The Zgounder deposit is described as a Neoproterozoic, epithermal, hypogene and is resulted from distinct stages of fluid circulation associated with two major events of mineral deposition (Essaraj et al., 1998):

- The first stage was characterized by the deposition of quartz with minor biotite and AsCo minerals with a variety of H2O-CO2-CH4-rich fluids equilibrated with metasediments. These fluids were maintained at high temperatures (around 400-450°C) over a wide range of pressures during the early brittle deformation of the Brown Formation after the emplacement of the Askaoun granite.
- The second stage corresponds to the major (Cu-Zn)-Ag (Hg) mineralization deposition and clearly postdates the As-Fe mineralization. Silver deposition occurs after the crystallization of quartz-sphalerite-chalcopyrite veins, but both Cu-Zn and Ag(Hg) mineralized-bearing fluids are NaCl-CaCl2 brines trapped under minimum temperatures of around 160°-200°C.

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 (sandstone), predominantly 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. Though preferentially at the contact zones between schist and dolerite, (Petruk, 1975; Popov et al., 1989). Native silver is observed in complex sets of microfractures, mainly at intersections with sulphide veinlets (Figure 26) 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 shale-sandstone 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).

Two successive stages of Zgounder paragenetic sequence were discussed by Marcoux and Wadjinny (2005): An early Fe-As stage (silver-bearing pyrite and arsenopyrite), followed by an Ag-bearing polymetallic (Zn, Pb, Cu, Hg; sphalerite and chalcopyrite) event. The late polymetallic event involved the formation of two generations of sphalerite with Fe-poor and Fe-rich components devoid of silver. Native silver is by far the most common form, representing 65 up to 90% of the total amount of silver at Zgounder. The silver mineralization consists of an Ag-Hg amalgam in the shape of 25 to 480 µm blebs (average 150 to 250 µm). Marcoux and Wadjinny (2005), revealed the presence of two generations of silver amalgam: large Ag-rich patches (85–95 wt% Ag, Ag17Hg) presumably corresponding to remobilized mineralization, and “normal” blebs containing 72 to 80 wt% Ag (Ag5Hg; close to eugenite), which represent the majority of the native silver deposit at Zgounder. Acanthite (Ag2S) is the major silver sulphide but far less abundant than native silver and often includes several micropatches of native silver.

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).

500 tpd process plant

Crushing
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 jaw crusher hopper will discharge on a middle-duty plate feeder which in turn will feed the primary jaw crusher. From the jaw crusher the mineralised material will be conveyed to a double deck vibrating screen in close circuit with a cone crusher. Top screen oversize falls by gravity into a smaller jaw crusher. The product of this crusher is mixed with the oversize of the bottom deck and are being conveyed to the cone crusher. Screen undersize is conveyed to two 500 tonne live load fine ore bins in parallel. Each fine ore bin has four apertures at the bottom discharging on a dedicated conveyor. Before entering the mill, the material is weighed with weight meters installed on each of the conveyors feeding the primary ball mill.

All in all, crushing capacity is approximately 100 tonnes per hour.

Grinding
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.

2,000 tpd process plant
For the 2,000 tonnes per day operation (2020 – 2027), ZMSM will need a complete new mill.

Crushing
A grizzly will scalp the oversize rock from both the underground and open pit mineralized material. The oversize will be broken in place with a pneumatic stationary rock breaker. Grizzly undersize falls into a hopper which in turn feeds an apron feeder. The apron feeder discharge on a series of belt conveyors which in turn discharge on an incline vibrating bar scalper. Bar scalper oversize falls by gravity into a jaw crusher while the undersize, the crushed ore and the fines from the apron feeder is ultimately conveyed to the fine ore bins. All in all, crushing capacity will be around 400 tonnes per hour to be in operation only one 8-hour shift per day.

Grinding
The fine material bins will discharge, via 2 apron feeders, on a set of belt conveyors feeding a grate discharge SAG mill in close circuit with a one deck vibrating screen. Circulating load ought to be in the order of 20% of the fresh incoming feed to the SAG mill. Screen oversize will be conveyed back to the SAG mill feed chute while the undersize will flow by gravity to two ball mills in parallel discharge pump box.

The two ball mills discharge, coupled to the SAG screen undersize is pumped to a set of Kreb type cyclones.

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).

500 tpd process plant
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 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 ........