There are three main mineralized zones at Mount Pleasant, namely: the Fire Tower Zone, Saddle Zone and North Zone, from south to north. At depth, the Fire Tower and North Zones have been subdivided as shown in a schematic longitudinal section (Figure 15).

The Fire Tower Zone and North Zone deposits are located approximately 1.0 km apart and are mostly less than 400 m vertically from surface. The Fire Tower Zone contains predominantly large (low grade) tungsten-molybdenum deposits and was previously mined underground for tungsten. Some small indium-bearing tin-base metal zones are also present. The North Zone contains the most important indium-bearing, tin-base metal "resources" outlined to date along with some poorly defined low-grade tungsten-molybdenum bodies (ADEX 1995). The Saddle Zone, located approximately halfway between the Fire Tower Zone and the North Zone, contains tin and some base metals and newly discovered tungsten-molybdenum mineralization.

North Zone
The tin and porphyry tungsten-molybdenum deposits of the North Zone represent two different periods of mineralization even though they overlap spatially. Indium-bearing tin-base metal zones in the North Zone appear to be principally associated with sphalerite and are more concentrated in the Deep Tin zone (Figure 16). The principal metallic minerals in these deposits are cassiterite, arsenopyrite, lollingite, sphalerite and chalcopyrite with lesser amounts of stannite, pyrite, marcasi ........

An open stope concept with temporary rib pillars with no backfill is recommended as a primary mining method for the tin-indium-zinc deposits of the Deep Tin Zone and Upper Deep Tin Zone. The stope sizes and mining limits would be based on the resource block model interpretation.

Stope sizes would vary widely and would produce from several hundred tonnes to a few ten thousand tonnes of ore and would be relatively narrow. Each stope would have an extraction drift, which would be positioned in parallel to the undercut drift with a series of draw points connected with the undercut.

In a typical stope, rows of 62.5 mm diameter production drill holes arranged in fans would be up drilled from the undercut. On a sublevel above rows of 87.5 mm diameter holes would be down drilled to follow the configuration of the stope walls and would account for the bulk of production volume for a given stope. The undercut production holes would be charged with explosives and blasted in vertical slices starting from the end of the undercut and sequentially progressed towards the limit of the stope. In a delayed sequence, the down holes drilled on the sublevel above would be charged with explosives and progressively blasted to follow the stope undercut advancement.

Only partial blast swell would be removed from the stope to provide free space for each consecutive blast. The broken ore in the stope would provide temporary passive support for the stope walls in order ........

- subscription is required.