The San Sebastián del Oeste area, including the Terronera Project, is underlain by an intermediate to felsic volcanic and volcaniclastic sequence correlated with the middle to lower Cretaceous Lower Volcanic Group of the Sierra Madre Occidental geological province. This volcano-sedimentary sequence consists of shale, sandstone, and narrow calcareous-clayey interbeds overlain by tuffs, volcanic breccias, and lava flows of mainly andesitic composition. The volcano-sedimentary units crop out in the north-central part of the district. Further to the north, granitic to granodioritic intrusive rocks are present.

In the San Sebastián del Oeste district, silver and gold mineralization represents the upper portion of an epithermal vein system. Illite, sericite, and adularia are characteristic alteration assemblages that typically occur in the veins and in the vein wall rocks. In higher elevation
areas, where limited mining (colonial-era artisanal mining), has occurred, such as the El Hundido and Real de Oxtotipan mines, the quartz is amorphous and milky white, indicative of a low-temperature environment.

The epithermal veins' silver-gold ± base metal mineralization is hosted in structurally controlled quartz and quartz breccia veins. The principal Terronera Vein has been traced by drilling for 1.5 km on strike and from the surface to the maximum depth of drilling at 546 m. The Terronera Vein strikes at approximately 145° and dips 80° east. The actual width o ........

The Terronera mine will be accessed via three declines developed from the surface. An internal decline will be used to access the La Luz deposit. The declines are designed at approximately 15% grade and will be developed as single face headings. The declines will collar on separate portals located at the process plant, the mine dry, and a temporary access portal at the upper level of the Terronera deposit. The dual decline will incorporate re-muck/sump and re-muck/electrical substation cut-outs on a nominal 159 m spacing. Passing bays are not included in the ramp design as the design supports using a dedicated decline for material transport to the surface, reducing the potential traffic interferences from routine operations.

Approximately 59% of the Terronera deposit will be mined using transverse and longitudinal SLS.

Transverse SLS is a high productivity and lower-cost mining method compared with CAF or drift-and-fill methods. The stope dimensions will be a maximum of 20 m high x 15 m wide x 15 m long and a minimum mining width of 8 m. The stopes will be mined in a bottom-up sequence and in a primary then secondary sequence laterally. Primary stopes will be backfilled with cemented rockfill. Secondary stopes will be filled with uncemented rockfill.

In areas where the ore is less than 8 m thick across strike, longitudinal SLS will be employed. Stopes will be mined in a bottom-up sequence. After the top and bottom cuts are established, the st ........

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