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).

Underground mining
At Zgounder the mineralized zones are generally vertical with irregular shapes and scattered mineralization. The cut and fill mining method is now used for exploitation and this method is considered ideal for steeply dipping high grade deposits. This mining method is also highly selective where high grade sections can be mined separately from the low grade rock that will be left in the stopes.

Cut and fill mining excavates the mineralized material in horizontal slices, starting from a bottom undercut advancing upward. The material is drilled, blasted, loaded and removed from the stope which is then backfilled with waste rock. The fill serves both to support stope walls and as a working platform when mining the next slice. Backfill selection is dependent on the quality of the host rock and the size of equipment working on top of the backfill.

Since the mine has previously been in production, few new developments are required above 2000m. The total required additional development required is estimated at 20% of mineralized material tonnage with an estimated average of 3.0 linear meters per working day. Provision in the capex sustaining capital for an average of around 6.0 linear meters per working day, including the ramp (3.4m x 4m section), for a total of 4,691 meters for the major access and a 315m internal shaft for the life of the mining operation (LOM).

The intent of Maya is to stepwise increase the Zgounder mill feed rate from +/- 200 tonnes per day to 2,000 tonnes per day.

First step is to increase the mill feed rate to 500 tpd (2018 -2020).

Second step is to increase the mill feed rate to 2,000 tpd (2020 -2027).

The 500 tpd process plant designed to recover the silver by a gravity-flotation process followed by the cyanide leaching of the gravity and the flotation concentrates will comprise two different entities.vThe upper mill (located at higher elevation), designed by Yantai Xinhai Mining Research & Design Co., Ltd. (Xinhai), which will be located some 1,5 km from the actual mill (actually under construction at the moment of writing this report) will incorporate the following sections : run of mine ore storage, a three stage crushing plant, two 500 tonne fine ore bins, a two stage grinding bay integrating gravity, a flotation section followed by gravity and flotation concentrates thickening and regrinding spaces.

The lower mill (actual Zgounder mill), except for the removal of the two small ball mils and the change of the present clarifier by 4 filter-presses will essentially remain the same as it is now. The “lower” mill will be fed by gravity from the gravity-flotation concentrates (cyclones O/F) coming from the “upper” mill.

Material coming from underground grading approximatively 300 g/t will be hauled from the mine by off the road haul trucks and when possible will dump directly into the out of mine crusher feed hopper. However, because the mining and crushing operations will not always be on the same time schedule, it is assumed that 25% of the time the haul trucks will proceed to a RoM stock pile and the rest of the time will dump directly into the crusher feed hopper. Secondary handling of the mineralized material will be by a front-end loader that will, among other things, be used to feed the crusher hopper with the stockpiled RoM mineralized material as necessary.

The new “upper” mill is designed for a 500 tpd operation. From the fine ore bins, mineralized material will be conveyed to a primary ball mill. The ball mill will discharge on a sawtooth wave jig followed by a shaking table. Gravity tailings will report to a spiral classifier. Coarse particles from the classifier will discharge directly into the ball mill feed chute while fine particles will be cycloned. Cyclones underflow will be reground in a secondary ball mill while cyclones overflow will flow by gravity to a reagents conditioner before flowing to the flotation rougher. Gravity concentrate having a weight of approximately 0.65% of the mill feed rate will be pumped directly to a thickener before being reground.

Flotation will comprise one rougher followed by one scavenger. Rougher concentrate along with the table concentrate will be pumped to a thickener prior being reground. Rougher tailings will be scavenged. Scavenger concentrate will be pumped to same thickener as rougher and table concentrates while scavenger tailings will be pumped to the tailings pond.

Rougher, scavenger and table concentrates will all be pumped two a thickener. Thickener overflow will report to the used water tanks while thickener underflow will be filter- pressed, repulped, cycloned and reground prior to leaching.

The “upper mill” regrind cyclone overflow will report by gravity to the actual “lower” mill thickeners in parallel. From the thickeners, pulp will be pumped to the first cyanidation tank of its dedicated leaching circuit. Each circuit consists of four identical 5 metre in diameter x 3.3 metre in height leach tanks operating in series for a total of eight tanks.

Contingent to the flotation mass pull, leaching time should be between 33 and 48 hours.

Each circuit consists of five 12 meters in diameter counter-current decantation (CCD) thickener type tanks for a total of ten tanks. 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 tailings pond. The overflow solution from each of the first CCD tanks passes to the silver recovery section.

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

Main equipment consists of four filter-presses, a standard Crowe tank connected to a vacuum pump, a zinc cone dust feeder, two 1 m x 1 m filter presses, a pregnant and a barren solution tanks. The filter press sludge is dried, depleted from the remnant mercury in a static furnace and then smelted in a Wabi type furnace.