The Guanaceví silver-gold district comprises classic, high-grade silver-gold, epithermal vein deposits, characterized by low sulphidation mineralization and adularia-sericite alteration.

The Santa Cruz mine property, which forms part of the main portion of the Guanaceví Mines Project, covers about a 3.0 km strike length of the Santa Cruz fault/vein system. The Santa Cruz vein is similar in many respects to other veins in the Guanaceví district, except that it is the only one to lie on the west side of the horst of Guanaceví Formation and associated facies, and it dips west instead of east.

In the Porvenir Dos area and the Deep Santa Cruz mine workings, a low angle rhyolite crystal-lapilli tuff and andesitic contact occurs high in the hanging wall of the Santa Cruz vein indicating a fault contact with Guanaceví Formation, which obviously cuts the contact.

The Santa Cruz vein is a silver-rich structure with lesser amounts of gold, lead and zinc. Mineralization has averaged 500 g/t silver and 1 g/t gold over 3 m true width. The minerals encountered are argentiteacanthite, limited gold, galena, sphalerite, pyrite and manganese oxides. Gangue minerals noted are barite, rhodonite, rhodochrosite, calcite, fluorite and quartz.

Mineralization exhibits evidence of episodic hydrothermal events which generated finely banded textures. The higher grade mineralization in the district is commonly associated with multiple phases of banding and brecciation. The first phase, deposition of white quartz, white calcite and pyrite in stockwork structures, often exhibits horse-tail structures bifurcating both in the horizontal and vertical sense to form imbricate pods. The second phase deposited semi translucent quartz with argentite, scarce gold, and oxides of manganese (2%) and rare lead and zinc sulfide (4%), the latter particularly in the lower part of the hydrothermal system. The second phase was accompanied by the deposition of barite, thodonite, rhodochrosite, fluorite and calcite.

This second phase comprises multiple pulses of mineralization expressed in the vein structures as bands of massive, banded or brecciated quartz. Massive and massive-to-banded quartz are commonly associated with carbonate which is predominantly manganoan calcite and calcitic rhodochrosite. Rhodonite is much less abundant than carbonates but is not uncommon.

In the Porvenir Dos area and in the deeper portion of North Porvenir, a footwall-hosted vein lies in the footwall of the Santa Cruz vein structure. In both areas, this footwall vein is either within Guanaceví Formation footwall rocks or is at the structural contact between the Guanaceví Formation and the Lower Volcanic Sequence andesite. It is banded to brecciated quartz plus carbonate and contains local scatterings (<1%) of sulfides (pyrite>sphalerite>galena>chalcopyrite) and rare pods (<50 cm) of sulfides. At the north end of North Porvenir, the footwall vein attains a true width of over 7 m with silver grades of approximately 400 g/t in some areas. In Porvenir Dos, the footwall vein is narrower than the Santa Cruz vein and is overall a lower-grade vein, although one high grade intercept (uncapped) has been recorded in drillhole PD 36-3, at 2,548 g/t silver over 1.25 m.

Conventional cut and fill mining or by long hole stope methods are employed at Guanaceví. Cut and fill stopes are generally 15m long and 5 m high, and long hole stopes are 15m long and 20m high. Access to the stoping areas is provided by a series of primary and secondary ramps located in the footwall. The ramps have grades from minus 15% to plus 12%, with plus or minus 12% as standard. The cross-cuts are 4 m by 4 m for the primary ramps and 3.5 m by 3.5 m for the secondary ramps.

In the upper parts of the mine, stope access is by short (10m to 40m) cross-cuts from the ramp to the vein/stope. These cross-cuts are generally 3.5m by 3.5m in cross-section and are usually driven down at minus 18% to intersect with the stope. As the stope advances up-dip on the vein, the back is taken down in these cross-cuts to maintain access until the cross-cut reaches a maximum inclination of 15%.

In the lower parts of the mine (below the water table) stope access is by 90m long cross-cuts to the vein/stope. The cross-cuts are generally 3.0m by 3.5m in cross-section and are driven at plus 1% to intersect the stope (for water drainage). As the stope advances up-dip on the vein, the back is taken down in the cross-cuts to maintain access until the cross-cut reaches a maximum inclination of plus 15%.

Mining in the stopes is done with jackleg drills. Back cuts are taken 2m to 2.5m high via vertical up-hole drilling or by breasting. The broken material is mucked out using scooptrams (2 yard or 3.5 yard depending on vein width). Waste fill from mine development is placed in the stope by the same scooptrams to within 2 m to 2.5 m of the back. When the vein is less than minimum mining width, the footwall is slashed to provide adequate width. This slashing is done during the fill cycle and the slashed material remains in the stope as fill.

In 2013 there was a move to using long hole methods in the narrower parts of the mine. The long hole method increases production heights from typically 1.8m to up to 15m and at a reduced cost. Dilution and hanging wall failure is controlled using cemented 11m long fortifying cable bolts.Mining dilution has been estimated by EDR as variable with a minimum of 0.4m of over break dilution and a minimum operational width of 2.2m. Additional dilution is derived from the footwall especially in sill development, from occasional hanging wall failure and from re-mucking of floor fill. In general, dilution is estimated at being between 15% and 32%, while unrecoverable ore is estimated at approximately 5%. The dilution material in almost all cases is mineralized.

Sill development that have high-grade ore in the floor are candidates for installing a concrete pillar. The sill is filled with one meter of cemented rock fill when stoping begins which allows for recovery of the sill pillar. The cemented rock fill consists of development waste mixed with 5% by weight ordinary Portland cement which is placed over a 5mm steel welded mesh on the sill floor. The cemented rock fill is mixed in a muck bay adjacent to the stope by the same scooptrams that place it into the stope. The cemented rock fill is placed into the sill starting at the entrance so that the scooptram is driving on top of the fresh fill to provide compaction. This method works well and is common in Mexico.

Crushing: ore bins, conventional crushing with a 30"x42" jaw crusher, 24”x36” jaw crusher, a 4-foot secondary cone and 3-foot tertiary cone crushers, a 5’x10’ vibrating screen (-½” to -5/8”).

Grinding: 5 ball mills, a 10.5’x12’ Hardinge, two 7’x7.5’ Denver, a 5’x 6’ Fimsa ball mill and an Allis-Chalmers 5’x4’.

The primary crushing circuit consist of the following process. Trucks loaded with ore from the mine arrive at the plant and are first weighed at the truck scale to keep track of the ore tonnage entering the plant. The trucks then dump the ore into the feed hopper of the primary crusher. The primary crusher is a jaw crusher with a capacity to process 400 tons per hour and crushes the material to 4". The ore is stacked by a conveyor stacker in the patio area of the primary crusher. Material is then transported by truck to the coarse ore bins at the front end of the tertiary crushing stage.

The tertiary crushing circuit consist of the following process. Material from the coarse ore bins is fed by apron feeder to the conveyor belts carrying the mineral to a screen for classification by size. The fine ore, - 1/2", is fed directly to the fine ore bins. The mineral that does not pass the screen size is sent to the tertiary crushers. During 2015 the area was remodeled to increase production capacity. The upgrades include:
• Symons 4’ crusher. Receives the larger mineral 4" or less.
• Telsmith 4’ crusher. Receives material larger than 4". This also has the option of receiving a little finer product, 1½" or finer.
• Telsmith 3’ crusher. Receives smaller fragments, 1" to ½".
• New FL Smith 20' x 6’ screen.

The tertiary crushing circuit is a closed circuit meaning that the ore will be returned to the crushers as many imes as necessary until it is reduced to a size of -1/2". The final crushed material is stored in the fine ore bins to await further processing.

The Guanaceví processing plant consists of the following circuits:

- Cyanidation and counter-current decantation (CCD) circuit: 16 leach tanks in two series (12 tanks of 20’x20’ and 4 tanks of 30’x30’).

- Merrill-Crowe circuit with 2 leaf clarifiers and one de-aeration tower.

- Refinery: two gas fired furnaces.

- Filtration: two filter presses, each with 131 plates of size 2,000x2,000 mm.

- Filters for dry tailings, and final disposal of dry tails.

Material from the fine ore bins (material -1/2") is transported to the mills through conveyors. Sodium cyanide in solution is added to begin the extraction kinetics of the silver and gold particles. Inside the ball mills the direct impact from the steel balls and the abrasive grinding of the steel balls on the ore combined with the action of the cyanide solution begin to leach the silver and gold from the ore.

Pulp leaving the mills has a 70-75% solid density, this ........