Mineral deposits at Del Toro occur in veins, chimneys, breccias and mantos. The deposits are associated with a quartz monzonite–granodiorite intrusion and are hosted by Cretaceous limestone and shale that has been altered to marble, hornfels, skarnoid and skarn.

Because of their spatial relation with intrusions and metamorphic/motasomatic rocks, the deposits are proposed to be of the intrusion-related hydrothermal type. Potassic alteration observed at depth in the San Juan mine suggests high-temperature alteration at depth. Although fluid inclusion- microthermometry studies have not been carried out for the Del Toro deposits, the association intrusions and skarn suggests they could be of the mesothermal to epithermal type. The occurrence of distal quartz– calcite veins containing fluorite in the Dolores mine is suggestive of an epithermal environment.

Mineralization to the south at San Nicolas and San Juan seems to be more mesothermal whereas the mineralization to the north in Dolores seems to be epithermal. No attempt was made to fit Del Toro deposits to the settings of the well-studied porphyries or epithermal deposits described by Sillitoe or Hedenquist elsewhere, since the geologic features observed suggest that Del Toro sits in between these end-member environments.

Mineral deposits at Del Toro occur in veins, chimneys, breccias and mantos. It is interpreted that some of the mineralization is skarn-related mesothermal in style, similar ........

Current production is sourced from three different underground mining areas (San Juan, Perseverancia, and Dolores).

In mineralisation that exhibits fair to good geotechnical conditions, Del Toro uses cut-and fill (resue) and shrinkage stoping. Both methods have been successfully employed and recover the mineralisation with limited ore loss and dilution, albeit at a low productivity. A recent trade-off study indicated that where mineralisation was greater than 1.0 m in width, longhole stoping with fill could be more productive and cost effective than the current methods. Overhand drift-and fill is planned for the Cuerpo 3 deposit.

Stope designs assumed:

• Dolores: a minimum mining width of 1.5 m was designed for longhole stopes and 1.0 m for cutand-fill zones; additional waste was included to meet the minimum mining width for access, therefore waste was designed and scheduled on either side of the mineralisation. Sills mined for longhole stoping areas were proposed to be 3.0 m wide, 4.0 m high, and suitable for modern drilling equipment. Production stopes were designed with a minimum width of 1.5 m and a vertical distance of 9.5 m. Stope panels were designed at 20 m long (9.5 m high). A ramp mined with an arched profile will be excavated to a width of 3.5 m and a height of 3.5 m, and will incorporate a minimum stand-off distance of 20 m to locate the ramp away from mineralisation. Planned development includes: access drifts, sills (development ........

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