The skarn zone at the El Limón deposit occurs at the stratigraphic level of the Cuautla Formation where marble is in contact with hornfelsed sedimentary rocks of the Mezcala Formation. Significant gold mineralization at El Limón is generally associated with the skarn, preferentially occurring in pyroxene-rich exoskarn but also hosted in garnet-rich endoskarn.

The El Limón Sur zone occurs approximately 1 km south of the main El Limón skarn deposit and appears to be an oxidized remnant of skarn emplaced at the contact between the intrusive and the host rocks represented by the marble and hornfels.

The Guajes skarn zone is developed in the same lithologies on the opposite side of the same intrusive present at El Limón. Marble (Morelos Formation) forms the footwall and a hornfels (Mezcala Formation) forms the hanging wall.

At the Guajes deposits the intrusion underlies the sedimentary rocks and the contact dips at about 30° to the west, sub-parallel to bedding.
At ELG Mine, gold occurs most often with early sulphide mineralization but also with late carbonate, quartz, and adularia. Native gold most commonly occurs in close association with bismuth and bismuth tellurides but also occurs with chalcopyrite and as inclusions in arsenopyrite. The dominant sulphides are pyrrhotite and pyrite with lesser but locally abundant amounts of chalcopyrite and arsenopyrite occurring in veinlets and open-space fillings.

The ELG Mine is being developed with standard open pit mining methods. Key characteristics of these deposits from an open pit mining perspective include very steep and irregular terrain, proximity to the village of La Fundición located downhill from the El Limón deposit, relatively competent bedrock, and poorly defined ore-waste contacts.

Dozing requirements will be performed by a fleet of two 455 kW tracked bulldozers and three 335 kW tracked bulldozers. These units were acquired in 2013 and 2014, since they were needed in the Guajes dozer pits at the start of pre-production development. After dozer pit mining is complete the units will be utilized in the truck-loader pits and on the waste dumps. Two 393 kW rubber-tired dozer units are included in the mine plan, to work principally on bench cleanup around the shovels, and on road maintenance.

The design basis for the ELG Process Plant is 14,000 tonnes per day at 90% mill availability. The ELG Process Plant has been in commercial operation since March 2016 and is currently operating at ~13,000 tpd. The current bottleneck in the ELG Process Plant is the grinding circuit, which is currently being optimized to balance the workload between the SAG Mill, Ball Mill and Pebble Crusher.

The basic process flow is crushing, grinding, agitation leaching, carbon adsorption, carbon acid and cold washes, carbon desorption (stripping), carbon regeneration, gold electrowinning, gold refining, tailing detoxification, tailing filtration and disposal. The ELG Process Plant designed for the ELG Mine Complex utilizes processes and equipment that is standard for the industry. In late 2016, the decision was made to add a SART plant to the process to alleviate operational issues caused by the presence of soluble copper in the ore. The SART plant is expected to be in full operation July of 2018.

The grinding circuit is decoupled from filtration of tailings. Ground pulp can be stored and leached into up to seven of existing eleven leach tanks. Normal operation only requires leaching in up to six tanks. As such, the grinding and leaching processes can continue for up to six hours while the filtration section is down for maintenance.

The following bullets summarize the process operations used to extract gold and silver from the ELG Mine Complex ore:

- Size reduction of the ore by a gyratory crusher, wet semi-autogenous grinding mill (SAG), and ball milling to liberate gold and silver minerals. A “pebble” crusher is operated in this circuit to deal with reject pebbles from the SAG mill.

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

- Cyanide leaching of the slurry in agitated leach tanks.

- Adsorption of precious metals onto activated CIP technology.

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

- Recovery of precious metal by electrowinning.

- Mixing electro-won 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.

- Removal of copper from a portion of the cyanide recovery thickener overflow using the SART process.

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

- Filtering of detoxified tailings to recover water for recycling back to the process.

- Disposal of the filtered detoxified tailings to a FTSF.

- Storage, preparation, and distribution of reagents used in the process. Reagents that require storage and distribution include: sodium cyanide, caustic soda, sodium hydrosulphide, diatomaceous earth, sulphuric acid, flocculant, copper sulphate, sodium metabisulphite, ammonium metabisulphite (MT2000), hydrochloric acid, and lime.