The Tom and Jason deposits are examples of stratiform, strata-bound sediment-hosted, exhalative (“SEDEX”) zinc-lead-silver-barite deposits (Goodfellow et al., 1993; Leach et al., 2005; Goodfellow et al., 2007; Goodfellow, 2007).

Zinc-lead-silver-barite mineralisation at the Tom deposit varies from well laminated and stratiform (parallel to sedimentary layering) to a brecciated stockwork zone adjacent to the Tom normal fault. The Tom West and Tom East zones, both of which are exposed at surface, are interpreted to have formed one continuous strata-bound controlled lens prior to folding and faulting of the Tom Sequence, whereas the Southeast Zone is interpreted to have formed in a separate sub-basin to the main graben structure hosting the Tom West and Tom East zones (Goodfellow, 1991). All three zones have been affected by folding, with evidence for the possible development of a crenulation cleavage as opposed to the chaotic folding of laminae due to soft-sediment deformation. Ferroan carbonate alteration and quartz veining are common in footwall conglomerates near vent facies at Tom West.

The Tom West Zone dips 60° to the southwest, has a strike extent of approximately 1 km and extends up to 400 m down dip. It is about 40 m thick at its widest point and breaks into two discrete layers in the centre at depth. Contacts vary from transition over <1 m or are faulted and abrupt. The highest-grade portion of the Tom West Zone occurs along the southern and near surface portion of the zone where Pb+Zn grades exceed 10% with elevated silver. The Tom West Zone hosts the bulk of the resource at the Tom deposit.

The Tom West Zone can be divided into a series of mineralization facies (after Goodfellow, 1991; 2007) consisting of:
• Vent facies – Stockwork of pyrite, pyrrhotite, galena, sphalerite, with minor chalcopyrite, arsenopyrite and tetrahedrite with a gangue of ferroan carbonates, quartz and barite subdivided into five types, including an upper high-grade zone with 15–30% Pb+Zn, Ag between 150 g/t and 200 g/t and a low Zn/(Zn+Pb) ratio.
• Pink facies – Interbedded barite, chert, cream-coloured sphalerite, fine grained pyrite and black Bacarbonate, overprinted by pink and yellow sphalerite resulting in locally high grades in the range of 10–30% combined Pb and Zn.
• Gray facies – Interbedded pink sphalerite, fine grained galena and pyrite, white to pale gray barite, pale grey chert and grey to white Ba-carbonate/Ba-feldspar, typically with grades in the range of 4–5% Pb+Zn with negligible Ag.
• Black facies – Black mudstone and chert interbedded with barite, witherite (Ba-carbonate) and finegrained sphalerite, galena and pyrite, typically with grades in the 4–10% Pb+Zn range and a high Zn/(Pb+Zn) ratio.

The Tom East Zone occurs near the hinge of the anticline that has folded the originally planar deposit, and which plunges northward in this area. It consists of interbedded high-grade sphalerite, galena, barite and chert thought to have formed within the same stratigraphic interval as Tom West (McClay and Bidwell, 1986).

The Tom Southeast Zone is not exposed at surface, and consists of a tabular, stratiform body 0.5 m to 6 m thick with a strike length of approximately 400 m and a down-dip extension of at least 350 m dipping 60–70° to the east. It is located near the nose of the southeast-plunging Tom anticline on its eastern limb. Mineralisation consists of finely laminated sphalerite, galena, pyrite and black cherty mudstone (Goodfellow, 1991).

The Jason Main Zone is located on the northern limb of the east-plunging Jason syncline, while the Jason South Zone occurs on the southern limb. The South Zone consists of two separate horizons whereas the Main zone is defined by a single horizon. These two separate zones are likely connected through the hinge of a syncline, but this has yet to be demonstrated through drilling. These horizons can be divided into several distinct mineralisation facies (zones), including (after Turner, 1991):
• Pb-Zn-Fe sulphide facies – Massive, banded sphalerite-galena and galena-pyrite overlain by debris flow deposits containing clasts of earlier deposited massive sulphides.
• Barite-sulphide facies – Interbedded fine-grained sphalerite, galena, barite, chert and ferroan carbonate forming the bulk of the mineralisation at Jason.
• Quartz-sulphide facies – Interbedded sphalerite, pyrite, quartz and carbonaceous chert with quartzcelsian (barium feldspar) bands in the lower lens.
• Massive pyrite facies – Massive pyrite beds interbedded with sphalerite, galena, chalcopyrite, pyrrhotite and quartz located near the Jason Fault.
• Ferroan carbonate facies – Massive beds of siderite and ankerite up to several metres across with irregularly distributed galena, sphalerite, pyrrhotite, pyrite, quartz, muscovite and pyrobitumen; spatially associated with a breccia pipe.

Initial material will be recovered at a rate of about 5,000 tonnes per day by conventional truck and shovel surface mining from both the Tom and Jason deposits. During the third year, production will transition to underground mining using Avoca-style sub-level retreat longhole (LH) stoping, vertical crater retreat (VCR) and alimak stoping. Stopes will be filled with a combination of waste rock and paste and cemented rock fill.

Open pit mining accounts for 13% or 4.2M tonnes of the total 32.7M tonnes of material mined and processed. VCR and LH methods account for 75% of the material mined and processed by underground methods.

Mining recovery and dilution factors were applied by mining method. Average open pit mining recovery and dilution were 95% and 10% respectively. Average underground mining recovery and dilution were 92% and 21% respectively.

Existing surface roads and underground development will be rehabilitated and utilized as part of the mine plan. Mine access portals at multiple elevations are planned to maximize natural ventilation and dewatering of underground operations. Open pits have been designed to maintain safe working distance from all major water ways.

Diesel powered mobile equipment would be used to conduct all open pit and underground mining activities. Underground crushing and conveying would provide low cost mineral transport from the Tom deposit, while the Jason mine being further from the mill site would utilize truck transport.

Crushing
Two crushing circuits will operate to process the mined material from the Tom and Jason deposits. The crushing plants for Tom will be located underground and will include a 42” x 48” jaw crusher with an installed power of 160 kW. Jason material will be stockpiled near the above ground jaw crusher or direct dumped through an 800 mm static grizzly into a dump pocket. Stockpiled ROM material will be re-handled by a front-end loader and fed into the crusher. The material will discharge through the static grizzly into a feed hopper. Oversize material from the static grizzly will be removed for later size reduction using a rock breaker. The Jason jaw crusher 636 mm x 1,016 mm (25” x 40”) with an installed power of 90 kW, will process 150 t/h. The crusher, with a closed side setting (CSS) of 125 mm, will produce a final product P80 of approximately 110 mm.

Product from the two crushers will be conveyed to the 5,000 tonne or 24 hour live crushed material stockpile.Two belt feeders, located in a corrugated tunnel under the stockpile, will be installed with variable frequency drives (VFD) to control the reclaim rate feeding the grinding circuit. Each belt feeder will be capable of providing the total throughput of 226 t/h.

Grinding
The grinding circuit will consist of a primary SAG mill followed by a secondary ball mill. The primary SAG mill will operate in open circuit, while the secondary ball mill will operate in reverse closed circuit with a cluster of hydrocyclones. The grinding circuit will be able to process a nominal throughput of 226 t/h (fresh feed), and produce a final product P80 of 50 µm.

Product from the crushing circuits will be conveyed to a 6.4 m diameter by 3.7 m long SAG mill with an installed power of 1,865 kW motor. A belt-scale on the feed conveyor will monitor feed rate. Water will be added to the SAG mill to maintain the slurry charge in the mill at a constant density of 70%. Slurry will overflow from the SAG mill onto a screen. The screen oversize will discharge onto a series of three recycle conveyors and returned to the feed end of SAG mill. The screen undersize at a transfer size (T80) of approximately 1,000 µm will flow into the cyclone feed pump box.

Product from the primary SAG mill screen undersize will flow into the cyclone feed pump box and combine with the secondary ball mill discharge before being pumped up to a cluster of ten (eight operating / two standby) 375 mm hydrocyclones for size classification. The coarse underflow will flow by gravity to the secondary ball mill, 5.5 m diameter by 9.3 m long ball mill with an installed power of 4,476 kW, for additional grinding. The fine cyclone overflow, at a final product P80 of 50 µm, will report to the Pb Conditioning Tank. The hydrocyclones have been designed for a 300% circulating load.

Lead Circuit
Cyclone overflow will flow by gravity to a 19 m3 Pb conditioning tank, which will provide 2 minutes of conditioning time prior to Pb flotation. Frother methyl isobutyl carbinol (MIBC), sulphide collector sodium xanthate (PAX), Zn depressant sodium cyanide (NaCN), pH modifier soda ash, zinc sulphate (ZnSO4) and carbon depressant PE26 will be added to the conditioning tank. The slurry will then gravitate to the rougher flotation circuit, which consists of six 20 m3 flotation tanks cells operating in series.

The Pb rougher concentrate from cells 1 and 2 will be pumped to a 1.5 m diameter x 8.0 m high flotation column. The column concentrate will report to the Pb concentrate thickener for dewatering, while the tailings will be pumped to the Pb regrind circuit.

Pb rougher concentrate from cells 3 through 6 will be collected in a common launder and pumped to the regrind circuit. The rougher concentrate and column tailings will be pumped to a cluster o ........