Financial statements

Note 1 - Principal accounting policies

Principal accounting policies (PDF 221KB)

Corporate information

The financial statements of the Group were authorised for issue in accordance with a directors' resolution on 6 March 2009. Rio Tinto plc and Rio Tinto Limited are listed and incorporated respectively on Stock Exchanges in the United Kingdom and Australia. Rio Tinto plc's registered office is at 5 Aldermanbury Square, London, EC2V 7HR, United Kingdom (registered number: 719885). Rio Tinto Limited's registered office is at 120 Collins Street, Melbourne, Australia, 3000.

Rio Tinto's business is finding, mining and processing mineral resources. Major products are aluminium, copper, diamonds, coal, uranium, gold, industrial minerals (borax, titanium dioxide, salt, talc), and iron ore. Activities span the world but are strongly represented in Australia and North America with significant businesses in South America, Asia, Europe and Africa.

Basis of preparation

The basis of preparation and accounting policies used in preparing the financial statements for the year ended 31 December 2008 are set out below.

The financial statements for the year ended 31 December 2008 have been prepared in accordance with International Financial Reporting Standards both as adopted by the EU ('EU IFRS') and as issued by the International Accounting Standards Board ('IFRS'), Interpretations issued from time to time by the International Financial Reporting Interpretations Committee ('IFRIC') adopted by the European Union that are mandatory for periods ended 31 December 2008, and in accordance with applicable United Kingdom law, applicable Australian law as amended by the Australian Securities and Investments Commission Order dated 27 January 2006 (as amended on 22 December 2006) and Article 4 of the European Union IAS regulation.

The EU IFRS financial information has been drawn up on the basis of accounting policies consistent with those applied in the financial statements for the year to 31 December 2007, except for the following:

IFRIC 11 - (IFRS 2) - Group and Treasury share transactions
IFRIC 14 (IAS 19) The limit on a defined benefit asset, minimum funding requirements and their interaction.

Both of the above interpretations have been endorsed by the EU. The Group has early adopted IFRIC 14. The effect of adopting IFRIC 11 and IFRIC 14 is not material to Group earnings or to shareholders' funds in the current or prior periods. Therefore, prior period information has not been restated.

IFRIC 12 Service concession arrangements is mandatory for 2008 but has not yet been endorsed by the EU. Adoption would not be material to Group earnings or to shareholders' funds in the current or prior periods.

The Group has not applied the following pronouncements: those which are expected to be most relevant to the Group are IFRS 8 and IAS 27 (revised).

Standards and interpretations endorsed by the European Union

IFRS 8 Operating Segments - mandatory for year 2009. The segmental information reported under the standard is that which the chief operating decision maker uses internally for evaluating the performance of operating segments and allocating resources to those segments.
IAS 1 Presentation of financial statements (revised) - mandatory for year 2009
IFRS 2 (Amendment) Share based payment - Vesting conditions and cancellations - mandatory for year 2009
IFRIC 13 Customer Loyalty programmes - mandatory for year 2009

Standards and interpretations not yet endorsed by the European Union

IFRIC 15 Agreements for the construction of real estate - mandatory for year 2009
IFRIC 16 Hedges of a net investment in a foreign operation - mandatory for year 2009
Amendment to IAS 32 and IAS 1 - Puttable financial instruments and obligations arising on liquidation - mandatory for year 2009 Improvements to IFRSs - This standard collates many minor changes to IFRS almost all of which are mandatory in 2009. The amendments most relevant to the Group relate to the classification of derivatives which are not hedges by maturity rather than as short term and the imputation of interest on government grants.
IAS 27 (revised) Consolidated and separate financial statements - mandatory for year 2010. The standard requires the effects of all increases or decreases in the ownership of subsidiaries to be recorded in equity if there is no change in control. They will therefore no longer result in goodwill or gains and losses. The standard also specifies the accounting when control is lost.
IFRS 3 (Amendment) Business combinations - mandatory for year 2010
Amendments To IFRS 1 First-time Adoption of International Financial Reporting Standards and IAS 27 Consolidated and Separate Financial Statements - Cost of an investment in a subsidiary, jointly controlled entity or associate - mandatory for year 2009
Eligible Hedged Items (an amendment to IAS 39 Financial Instruments: Recognition and Measurement) - mandatory for year 2010
IFRIC 17 Non cash distributions to owners - mandatory for year 2010
IFRIC 18 Transfers of assets from customers - mandatory for transfers of assets from customers on or after 1 July 2009.

The Group is evaluating the impact of the above pronouncements. The revision to IAS 27 would have a material effect on the income statement in 2009 if early adopted and if applied to the Chinalco strategic partnership. The Chinalco strategic partnership is subject to approval by the shareholders of Rio Tinto, governments and other regulators. The Group does not currently expect to early adopt the revision to IAS 27. Otherwise, the above changes are not expected to be material to the Group's earnings or to shareholders' funds.

Judgements in applying accounting policies and key sources of estimation uncertainty

Many of the amounts included in the financial statements involve the use of judgement and/or estimation. These judgements and estimates are based on management's best knowledge of the relevant facts and circumstances, having regard to previous experience, but actual results may differ from the amounts included in the financial statements. Information about such judgements and estimation is contained in the accounting policies and/or the Notes to the financial statements, and the key areas are summarised below.

Areas of judgement that have the most significant effect on the amounts recognised in the financial statements are:

Merger accounting for the 1995 merger of the economic interests of Rio Tinto plc and Rio Tinto Limited into the dual listed companies ('DLC') structure (page 6).
Review of asset carrying values and impairment charges and reversals note 1(e) and (i), note 5 and note 11
Revision of provisional fair values allocated on acquisition - note 41
Estimation of asset lives, note 1 (e and i)
Determination of ore reserve estimates - note 1( j)
Close down, restoration and clean up obligations - note 1(k)
Deferral of stripping costs - note 1(h)
Recognition of deferred tax on mineral rights recognised in acquisitions - note 1(m)
Capitalisation of exploration and evaluation costs - note 1(f)
Identification of functional currencies - note 1(d)
The definition of Underlying earnings - note 2

Key sources of estimation uncertainty that have a significant risk of causing a material adjustment to the carrying amounts of assets and liabilities within the next financial year are:

Review of asset carrying values and impairment charges and reversals note 1(e) and (i), note 5 and note 11
Estimation of close down and restoration costs and the timing of expenditure - note 1(k) and note 27
Estimation of environmental clean up costs and the timing of expenditure - note 1(k) and note 27
Recoverability of potential deferred tax assets - note 1 (m) and note 18 (d)
Estimation of liabilities for post retirement costs - note 49

(a) Accounting convention

The financial information included in the financial statements for the year ended 31 December 2008, and for the related comparative period, has been prepared under the historical cost convention, except for derivative financial instruments, available for sale investments and assets held for sale, which have been measured at fair value as set out in the notes below.

(b) Basis of consolidation

The financial statements consist of the consolidation of the accounts of Rio Tinto plc and Rio Tinto Limited (together 'the Companies') and their respective subsidiaries (together 'the Group').

All intragroup balances, transactions, income and expenses and profits or losses, including unrealised profits from intragroup transactions, have been eliminated on consolidation. Unrealised losses are eliminated in the same way as unrealised gains except that they are only eliminated to the extent that there is no evidence of impairment.

Subsidiaries: Subsidiaries are entities over which the Companies have the power to govern the financial and operating policies in order to obtain benefits from their activities. Control is presumed to exist where the Companies own more than one half of the voting rights (which does not always equate to percentage ownership) unless it can be demonstrated that ownership does not constitute control. Control does not exist where other parties hold veto rights over significant operating and financial decisions. In assessing control, potential voting rights that are currently exercisable or convertible are taken into account. The consolidated financial statements include all the assets, liabilities, revenues, expenses and cash flows of the Companies and their subsidiaries after eliminating intercompany transactions as noted above.

For partly owned subsidiaries, the net assets and net earnings attributable to outside shareholders are presented as 'Amounts attributable to outside equity shareholders' in the consolidated balance sheet and consolidated income statement.

Associates: An associate is an entity, that is neither a subsidiary nor a joint venture, over whose operating and financial policies the Group exercises significant influence. Significant influence is presumed to exist where the Group has between 20 per cent and 50 per cent of the voting rights, but can also arise where the Group holds less than 20 per cent if it has the power to be actively involved and influential in policy decisions affecting the entity. The Group's share of the net assets, post tax results and reserves of associates are included in the financial statements using the equity accounting method. This involves recording the investment initially at cost to the Group, which therefore includes any goodwill on acquisition, and then, in subsequent periods, adjusting the carrying amount of the investment to reflect the Group's share of the associate's results less any impairment of goodwill and any other changes to the associate's net assets such as dividends. Unrealised gains on transactions between the Group and its associates are eliminated to the extent of the Group's interest in the associates.

Joint ventures: A joint venture is a contractual arrangement whereby two or more parties undertake an economic activity that is subject to joint control. Joint control is the contractually agreed sharing of control such that significant operating and financial decisions require the unanimous consent of the parties sharing control. In some situations, joint control exists even though the Group has an ownership interest of more than 50 per cent because of the veto rights held by joint venture partners. The Group has two types of joint ventures:

Jointly controlled entities ('JCEs'): A JCE is a joint venture that involves the establishment of a corporation, partnership or other entity in which each venturer has a long term interest. JCEs are accounted for using the equity accounting method. In addition, the carrying value will include any long term debt interests that in substance form part of the Group's net investment.

Jointly controlled assets ('JCAs'): A JCA is a joint venture in which the venturers have joint control over the assets contributed to or acquired for the purposes of the joint venture. JCAs do not involve the establishment of a corporation, partnership or other entity. This includes situations where the participants derive benefit from the joint activity through a share of the production, rather than by receiving a share of the results of trading. The Group's proportionate interest in the assets, liabilities, revenues, expenses and cash flows of JCAs are incorporated into the Group's financial statements under the appropriate headings.

The Group uses the term 'Equity accounted units' to refer to associates and jointly controlled entities collectively.

Where necessary, adjustments are made to the results of subsidiaries, joint ventures and associates to bring their accounting policies into line with those used by the Group.

Acquisitions

On the acquisition of a subsidiary, the purchase method of accounting is used whereby the purchase consideration is allocated to the identifiable assets, liabilities and contingent liabilities (identifiable net assets) of the subsidiary on the basis of fair value at the date of acquisition. Provisional fair values allocated at a reporting date are finalised within twelve months of the acquisition date.

When part or all of the amount of purchase consideration is contingent on future events, the cost of the acquisition initially recorded includes a reasonable estimate of the fair value of the contingent amounts expected to be payable in the future. The cost of the acquisition is adjusted when revised estimates are made, with corresponding adjustments made to goodwill until the ultimate outcome is known.

The results of businesses acquired during the year are brought into the consolidated financial statements from the date on which control, joint control or significant influence commences and taken out of the financial statements from the date on which control, joint control or significant influence ceases.

Disposals

Individual non current assets or 'disposal groups' (ie groups of assets and liabilities) to be disposed of, by sale or otherwise in a single transaction, are classified as 'held for sale' if the following criteria are met:

the carrying amount will be recovered principally through a sale transaction rather than through continuing use, and
the disposal group is available for immediate sale in its present condition subject only to terms that are usual and customary for such sales, and
the sale is highly probable.

Disposal groups held for sale are carried at the lower of their carrying amount and fair value less costs to sell and are presented separately on the face of the balance sheet with the related assets and liabilities being presented as a single asset and a single liability respectively. Comparative balance sheet information is not restated. Disposal groups acquired with a view to resale are held at fair value determined at the acquisition date and no profits or losses are recognised between acquisition date and disposal date.

For a disposal group held for sale that continues to be carried at its carrying amount, the profit on disposal, calculated as net sales proceeds less the carrying amount, is recognised in the income statement in the period during which control passes to the buyer. Where the fair value less costs to sell of a disposal group is lower than the carrying amount at the time of classification as held for sale, the resulting charge is recognised in the income statement in that period. On classification as held for sale, the assets are no longer depreciated. When the fair value less costs to sell of a disposal group falls below the carrying amount during the period in which it is classified as held for sale, the charge is included in the income statement at that time.

If the disposal group or groups represent a separate major line of business or geographical area of operations, or are part of a single coordinated plan to dispose of a separate major line of business or geographical area of operations, or are subsidiaries acquired exclusively with a view to resale, they are classified as discontinued operations. The net results attributable to such discontinued operations are shown separately and comparative figures in the income and cash flow statements are restated.

(c) Sales revenue

Sales revenue comprises sales to third parties at invoiced amounts, with most sales being priced ex works, free on board (f.o.b.) or cost, insurance and freight (c.i.f.). Amounts billed to customers in respect of shipping and handling are classed as sales revenue where the Group is responsible for carriage, insurance and freight. All shipping and handling costs incurred by the Group are recognised as operating costs. If the Group is acting solely as an agent, amounts billed to customers are offset against the relevant costs. Revenue from services is recognised as services are rendered and accepted by the customer.

Sales revenue excludes any applicable sales taxes. Mining royalties are presented as an operating cost or, where they are in substance a profit based tax, within taxes. Gross sales revenue disclosed as part of the income statement includes the Group's share of the sales revenue of equity accounted units. To avoid duplication, this excludes sales by jointly controlled entities to third parties of products purchased from the Group and excludes charges by jointly controlled entities to the Group. Co-product revenues are included in sales revenue.

A large proportion of Group production is sold under medium to long term contracts, but sales revenue is only recognised on individual sales when persuasive evidence exists that all of the following criteria are met:

the significant risks and rewards of ownership of the product have been transferred to the buyer;
neither continuing managerial involvement to the degree usually associated with ownership, nor effective control over the goods sold, has been retained;
the amount of revenue can be measured reliably;
it is probable that the economic benefits associated with the sale will flow to the Group; and
the costs incurred or to be incurred in respect of the sale can be measured reliably.

These conditions are generally satisfied when title passes to the customer. In most instances sales revenue is recognised when the product is delivered to the destination specified by the customer, which is typically the vessel on which it will be shipped, the destination port or the customer's premises.

Sales revenue is commonly subject to adjustment based on an inspection of the product by the customer. In such cases, sales revenue is initially recognised on a provisional basis using the Group's best estimate of contained metal, and adjusted subsequently.

Certain products are 'provisionally priced', ie the selling price is subject to final adjustment at the end of a period normally ranging from 30 to 180 days after delivery to the customer, based on the market price at the relevant quotation point stipulated in the contract.

Revenue on provisionally priced sales is recognised based on estimates of the fair value of the consideration receivable based on forward market prices. At each reporting date provisionally priced metal is marked to market based on the forward selling price for the quotational period stipulated in the contract. For this purpose, the selling price can be measured reliably for those products, such as copper, for which there exists an active and freely traded commodity market such as the London Metals Exchange and the value of product sold by the Group is directly linked to the form in which it is traded on that market.

The marking to market of provisionally priced sales contracts is recorded as an adjustment to sales revenue.

(d) Currency translation

The functional currency for each entity in the Group, and for jointly controlled entities and associates, is the currency of the primary economic environment in which it operates. For many entities, this is the currency of the country in which they operate. Transactions denominated in other currencies are converted to the functional currency at the exchange rate ruling at the date of the transaction unless hedge accounting applies. Monetary assets and liabilities denominated in foreign currencies are retranslated at year end exchange rates.

The US dollar is the currency in which the Group's Financial statements are presented, as it most reliably reflects the global business performance of the Group as a whole.

On consolidation, income statement items are translated from the functional currency into US dollars at average rates of exchange. Balance sheet items are translated into US dollars at year end exchange rates. Exchange differences on the translation of the net assets of entities with functional currencies other than the US dollar, and any offsetting exchange differences on net debt hedging those net assets, are recognised directly in the foreign currency translation reserve via the statement of recognised income and expense.

Exchange gains and losses which arise on balances between Group entities are taken to the foreign currency translation reserve where the intragroup balance is, in substance, part of the Group's net investment in the entity.

The balance of the foreign currency translation reserve relating to an operation that is disposed of is transferred to the income statement at the time of the disposal.

The Group finances its operations primarily in US dollars but part of the Group's US dollar debt is located in subsidiaries having functional currencies other than the US dollar. Except as noted above, exchange gains and losses relating to such US dollar debt are charged or credited to the Group's income statement in the year in which they arise.This means that the impact of financing in US dollars on the Group's income statement is dependent on the functional currency of the particular subsidiary where the debt is located.

Except as noted above, or in note (p) below relating to derivative contracts, all exchange differences are charged or credited to the income statement in the year in which they arise.

(e) Goodwill and intangible assets (excluding exploration and evaluation expenditure)

Goodwill represents the difference between the cost of acquisition and the fair value of the identifiable assets, liabilities and contingent liabilities acquired. Goodwill is initially determined based on provisional fair values. Fair values are finalised within 12 months of the acquisition date. Goodwill on acquisition of subsidiaries is separately disclosed and goodwill on acquisitions of associates and JCEs is included within investments in equity accounted units. For non wholly owned subsidiaries, minority interests are initially recorded based on the minorities' proportion of the fair values of the identifiable assets and liabilities and contingent liabilities recognised at acquisition.

In 1997 and previous years, goodwill was eliminated against reserves in the year of acquisition as a matter of accounting policy, as was then permitted under UK GAAP. Such goodwill was not reinstated under subsequent UK accounting standards or on transition to IFRS.

Goodwill, including goodwill in equity accounted units is not amortised; rather it is tested annually for impairment. Goodwill is allocated to the cash generating unit or group of cash generating units expected to benefit from the related business combination for the purposes of impairment testing which is carried out in accordance with accounting policy note 1(i). Goodwill impairments cannot be reversed.

Intangible assets acquired as part of an acquisition of a business are capitalised separately from goodwill if the asset is separable or arises from contractual or legal rights, and the fair value can be measured reliably on initial recognition.

Purchased intangible assets are initially recorded at cost and finite life intangible assets are amortised over their useful economic lives on a straight line or units of production basis, as appropriate. Intangible assets having indefinite lives and intangible assets that are not yet ready for use are not amortised and are reviewed annually for impairment in accordance with accounting policy note 1(i).

Intangible assets are considered to have indefinite lives when, based on an analysis of all of the relevant factors, there is no foreseeable limit to the period over which the asset is expected to generate cash flows for the Group. The factors considered in making this determination include the existence of contractual rights for unlimited terms; or evidence that renewal of the contractual rights without significant incremental cost can be expected for indefinite periods into the future in view of the Group's future investment intentions. The life cycles of the products and processes that depend on the asset are also considered.

Where amortisation is calculated on a straight line basis, the following useful lives have been determined for classes of intangible assets.

Trademark, patented and non patented technology
Trademarks	14 to 20 years
Patented and non patented technology	10 to 20 years
Other intangible assets
Internally generated intangible assets and computer software	2 to 5 years
Other intangible assets	2 to 20 years
Contract based intangible assets
Power contracts	2 to 39 years
Other purchase and customer contracts	5 to 15 years

(f) Exploration and evaluation

Exploration and evaluation expenditure comprises costs that are directly attributable to:

researching and analysing existing exploration data;
conducting geological studies, exploratory drilling and sampling;
examining and testing extraction and treatment methods; and/or
compiling prefeasibility and feasibility studies.

Exploration expenditure relates to the initial search for deposits with economic potential. Evaluation expenditure arises from a detailed assessment of deposits or other projects that have been identified as having economic potential.

Expenditure on exploration activity is not capitalised.

Capitalisation of evaluation expenditure commences when there is a high degree of confidence in the project's viability and hence it is probable that future economic benefits will flow to the Group.

The carrying values of capitalised amounts are reviewed twice per annum by management and the results of these reviews are reported to the Audit committee. In the case of undeveloped projects there may be only inferred resources to form a basis for the impairment review. The review is based on a status report regarding the Group's intentions for development of the undeveloped project. In some cases, the undeveloped projects are regarded as successors to ore bodies, smelters or refineries currently in production. Where this is the case, it is intended that these will be developed and go into production when the current source of ore is exhausted or to replace the reduced output, which results where existing smelters and/or refineries are closed. It is often the case that technological and other improvements will allow successor smelters and/or refineries to more than replace the capacity of their predecessors.

Subsequent recovery of the resulting carrying value depends on successful development or sale of the undeveloped project. If a project does not prove viable, all irrecoverable costs associated with the project net of any related impairment provisions are written off.

(g) Property, plant and equipment

Property, plant and equipment are stated at cost, less accumulated depreciation and accumulated impairment losses. The cost of property, plant and equipment comprises its purchase price, any costs directly attributable to bringing the asset to the location and condition necessary for it to be capable of operating in themanner intended by management and the estimated close down and restoration costs associated with the asset. Once amining project has been established as commercially viable, expenditure other than that on land, buildings, plant and equipment is capitalised under 'Mining properties and leases' together with any amount transferred from'Exploration and evaluation'.

In open pit mining operations, it is necessary to remove overburden and other waste materials to access ore from which minerals can be extracted economically. The process of mining overburden and waste materials is referred to as stripping. During the development of a mine (or pit), before production commences, stripping costs are capitalised as part of the investment in construction of the mine.

Costs associated with commissioning new assets, in the period before they are capable of operating in the manner intended by management, are capitalised. Development costs incurred after the commencement of production are capitalised to the extent they are expected to give rise to a future economic benefit. Interest on borrowings related to construction or development projects is capitalised until the point when substantially all the activities that are necessary to make the asset ready for its intended use are complete.

(h) Deferred stripping

As noted above, stripping costs incurred in the development of a mine (or pit) before production commences are capitalised as part of the cost of constructing the mine (or pit) and subsequently amortised over the life of the mine (or pit) on a units of production basis.

Where a mine operates several open pits that are regarded as separate operations for the purpose of mine planning, stripping costs are accounted for separately by reference to the ore from each separate pit. If, however, the pits are highly integrated for the purpose of mine planning, the second and subsequent pits are regarded as extensions of the first pit in accounting for stripping costs. In such cases, the initial stripping (ie overburden and other waste removal) of the second and subsequent pits is considered to be production phase stripping relating to the combined operation.

The Group defers stripping costs incurred subsequently, during the production stage of its operations, for those operations where this is the most appropriate basis for matching the costs against the related economic benefits and the effect is material. This is generally the case where there are fluctuations in stripping costs over the life of the mine (or pit). The amount of stripping costs deferred is based on the ratio ('Ratio') obtained by dividing the tonnage of waste mined either by the quantity of ore mined or by the quantity of minerals contained in the ore. Stripping costs incurred in the period are deferred to the extent that the current period Ratio exceeds the life of mine (or pit) Ratio. Such deferred costs are then charged against reported profits to the extent that, in subsequent periods, the current period Ratio falls short of the life of mine (or pit) Ratio. The life of mine (or pit) Ratio is based on proved and probable reserves of the mine (or pit).

The life of mine (or pit) waste-to-ore ratio is a function of the pit design(s) and therefore changes to that design will generally result in changes to the Ratio. Changes in other technical or economic parameters that impact on reserves will also have an impact on the life of mine (or pit) Ratio even if they do not affect the pit design(s). Changes to the life of mine (or pit) Ratio are accounted for prospectively.

In the production stage of some mines (or pits), further development of the mine (or pit) requires a phase of unusually high overburden removal activity that is similar in nature to preproduction mine development. The costs of such unusually high overburden removal activity are deferred and charged against reported profits in subsequent periods on a units of production basis. This accounting treatment is consistent with that for stripping costs incurred during the development phase of a mine (or pit), before production commences.

If the Group were to expense production stage stripping costs as incurred, there would be greater volatility in the year to year results from operations and excess stripping costs would be expensed at an earlier stage of a mine's operation.

Deferred stripping costs are included in 'Mining properties and leases' within property, plant and equipment or in investments in equity accounted units, as appropriate. These form part of the total investment in the relevant cash generating unit, which is reviewed for impairment if events or changes in circumstances indicate that the carrying value may not be recoverable. Amortisation of deferred stripping costs is included in net operating costs or in the Group's share of the results of its equity accounted units, as appropriate.

(i) Depreciation and impairment

Depreciation of non current assets

Property, plant and equipment is depreciated over its useful life, or over the remaining life of the mine if shorter. The major categories of property, plant and equipment are depreciated on a units of production and/or straight-line basis as follows:

Units of production basis

For mining properties and leases and certain mining equipment, the economic benefits from the asset are consumed in a pattern which is linked to the production level. Except as noted below, such assets are depreciated on a units of production basis.

Straight line basis

Assets within operations for which production is not expected to fluctuate significantly from one year to another or which have a physical life shorter than the related mine are depreciated on a straight line basis as follows:

Land and Buildings
Land	Not depreciated
Buildings	5 to 50 years
Plant and equipment
Other pland and equipment	3 to 35 years
Power assets	25 to 100 years
Capital work in progress	Not depreciated

Residual values and useful lives are reviewed, and adjusted if appropriate, at each balance sheet date. Changes to the estimated residual values or useful lives are accounted for prospectively. In applying the units of production method, depreciation is normally calculated using the quantity of material extracted from the mine in the period as a percentage of the total quantity of material to be extracted in current and future periods based on proved and probable reserves and, for some mines, other mineral resources. Such non reserve material may be included in depreciation calculations in limited circumstances and where there is a high degree of confidence in its economic extraction. Development costs that relate to a discrete section of an ore body and which only provide benefit over the life of those reserves, are depreciated over the estimated life of that discrete section. Development costs incurred which benefit the entire ore body are depreciated over the estimated life of the ore body.

Impairment of non current assets

Property, plant and equipment and intangible assets with finite lives are reviewed for impairment if there is any indication that the carrying amount may not be recoverable. Impairment is normally assessed at the level of cash-generating units which, in accordance with IAS 36 'Impairment of Assets', are identified as the smallest identifiable group of assets that generates cash inflows, which are largely independent of the cash inflows from other assets.

In addition, an impairment loss is recognised for any excess of carrying amount over the fair value less costs to sell of a non current asset or disposal group held for sale.

Goodwill, including that related to equity accounted units, and indefinite-lived intangible assets are reviewed for impairment annually or at any time during the year if an indicator of impairment is considered to exist. Goodwill acquired through business combinations is allocated to groups of cash-generating units that are expected to benefit from the related business combination. The groups of cash-generating units represent the lowest level within the Group at which goodwill is monitored for internal management purposes and these groups are not larger than the reporting segments determined in accordance with IAS 14 'Segment Reporting'.

When an impairment review is undertaken, recoverable amount is assessed by reference to the higher of value in use (being the net present value of expected future cash flows of the relevant cash generating unit) and fair value less costs to sell ('fair value'). The best evidence of fair value is the value obtained from an active market or binding sale agreement. Where neither exists, fair value is based on the best information available to reflect the amount the Group could receive for the cash generating unit in an arm's length transaction. This is often estimated using discounted cash flow techniques.

Where recoverable amount is assessed using discounted cash flow techniques, the resulting estimates are based on detailed mine and/or production plans. For value in use, recent cost levels are considered, together with expected changes in costs that are compatible with the current condition of the business and which meet the requirements of IAS 36.

The cash flow forecasts are based on best estimates of expected future revenues and costs, including the future cash costs of production, capital expenditure, close down, restoration and environmental clean up. These may include net cash flows expected to be realised from extraction, processing and sale of mineral resources that do not currently qualify for inclusion in proved or probable ore reserves. Such non reserve material is included where there is a high degree of confidence in its economic extraction. This expectation is usually based on preliminary drilling and sampling of areas of mineralisation that are contiguous with existing reserves. Typically, the additional evaluation to achieve reserve status for such material has not yet been done because this would involve incurring costs earlier than is required for the efficient planning and operation of the mine.

Where the recoverable amount of a cash generating unit is dependent on the life of its associated ore body, expected future cash flows reflect long term mine plans, which are based on detailed research, analysis and iterative modelling to optimise the level of return from investment, output and sequence of extraction. The mine plan takes account of all relevant characteristics of the ore body, including waste to ore ratios, ore grades, haul distances, chemical and metallurgical properties of the ore impacting on process recoveries and capacities of processing equipment that can be used. The mine plan is therefore the basis for forecasting production output in each future year and for forecasting production costs.

The Group's cash flow forecasts are based on estimates of future commodity prices, which assume market prices will revert to the Group's assessment of the long term average price, generally over a period of three to five years. These long term commodity prices, for most commodities, are derived from an analysis of the marginal costs of the producers of these commodities. These assessments often differ from current price levels and are updated periodically. In some cases, prices applying to some part of the future sales volumes of a cash generating unit are predetermined by existing sales contracts. The effects of such contracts are taken into account in forecasting future cash flows.

The discount rates applied to the future cash flow forecasts represent an estimate of the rate the market would apply having regard to the time value of money and the risks specific to the asset for which the future cash flow estimates have not been adjusted. The Group's weighted average cost of capital is used as a starting point for determining the discount rates, with appropriate adjustments for the risk profile of the countries in which the individual cash generating units operate.

For operations with a functional currency other than the US dollar, the impairment review is undertaken in the relevant functional currency. The great majority of the Group's sales are based on prices denominated in US dollars. To the extent that the currencies of countries in which the Group produces commodities strengthen against the US dollar without commodity price offset, cash flows and, therefore, net present values are reduced.

When calculating value in use, IAS 36 requires that calculations should be based on exchange rates current at the time of the assessment.

Non financial assets other than goodwill that have suffered an impairment are tested for possible reversal of the impairment whenever events or changes in circumstances indicate that the impairment may have reversed.

(j) Determination of ore reserve estimates

The Group estimates its ore reserves and mineral resources based on information compiled by Competent Persons as defined in accordance with the Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves of December 2004 (the JORC code). Reserves, and for certain mines, other mineral resources, determined in this way are used in the calculation of depreciation, amortisation and impairment charges, the assessment of life of mine stripping ratios and for forecasting the timing of the payment of close down and restoration costs and clean up costs.

In assessing the life of a mine for accounting purposes, mineral resources are only taken into account where there is a high degree of confidence of economic extraction.

There are numerous uncertainties inherent in estimating ore reserves, and assumptions that are valid at the time of estimation may change significantly when new information becomes available. Changes in the forecast prices of commodities, exchange rates, production costs or recovery rates may change the economic status of reserves and may, ultimately, result in the reserves being restated.

(k) Provisions for close down and restoration and for environmental clean up costs

Close down and restoration costs include the dismantling and demolition of infrastructure and the removal of residual materials and remediation of disturbed areas. Estimated close down and restoration costs are provided for in the accounting period when the obligation arising from the related disturbance occurs, whether this occurs during the mine development or during the production phase, based on the net present value of estimated future costs. Provisions for close down and restoration costs do not include any additional obligations which are expected to arise from future disturbance. The costs are estimated on the basis of a closure plan. The cost estimates are updated annually during the life of the operation to reflect known developments, eg revisions to cost estimates and to the estimated lives of operations, and are subject to formal review at regular intervals.

Close down and restoration costs are a normal consequence of mining, and the majority of close down and restoration expenditure is incurred at the end of the life of the mine. Although the ultimate cost to be incurred is uncertain, the Group's businesses estimate their respective costs based on feasibility and engineering studies using current restoration standards and techniques.

The amortisation or 'unwinding' of the discount applied in establishing the net present value of provisions is charged to the income statement in each accounting period. The amortisation of the discount is shown as a financing cost, rather than as an operating cost.

The initial closure provision together with other movements in the provisions for close down and restoration costs, including those resulting from new disturbance, updated cost estimates, changes to the estimated lives of operations and revisions to discount rates are capitalised within property, plant and equipment. These costs are then depreciated over the lives of the assets to which they relate.

Where rehabilitation is conducted systematically over the life of the operation, rather than at the time of closure, provision is made for the estimated outstanding continuous rehabilitation work at each balance sheet date and the cost is charged to the income statement.

Provision is made for the estimated present value of the costs of environmental clean up obligations outstanding at the balance sheet date. These costs are charged to the income statement. Movements in the environmental clean up provisions are presented as an operating cost, except for the unwind of the discount which is shown as a financing cost. Remediation procedures may commence soon after the time the disturbance, remediation process and estimated remediation costs become known, but can continue for many years depending on the nature of the disturbance and the remediation techniques.

As noted above, the ultimate cost of environmental remediation is uncertain and cost estimates can vary in response to many factors including changes to the relevant legal requirements, the emergence of new restoration techniques or experience at other mine sites. The expected timing of expenditure can also change, for example in response to changes in ore reserves or production rates. As a result there could be significant adjustments to the provision for close down and restoration and environmental clean up, which would affect future financial results.

(l) Inventories

Inventories are valued at the lower of cost and net realisable value, primarily on a weighted average cost basis. Average costs are calculated by reference to the cost levels experienced in the current month together with those in opening inventory. Cost for raw materials and stores is purchase price and for partly processed and saleable products is generally the cost of production. For this purpose the costs of production include:

labour costs, materials and contractor expenses which are directly attributable to the extraction and processing of ore;
the depreciation of mining properties and leases and of property, plant and equipment used in the extraction and processing of ore; and
production overheads.

Stockpiles represent ore that has been extracted and is available for further processing. If there is significant uncertainty as to when the stockpiled ore will be processed it is expensed as incurred. Where the future processing of this ore can be predicted with confidence, eg because it exceeds the mine's cut off grade, it is valued at the lower of cost and net realisable value. If the ore will not be processed within the 12 months after the balance sheet date it is included within non current assets. Work in progress inventory includes ore stockpiles and other partly processed material. Quantities are assessed primarily through surveys and assays.

(m) Taxation

Current tax is the tax expected to be payable on the taxable income for the year calculated using rates that have been enacted or substantively enacted by the balance sheet date. It includes adjustments for tax expected to be payable or recoverable in respect of previous periods.

Temporary differences are the difference between the carrying value of an asset or liability and its tax base. Full provision is made for deferred taxation on all temporary differences existing at the balance sheet date with certain limited exceptions. The main exceptions to this principle are as follows:

tax payable on the future remittance of the past earnings of subsidiaries, associates and jointly controlled entities is provided for except where the Group is able to control the remittance of profits and it is probable that there will be no remittance in the foreseeable future;
deferred tax is not provided on the initial recognition of an asset or liability in a transaction that does not affect accounting profit or taxable profit and is not a business combination, such as on the recognition of a provision for close down and restoration costs and the related asset or on the recognition of new finance leases. Furthermore, with the exception of the unwind of discount, deferred tax is not recognised on subsequent changes in the carrying value of such assets and liabilities, for example where the related assets are depreciated or finance leases are repaid; and
deferred tax assets are recognised only to the extent that it is more likely than not that they will be recovered. Recoverability is assessed having regard to the reasons why the deferred tax asset has arisen and projected future taxable profits for the relevant entity (or group of entities).

Deferred tax is provided in respect of fair value adjustments on acquisitions. These adjustments may relate to assets such as mining rights that, in general, are not eligible for income tax allowances. In such cases, the provision for deferred tax is based on the difference between the carrying value of the asset and its nil income tax base. The existence of a tax base for capital gains tax purposes is not taken into account in determining the deferred tax provision relating to such mineral rights because it is expected that the carrying amount will be recovered primarily through use and not from the disposal of mineral rights. Also, the Group is only entitled to a deduction for capital gains tax purposes if the mineral rights are sold or formally relinquished.

Current and deferred tax relating to items recognised directly in equity are recognised in equity and not in the income statement.

(n) Post employment benefits

For defined benefit post employment plans, the difference between the fair value of the plan assets (if any) and the present value of the plan liabilities is recognised as an asset or liability on the balance sheet. Any asset recognised is restricted, if appropriate, to the present value of any amounts the Group expects to recover by way of refunds from the plan or reductions in future contributions. Actuarial gains and losses arising in the year are taken to the statement of recognised income and expense. For this purpose, actuarial gains and losses comprise both the effects of changes in actuarial assumptions and experience adjustments arising because of differences between the previous actuarial assumptions and what has actually occurred.

Other movements in the net surplus or deficit are recognised in the income statement, including the current service cost, any past service cost and the effect of any curtailment or settlements. The interest cost less the expected return on assets is also charged to the income statement. The amount charged to the income statement in respect of these plans is included within operating costs or in the Group's share of the results of equity accounted units as appropriate.

The most significant assumptions used in accounting for pension plans are the long term rate of return on plan assets, the discount rate and the mortality assumptions. The long term rate of return on plan assets is used to calculate interest income on pension assets, which is credited to the Group's income statement. The discount rate is used to determine the net present value of future liabilities. Each year, the unwinding of the discount on those liabilities is charged to the Group's income statement as the interest cost. The mortality assumption is used to project the future stream of benefit payments, which is then discounted to arrive at a net present value of liabilities.

The values attributed to plan liabilities are assessed in accordance with the advice of independent qualified actuaries.

The Group's contributions to defined contribution pension plans are charged to the income statement in the period to which the contributions relate.

(o) Cash and cash equivalents

For the purposes of the balance sheet, cash and cash equivalents comprise cash on hand, deposits held on call with banks and short term, highly liquid investments that are readily convertible into known amounts of cash and which are subject to insignificant risk of changes in value. For the purposes of the cash flow statement, cash and cash equivalents are net of bank overdrafts that are repayable on demand which are shown as current liabilities on the balance sheet.

(p) Financial instruments

(i) Financial assets

The Group classifies its financial assets in the following categories: at fair value through profit or loss, loans and receivables, available-for-sale and held to maturity investments. The classification depends on the purpose for which the financial assets were acquired. Management determines the classification of financial assets at initial recognition.

(a) Financial assets at fair value through profit or loss

Derivatives are included in this category unless they are designated as hedges. Assets in this category are classified as current assets. Generally, the Group does not acquire financial assets for the purpose of selling in the short term.

Financial assets carried at fair value through profit or loss are initially recognised at fair value and transaction costs are expensed in the income statement.

(b) Loans and receivables

Loans and receivables are non derivative financial assets with fixed or determinable payments that are not quoted in an active market. They are classified as current assets or non current assets based on their maturity date. Loans and receivables comprise trade and other receivables', 'other financial assets' and 'cash and cash equivalents' in the balance sheet. Loans and receivables are carried at amortised cost less any impairment.

(c) Available-for-sale financial assets

Available-for-sale financial assets are non derivatives that are either designated as available for sale or not classified in any of the other categories. They are included in non-current assets unless the Group intends to dispose of the investment within 12 months of the balance sheet date.

Changes in the fair value of available-forsale financial assets denominated in a currency other than the functional currency of the holder other than equity investments, are analysed between translation differences and other changes in the carrying amount of the security. The translation differences are recognised in profit or loss. Any impairment charges are also recognised in profit or loss, while other changes in fair value are recognised in equity.

When financial assets classified as available-for-sale are sold, the accumulated fair value adjustments recognised in equity are included in the income statement within 'net operating costs'.

Dividends on available-for-sale equity instruments are also recognised in the income statement within 'interest receivable and similar income' when the Group's right to receive payments is established.

Financial assets not carried at fair value through profit and loss are initially recognised on the trade date at fair value plus transaction costs.

Financial assets are derecognised when the investments mature or are sold, and substantially all the risks and rewards of ownership have been transferred.

(ii) Financial liabilities

Borrowings and other financial liabilities are recognised initially at fair value, net of transaction costs incurred and are subsequently stated at amortised cost. Any difference between the amounts originally received (net of transaction costs) and the redemption value is recognised in the income statement over the period to maturity using the effective interest method.

Borrowings and other financial liabilities are classified as current liabilities unless the Group has an unconditional right to defer settlement of the liability for at least 12 months after the balance sheet date.

(iii)Derivative financial instruments and hedge accounting

The Group's policy with regard to 'Financial risk management' is set out in note 33. When the Group enters into derivative contracts these transactions are designed to reduce exposures related to assets and liabilities, firm commitments or anticipated transactions.

Commodity based contracts that meet the definition of a derivative in IAS 39 but are entered into in accordance with the Group's expected purchase or sales requirements are recognised in earnings as described in note 1(c) Sales revenue above.

All other derivatives are initially recognised at their fair value on the date the derivative contract is entered into and are subsequently remeasured subject to IAS 39 at their fair value at each balance sheet date. The method of recognising the resulting gain or loss depends on whether or not the derivative is designated as a hedging instrument and, if so, the nature of the item being hedged. The Group designates certain derivatives as either hedges of the fair value of recognised assets or liabilities or of firm commitments (fair value hedges) or hedges of highly probable forecast transactions (cash flow hedges).

At the inception of a hedge relationship, the Group formally designates and documents the hedge relationship to which the Group wishes to apply hedge accounting and the risk management objective and strategy for undertaking the hedge. The documentation includes identification of the hedging instrument, the hedged item or transaction, the nature of the risk being hedged and how the entity will assess the hedging instrument's effectiveness in offsetting the exposure to changes in the hedged item's fair value or cash flows attributable to the hedged risk. Hedges that are expected to be highly effective in achieving offsetting changes in fair value or cash flows are assessed on an ongoing basis to determine that they actually have been highly effective throughout the financial reporting periods for which they were designated.

- Fair value hedges: Changes in the fair value of derivatives that are designated and qualify as fair value hedges are recorded in the income statement, together with any changes in the fair value of the hedged asset or liability or firm commitment that is attributable to the hedged risk. Where derivatives are held with different counterparties to the underlying asset or liability or firm commitment, the fair values of the derivative assets and liabilities are shown separately in the balance sheet as there is no legal right of offset. The gain or loss relating to the effective portion of interest rate swaps hedging fixed rate borrowings is recognised in the income statement within 'interest payable and similar charges'.

- Cash flow hedges: The effective portion of changes in the fair value of derivatives that are designated and qualify as cash flow hedges is recognised in equity. The gain or loss relating to the ineffective portion is recognised immediately in the income statement within 'net operating costs'. Amounts accumulated in equity are recycled in the income statement in the period when the hedged item affects profit or loss, for example when the forecast sale that is being hedged takes place. The realised gain or loss relating to the effective portion of forward foreign exchange or commodity contracts hedging sales is recognised in the income statement within 'sales revenue'. When the forecast transaction that is being hedged results in the recognition of a non financial asset the gains and losses previously deferred in equity are transferred from equity and adjust the cost of the asset. The gains and losses are recognised subsequently in the income statement within 'net operating costs' when the non financial asset is amortised.

When a cash flow hedging instrument expires or is sold, or when a cash flow hedge no longer meets the criteria for hedge accounting, although the forecasted transaction is still expected to occur, any cumulative gain or loss relating to the instrument which is held in equity at that time remains in equity and is recognised when the forecast transaction is ultimately recognised in the income statement. When a forecast transaction is no longer expected to occur, the cumulative gain or loss that was reported in equity is immediately transferred to the income statement.

When a fair value interest rate hedging instrument expires or is sold, or when a fair value interest rate hedge no longer meets the criteria for hedge accounting, the fair value adjustments which have been made to the hedged item are amortised through the income statement over its remaining life.

- Derivatives that do not qualify for hedge accounting: Any derivative contracts that do not qualify for hedge accounting, are marked to market at the balance sheet date. In respect of currency swaps, the gain or loss on the swap and the offsetting gain or loss on the financial asset or liability against which the swap forms an economic hedge are shown in separate lines in the income statement within the line 'net gains on derivatives not qualifying for hedge accounting'. In respect of other derivatives, the mark to market may give rise to charges or credits to the income statement in periods before the transaction against which the derivative is held as an economic hedge is recognised. These charges or credits would be recognised in the line 'net gains on derivatives not qualifying for hedge accounting'.

- Embedded derivatives: Derivatives embedded in other financial instruments or other host contracts are treated as separate derivatives when their risks and characteristics are not closely related to their host contracts. In some cases, the embedded derivatives may be designated as hedges and will be accounted for as described above.

(iv) Fair value

Fair value is the amount at which a financial instrument could be exchanged in an arm's length transaction between informed and willing parties. Where relevant market prices are available, these have been used to determine fair values. In other cases, fair values have been calculated using quotations from independent financial institutions, or by using valuation techniques consistent with general market practice applicable to the instrument.

(i) The fair values of cash, short term borrowings and loans to joint ventures and associates approximate to their carrying values, as a result of their short maturity or because they carry floating rates of interest.

(ii) The fair values of medium and long term borrowings is calculated as the present value of the estimated future cash flows using an appropriate market based yield curve. The carrying value of the borrowings is amortised cost.

(iii) Derivative financial assets and liabilities are carried at fair value based on published price quotations for the period for which a liquid active market exists. Beyond this period, the Group's own assumptions are used.

The fair values of the various derivative instruments used for hedging purposes are disclosed in note 34. Movements on the hedging reserve are disclosed within note 30. The full fair value of a derivative that qualifies for hedge accounting is classified as a non current asset or liability if the remaining maturity of the hedged item is more than 12 months, and as a current asset or liability, if the remaining maturity of the hedged item is less than 12 months.

(v) Impairment of financial assets

Available-for-sale financial assets The group assesses at each balance sheet date whether there is objective evidence that a financial asset or a group of financial assets is impaired. In the case of equity securities classified as available for sale, an evaluation is made as to whether a decline in fair value is 'significant' or 'prolonged' based on an analysis of indicators such as significant adverse changes in the technological, market, economic or legal environment in which the company invested in operates.

If an available-for-sale financial asset is impaired, an amount comprising the difference between its cost (net of any principal payment and amortisation) and its current fair value, less any impairment loss previously recognised in the income statement is transferred from equity to the income statement. Reversals in respect of equity instruments classified as availablefor- sale are not recognised in the income statement. Reversals of impairment losses on debt instruments are reversed through the income statement, if the increase in fair value of the instrument can be objectively related to an event occurring after the impairment loss was recognised.

(vi) De-recognition of financial assets and liabilities

Financial assets

A financial asset is derecognised when its contractual rights to the cash flows that comprise the financial asset expire or substantially all the risks and rewards of the asset are transferred.

Financial liabilities

A financial liability is derecognised when the obligation under the liability is discharged, cancelled or expired. Gains and losses on derecognition are recognised within finance income and finance costs respectively.

Where an existing financial liability is replaced by another from the same lender on substantially different terms, or the terms of an existing liability are substantially modified, such an exchange or modification is treated as a de-recognition of the original liability and the recognition of a new liability, and the difference in the respective carrying amounts is recognised in the income statement.

(vii) Trade receivables

Trade receivables are recognised initially at fair value and are subsequently measured at amortised cost reduced by any provision for impairment. A provision for impairment of trade receivables is established when there is objective evidence that the Group will not be able to collect all amounts due. Indicators of impairment would include financial difficulties of the debtor, likelihood of the debtor's insolvency, default in payment or a significant deterioration in credit worthiness. Any impairment is recognised in the income statement within 'net operating costs'. When a trade receivable is uncollectable, it is written off against the allowance account. Subsequent recoveries of amounts previously written off are credited against 'net operating costs' in the income statement.

(viii) Trade payables

Trade payables are recognised initially at fair value and subsequently measured at amortised cost using the effective interest method.

(q) Share based payments

The fair value of cash-settled share plans is recognised as a liability over the vesting period of the awards. Movements in that liability between accounting dates are recognised as an expense. The grant date fair value of the awards is determined from the market value of the shares at the date of award and adjusted for any market based vesting conditions attached to the award eg relative Total Shareholder Return ('TSR') performance. Fair values are subsequently remeasured at each accounting date to reflect the market value of shares at the measurement date and, where relevant, the number of awards expected to vest based on the current and anticipated TSR performance. If any awards are ultimately settled in shares, the liability is transferred directly to equity as part of the consideration for the equity instruments issued.

The Group's equity-settled share plans are settled either by the issue of shares by the relevant parent company, by the purchase of shares on market or by the use of shares previously acquired as part of a share buyback. The fair value of the share plans is recognised as an expense over the expected vesting period with a corresponding entry to retained earnings for Rio Tinto plc plans and to other reserves for Rio Tinto Limited plans. If the cost of shares acquired to satisfy the plans exceeds the expense charged, the excess is taken to the appropriate reserve. The fair value of the share plans is determined at the date of grant, taking into account any market based vesting conditions attached to the award (eg Total Shareholder Return). The Group uses fair values provided by independent actuaries calculated using a lattice based option valuation model.

Non market based vesting conditions (eg earnings per share targets) are taken into account in estimating the number of awards likely to vest. The estimate of the number of awards likely to vest is reviewed at each balance sheet date up to the vesting date, at which point the estimate is adjusted to reflect the actual awards issued. No adjustment is made after the vesting date even if the awards are forfeited or not exercised.

Further information about the treatment of individual share based payment plans is provided in note 48.

(r) Contingencies

Contingent liabilities are not recognised in the financial statements but are disclosed by way of note unless their occurrence is remote.

Contingent assets are not recognised in the financial statement but they are disclosed by way of note if they are deemed probable.

(s) Share capital

Ordinary shares are classified as equity. Incremental costs directly attributable to the issue of new shares or options are shown in equity as a deduction, net of tax, from the proceeds.

Where any group company purchases the Group's equity share capital (treasury shares), the consideration paid, including any directly attributable incremental costs (net of income taxes) is deducted from equity attributable to Rio Tinto's equity shareholders. Where such shares are subsequently reissued, any consideration received, net of any directly attributable incremental transaction costs and the related income tax effects, is included in equity attributable to Rio Tinto's equity shareholders.

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