized material below cut-off grade is blasted down and used as backfill as needed.

The minimum mining width is 2.0 m, and planned dilution is included in the mine design, which varies according to the ground conditions, vein width, and the dip of the vein. The dilution factors range from 5% to 20%, with an average of approximately 10%. Mined areas are measured to compare the width of the vein and the width of the cut on a regular basis; as mining advances, this comparison is used as means of reconciliation and to build the historical database of the dilution and mining recovery factors. Sills and access drifts are excavated at 2.5 m wide by 3.0 m high, cross-cuts and access ramps to the stopes are excavated 3.0 m wide by 3.0 m high, and main access ramps are excavated 4.0 m wide by 4.5 m high.

Based on the geotechnical characteristics and the geometry of the breccias, First Majestic has started the implementation of a variant of Incined Caving for the San Javier and Milagros breccias. This configuration allows the extraction of ore by building draw-points at different elevations, starting from the outside of the deposits and working inwards as the lower levels are developed.

Based on the constraining shapes generated for resource constraining, two main blocks have been identified, the first to be extracted is a block for the San Javier breccia with bottom elevation 1,740 masl. A second block has been delimited in the Milagros breccia with bottom elevation 1,550 masl.

A review was carried out to assess the applicability of the possible mining methods, including caving and non-caving methods, to mine the Ojuelas deposit. Their applicability was scored using the University of British Columbia mining method selection matrix, or UBC method, to narrow down the potential methods that are appropriate given the characteristics of the orebody and country rocks.

Based on a selection matrix, Block Caving, Sublevel Caving and Cut and Fill mining methods were the top three methods identified, in that order. Due to the geometry of the Ojuelas orebody, applying a standalone block caving or sublevel caving method could negatively impact the economics of the project, therefore, a combination of inclined caving and block caving methods is proposed as one of the methods to be further evaluated in mining the Ojuelas deposit. The upper zone, which has a moderate dipping and thin mineralization zone, will be mined with the incline caving method, whereas the lower portion that has a flatter dipping and thicker mineralization will be mined with a block caving method. The mining will be done in a top-down fashion.

Inclined caving uses block caving principles with a truncated sub-level caving mining layout. The cave is initiated by undercutting the orebody at the inclined footwall area. The caving is advanced downward. The principles of gravity flows and draw interactions applied in block caving and sublevel caving are also applied in this mining method. Once all of the ore in the sublevels has been extracted, the block cave will be initiated at the bottom to remove the remainder of the reserve.

The installed plant capacity of the processing plant is 3,000 tpd for the crushing/grinding area.

The processing plant (Plant No. 1) consists of three-stage crushing and ball mill grinding circuits.

ROM material delivered from the mine is dumped into a steel-made coarse ore bin of 300 tonne capacity. The coarse ore bin is equipped with a steel rail grizzly in its upper part. The grizzly has openings of 12” x 12”; oversize material is reduced in size using a hydraulic hammer.

The coarse ore bin has a lower discharge chute that discharges into a vibrating feeder grizzly of 4” opening. The -12” + 4” material is fed into a 24” x 36” primary jaw crusher, and reduced to a minus 3” to 3-½”. This product is transported by a 30” wide belt conveyor to the two primary vibrating screens. These screens have only one sieve with an aperture of 3/8” x 3/8”. The lower discharge of the screens contains material from 80 to 90% minus 1/4” (6,350 µm).

The grinding section is comprised of two ball mill circuits: a recently installed Metso ball mill and the two ball mills previously used, which are currently maintained as back-up. Current grinding capacity is of 125 tpd. The dimensions and sizes of the equipment are:
- 12’ x 24’ Metso Mill (1800 HP)
- D-26” Krebs cyclones, and
- 10”x8” 250 HP Envirotech pumps
- two back-up ball mills 9-1/2’ x 11’ and 9’ x 12

The mill at the La Encantada cyanidation plant processes silver minerals through a leaching method producing doré bars. The installed plant capacity of the processing plant is 3,000 tpd for the crushing/grinding area, and 4,500 tpd for the cyanidation circuit.

The processing plant flowsheet consists of three-stage crushing, ball mill grinding, a leaching circuit, and a Merrill-Crowe system, followed by smelting of the precipitate and final tailings filtration.

The processing plant is divided into two parts: Plant No. 1 and Plant No. 2. Plant No. 1 is comprised of crushing and grinding circuits, while Plant No. 2 is comprised of leach tanks, countercurrent tanks (CCD), Merrill-Crowe section, smelting furnace, and tailings filtration.

The product of the grinding circuit (Plant No. 1) is pumped to the Plant No. 2 (8”X6” 200 HP Envirotech pump) and fed into the primary thickener.

The following reagent dosages are added to the process:
- Cya ........