The Solwara 1 deposit is a stratabound SMS located on the flank and crest of a sub-sea volcanic mound that extends approximately 150-200 m above the surrounding seafloor. The average depth of the deposit is about 1,550 m below sea leval (BSL). The slopes of the mound are relatively steep and interrogation of a coarse digital terrain model (DTM) indicates slopes are generally in the range of 15° to 30° but can be locally steeper. There are some flatter areas near the crests of the ridges where much of the deposit is located.

The Solwara 1 deposit is located on the crest and slopes of the Suzette volcanic edifice at an average depth of 1,520 mbsl. Suzette is the northernmost edifice of the Su Su knolls, which also includes North Su and South Su, at 1,150 and 1,320 mbsl respectively.

Su Su knolls are part of a NNW trending volcanic ridge that is about 7 km long and comprises basalt to dacite lavas and breccias. At Suzette, hydrothermal mineralisation is found along the top and flanks of the ridge including chimneys and clay-altered volcanics. Coherent volcanic facies including pillow lavas, sheet and block-jointed lavas are exposed. Volcaniclastic facies include breccias, talus and fine grained volcanic sediments. The Solwara 5, Solwara 9 and South Su prospects are also located on this ridge.

Solwara 12 is located on the SE edge of the Desmos Caldera on a distinctive knoll at around 1,850 mbsl to 1,900 mbsl. The mapped chimney field is around 200 m across and includes clusters of old, inactive chimneys with sediment cover in-between. The Solwara 12 outcropping chimneys are large (up to 10 m high).

Solwara 1 is a tabular flat-lying deposit of massive sulfide-dominant mineralisation lying on the Suzette volcanic edifice. Suzette rises 150 to 200 m above the surrounding seafloor. The edifice locally has steep flanks of up to 30 degrees; but the top comprises a flatter undulating terrain with volcanic rocks, hydrothermal chimneys, and minor sediment cover.

Exposed and drilled volcanic rocks comprise lavas (block jointed and pillows) and breccia (block lava to volcanic talus). Compositions are dominated by tholeiitic to calc-alkaline basaltic andesite to dacite. Some volcanics occur as thin volcanic flows that cap part of the main sulfide-dominant mineralisation within the eastern and northern zones of the deposit.

The main area of the Solwara 1 deposit contains numerous hydrothermal vents or chimneys. Nautilus has sampled many of the chimneys across the deposit and they are composed dominantly of chalcopyrite and pyrite, with minor amounts of sphalerite, and sulfates (barite and anhydrite). Chimney heights generally range from 2 to 10 m and have been observed up to 15 m in height. Where chimney development is strongest the chimneys coalesce into distinct mounds or occur in linear zones that are interpreted to be related to underlying structural features.

Drilling has found massive sulphides below the chimneys, and hydrothermal clay altered volcanics grading to fresh volcanics below the massive sulphides.

Unconsolidated sediments (clay to sand-size particles) are found extensively on top of volcanic and mineralised units. These sediments are from nearby hydrothermal and volcanic venting as well as lesser pelagic input.

The selected mining method is based on a common surface mining method, open pit benching. The process of mining is the same as terrestrial mines: to expose mineralised material, achieve fragmentation, load and haul. Fragmentation at Solwara 1 will be achieved by mechanical cutting rather than drill-and-blast.

The three main mining tasks (sediment removal, rock cutting, and transfer of fragmented cuttings to surface) are performed by three seafloor production tools and a positive displacement pump, which are the four machines listed below and known collectively as the seafloor production equipment.
• Auxiliary cutter
• Bulk cutter
• Collection machine
• Subsea slurry lift pump

The seafloor production equipment will be remotely controlled by operators located on board the production support vessel. The seafloor production equipment will be periodically serviced on the deck of the production support vessel. Power will be supplied to the seafloor production equipment via umbilical power cables that connect the units to the production support vessel.

The production support vessel will serve several functions. It will generate power, house the mining crew, provide a platform for the launch, recovery and servicing of the seafloor production tools, and provide a place for dewatering and temporary storage of mineralised material before shipment to offtakers for further processing, smelting and precious metals recovery.

Broken mineralised material will be pumped to surface via the riser and lifting system directly to a dewatering plant, which is located on the production support vessel. The dewatering plant is the only mineral processing function that will occur at Solwara 1 prior to mineralised material storage, transfer and shipment. It is important to note from an environmental management perspective that no surfactants, filter aids or other processing chemicals will be used in the operation of the dewatering plant.

The proposed dewatering plant has a similar function to a coal washing plant, which is separation ........