Kevitsa is a magmatic, layered-intrusive, Ni-Cu-PGE deposit. Layered intrusions are the host for various types of mineralisation such as; chrome, PGE, copper and nickel deposits. Typically a single intrusion contains several types of mineralisation as distinctive layers.

The main Kevitsa Ni-Cu-PGE mineralisation is located at the centre of the main ultramafic intrusive, which is composed predominantly of olivine websterite and olivine pyroxenite. The sulphide mineralisation is disseminated in style and the overall mineralisation volume is irregular in shape. The mineralised zones are cut by several steep faults and shear zones, thought to locally offset mineralisation.

Two economically important mineralisation styles can be distinguished; regular Ni-Cu mineralisation and Ni-PGE mineralisation. The predominant mineralisation type is Ni-Cu and comprises approximately 95 % of the deposit. Ni and Cu grade variability is relatively low but there are discrete zones of Cu and Ni-rich mineralisation. The mineralisation is characterized by a Ni tenor of between 0.1 to 0.7% Ni. The Ni-PGE zones appear to be structurally controlled and more discreet compared to the regular Ni-Cu zones and is distinguished by a higher Ni tenor.

The main sulphide minerals are chalcopyrite and pentlandite occurring together with pyrrhotite and magnetite. The sulphide grain size varies from fine to medium and occurs predominantly between the cumulate minerals displaying primary magmatic textures. Locally sulphides occur as semimassive veinlets and pyrrhotite-rich net-textured zones. Cu-rich veinlets, typically a pyrrhotitechalcopyrite-magnetite assemblage, are associated with carbonate veining and are likely related to local hydrothermal remobilization. The Ni-PGE mineralisation has a higher Ni content in additional mineral phases such as millerite. The range of PGE minerals is considerable and the dominant minerals are Pt-Pd bismuth tellurides and sperrylite (Gervilla and Kojonen, 2002). PGE minerals occur mainly as inclusions in amphibolite which is most likely due to local alteration. Origin of the PGE mineralisation remains debatable (Mutanen, 1997; Hanski et al., 1997; Yang, Maier, Hanski, Lappalainen, Santaguida, and Määttä, 2012; Vaillant, Barnes, Fiorintini, Santaguida, and Törmänen, 2015).

The Kevitsa mine is a moderate-sized open pit mining operation using conventional truck and shovel operations.

Mine development required a pre-production phase of almost 12 months for pre-stripping to expose sufficient ore to ensure steady ore production. The open pit mining method utilizes drilling and blasting, loading with hydraulic excavators, and transport by trucks. The overall pit slope angle will be 43° to 46° including ramps. Trucks haul the ore to the Process plant where it is either direct tipped into the primary crusher or stockpiled on the ROM Pad for blending.

The circuit is currently capable of treating 9 Mtpa of ore, equivalent to 1,125tph at 91.3% (8,000hrs per year) availability.

ROM ore from the open pit is crushed in a gyratory crusher to 80% minus 150mm, followed by screening on a double deck vibrating screen for pebble generation. The screen oversize and undersize is recombined and conveyed to the mill feed stockpile.

Mid-size material is used as grinding media in the pebble mill, and is conveyed to a storage bin. Excess mid-size material, overflowing the pebble bin, is cone crushed in secondary and tertiary crushers and returned to the stockpile feed conveyor, rejoining the coarse and fine material from the screening plant.

Material from the stockpile, comprising coarse lumps and fines is conveyed to two 7MW AG mills operating in parallel. The mills operate partially in closed circuit with hydrocylones, and partially in open circuit with a portion of the discharge slurry being pumped from each mill to the pebble mill. The 14MW pebble milling circuit operates in closed circuit with a dedicated set of hydrocyclones. Pebbles are fed from the pebble bin to the pebble mill as grinding media.

Overflow from the cyclones on all three mills at a size of 80% passing 75 microns gravitates to the copper flotation circuit, and underflow is returned to the AG or pebble mills.

Cyclone overflow slurry is collected in a surge tank, and pumped to copper flotation. Copper flotation tailings are pumped to nickel flotation, and nickel flotation tailings to the sulphide flotation circuit.

Copper rougher and scavenger flotation concentrates are subject to regrind in a high intensity grinding (HIG) mill to assist in separation of copper and nickel minerals and cleaned in 4 stages of cleaners operating in counter current mode (concentrate moving from 1st to 4th cleaners, and tailings from each bank moving upstream. Fourth cleaner concentrate is the final concentrate, whilst first cleaner tails are pumped to nickel flotation.

The nickel cleaning circuit is similar, except that there are 5 cleaner stages, and the regrind mill is employed on the 2nd cleaner cons.

The sulphide flotation circuit comprises rougher flotation and a single cleaning stage. This circuit is employed to remove residual sulphides from the bulk of the flotation tailings so that they will be none acid generating when pumped to the tailings storage facility. Sulphide concentrates are stored in a lined storage pond.

Copper and nickel concentrates are thickened and filtered prior to transportation to off-site smelters.

Water supply to the circuit comprises raw water from the Vajukoski Pond, and process water, which is a combination of run-off water from the site, pit dewatering water, and decant water from the tailings pond.