The mineral deposits at Topia are adularia-sericite-type, silver-rich, polymetallic epithermal veins. Silver-gold-lead-zinc mineralization is found in fissure-filling veins along sub-parallel faults cutting andesitic flows, breccias, and pyroclastics. Deposits are usually characterized by multiple veins in areas measuring 10 to 15km2 with individual veins generally less than 2m in thickness but up to 3-4km in length.

Mineralization within the veins consists mainly of massive galena, sphalerite, with lesser pyrite, arsenopyrite, and tetrahedrite in a gangue of quartz, barite, and calcite. The vein constituents often include minor adularia and sericite, and the wider fault zones contain significant proportions of clay as both gouge and alteration products. Ore minerals occur as cavity-filling masses, comprising millimetre-scaled crystals of galena and sphalerite. Some observations on metal zoning include, the lower parts of the mines are reported to contain slightly higher copper-gold content than at higher elevations; high silver grades are associated with higher proportions of base metals; the mines are located over an extreme range of elevations (1,000 – 1,800masl) on the Property and that each has vertical limits of mineralization from 100-200m with the deeper seated and more southern mines tending to have more arsenopyrite and the more western mines having more pyrite.

The veins range in thickness from a few centimetres to two metres. They are very continuous along strike, with the main veins extending more than 4km. The Madre vein has been mined for 3.5km and the Cantarranas vein for 2.4km. Many of the other veins have been mined intermittently over similar strike lengths. Vertically, the veins grade downward to barren coarse-grained quartz-rich filling and upwards to barren cherty quartz-calcite-barite vein filling. The main host rock is andesite of the Lower Volcanic Series, which is usually competent, making for generally good ground conditions within the mine. In wider sections, with greater clay content and/or zones of structural complexity, ground conditions are less favourable.

For the narrower veins at Topia, mining is conducted by conventional cut and fill stoping with resuing to selectively mine the ore and leave the waste for backfill. Drilling is performed with jackleg drills and ore is hand mucked in the stope and dropped down timber crib muck passes which are carried upwards as the stoping advances. Ore is hand sorted at the face so that only the higher-grade ore is removed from the stope. Man-access and ventilation is provided in timber crib man-ways adjacent to the muck passes. The level interval for the stopes is typically 40m.

The use of ground support in the small tunnels and narrow stopes is infrequent as the small headings require little support.

From the muck passes the ore is pulled via manual chutes, loaded into small rail cars and hand trammed to a dump at the portal. At the surface ore dump, the ore may again be hand sorted to remove waste material. Waste from the hand sorting or from excess development is generally dumped over the bank of the hillside at these smaller mines. Ore is then picked up by front end loader and loaded into highwaystyle 10t- to 20t-capacity dump trucks to be hauled to the mill.

Along the Argentina and Don Benito veins, in the Argentina and 1522 Mines respectively, there are significant areas with vein widths of 0.5 to one metre. In these wider areas, mining is planned on the basis of mechanized cut and fill with resuing to selectively mine the ore and leave the waste for backfill. Equipment used includes small 2-yd3 LHD’s for development and 1-yd3 and 0.5-yd3 LHD’s for mucking in the stopes. Development access is provided via decline. Ground support consists of rock bolts and mesh as required. Rock bolts include a combination of cement-grouted rebar and split set which gives initial support from the split set bolt and then longer term support from the cement grouted portion of the bolt.

Sublevels are 40 metres apart in the mechanized cut and fill areas. Waste is generated from material beside the vein which is blasted separately from the ore and then left as fill, or from the waste development in the mine.

Lifts in the cut and fill stope are taken with horizontal holes (breasting) as the use of uppers drilling (to increase productivity and production) generated a ragged back in the stope and led to problems with ground support.

Ore is hauled from the stopes by LHD and then loaded into a truck for haulage to the mill.

The mill employs conventional crushing, grinding, and flotation to produce lead and zinc sulfide concentrates. The operation runs seven days a week, 24 hours per day, with Sunday day-shift reserved for maintenance.