Cosmos’ cluster, or ‘camp’ of nickel sulphide deposits, occurs within or adjacent to a local sequence of ~2.7 billion year (Ga) old (Archean age), and now metamorphosed, komatiitic lavas that are part of the Agnew-Wiluna Greenstone Belt (AWGB) of the Kalgoorlie Terrane of the Eastern Yilgarn Craton.

The genetic formation model for the nickel mineralisation is the ‘Kambalda-style’ model where precipitation of nickel sulphides is interpreted to occur in channelised komatiitic lava flows and/or lava tubes. This model proposes two dominant deposit types – Type 1 and Type 2.

‘Type 1’ deposits are interpreted to have formed where the hottest lava in the centre of a lava channel thermally erodes into a sulphidic substrate and massive sulphides accumulate at the channel’s base. This high-grade primary formation style is applicable to the Cosmos, Cosmos Deeps, AM1, AM2, parts of AM5 and the Odysseus Massive zones.

Type 1 deposits are often subject to mobilisation into structural sites when massive sulphide bodies behave plastically or even re-melt under the high metamorphic temperatures and pressures that are generated by local or regional tectonic faulting and/or folding events. The Cosmos Deeps and the Odysseus Massive zone are examples of this remobilisation style.

‘Type 2’ deposits are interpreted to have formed from cooler and slower-flowing lavas than those for Type 1 deposits. In this model, the mineral olivine is envisaged to crystallise from these cooler lavas, with the olivine grains settling to the channel’s base shortly after the precipitation of sulphides. In this model, the coeval sulphides crystallise between the olivine grains, giving rise to a disseminated to ‘matrix’ textured nickel sulphide mineralisation that builds up from the channel base. This style of mineralisation is applicable to the AM5, AM6 and Odysseus disseminated zones at Cosmos.

The sulphide nickel assemblages at Cosmos are ‘high tenor’, meaning that the sulphides are dominated by the nickel-bearing mineral pentlandite (Pe). The sulphide assemblages also contain the sulphide mineral pyrrhotite (Po), with minor amounts of pyrite (Py) and chalcopyrite (Py), and in some pla

The mineralisation typically occurs in association with the basal zone of high magnesium oxide (MgO) cumulate ultramafic rocks.

ODS occurs within the Cosmos ultramafic and is located approximately 1,000-1,100m below surface. The AM5 and AM6 zones are both situated to the south and are thought to be genetically related to Odysseus given they all exhibit similar mineralisation characteristics (grade, tenor and sulphide type)

ODS is an elongated, oblate tubular body that strikes north-south (355°) for over 330m, dips 45° east and plunges -5° to the north. Sulphide mineralisation is best concentrated 20-30m above the footwall and consists of highly disseminated to net-textured pentlandite-pyrrhotite in the central and basal zones and pentlandite-pyrite at the edges of the deposit. A higher-grade central core containing >1.5% Ni can reach a thickness of 65m. The central core is enveloped by disseminated sulphides of lower grade (0.5-1.5% Ni). Sulphide mineralisation bifurcates at the northern end and eventually terminates, due to steeply dipping cross cutting pegmatite dykes that are interpreted to have been intruded along brittle fault structures.

The ODN orebody is located 1,000-1,075m below surface and is interpreted to be the northern continuation of Odysseus mineralisation. The ODN and ODS deposits appear to be bifurcated and offset by northeast striking faults now sealed with pegmatite. The entire ODN orebody is dextrally offset ~60m in relation to Odysseus and the dip is rotated 50° counter-clockwise (now near horizontal).

Cosmos Nickel Complex is located 30km north of Leinster and include high grade deposits at Cosmos, Cosmos Deeps, Prospero, Tapinos, AM1, AM2, AM4 and Odysseus North Massive Sulphide, medium grade deposits at AM5 and AM6 and large low-grade Mt Goode deposit.

The Cosmos Project comprises the development of the Odysseus underground mine focused on the production of nickel concentrate. First production expected mid-2023.

WSA’s(Western Areas Limited) 2018 FS was a detailed analysis that confirmed the technical feasibility and economic viability of a 10-year underground mine at Odysseus based on the assumption of an average 0.9Mt/a of processing to produce ~14.6kt/a of a 16.5% Ni saleable concentrate. This production target was based on the 8.14Mt grading 2.02% Ni designed to be extracted from the Odysseus 2018 MRE discussed above. Processing was targeted to commence from October 2022, with a ramp up to full production in FY24. The FS also considered the inclusion of AM6 to extend the mine life, with a subsequent PFS confirming the Ore Reserves for AM6.

IGO is in the process of implementing an optimisation strategy and plan for the project. This will involve expanding the scope of the project along with de-risking some elements of what was originally planned. These changes include:
- coupling completion of the shaft with that of the processing plant;
- completion of additional underground mining development to create multiple working areas to enable higher production rates in the initial stages of the life of mine;
- expansion of the processing plant construction scope to increase the nameplate capacity from the originally envisaged 0.75Mtpa to 1.1Mpta; and
- strengthening of site infrastructure.

Mining
The mining method selected is top-down, longhole stoping with paste backfill, using acentre-out mining sequence. Average production levels when at steady state are 900kt per year.

The underground mine design includes infrastructure suitable for the planned mining method and production rate, including an access decline, hoisting shaft, pump stations, underground workshop, underground sizer and general mining infrastructure.

Surface infrastructure is already present at site and allowance is made in the study to upgrade and refurbish the infrastructure to meet project targets.

The metallurgical process is a well-tested technology for recovery of nickel sulphides and comprises two stages of fragmentation with wet screening for size classification, one milling stage with cyclone size classification and two stages of flotation (rougher and cleaner) with an intermediate regrinding stage.

For the purpose of the feasibility study a smeltable concentrate with grade of 16.5% Ni and 10–12% MgO Fe:MgO levels from 2.2 to 2.6 was selected. Odysseus concentrates are very clean with no deleterious elements.