Vein deposits at La Guitarra have physiochemical and mineralogical characteristics of the Intermediate Sulphidation epithermal type and fit thevein deposit model proposed by Buchanan(1981). Epithermal deposits form atshallow depths in volcanic-hydrothermal and geothermal environments. They define a spectrum with two end members, low and high sulfidation (Hedenquist et al., 1998). Intermediate Sulphidation epithermal deposits form part of the epithermal spectrum and their genesis is complex due to the involvement of fluids with meteoric or magmatic origin during their formation and to the fluid evolution.

There are in excess of one hundred epithermal veins within the property in five main vein systems: Comales–Nazareno, Coloso (Jessica and Joya Larga veins), La Guitarra (NW, Central and SE zones), Mina de Agua and El Rincón. The vein systems at La Guitarra property form a belt with an approximate width of 4 km that strikes NW – SE in excess of 15 km. Individual veins pinch and swell and vary in width from tens of centimetres to more than twenty metres. Economic zones, widths usually between 1 and 4 metres, are embedded in quartz (vein structure) having widths up to 20 metres (e.g. Guitarra vein). The ore shoots or economic zones can either be localized in the hanging wall or the foot wall of the vein structure.

Gangue mineralogy consists of banded quartz, amethyst quartz, colloform chalcedony, finegrained crystalline quartz, calcite, fluorite, pyrite, mar ........

The La Guitarra Silver Mine comprises two operating mines, La Guitarra and Coloso, and three past producing areas, the Nazareno, Mina de Agua and El Rincón, which are now considered as exploration areas.

Given the narrow vein conditions, mining in La Guitarra Silver Mine is undertaken using primarily the conventional overhand cut-and-fill mining method, with limited application of longhole stoping in areas where the vein is found with thickness of 3 or more metres in width.

The cut-and-fill stoping cycle is started with blast holes drilled using hand held jackleg drills followed by blasting using conventional mining explosives. After blasting, LHD’s are used to muck the blasted ore. The cut and fill stopes are generally 100 m in length along strike and extend between levels which are typically spaced 15 to 30 m apart vertically. Each cut is 2.5 to 3.0 m in height. Depending on ground conditions, the blast holes are drilled either upward or horizontally. Waste and mineralized material below cut-off grade is blasted down and used as backfill as needed.

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