The Project is situated within the Mesozoic carbonate-rich Morelos Platform, which has, in the Project area, been intruded by Palaeocene granodiorite stocks. Sedimentary rocks within the Morelos Platform include basal crystalline limestone and dolomite of the Morelos Formation, silty limestone and sandstone of the Cuautla Formation and upper platformal to flysch-like successions of intercalated sandstones, siltstones and lesser shales of the Mezcala Formation.

The Media Luna area is characterized by a structurally complex sequence of Morelos Formation (marble and limestone) and Mezcala Formation (shale and sandstone) intruded by the El Limon granodiorite stock. The contact between the Morelos Formation and the El Limon granodiorite stock is exposed in the northeastern sector of the area and Mezcala Formation sediments are present in the southern portion of the area. Morelos Formation limestone is typically converted to grey to white marble along dike and sill contacts, often accompanied by clay and iron-oxide. The Mezcala Formation is locally converted to biotite–hornfels where cut by dikes and sills.

Hydrothermal alteration at Media Luna is dominated by prograde and retrograde skarn formation. Prograde skarn alteration can also be described as exoskarn and endoskarn where it is developed in sedimentary wall rocks and intrusive rocks respectively. Exoskarn typically consists of massive coarse to fine-grained pyroxene and garnet. The contact between exoskarn and marble is typically sharp. Endoskarn alteration closest to the contact with exoskarn-altered rocks is typically massive garnet-pyroxene. Massive skarn quickly grades to garnet–pyroxene veins and veinlets with garnet cores and pyroxene halos. There is a clear association of gold, copper and other metals with retrograde chlorite/phlogopite, calcite ± quartz ± epidote alteration of the skarns. Intrusions show evidence of potassic and argillic alteration.

Mineralization identified within the Project is typical of intrusion-related gold and gold- copper skarn deposits.

Based on a review of the geology and shape of the Media Luna resource along with a high level geotechnical review, LHOS was selected as the main mining method. In areas where the resource is narrow, C&F stoping is utilized.

Preliminary mining stope shapes were estimated using CAE’s Minable Shape Optimizer (MSO). The range of stope dimensions evaluated were first constrained by geotechnical parameters and maximum allowable hydraulic radii followed by an economic evaluation. This work resulted in the selection of LHOS nominal stope size of 25m high by 20m wide by 30m long. Development was planned to provide access using sublevels at 25 m spacing (elevation). C&F stopes were design in areas where LHOS could not be used. Based on the conceptual mine plan, LHOS would contribute approximately 66% of the total production with the remaining 34% being C&F.

LHOS would be the primary mining method employed. This method was selected based on its lower operating cost, high productive capacity, and flexibility relative to other mining methods. Mining has been planned from the bottom up using a primary-secondary mining sequence. This design and sequencing allows for a number of stopes to be in production simultaneously which supports the planned production rate of 7,000 tonnes per day.

In narrow sections of the deposit (less than 7 m wide) overhand C&F method would be utilized without pillars as shown in Figure 24-17. In areas with mineralization greater than 7 meters in width, the Post Pillar Cut and Fill (PPC&F) mining method would be utilized. . Pillar dimensions are 4 meters by 4 meters with a span between pillars of 5 meters.

The concept that had the most impact on the design and outcomes of the ML Project was the decision to process the Media Luna mineralized material through the processing plant built for the ELG Mine versus building of a stand-alone processing plant.

The design basis for the processing facility is 14,000 tonnes per day or 5,040,000 tonnes per year at 90% mill availability. This section presents the process design criteria that will govern the design of the processing facility (mill) including crushing, grinding, agitation leaching, carbon adsorption, carbon desorption (stripping), carbon regeneration, gold electrowinning, gold refining, tailing detoxification, tailing filtration and disposal. The process plant designed for the ELG Mine utilizes processes and equipment which are standard for the industry. This includes cyanide leach followed by carbon-in-pulp recovery, and utilizing filtered tailing for disposal.

-Size reduction of the ore by a gyratory crusher, wet semi-autogenous grinding mill (SAG), and ball milling to liberate gold and silver minerals.

-Thickening of ground slurry to recycle water to the grinding circuit.

-Recovery of precious metals contained in the recycle water by carbon columns (CIC).

-Cyanide leaching of the slurry in agitated leach tanks.

-Adsorption of precious metals onto activated carbon by carbon-in-pulp (CIP) technology.

-Removal of the loaded carbon from the CIP and CIC circuits and further treatment by acid washing, stripping with hot caustic-cyanide solution, and thermal reactivation of stripped carbon.

-Recovery of precious metal by electrowinning.

-Mixing electrowon sludge with fluxes and melting the mixture to produce a gold-silver doré bar which is the final product of the ore processing facility.

-Thickening of CIP tailings to recycle water to the process.

-Detoxification of residual cyanide in the tails stream using the SO2/Air process.

-Filtering of detoxified tailings to recover water to recycle to the process.

-Disposal of the filtered detoxified tailings to a dry stack tailings pad.

-The water from filtrate solution pond is recycled for reuse in the process. Water stream types include: process water, fresh water and potable water.

-Storage, preparation, and distribution of reagents to be used in the process. Reagents which require storage and distribution include: sodium cyanide, caustic soda, flocculant, copper sulphate, sodium metabisulphite, hydrochloric acid, and lime.