2021 Annual Report

Notes to the consolidated financial statements 30 June 2021 (continued) 15 Mine properties (continued) (a) Recognition and measurement (continued) (ii) Mine properties in production (continued) Amortisation is provided on a units-of-production basis, with separate calculations being made for each mineral resource. The units-of-production method results in an amortisation charge proportional to the depletion of the economically recoverable mineral resources (comprising proven and probable reserves). A regular review is undertaken of each area of interest to determine the appropriateness of continuing to carry forward costs in relation to that area of interest. An impairment exists when the carrying value of mine properties exceeds its estimated recoverable amount. The asset is then written down to its recoverable amount and the impairment losses are recognised in profit or loss. (iii) Deferred stripping Stripping activity costs incurred in the development phase of a mine are capitalised as part of the cost of constructing the mine and subsequently amortised over the life of the mine on a units-of-production basis. Stripping activity incurred during the production phase of a mine is assessed as to whether the benefit accruing from that activity is to provide access to ore that can be used to produce ore inventory, or whether it in addition provides improved access to ore that will be mined in future periods. To the extent that the benefit from the stripping activity is realised in the form of inventory produced, the Group accounts for those stripping activity costs in accordance with AASB102 Inventories . A stripping activity asset is brought to account if it is probable that future economic benefits (improved access to the ore body) will flow to the Group, the component of the ore body for which access has been improved can be identified and costs relating to the stripping activity can be measured reliably. The amount of stripping activity costs that are capitalised is determined based on a comparison of the stripping ratio in the relevant period with the life of mine stripping ratio. To the extent that there is a period of sustained stripping that exceeds the average life of mine stripping ratio, mine waste stripping costs are capitalised to the stripping activity asset. Such capitalised costs are amortised over the life of that mine on a units-of-production basis. The life of mine ratio is based on ore reserves of the mine. Changes to the life of mine are accounted for prospectively. (b) Key estimates and judgements (i) Proved and probable ore reserves The Group uses the concept of life of mine to determine the amortisation of mine properties. In determining life of mine, the Group prepares ore reserve estimates in accordance with the JORC Code 2012, guidelines prepared by the Joint Ore Reserves Committee of The Australasian Institute of Mining and Metallurgy, Australian Institute of Geoscientists and Minerals Council of Australia. The estimate of these proved and probable ore reserves, by their very nature, require judgements, estimates and assumptions. Where the proved and probable reserve estimates need to be modified, the amortisation expense is accounted for prospectively from the date of the assessment until the end of the revised mine life (for both the current and future years). (ii) Deferred stripping The Group defers advanced stripping costs incurred during the production stage of its open cut mining operations. This calculation requires the use of judgements and estimates, such as estimates of tonnes of waste to be removed over the life of the mining area and economically recoverable reserves extracted as a result. Changes in a mine's life and design may result in changes to the expected stripping ratio (waste to mineral reserves ratio). Any resulting changes are accounted for prospectively. IGO Limited 32 Notes to The Consolidated Financial Statements 30 June 2021 102 — IGO ANNUAL REPORT 2021