The Zgounder deposit is described as a Neoproterozoic, epithermal, hypogene system and shares common characteristics (e.g. Age, Ag-Hg mineralization and epithermal-type model) with the giant Imiter deposit (Marcoux and Wadjinny, 2005).

The origin of the Zgounder silver mineralization are thus Na-Ca brines and the main driving mechanisms for silver deposition are associated with the dilution and cooling process (Essaraj et al., 1998).

The silver mineralization occurs at the top of the Brown Formation (sandstones) mainly along the contact and within the dolerite sill. The economic silver concentrations at Zgounder are present mainly as vertical columns, complex clusters, shear zones, veinlets and at the intersection of the E-W and N-S fractures, preferentially at the contact zone between schist and dolerite, (Petruk, 1975; Popov et al., 1989).

Within the bodies, mineralization occurs in millimetric beds, pyritized, as well as veinlets filled by quartz cement and sulphides. Native silver is observed in complex sets of microfractures, mainly at intersections with sulphide veinlets and locally accompanied by a chlorite rich alteration. Small Ag grains (average size of 50 µm) are also found in corrosion zones of early sulphides or disseminated within the schist and dolerite. Tension gashes originally trapped the silver mineralization within a NNE-oriented shear zone affecting the shalesandstone beds (Brown Formation) that contain anomalous Ag values. The silver was then likely remobilized by EW-oriented structures forming isolated Ag-mineralized lenses and fissures. The silver mineralization extends laterally over 1,000 m with a subvertival dip to the south. The vertical extension of the body is offset by sub-horizontal faults with a northward movement of 10 to 30 m, pushing the mineralized zones in steps or blocks (Bounajma, 2002).

It is first recommended to resume mining with open stopes, relying on sublevels long-hole mining for small to medium size stopes. Backfilling shall be provided for larger stopes and those with of mechanical unstable rock conditions, or stopes having dimensions above safe theoretical recommendations, where the Avoca mining method is recommended by SGS Geostat.

The highly regarded Avoca mining method should be implemented if unstable rock conditions are encountered. This method is similar to the open long-hole method, however backfill is used during or after each horizontal lift to minimize dilution and reinforce stope stability. The most economical fill is the waste material resulting from mine developments.

The processing plant is designed to recover the silver by direct cyanidation. The mill will incorporate the following sections: run-of-mine storage, a two-stage crushing plant, crushed storage, single-stage ball milling with cyclone classification, leaching (cyanidation), zinc cementation (Merrill Crowe), refining, tailings, water and reagents distribution. At the start of the operation the mill will not be connected to a central Program Logic Controller (PLC). The mill process will be conventional with operation relying on operators’ experience and skill supported by individual mill control devices: conveyor scales, pH meters, automatic samplers, flow meters, AA analyzer, colorimetric determination of silver with rhodanine, etc.

Material grading approximately 317 g/t Ag is hauled from underground by haul trucks and when possible, it is dumped directly on a 300 x 300 mm static grizzly above the crusher feed hopper. Due to the inconsistent schedules for mining and crushing operations, it is assumed that the haul trucks will transport 25% of the loads to a RoM stock pile; the rest will be dumped directly onto the grizzly. The RoM stockpile area is sized to hold approximately 2,000 tonnes. Secondary handling will be performed by a 958 Caterpillar front end loader (or equivalent) that will, among other things, be used to feed the crusher hopper with stockpiled RoM as necessary.

A large portion of the material will be coarser than the grizzly aperture, a result of the long-hole mining method. The oversized rock will be broken in place with a stationary hydraulic rock breaker. Material falls from the grizzly into an out-of-mine hopper having a volume of 10 m3 . The hopper feeds an 800 mm x 600 mm jaw crusher using a vibrating feeder. From the jaw crusher, the material falls on a 650 mm conveyor belt feeding a 100 tonne coarse bin. From the coarse bin, it is conveyed to a 6.0 m2 double deck screened-in closed circuit with a 3 foot Symons short head cone crusher. Undersize screen material (10 mm) is conveyed to two 5200 mm x 6000 mm (~170 tonnes live load) bins in parallel. Each bin has a dedicated feeder at the bottom. Before entering the mill, the material is weighed with weightometers installed on each of the conveyors feeding the ball mills.

Presently, each of the fine bins feeds an approximately 3 m long x 1.70 m diameter ball mill located in a small, covered building. Each ball mill has two discharge pumps, one in operation and one standby. Each pump pumps mill discharge slurry at approximately 70% solid to a 10” Krebs type cyclone. Each cyclone underflow returns to its dedicated ball mill while the cyclone overflow of 40% solid and P80 = ~75 µm fineness proceeds to the leaching section (bypassing the unnecessary thickeners) with an identical circuit for each mill. Circulating load is deemed to be in the range of 300%.

Each cyclone at approximately 40% solids overflows by gravity to the first cyanidation tank of its dedicated leaching circuit. Each circuit consists of four identical 5 metres in diameter by 3.3 metres in height leach tanks operating in series for a total of eight tanks.

Each circuit consists of five, 12 meters in diameter counter-current decantation (CCD) thickener type tanks, totalling ten. The overflow solution from each tank is enriched by being pumped up to the preceding one while the underflow (slurry) is depleted from its silver content by being pumped down to the next tank. The tailings pump boxes and pumps are installed to pump the tailings slurry from both the final CCD tanks to the cyanide destruction circuit. The overflow solution from each of the first CCD tanks passes to the silver recovery section (Drawing 2014 – 09).

The silver recovery section is housed in a secure, covered building and is common to both mill circuits. It incorporates the Merrill Crowe process for the recovery of silver using zinc dust cementation.

Main equipment consists of a 20-leaf clarifier, a standard Crowe tank connected to a vacuum pump, a zinc cone dust feeder, two 1 m x 1 m filter presses, a loaded and a barren solution tank.

The filter press sludge is dried, depleted from the remnant mercury in a static oven, and then smelted in a Wabi type furnace.