The Escobal deposit formed in an intermediate-sulfidation epithermal quartz vein system of probable Upper Miocene to Lower Pliocene age. These deposits are commonly included in the low-sulfidation epithermal class of deposits. Distinguishing characteristics of an “intermediate sulfidation” environment include mineral assemblages indicating a sulfidation state between those of high and low sulfidation types, relatively high total sulfide content of 5 to 10 percent, low-iron “blond” sphalerite, presence of silver sulfosalts, and association with andesitic to dacitic volcanics. Magmatic- associated fluids are implied.

Epithermal deposits form as high-temperature mineralizing fluids rise along structural pathways and deposit quartz and precious- and base-metal minerals in open spaces in response to boiling, which is usually coincident to a release of pressure within the hydrothermal system. This quartz and metal deposition, followed by resealing of the system, is repeated over the life of the hydrothermal system resulting in crosscutting and overprinted breccia and vein textures. Typically, the largest and highest grade deposits are associated with long hydrothermal systems marked by complex overlapping veins.

These deposits are strongly structurally controlled. Mineralizing fluids are directed along structural pathways with high- grade “ore shoots” typically concentrated in open dilatant zones. These dilatant zones commonly form where inflections oc ........

Active mining areas in the Escobal mine are accessed through two main portals, called the East and West portals. These two primary declines provide access to the Central Zone. A third primary ramp is being driven into the East Zone from the Central Zone. Access ramps are driven from the main ramp system to establish sublevel footwall laterals driven parallel to the vein in transverse mining areas on 25 m vertical intervals, with stopes accessed from the footwall laterals. In longitudinal mining area, development is done on vein also on 25 m vertical intervals.

Production from the Escobal mine is achieved via longhole stoping methods. Two variations of this mining method are utilized. Where the vein dimension across the strike is less than 15 m, longitudinal longhole stoping is applied. This method consists of driving horizontal drifts, spaced 25 m vertically, along the strike of the vein and then blasting the ore vertically from the upper level (“over-cut”) to the lower level (“under-cut”).

Breaking slots are established at the extreme ends of the stope to provide a void space for production blasting. These breaking slots are excavated utilizing Cubex drills equipped with V-30 blind bore reaming heads to bore a 30-inch diameter raise between the upper-cut and under cut for each stope. Once the breaking slots are complete, the stope faces retreat towards the accesses by drilling holes between the over-cut and under-cut, charging the holes with explo ........

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