3. SIGNIFICANT ACCOUNTING JUDGEMENTS, ESTIMATES AND ASSUMPTIONS  (CONTINUED) • Classification of and valuation of investments • Impairment of capitalised exploration and evaluation expenditure • Impairment of capitalised mine development expenditure • Impairment of property, plant and equipment 73  NOTES TO THE CONSOLIDATED FINANCIAL STATEMENTS FOR THE YEAR ENDED 30 JUNE 2011 Property, plant and equipment is reviewed for impairment if there is any indication that the carrying amount  may not be recoverable. Where a review for impairment is conducted, the recoverable amount is assessed by  reference to the higher of “value in use” (being net present value of expected future cash flows of the relevant  cash generating unit) and “fair value less costs to sell”. In determining the value in use, future cash flows are based on: The future recoverability of capitalised mine development expenditure is dependent on a number of factors,  including the level of proved, probable and inferred mineral resources, future technological changes, which  could impact the cost of mining, future legal changes (including changes to environmental restoration  obligations) and changes to commodity prices. To the extent that capitalised mine development expenditure is determined not to be recoverable in the future,  profits and net assets will be reduced in the period in which this determination is made. In addition, exploration and evaluation expenditure is capitalised if activities in the area of interest have not  yet reached a stage that permits a reasonable assessment of the existence or otherwise of economically  recoverable reserves. To the extent it is determined in the future that this capitalised expenditure should be  written off, profits and net assets will be reduced in the period in which this determination is made. To the extent that capitalised exploration and evaluation expenditure is determined not to be recoverable in  the future, profits and net assets will be reduced in the period in which this determination is made. Factors that could impact the future recoverability include the level of reserves and resources, future  technological changes, which could impact the cost of mining, future legal changes (including changes to  environmental restoration obligations) and changes to commodity prices. The future recoverability of capitalised exploration and evaluation expenditure is dependent on a number of  factors, including whether the Consolidated Entity decides to exploit the related lease itself or, if not, whether it  successfully recovers the related exploration and evaluation asset through sale. The Consolidated Entity has decided to classify investments in listed securities as “available-for-sale”  investments and movements in fair value are recognised directly in equity. The fair value of listed shares has  been determined by reference to published price quotations on an active market. (ii) Significant accounting estimates and assumptions (Continued) •  estimates of the quantities of ore reserves and mineral resources for which there is a high degree of  confidence of economic extraction; •  future production levels; •  future commodity prices; and •  future cash costs of production and capital expenditure. Variations to the expected cash flows, and the timing thereof, could result in significant changes to any  impairment losses recognised, if any, which in turn could impact future financial results.