The Savannah sulphide rich nickel, copper and cobalt orebody is hosted by the layered mafic-ultramafic Savannah Intrusion which is enveloped by aluminous metasediments and para-gneisses of the Tickalara Metamorphics. The Savannah Orebody is mostly confined to a marginal norite unit up to 40 metres thick developed above the base of the intrusion. Areas of massive, matrix and disseminated sulphide mineralisation, dominated by pyrrhotite, chalcopyrite, pentlandite and minor pyrite occur throughout the marginal norite unit.

Prior to the development of the Savannah Open Pit, the marginal norite unit outcropped as a prominent 250 metre long limonite-goethite gossan with fresh sulphide mineralisation developing approximately 20 metres below surface. At approximately 500 metres below the surface, a significant sub-horizontal fault, the 500 Fault, cuts the orebody and offsets it 200 metres to the northwest. Mineralisation above the 500 Fault is referred to as the “Upper Zone” and below the 500 Fault as the “Lower Zone”.

The host unit of the Copernicus nickel sulphide deposit is the layered mafic-ultramafic Copernicus Intrusion. The intrusion, which has an overall gabbroic composition, is enveloped by amphibole rich meta-sediments and para-gneisses of the Tickalara Metamorphics. It outcrops as a lens-shaped body with maximum dimensions of 600 metres along strike by 100 metres thick. It dips moderately to the west and has a pronounced northward plunge of approximately 40 degrees. Sulphide rich nickel, copper and cobalt mineralisation at Copernicus is confined to a discreet cumulate-textured meta-pyroxenite unit located within the Copernicus Intrusion. The pyroxenite unit is lens-shaped and dips west and plunges north with the Copernicus Intrusion. The sulphide mineralisation is preferentially developed at the northern end of the pyroxenite unit where it forms sulphidebearing cumulates rich in pyrrhotite-chalcopyrite-pentlandite and pyrite. Sulphide textures vary from net (matrix) textured mineralisation containing 5-10% sulphides to coarse-grained blebs and massive sulphide-rich stringer mineralisation, containing upwards of 50-70% sulphide. The mineralised pyroxenite has a maximum thickness of 35 metres and a down dip extent of between 100-150 metres. The down-plunge (strike) dimension to the north has been drilled over a strike length of 750 metres.

The majority of the ore was mined via long-hole open stoping, which is a highly mechanised and low cost method. Access to the top and bottom of the ore block is established with tunnels, a slot raise is created, and holes are then drilled to blast vertical slabs off the ore block. Once the ore block has been blasted and extracted, the stopes are filled with paste (tailings and cement mix) to stabilise the void and allow extraction of adjoining ore blocks. The minimal waste material mined is either stockpiled underground or trucked to surface.

The Copernicus orebody was mined using conventional open cut methods, involving drilling, blasting and excavation using contractors.

The process plant at Savannah comprises a single stage crusher, SAG mill, flotation, thickening and filtering stages to produce a bulk nickel, copper, cobalt concentrate. Metallurgical recoveries average 86-89% for nickel, 94-97% for copper and 89-92% for cobalt. The plant was originally designed for a throughput of 750,000 tonnes per annum, but has consistently outperformed the design specifications. Recent plant trials indicate the plant can operate at in excess of 1 million tonnes per annum.

The Copernicus open pit operations re-commenced in December 2014 and were completed in April 2016. The ore was trucked to Savannah where it was blended and processed with Savannah ore producing a nickel, copper, cobalt concentrate.