The Bisie tin deposit is a cassiterite-bearing stock-work or vein system adjacent and possibly distal to underlying source granite. The mineralization at Bisie is unusual and different from other classic tin deposits. The deposit has up to 0.5 % rare earth elements (REE) and very high grade tin (with some sample assays reaching greater than 60 % Sn).

The deposit can be simply described as a number of steeply dipping tabular sheets of variable grade mineralization consisting of irregular veins and disseminations of cassiterite that is complex on a small scale.

On a regional scale the metamorphic rock units generally strike northwest-southeast. The ridge hosting the Bisie mineralization strikes north-south as far as the Oso River in the north, after which the strike of the ridge changes to the northwest-southeast. Regional scale folding is evident in the satellite imagery.

The stratigraphic rock package hosting the Bisie deposit has been divided into five separate units.
From hangingwall to footwall, a general description of the major units is as follows:

• Carbonaceous shale (CBSH) - dark grey to black, thinly bedded (0.5 cm to 2 cm), fine grained, carbonaceous siltstone-shale greater than 150 m true thickness. Contains abundant quartz-tourmaline-carbonate veins and minor pyrite.

• Meta-sediment (METS) - pale grey, thinly bedded (0.5 cm to 2 cm), fine-grained siltstone-shale 30 m to 40 m true thickness. The host rock has been moderately silica-magnetite altered. Magnetite occurs as either discrete bands (1 cm to 2 cm), pervasive, disseminated alteration or stock-work veins.

• Quartz-sericite schist (QSSH) - in drill core appears more like a feldspar-rich, polymictic tuff. Pale to dark grey-green, thinly bedded (~1 cm) to massive, medium grained (1 mm to 5 mm), feldspar-sericite rich tuff 80 m to 90 m true thickness.

• Mica schist (MSCH) - pale to dark grey, laminated to moderately banded (0.5 cm to 5 cm), fine grained mica-rich schist 100 m to 150 m true thickness. Intensity of dark and light coloured bands varies according to biotite-muscovite content.

• Amphibolite (AMPH) - the current interpretation is that this unit was originally a separate mafic-ultramafic unit hosted within the MSCH overprinted with intense chlorite-talc-garnet alteration; however this has not been confirmed. Dark green to black, moderately banded (1 cm to 5 cm) to massive, fine grained to porphyroblastic (garnet), chlorite schist 20 m to 30 m true thickness. Hosts the tin and base metal mineralization at Bisie.

The stratigraphic package dips east between 60° and 75° and appears to steepen down-dip and towards the east. The Mpama North ridge crest is more or less defined by the AMPH which probably resists erosion due to the massive, coherent nature of the rock and high chlorite content. The QSSH appears more susceptible to weathering and erosion due to its' high feldspar-sericite content. The base of complete oxidation (BOCO) is approximately 10 m along the ridge crest and approximately 50 m in the OSSH. Overall the BOCO averages 30 m.

The units most affected by alteration are the QSSH and MSCH particularly in the hangingwall of the tin mineralization:

• QSSH - contains areas where the original rock has undergone intense silica alteration (SILZ) and also intense sericite alteration of the original QSSH. To a lesser degree, QSSH is effected by biotite alteration and named biotite schist (BSCH). Where intensely chloritised the OSSH is termed amphibolite (AMPH)

• MSCH - is frequently termed BSCH where it comprises intense biotite alteration of the original MSCH is also referred to as amphibolite schist (ASCH) in places which usually occurs as a weak, chlorite alteration halo surrounding the AMPH.

As the alteration results in the same rock types in different parts of the stratigraphy, there appears to be an overlap between the MSCH and QSSH making the lithological boundary poorly defined in places.

Mineralization.
The bulk of the tin mineralization at Bisie is hosted within the north-south striking, east dipping amphibolite unit over 1 km to 3 km along the Mpama ridge, east of the granite intrusive. Mineralization is multi-phase and the paragenetic sequence appears similar in nature to the San Rafael deposit in Peru (Pearl, 2011; Alphamin Report, 2013).

Structural and mineralogical evidence from drill core indicates cassiterite was emplaced first, followed by copper mineralization in the form of chalcopyrite and bornite, then by lead and zinc mineralization occurring as sphalerite and galena. There is also evidence of late-stage quartz-chalcopyrite veining which cross-cuts the mineralization with veins trending north-northwest.

Chlorite alteration is widespread and appears to be the result of late stage fluids entering the system. The host rocks are predominantly highly chlorite-altered amphibolites and fine to medium grained, mica-chlorite-garnet schists. The tin and copper mineralization is predominantly found in zones dominated by intense chlorite alteration, however, cassiterite mineralization with no chlorite alteration has been intersected in the hangingwall and footwall vein zones hosted in MSCH.

The most common style of cassiterite mineralization observed in drill core comprises discrete, massive veins ranging from 2 mm to 1.80 m true thickness. Finely disseminated cassiterite is also present though less visible to the naked eye. High grade cassiterite chutes 20 m wide by 8 m thick have been historically mined by artisanal miners in the upper parts of the deposit, which most likely comprised a number of closely spaced vein sets.

The individual cassiterite veins are massive, pinkish brown, fine-grained and often botryoidal, and show compositional layering thought to be due to variations in iron content. This form of cassiterite has often been referred to as "wood tin".

The dominant structural control on mineralization is the north-south trending, brittle-ductile shear zone that runs more or less parallel to the cassiterite mineralized zones. It occurs predominantly as a single structure, with minor hangingwall and footwall splays particularly in the upper, more brittle parts of the structure. In the upper parts of the structure, above the 700RL, brittle fracturing has resulted in the development of up to four, lower grade vein systems whilst below the 700RL, ductile deformation has resulted in the development of a single, narrower, higher grade vein system.

Both tin mineralization and copper mineralization seems to be concentrated in two high grade chutes, referred to by Alphamin as the upper high grade chute and lower high grade chute. Mineralization between these two chutes is lower grade as these areas contain narrower, more widely spaced cassiterite veins. Both chutes run parallel to each other and plunge to the north at approximately 35°.

Most of the copper mineralization occurs in the form of blebs, lenses and veins, with the latter two being sub-parallel to foliation, and a late-stage quartz-chalcopyrite vein set trending northwest. In addition to the quartz veins, chalcopyrite also occurs with pyrite and to a lesser extent arsenopyrite. Chalcopyrite and bornite also occur as fracture fillings within the cassiterite. Higher grade copper intercepts usually occur adjacent to and overlapping the high grade tin intercepts, particularly with the lower high grade chute.

In contrast to Mpama North, lead-zinc mineralization is better developed at Mpama South. Most of the zinc mineralization is hosted within massive to semi-massive pyrite in the hangingwall of the cassiterite bearing zone coincident with minor lead and silver mineralization. Small quantities of zinc mineralization are also found together with the tin and copper mineralization. The degree of galena and sphalerite replacement of the pyrite appears to be structurally controlled with replacement along late stage structures.

Geological Considerations
The ore body dips at approximately 60° to 65° to the east and strikes close to North-South. The mineralized zone plunges approximately 25° towards the north. The mineralization is open in a northerly plunging direction and for a limited extent to the south. The strike of the payable zone ranges from 490m in the shallow areas to 150m in the deeper areas of the mine. The deposit remains open at depth.

The Mpama North orebody consists of a single mineralized zone of 5 to 10m wide. The Main Vein zone of the deposit, which accounts for approximately 97.5% of the Mineral Resource (by tin content), is on average approximately 9 m thick. It narrows (~2m) at the margins and can be up to 20 m thick in the central, and generally higher grade, area. The zones that occur several metres above and below the main zone are generally considerably narrower than the Main Vein zone and cover areas of between 100 m and 200 m in the dip and strike directions.

The orebody is accessed via a central decline and a series of levels and ore drives. A number of other ancillary excavations are also used either for access to or extraction and transportation of the ore. The dimensions of each of the excavations is driven by the selected mining method, access design, equipment selection and ventilation requirements.

Cut and fill mining was initially used at Mpama North. During this time the mine experienced difficulty in building up and maintaining the targeted production rate. In an effort to ease the bottleneck on production long hole stoping with waste backfill was trialled. This method proved very successful at Mpama North and the mine currently uses this mining method.

A description of the method as it is currently being implemented at Bisie i.e. the actual methodology is discussed herein.

The stoping blocks have been designed to include the full width of the ore body. Level waste drives or footwall drives are positioned along strike in the footwall of the orebody. Access to the levels is via the central decline or ramp, developed at minus 90 . Stope crosscuts are developed from the waste drive to the hangingwall contact of the orebody. Ore drives are then developed from the stope crosscuts, along strike (and parallel to the footwall drives).

All stoping takes place in a longitudinal formation, i.e. an ore drive is developed parallel to the strike direction of the orebody. The mining takes place in a bottom up sequence within an echelon. An echelon consists of four levels, three production levels and a top holing level at the top of the echelon, directly below the sill pillar. Sill pillars separate the echelons from each other.

Dip pillars, or rib pillars, are located along strike and will be spaced at distances ranging from 20m to 50m depending on geotechnical guidelines. The spacing of the rib pillars defines the stope length. The width of the rib pillars increases with depth and varies from 3.0 m to 6.5 m as specified in the geotechnical guidelines.

On average, a sill pillar thickness of 8 m every 59m vertically, will generate a 13.6 % pillar loss on dip. The rib pillars (3 m with spacing depending on geotechnical domain) will contribute from 6% to 13% to pillar loss.

The mine plan includes the mining of the sill pillars once an echelon is completely mined out. For sill pillar mining a mining recovery of 61 % is applied.

Stope blast hole drilling is done by an electrohydraulic production drill rig drilling typically 76 mm diameter holes. Typically, one metre of blast hole produces 5.0 tonnes of ore.

Stoping
The stopes are mined in a bottom up sequence. Once a stope has been mined and backfilled with waste rock, the stopes adjacent to it and the one above can be mined. Mining of two adjacent stopes simultaneously is not allowed due to safety concerns should a rib pillar fail.

The stope slot raises are developed by bottom-up long hole blasting methods. Once the slot raise is complete the slot is opened up to the full width of the orebody, creating a mining face, from where stope blasting can commence, advancing back towards the stope access cross cut. The technique currently in use is for a stope to be pre-drilled, charged and then blasted in a single blast. If required safe entry can be gained into the stope on the upper level by driving on the blasted muckpile. If required stope support can be installed prior to mucking of the stope.

The primary mining fleet at Bisie consists of Epiroc equipment, 10 tonne loaders (LHDs) and 36 tonne articulated dump trucks (ADTs). The long hole drill rigs are Epiroc S1L units while the development jumbos are Epiroc S1D and a Troiden 55D.

The mine currently has an operational plan which targets 36,000 tonnes per month of ore, however there is some flexibility in the production rate as the processing plant can handle up to 40,000 tonnes per month. A target of 15,000 tonnes per year of contained Sn in run of min ore is the current budgeted plan.

The plant is fed with ore by front-end-loader (FEL) from a RoM stockpile where blending of ore can occur. A primary jaw crusher reduces the ore from approximately 450mm to less than 150mm. The ore is then screened and crushed in a secondary and a tertiary cone crusher. The tertiary crusher is in closed circuit with a screen. The final crusher product is - 8mm. Crushed ore is stored on a crushed RoM stockpile which offers a second opportunity to blend to meet desired plant feed characteristics. A FEL reclaims the crushed ore and discharges it into a hopper.

The high-grade concentrate is milled to 80% -425 µm to further liberate tin. A ball mill in closed circuit with a screen is used for milling. The final concentrate is combined with concentrate from the low-grade circuit and reground in a closed-circuit ball mill to 80% -106µm to liberate sulphides prior to flotation.

The process plant was originally designed to treat 390ktpa of ore to produce 10ktpa of contained tin in concentrate at 62% tin.

Alphamin has been operating the Mpama North process plant since mine and plant commissioning in 2018. Several operational and capital projects have optimised and increased its performance and recoveries since its original design and construction.

Indeed, subsequent optimisation, debottlenecking and capital projects have improved the treatment capacity to a potential ~460ktpa with production of 12-13ktpa of contained tin in concentrate.

The process plant comprises the following processes:

• Crushing of Run of Mine (RoM) ore to -8mm;
• Screening of the crushed ore into -8mm +1mm fraction which deports to the HG (high-grade) Circuit and -a -1mm fraction which deports to the LG (low-grade) Circuit;
• The -8mm +1mm is processed by jigging;
• The jig concentrate in the HG Circuit is milled to 80 % -425µm ........