The Caylloma polymetallic and silver-gold rich veins are characteristic of a typical low sulfidation epithermal deposit according to the classification of Corbett (2002) having formed in a relatively low temperature, shallow crustal environment. The epithermal veins in the Caylloma District are characterized by minerals such as pyrite, sphalerite, galena, chalcopyrite, marcasite, native gold, stibnite, argentopyrite, and various silver sulfosalts (tetrahedrite, polybasite, pyrargyrite, stephanite, stromeyerite, jalpite, miargyrite and bournonite). These are accompanied by gangue minerals such as quartz, rhodonite, rhodochrosite, johannsenite (Mn-pyroxene) and calcite.

Veins in the Caylloma District show structural patterns and controls typical of other vein systems hosted by Tertiary volcanic rocks in the western Peruvian Andean range. The Caylloma District vein system was developed as a set of dilatational structures as a consequence of tension generated during the main compressional event of the Andes. Veins are persistent along strike and dip. Locally, veins are displaced by post-mineral faulting along a north-northwest bearing. Horizontal displacement along these faults is minor and ranges from centimeters up to a few meters. No significant vertical displacement is observed on the structures. The vein system is not affected by any folding.

Three types of hydrothermal alteration have been identified at the Caylloma Mine: (1) quartz- adularia; (2) ........

The mining method applied in the exploitation of the main vein (Animas) is overhand cut-and-fill using either mechanized, semi-mechanized or conventional extraction methods. All mining is undertaken by contractors in a southwest to northeast direction following the strike of the vein. Production capacity at the mine is 1,500 tpd. The following describes the cut-and-fill mechanized, semi-mechanized, and conventional extraction methods.

Mechanized cut-and-fill
Mechanized mining uses a jumbo drill rig and scoop tram for loading. The ore haulage is performed by trucks. Rock support is applied through rock bolts and shotcrete. The average mining width ranges between 3.5 m and 17 m. Mechanized mining is regarded as only being suitable for the Animas, Animas NE and their associated splays, as well as the Nancy vein based on the geological structure and geotechnical studies. Mechanized cut-and-fill comprises 93 % of mining planned in the LOM.

The mechanized mining sequence includes: drilling (with a jumbo drill rig), blasting, support, loading (with a scoop tram) and haulage.

Semi-mechanized cut-and-fill
Semi-mechanized mining is performed using handheld drilling equipment (jacklegs) and scoops for loading. Ore haulage is performed by truck. Rock support is supplied using rock bolts installed using manual drilling and installation techniques. Semi-mechanized mining is applied to narrow veins with average widths between 0.8 m and 2.0 m.
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