Two distinct styles of manganese mineralization are observed on the Property: stratiform manganese deposits, and vein manganese deposits. The mineralization style responsible for the majority of manganese on the Property is stratiform manganese, which occurs within the Chapin Wash Formation. These deposits have typical grades of around 3% to 4% Mn and locally 6% to 10% Mn. Some workers interpret these deposits to be syngenetic with the host sediments, whereas others interpret remobilization of manganese and potassium by secondary metosomatic fluids. Some secondary redistribution of manganese occurred because of interaction with meteoric water.

Manganese also occurs within veins, breccias (some of which have been interpreted as possible volcanic vents), and fracture and fault zone cement, and overall this style of mineralization is referred as vein manganese. Mineralized veins are locally common within or near the stratiform deposits although they do occur in other units in addition to the Chapin Wash Formation, particularly within the Sandtrap Conglomerate. Vein manganese deposits are several million years younger than stratiform deposits, and although they are not obviously related, their spatial association does suggest some genetic link. Vein-type deposits are smaller, irregular and locally higher grade than the stratiform deposits and their size currently does not support large tonnage bulk mining practices.

Tetra Tech developed an open pit, truck shovel mine plan for the Artillery Peak manganese deposit, involving mining an average 7,000 t d of mineral resource and 17,220 t d of waste over a 21-year LOM. The mine plan will include a haul backfill system for co-disposal of all waste products within previously mined-out areas of the open pit. The annual MM production is set at 50,000 t a, with maximum processing rate of 2.55 Mt a. For the duration of the LOM, mineral resource containing 1,106,000 t of manganese will be delivered to the mill, for a recovered total of 994,499 t of recovered MM.

The proposed processing plant is designed to process mill feed containing 2.2% to 3.5% Mn in the range of 3,500 t/d to 7,000 t/d, to produce 50,000 t/a of EMM at a purity of higher than 99.7% Mn and an overall recovery of 88 to 93% Mn. Anhydrous sodium sulphate will be produced as a byproduct.

The ROM mill feed will be trucked from the open pit to the crushing facility located at the plant site. Two stages of crushing will reduce the ROM feed to a particle size of 100% passing 5 mm. The first stage of the crushing will use a sizer crusher in an open circuit. The second stage of crushing will use an impact crusher in a closed circuit with a dry screen. The product from the crushing circuit will be stored in two 7,000-t surge bins prior to being conveyed to the leaching circuit.

The crushed mill feed will be leached in two stages: pre-conditioning leaching with acidic solution containing sulphuric acid (mainly recycled from downstream washing circuits), and sulphur dioxide reductive leaching. The insoluble manganese in the 4+ oxidation state can be readily reduced to the soluble 2+ oxidation state by adding sulphur dioxide. Both leaching agents—sulphur dioxide and sulphuric acid—will be generated from burned liquid sulphur on-site.

The leached slurry after aeration will be directed to the counter-current decantation (CCD) circuit, where the manganese-bearing pregnant leach solution (PLS) will be separated from the leach residue. The leach residue will be subjected to multiple stages of CCD washing, followed by further dewatering in pressure filters to reduce water consumption and water content of the residue for waste rock/residue codeposit. The washed leach residue will be back-hauled by truck to the excavated area within the open pit and blended for co-disposal with waste rock.

The PLS will be treated by two stages of purification to remove any impurities (such as iron, aluminum, zinc, nickel, etc.) which may have detrimental effects on the downstream operations.

The purified PLS containing mainly manganese sulphate and manganese dithionate is directed to the manganese carbonate precipitation circuit. The precipitation of manganese carbonate is achieved by mixing the purified PLS with sodium carbonate.
In the precipitation process, soluble sodium sulphate and sodium dithionate are effectively eliminated from the manganese carbonate product. The resulting manganese carbonate precipitate will then be separated from the solution by thickening and filtration. The sodium sulphate and sodium dithionate solution will be sent to the nanofiltration/ mechanical vapour recompression (MVR) evaporation system to recover sodium sulphate and water.

The manganese carbonate solids will be dissolved by the acidic spent electrolyte solution produced from the manganese electrowinning circuit. This solution is further purified in two stages to remove any impurities and to generate the manganese electrolyte feed for subsequent use in the EMM electrowinning process.

The electrolyte feed (neutral manganese sulphate) will be pumped into the electrowinning cells where the anode and cathode compartments are separated by semi-permeable diaphragms. At the cathode, Mn2+ will be reduced to Mno(s) anddeposited onto the cathode plate. Depending on process conditions, cathodic hydrogen gas and anodic oxygen or manganese dioxide will be generated, respectively, due to competing side reactions.

Manganese metal obtained at the steel cathode plates will have an overall purity of over 99.7% Mn. The deposited manganese will be treated by washing and passivation prior to being peeled from the cathode plate. The manganese metal flakes will be transported to the manganese stock silo, and then bagged for shipment.

The sodium sulphate and sodium dithionate solution from the manganese carbonate precipitation circuit will be further processed to recover the sodium sulphate produced as a byproduct and water, which will be reused as process water.

The heat generated from the liquid sulphur burner will be recovered and used to generate electricity by a steam turbine, and/or provide direct heating in the form of intermediate steam, as needed in the process.