EX-99 2 exhibit99-1.htm

| Notice to ASX

Increase to Mount Thorley Warkworth Mineral Resources

24 January 2017

Rio Tinto today announces an increase of Rio Tinto Coal Australia’s managed thermal coal resources at Mount Thorley Warkworth in New South Wales, Australia, compared to the previous estimates reported in R io Tinto’s 2015 Annual Report. The announcement of this increase is made simultaneously with the announcement by Rio Tinto that it has entered into a binding agreement for the sale of its Australian wholly-owned subsidiary Coal & Allied Industries Limited, which in turn holds an 80 per cent interest in the Mt Thorley mine and a 55.6 per cent interest in the Warkworth mine (as well as a 67.6 per cent interest in the Hunter Valley Operations mine and a 36.5 per cent interest in a coal export terminal at the Port of Newcastle).

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 ASX Listing Rules. As such, the reported increases relating to Mount Thorley Warkworth require the additional supporting information set out in this release and its appendix.

Mount Thorley Mineral Resources exclusive of Ore Reserves have increased by 208 Mt, from 114 Mt to 322 Mt.

Warkworth Mineral Resources exclusive of Ore Reserves have increased by 353 Mt, from 613 Mt to 966 Mt.

This increase in Mineral Resources reflects a continuation of work on Rio Tinto Coal Australia deposits previously announced on 28 November 2014 and 3 March 2016. The updates are based on a rigorous examination of leases that included a reinterpretation of the geological model, employment of new datasets and adopting improved Mineral Resource estimation methods.

Minerals Resources are quoted on a 100 per cent basis. Rio Tinto’s interest as at 24 January 2017 is listed in the schedule (Figure 1).

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Summary of information to support the Mineral Resources estimates

Mineral Resource Estimates for Mount Thorley Warkworth are supported by the information set out in the appendix to this release in accordance with JORC Code Table 1 (Sections 1 to 3), and also located at www.riotinto.com/JORC.

An increase in Mount Thorley Warkworth Mineral Resources follows the completion of strategic optimization studies for opencast deposits. Geology models supporting the Mineral Resource increase were updated to incorporate new and legacy drilling data, leading to revised interpretations of coal seam structure, yield and quality.

The following summary of information for Mineral Resource Estimates is provided in accordance with Chapter 5.8 of ASX Listing Rules.

Geology and geological interpretation

Mount Thorley Warkworth (MTW) is an integrated operation comprising two open cut mines located adjacent to each other, 15 kilometres south-west of Singleton within the Sydney Basin of New South Wales (NSW).

Rio Tinto Coal Australia (RTCA) has constructed a single geology model underlying the MTW leases. The geology model contains comprehensive datasets and well defined interpretations for coal quality and geological structure, including coal seam continuity and faulting. Coal seam sub-crops, limits of oxidation and igneous intrusions are well defined. The geology model is supported by surface outcrop mapping, drilling and airborne geophysical data. A total of 2,670 holes are drilled into the MTW deposit.

Drilling techniques

Open hole drilling was the preferred method for delineating coal and waste structure. Core drilling, including 4C (100mm), HQ3 and PQ3 diameters was also completed for all deposits for the purpose of coal quality, geotechnical and gas characterization. Large diameter 8C (200mm) holes have also been drilled for the purpose of characterizing coal quality and to support sizing studies. Downhole geophysical logging was completed for the majority of drill holes in all deposits, employing a comprehensive suite of down hole tools to collect calliper, gamma, density, neutron and sonic measurements. Acoustic scanner measurements were also routinely completed for cored holes to obtain additional data for geotechnical assessments.

Sampling, sub-sampling method and sample analysis method

Sampling of drill core was completed according to a universal standard set of instructions. Samples were bagged at the drill site and then transported to an external accredited laboratory for analysis. All samples were weighed, air-dried and then re-weighed before being crushed to a nominal size. A rotary splitter was used to divide the sample into portions available for further analysis. For all deposits coal quality analysis was by a three-stage method comprising raw analysis for all plies followed by washability and product testing on composite samples. All sample treatment and analysis was conducted according to procedures which adhere to Australian or International equivalent standards in National Association of Testing Authorities certified laboratories.

Criteria used for classification

RTCA employs a standard methodology for classifying Mineral Resources into inferred, measured and indicated confidence categories. Drill holes were assessed according to the value and reliability of contained data to contribute a point of observation to Mineral Resource classifications. Structure and coal quality confidence limits were plotted separately on a seam group basis with classification of coal inventory into areas of low, medium or high confidence. These were combined to delineate areas of Measured, Indicated and Inferred coal inventory as a basis for classifying Mineral Resource tonnage estimates.

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A range of drill hole spacing limits were identified to reflect the inherent variability of each seam group modelled within each structural domain of the deposit. Structure classifications correspond with drill hole spacing distances of 150m to 250m for high, 300m to 500m for medium and 1,200m to 2,000m for low confidence limits. Coal quality classifications correspond with drill hole spacing distances of 300m to 500m for high, 600m to 1,000m for medium and 1,800m to 3,000m for low confidence limits.

Estimation methodology

Geology models were constructed employing coal industry standard software. For structural modelling a Finite Element Method (FEM) interpolator was employed. For coal quality modelling an inverse distance squared interpolator was employed. All surfaces and coal qualities were interpolated into grids with 20m2 to 50 m2 node spacing. Modelling was completed on an iterative basis by checking cross sections and contours of structural and coal quality attributes. Database values were posted on contours to provide a further check. For all deposits a volume / tonnage check was completed with predecessor models to provide final validation.

Reasonable prospects for eventual economic extraction

RTCA employs a standard approach to identify Mineral Resource volumes with reasonable prospects for eventual economic extraction.

For opencast deposits a minimum coal thickness of 0.25m and density of 1.8 g/m3 were applied as cut-off parameters for reporting Mineral Resources. Opencast resource volumes correspond with the limits of a “break even” ($0 margin) Ler chs-Grossman optimised shell. This method identifies the maximum depth or lowermost seam to be considered.

For underground resources a minimum coal thickness of 1.8m and certain depth limits provide cut-off parameters for reporting Mineral Resources. Underground Mineral Resources correspond with practically mineable coal seam volumes employing longwall or board and pillar methods. Underground Mineral Resources must support longwall mining layouts with a break-even” or better economic result, including reasonable development capital costs.

Competent Persons Statement

The information in this report that relates to Mineral Resources is based on information compiled by Dr Richard Ruddock, a Competent Person who is a Member of The Australasian Institute of Mining and Metallurgy. Dr Ruddock is a full-time employee of the company.

Dr Ruddock has 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 C ode for Reporting of Exploration Results, Mineral Resources and

Ore Reserves’. Dr Ruddock consents to the inclusion in the report of the matters based on the information in the form and context in which it appears.

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Contacts

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