The manganese contained in the Plymouth deposit is predominantly in the form of a carbonate (rhodochrosite) whilst the iron exists in both oxide (hematite, magnetite and ilmenite) and carbonate minerals (predominantly siderite). The deposit type is sedimentary in origin and of the stratiform, BIF type. The host sequence consists of Silurian red and grey siliciclastic to calcareous siltstones and shales that have been metamorphosed under lower greenschist facies conditions. In addition to the main oxide, silicate and carbonate facies iron-manganese concentrations, host rocks contain minor magnetite and traces of pyrite in grey siltstone and black shale intervals. The manganese rich iron formation deposits occur in stratiform bodies and represent spatially distinct intervals that accumulated contemporaneously with surrounding sedimentary strata.

Iron and manganese are considered to have been deposited from seawater in an oxidizing environment and host strata have subsequently been structurally thickened through folding and faulting related to the Acadian Orogeny (middle to early Late Devonian in age). Some subsequent remobilization of manganese has occurred and resulted in re-deposition of manganese carbonate and oxides in fracture zones. Additional surficial weathering has also resulted in very limited oxidation at the overburden-bedrock interface, but is typically estimated to be limited to centimetres depth into bedrock.

Historical interpretation of the mineralization of the Plymouth deposit indicated that the iron manganese mineralization can be subdivided into iron-manganese oxide, silicatecarbonate-oxide, and carbonate facies (Sidwell 1957; Gilders 1976; Roberts and Prince 1990). These stratiform deposits are analogous to the Type IIA deposits of bedded manganese oxides and carbonates described by Macharmer (1987). The ironmanganese oxide facies present on the Property is represented by red to maroon siltstone and red chert and is characterized by the mineral assemblage magnetite, hematite, braunite (Mn+2Mn+36[O8SiO4]) and bixbyite ([Mn,Fe]2O3) and ranges between 30% and 80% iron-manganese oxides. Iron and manganese mineralization is also present in the form of rhodochrosite (MnCO3) and minor sursassite (Mn2Al3[(SiO4)(Si2O7)(OH)3]) crosscuts syngenetic iron-manganese mineralization in the Deposit (Sidwell 1957). Layers of iron-manganese mineralization are also locally observed to be crosscut by veins of quartz, quartz-carbonate, chlorite, and sulphide (Way et al. 2009).

The mining operation will use a conventional open pit mining method, off-highway haul trucks, and hydraulic excavator. The waste rock and mineral resource will be drilled and blasted using typical grade control methods and blasthole sampling.

Tetra Tech used an overall pit slope angle of 45°, as the required geotechnical data was not available to support the analysis required to assess the pit slope angles. Tetra Tech based this pit slope angle on estimates from previous projects and believes that this value is reasonable.

A conventional two-stage crushing plant is used to reduce the size of the ROM mill feed to the required size for grinding. After primary size reduction by the jaw crusher, the crushed material is conveyed to a screen where the oversize material is fed to a secondary cone crusher for final crushing. Final crushed material is stored in a fine ore storage silo.

The grinding circuit also utilizes a conventional two-stage, rod mill-ball mill configuration with the rod mill operating in open circuit and the ball mill operating in closed circuit. Size classification in the grinding circuit is by hydrocyclones. The target grind size of 80% passing 20 µm is based on achieving a similar particle size distribution in the feed to the pre-concentration circuit to that which was used in the preliminary magnetic separation test work.

The ground material will be fed as slurry through a dual-stage wet drum LIMS to remove ferromagnetic iron prior to entering the HGMS circuit. Based upon the preliminary bench scale test results, which demonstrated that a 55% iron product could be obtained on a single pass LIMS, a cleaning stage has been added to the conceptual design of the LIMS circuit to produce a saleable 62% iron, iron ore fines product. The LIMS magnetic concentrate product is filtered, dried and packaged in 1-t bulk bags for shipment to an end user.

The LIMS tails feed the high gradient portion of the magnetic separation circuit, which consists of rougher and cleaner stages with the final concentrate (magnetic fraction) subsequently being thickened and dewatered to 10% moisture for hydrometallurgical processing. HGMS rougher tailings are directed to tailings treatment, where they will be neutralized with lime, thickened and co-disposed with other hydrometallurgical solid residues in a lined tailings management area.

Dewatered HGMS cleaner concentrate is conveyed to the leach feed holding tank where it is mixed with acidic spent electrolyte solution from the electrowinning circuit. Dewatering of the\ concentrate was found to be necessary to maintain the target pulp density in the leach while still allowing for a maximum recycle of spent electrolyte to supply a portion of the leach acid requirements. A small portion of the recycled spent electrolyte is bled to wastewater treatment (WWT) to control the build-up of impurities and to maintain the water balance in the circuit. The bleed stream is directed through a manganese precipitation step and an ammonia recovery step prior to being routed to WWT in order to recover soluble manganese and ammonia from the solution. Residue wash water streams, which contain moderate concentrations of soluble manganese and ammonium sulphate, are also routed to these unit operations prior to treatment and disposal of the barren process effluent. The manganese is recovered as a solid residue that is recycled to the sulphuric acid leach step to improve on the overall recovery of manganese within the hydrometallurgical circuit. Following the manganese hydroxide precipitation step, a steam ammonia stripper is used to strip ammonia from the liquid effluent stream.

From the leach feed tank, the slurry overflows into cascading continuously stirred tank reactors (CSTRs) where sufficient quantities of makeup sulphuric acid are added to maintain the target leach pH set-point and satisfy the leach acid\ requirements. Given the large quantity of sulphuric acid required for the leach, a sulphuric acid plant has been included for on- site acid production as an option to the direct purchase of sulphuric acid to reduce operating costs and logistic concerns. In addition to satisfying the acid requirements for the process, the exothermic nature of the acid production process allows for generation of steam. High pressure steam is used to produce electricity via a turbine generator arrangement, while low pressure steam is used in the process to supplement heating requirements. For direct purchase of sulphuric acid, it is assumed that 93% sulphuric acid will be delivered in bulk tanker loads with an allowance for several days of on-site acid storage.

The pregnant leach solution, and leach residue from the sulphuric acid leach section of the plant overflow into a series of cascading CSTRs in which the primary iron precipitation reaction takes place. To optimize on the process economics and efficiency, pulverized limestone is added to the primary iron precipitation reaction to partially neutralize the slurry and air is injected into the reactors to facilitate conversion of ferrous iron to ferric. The majority of the soluble iron is removed in the primary iron precipitation stage. As a result of lime/limestone addition, gypsum (calcium sulphate) and several other impurities, such as aluminum, arsenic, copper and zinc are co- precipitated in both the primary and secondary iron precipitation stages. The leach residue along with the precipitated solids from the primary iron precipitation reaction are directed to a thickener and the solid residue is subsequently filtered and thoroughly washed by counter-current displacement washing using a vacuum belt filter. The leach-primary iron precipitation residue is conveyed to the tailings treatment tank where it is re-pulped in recycled process water along with the pre-concentration circuit tailings and other solid residues. The slurried residues are neutralized with lime and pumped to the tailings disposal area at a pulp density that is consistent with the selection of a thickened tailings disposal strategy.

The leach-primary iron precipitation residue thickener overflow and filtrate streams are recombined and are pumped to the secondary iron precipitation stage. Calcined lime is used to further neutralize the pregnant leach solution, resulting in the near-complete removal of soluble iron from the advance electrolyte. The precipitated solids from the second stage iron precipitation reaction are returned to the leach to recover any coprecipitated manganese.

A limestone calcining facility has been included for on-site production of quicklime (CaO) for use in the secondary iron precipitation, manganese precipitation and tailings neutralization reactions. Pulverized limestone will be used directly for neutralization in the primary iron precipitation reaction and all limestone used for the Project will be sourced from a nearby, owner controlled quarry in an effort to reduce operating costs associated with purchase and shipping of lime from independent processors. For the purpose of the current study the kiln will be fired on CNG.

Following the two-stage iron precipitation step, the advance electrolyte is further purified by sulphide precipitation using ammonium sulphide to remove residual heavy metals such as zinc, arsenic, copper, lead, cobalt and nickel. The effluent from the sulphide precipitation step is pumped through a pre-coated plate-and-frame filter to capture the fine precipitate for disposal in the tailings disposal area. The advance electrolyte is aged for a period of time and re-filtered to remove any additional heavy metal sulphides. The filtrate from the advance electrolyte polishing filter is pumped through primary and polishing activated carbon columns, arranged in series, to adsorb any organics and residual reactive sulphide species which may become occluded with the cathodic deposit and contaminate the final EMM flake product.

Purified manganese sulphate advance electrolyte is fed to the electrowinning cells for recovery of manganese as EMM. EMM sheets produced from electrowinning are harvested, washed, dried and crushed to produce a minimum 99.7% pure EMM flake product.