According to Pearson and Speirs (2009), El Limón’s vein system is classified as a low sulphidation epithermal system. Gold mineralization in the Limón district is structurally controlled and forms veins that occupy pre-existing fault structures and extensional openings formed during mineralization. The veins are quartz dominant with lesser and variable quantities of calcite, and minor adularia. Pyrite is the predominant sulphide, but with a content of less than one percent. Trace amounts of chalcopyrite, sphalerite, arsenopyrite, altaite, gold tellurides, and native gold are also reported to occur. Gold is present in both banded quartz and silicified breccias that form the veins. Gold is very fine grained within the quartz vein and is relatively uniformly distributed throughout the higher grade parts of the veins. Only once has visible gold been reported on the Project concession. The productive vein systems are approximately one to two kilometres long, with vein widths from less than one metre up to 25 m. Individual mineralized shoots within the veins range from 60 m to 450 m long horizontally, and from 40 m to 290 m vertically. Strike orientations vary from north-northwest through northeast to east-west, and dips are from 40° to nearly vertical. All economic gold mineralization discovered and mined to date lies within 400 m of surface. The productive and prospective elevations within the vein systems vary across the district. Post-mineral faults locally disrupt and offset ........

The active El Limón mining units include Santa Pancha 1 UG, Panteón UG, Veta Nueva UG, and the Limón Central OP.

El Limón’s underground mines are trackless mechanized operations that have ramp access. The deposits being mined consist of narrow steeply dipping veins, and ore is mined with longitudinal sublevel stoping type mining methods. Santa Pancha 1 and Veta Nueva are producing mines, while Panteón is still at the development stage. Santa Pancha 1 is an old mine redeveloped as a trackless operation and has been in production since 2015. Panteón is a former producing mine that was idle for almost two decades until Calibre initiated a project to mine several of its remaining zones. Veta Nueva is a new mine that began producing ore in 2019.

The Limón Central OP is a conventional open pit mine with six metre bench heights, using drilling and blasting for rock breakage, and excavators and trucks for materials handling.

Underground Mining
El Limón has two underground mines, Santa Pancha 1 and Veta Nueva, that are in production and a third, Panteón, that is presently under development. All the underground mines are mechanized and use sublevel-stoping type mining methods.

Santa Pancha 1
The mining method applied at Santa Pancha 1 is uphole sublevel retreat stoping with no backfill. It involves dividing the vein into sublevels and mining the horizons of ore between veins as lifts in a topdown sequence. Longholes are drilled as u ........

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Water supply for exploration and operation activities is taken from three groundwater supply wells and six surface water withdrawal locations authorized by the National Water Authority (Autoridad Nacional del Agua [ANA]). The well located in the Santa Pancha site provides water for underground drilling. The two wells located in El Limón site are used for irrigation of the San José garden centre and for ore processing, respectively. Surface water withdrawal is used for exploration drilling, underground drilling, and ore processing.

Water from the TSF is reclaimed directly to the process plant. Two TSF barge pumps control the volume of supernatant water stored in the tailings pond. Seepage from the TSF is collected and either pumped back to the tailings pond or released to the environment if it meets water quality standards.