Prepared by EDGARX.com

Notice to ASX

Change to IOC Mineral Resources

2 March 2017

Included in Rio Tinto’s annual Mineral Resources and Ore Reserves tables, released to the market today as part of its 2016 Annual report, is a decrease in Mineral Resources at Rio Tinto’s 59 per cent-owned Iron Ore Company of Canada (IOC) mine in Labrador City, Labrador and Newfoundland, Canada.

The updated Mineral Resources are reported in accordance with the Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves, 2012 (JORC Code) and the ASX Listing Rules. As such, the reported decrease relating to the IOC operations requires the additional supporting information set out in this release and its appendix. Mineral Resources are quoted on 100% basis.

Rio Tinto’s Ore Reserves and Mineral Resources are set out in full in its 2016 Annual report.

During 2016, IOC Mineral Resources have decreased by 674Mt from 2,762 Mt to 2,088Mt, a 24 per cent decrease.

This change follows both technical and financial reassessment of the Mineral Resources and does not impact IOC’s Ore Reserves. The current life of mine plan anticipates a production life extending to 2042, based on the reported Ore Reserves only.

Resources at IOC are reported additional to reserves.

The updated Mineral Resource estimate comprises:

Measured Resource: 172mt @ 40.2% Fe
Indicated Resource: 844Mt @ 38.3% Fe
Inferred Resource: 1,072Mt @ 37.9% Fe
Total Mineral Resource: 2,088Mt @ 38.3% Fe

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2016 Annual report Mineral Resources table, showing line items relating to the IOC changes

Resources at end 2016

Total resources 2016 compared with 2015

Likely

mining

method (a)

Measured

Indicated

Inferred

2016

2015

IRON ORE (b)

Millions

Fe %

Millions

Fe %

Millions

Fe %

Millions

Fe %

Millions

Fe %

Rio Tinto

of tonnes

of tonnes

of tonnes

interest %

Iron Ore Company of

O/P

Canada (Canada) (c)

172

40.2

844

38.3

1072

37.9

2088

2762

38.3

37.6

58.7

Notes

(a)	Likely mining method: O/P = open pit; O/C = open cut; U/G = underground; D/O = dredging operation.
(b)	Iron ore Resources tonnes are reported on a dry weight basis.
(c)	Resources at Iron Ore Company of Canada decreased following updated economic studies in addition to a revised geological model and Resource classification. A JORC table 1 in support of these changes will be released to the market contemporaneously with the release of this Annual report and can be viewed at riotinto.com/JORC. Resources at Iron Ore Company of Canada are reported on an in-situ dry basis and are estimated to produce marketable product (59 per cent pellets and 41 per cent concentrate for sale) at a natural moisture content of two per cent of 69 million tonnes at 65 per cent iron (Measured), 329 million tonnes at 65 per cent iron (Indicated) and 412 million tonnes at 65 per cent iron (Inferred) using process recovery factors derived from current IOC concentrating and pellet operations.

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Summary of information to support the Mineral Resources estimates

Decreases in the Mineral Resource estimate for IOC are supported by the information set out in the appendix to this release and located at riotinto.com/JORC in accordance with the Table 1 checklist (Sections 1 to 3) in the JORC Code.

The 24% Mineral Resource reduction results from:

A reduction in projected long-term iron ore prices (17 per cent);
Adjusted resource classifications (two per cent)
Updated geological interpretation (five per cent)

The following summary of information for Mineral Resource estimates is provided in accordance with rule 5.8 of the ASX Listing Rules.

Geology and geological interpretation

IOC’s Mineral Resources are located near the southern end of the Labrador Geosyncline in eastern Canada, within the lithotectonic Gagnon Terrane, in the Grenville Province of Western Labrador. IOC’s Mineral Resources lie within the Lower Proterozoic (c.a. 2.0 Ga) Sokoman iron formation of the Knob Lake Group. The Middle Iron Formation (MIF) of the Sokoman formation contains the economically viable iron ore.

The Knob Lake Group was deformed and subjected to metamorphism ranging from greenschist to upper amphibolite facies within a northwesterly-verging ductile fold and thrust belt, during the Grenville Orogeny.

The Middle Iron Formation comprises a sequence of quartz-magnetite, and/or quartz-specularite-magnetite, and/or quartz-specularite-magnetite-carbonate, and/or quartz-specularite-magnetite-anthophyllite gneiss and schist units. A vertical zonation is typically present with finer grained quartz magnetite dominated iron formation forming the basal section. The upper portion of the Middle Iron Formation horizon is predominantly comprised of coarser grained quartz hematite iron formation. Drilling techniques All of IOC’s Mineral Resources are defined using diamond core drilling only. Approximately 500,000 m have been drilled on the Mineral Resource deposits, with 60 per cent of this drilling having taken place since 2004. All of the recent resource definition drilling has used NQ sized core. Geotechnical drilling uses HQ sized core. Historically, BQ sized core was also used for resource definition.

Hole dip surveys have been routinely carried out on all holes. Gyro surveys of longer holes (>150m) have only been carried out since 2015. All hole collars are surveyed after drilling.

Drill holes spacings vary by deposit. Deposits are generally drilled initially at wide spacings (typically 244m x 244m) before being progressively infilled to 122m x 122m (inferred resource) and finally 61m x 61m (measured resource).

Sampling, sub-sampling method and sample analysis method

Drill core is logged, photographed and then split, with half core being sent to the IOC laboratory for analysis. Some core has historically been sent to external laboratories for analysis, but most has been analysed by the IOC laboratory. Some of the earlier core was drilled at smaller diameter (BQ) with whole core being sent for analysis.

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The current sample length is four metres, although five-metre samples were used from 2004 to 2008. Samples are limited to a single lithological unit, with shorter samples being taken when contacts are encountered. All mineralised lithologies are sampled and waste units are sampled adjacent to contacts. Narrow waste units are generally completely sampled, whereas thicker waste units have samples taken adjacent to contacts and at intervals within the unit. Large waste units (eg the upper and lower units of the Sokoman formation) are generally only sampled at the contact with the MIF. Intervals with logged fibrous amphiboles are not sampled.

Core samples are coarse crushed, then riffle split during several crushing stages to a 20g sample which is pulverised to produce a sample for assaying. Iron grade is assayed by titration, magnetite by Satmagan (calibrated), carbonate and combined water are assayed by absorption method in a Leco furnace and all other assays are carried out by XRF techniques on fused beads.

QA/QC checks were implemented in 2004 and consist of duplicate analysis of half core, coarse rejects, and pulp rejects, at a frequency of 1:50. Monitor standards have been created from various ore types from IOC deposits, these are submitted on the basis of 1 per lab batch (approximately 1:12). The monitor ore type that is submitted is type that best represents the sample batch being submitted eg. a high magnetite monitor submitted for a sample batch containing high magnetite mineralogy. Blank samples, consisting of >95 per cent pure quartzite, have been inserted at a rate of 1:49 samples since 2012.

Density analysis is performed at a rate of one in every four drill core samples during drilling projects using a water immersion method. Vuggy and friable samples have been sent to an external lab for wax coated density analysis since 2015.

The coarse rejects are composited into nominally 16m composites (ie equivalent to four assay intervals for iron recovery testing (on a shaking table) by an external testing laboratory. Half core samples are also collected from the same 16m intervals for grind energy testing (SPI testing) by a second external testing laboratory.

Criteria used for classification

Resource classifications are determined on a section by section basis utilizing drill spacing and geological complexity as the main criteria. Areas of limonite or poor core recovery are lowered in classification due to potential uncertainty. Sectional polygons are evaluated for continuity along strike and then joined to form a continuous triangulated solid. Resource classification takes subjective account of geological and mineralisation continuity, drill density, core recovery and confidence in assay results (based on presence or absence of QA/QC programs).

In general, areas having a 61x61m drill spacing are considered Measured Resources. Areas with 120x61m are classified as Indicated Resources and areas with greater than 120x120m drill spacing are considered to be Inferred Resources. Areas with drill spacings greater than 244m along strike or 122m across strike are not considered to meet Mineral Resource reporting standard. Any Measured areas with poor core recovery or strong limonitic alternation are lowered to an Indicated classification to reflect these as areas of geological or metallurgical uncertainty.

In 2015, two of the Mineral Resource deposits still used an older, script-based classification methodology. This older methodology was replaced with the above sectional resource category methodology in all models for 2016 reporting, which has resulted in a two per cent reduction in Mineral Resources.

Estimation methodology

Geological models of the folded deposits are generated from logged drill hole geological contacts, with surface outcrop mapping and pit face mapping also used where available. Updated interpretations have resulted in a five per cent reduction in the Mineral Resource estimate.

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Mineral Resource models use a sub-blocking methodology, with a minimum block size of 5m x 5m x 3.425m.

Samples are composited to 12m lengths for assays and 16m lengths for metallurgical data (grind energy and iron recovery). Geological units are divided into structural domains for interpolation, based on the fold geometry. Grades are interpolated within each domain using inverse distance techniques. Four estimation passes are used with progressively increasing search radii, with the final pass using a 600m search radius. Any blocks which are not populated after four interpolation passes are assigned the average grade for that lithological unit. No cutting or capping is applied to any sample or composite data.

Reconciliations between reported concentrator feed and Ore Reserve models are used to provide an indication of the accuracy of Mineral Resource estimates. These reconciliations indicate that Proved Ore Reserves (the equivalent of Measured Mineral Resources) reconcile very well with actual production.

Cut-off grades

Modelling indicates that 99 per cent of oxide mineralised material in the middle iron formation has a weight yield greater than 30 per cent. At projected long term prices and costs, the breakeven cut-off grade is less than 30 per cent, so the entire middle iron formation is effectively above cut-off. Consequently, mineral resource definition is based on lithology (ie all oxide mineralised middle iron formation), rather than cut-off.

Mining and Metallurgical Methods and Parameters

IOC uses regularisation of Mineral Resource block models to estimate dilution and ore loss in the mining process. Reconciliations between regularised block models and actual production indicate that this approach provides acceptable estimates. Iron recovery in the concentrator is estimated using recoveries measured on a laboratory shaking table, adjusted with a correction factor derived from reconciliations between the modelled iron recovery and actual iron recovery. Grind energy consumption is interpolated in the Resource model based on metallurgical testing. Reconciliations between the modelled grind energy and actual grind energy indicate that this approach is acceptable. Reasonable prospects for eventual economic extraction IOC’s Mineral Resources are constrained using pit shells generated by the Whittle pit optimisation software. IOC uses the same economic and production parameters to constrain Mineral Resources and Ore Reserves. The reduced prices used for the end 2016 Mineral Resource have resulted in a 17 per cent reduction in the resource estimate. The use of the lower price was based on a reassessment of the long term market outlook.

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Competent Persons Statement

The material in this report that relates to Mineral Resources is based on information prepared by Tim Leriche, Ramsey Way and Bronwen Wallace, who are Competent Persons and Members of Professional Engineers and Geoscientists Newfoundland and Labrador. All are full-time employees of Rio Tinto.

Mr Leriche, Mr Way and Ms Wallace have sufficient experience that is relevant to the style of mineralisation and type of deposit under consideration and to the activity being undertaken to qualify as Competent Persons as defined in the 2012 Edition of the ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’. Each of Mr Leriche, Mr Way and Ms Wallace consents to the inclusion in the report of the material based on the information that he or she has prepared in the form and context in which it appears.

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