Prepared by EDGARX.com

Notice to ASX

Increase to Jadar Project 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, are increases in Mineral Resources for Rio Tinto’s 100 per cent-owned Jadar Lithium and Borates Mineral Project in Jadar, Serbia.

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 increases relating to the Jadar project requires the additional supporting information set out in this release and its appendix.

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

During 2016, Jadar Mineral Resources have increased by 19Mt from 117Mt to 136Mt, a 16 per cent increase, including the first release of Indicated category Mineral Resources.

The updated Mineral Resource estimate comprises:

Indicated Resource: 52.4 Mt @ 1.79% Li2O, 19.2% B2O3
Inferred Resource: 83.3 Mt @ 1.90% Li2O, 13.0% B2O3
Total Mineral Resource: 135.7 Mt @ 1.86% Li2O, 15.4% B2O3

Equivalent borate product resources are 21Mt of B2O3.

The upgrades have resulted from continuing orebody knowledge programmes undertaken at Jadar by Rio Tinto. This increase in orebody knowledge has been obtained from the following work programmes which represent components of the Pre-Feasibility study currently underway:

3D seismic data processing and interpretation.
Consolidating and analysing a large volume of new geology data sets from previous drilling campaigns.
Reinterpreting and standardising all Jadar structural and geology models, allowed by the expanded range of available data sets.
Improved understanding of the lithostratigraphy and controls on mineralisation.
Adopting new Mineral Resource estimation methods.

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Appendix

Jadar Project - Table 1

The following table provides a summary of important assessment and reporting criteria used at the Jadar Project for the reporting of mineral resources in accordance with the Table 1 checklist in The Australasian Code for the Reporting of Exploration Results, Mineral Resources and Ore Reserves (The JORC Code, 2012 Edition). Criteria in each section apply to all preceding and succeeding sections. Section 4 is omitted due no reported Reserves.

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

Resources at end 2016

Total resources 2016 compared with 2015

Likely

mining

method (a)

Measured

Indicated

Inferred

2016

2015

BORATE (b)

Millions

B2O3 %

Millions

B2O3 %

Millions

B2O3 %

Millions

B2O3 %

Millions

B2O3 %

Rio Tinto

of tonnes

of tonnes

of tonnes

interest %

Jadar (Serbia) (c)

U/G

100.00

Resources at end 2016

Total resources 2016 compared with 2015

Likely

mining

method (a)

Measured

Indicated

Inferred

2016

2015

LITHIUM

Millions

Li2O %

Millions

Li2O %

Millions

Li2O %

Millions

Li2O %

Millions

Li2O %

Rio Tinto

of tonnes

of tonnes

of tonnes

interest %

Jadar (Serbia) (c)

U/G

1.8

1.9

136

1.9

117

1.8

100.00

Notes

(a)	Likely mining method: O/P = open pit; O/C = open cut; U/G = underground; D/O = dredging operation.
(b)	Borates Resources are reported as in situ B2O3, rather than marketable product as in Reserves.
(c)	Resources at Jadar increased following additional drilling and an updated geological model supported by a 3D seismic survey. 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/factsheets/JORC. Borate resources are quoted as product at 21mt B2O3. The equivalent in situ Resource is 52 million tonnes at 19.2 per cent B2O3 (Indicated) and 83 million tonnes at 13.0 per cent B2O3 (Inferred).

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Summary of information to support the Mineral Resources estimates

Increases in the Mineral Resource estimate for the Jadar Project 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.

All models (structural and geological) supporting the Mineral Resource increase were updated to incorporate new and legacy drilling and 3D seismic data, leading to revised interpretations of main structures, geology and Lower Jaderite Zone grade continuity.

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

The Jadar deposit, discovered in 2004 in western Serbia is a concentration of lithium and borates in a mineral at that time new to science, named Jadarite. It lies in a valley within flat-lying farmland area of 3.0 by 2.5 km, at depths from 100 m to 720 m below surface. The deposit includes three types of mineralization occurring as stratiform lenses of variable thickness, and hosted in gently dipping sequence of mainly fine-grained sediments that is crossed by faults:

Jadarite LiNaSiB 3O7(OH) mineralization, so far unique to this deposit, is mainly concentrated in three gently dipping tabular zones known as the Upper, Middle and Lower Jadarite Zones (UJZ, MJZ and LJZ),
Sodium borates (mainly Ezcurrite, but also Kernite and Borax) as lenses interbedded with Jadarite, mainly enclosed or adjacent to the LJZ with a more restricted areal distribution,
Gypsum, in the gypsum zone in the upper part of the stratigraphic sequence (sub economic).

All Jadar geology models contain comprehensive datasets and well defined interpretations of the main structures and geological units. All models are supported by various drilling programs and a full range of downhole logging and geophysical surveys, as well as 3D seismic survey of the extended deposit area, supported by data processing and interpretation, that has enhanced understanding of main structural fault systems controlling the location of the Jadarite mineralisation.

Drilling techniques

The HQ3 core drilling was the predominant drilling type for the Jadar deposit. Since 2004, a total of 310 drill holes (aggregate depth of 125,605 m) were drilled for resource definition, geotechnical, hydrogeological, sterilisation drilling purposes. This includes 11, large-diameter (500 mm), reverse circulation drill holes and 14 PQ core holes, that primarily, but not exclusively, served for the collection of a bulk samples required for the metallurgical test-work program.

Resource estimation is supported by total of 175 drill holes with an aggregate depth of 100,622 m. The drill holes are normally planned and executed as vertical drill holes, except for 37 inclined holes, that were orientated to intercept structural features. All holes were consistently downhole surveyed after drilling was completed. Downhole logging included various probes for deviation surveys, calliper and temperature as well as other logging methodologies to detect and define the orientation of bedding and structures and/or other geotechnical characteristics.

Drill hole spacing (random arrangement-semi grid) ranges from 25 m in the central part, moving up to 500 m in the peripheral areas (130 m on average) and is considered sufficient to establish geological and grade continuity to support the current Mineral Resource classifications.

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Sampling, sub-sampling method and sample analysis method

All samples for assaying and density determination are taken from predominant HQ3 (some PQ3 and rarely NQ3) vertical or occasionally inclined core drilling. Sampling was completed at RT drill core storage facility, after logging, based on sampling criteria determined by lithology and mineralogy, in accordance with established formal protocols.

From 2015 onwards, the sample lengths were assigned based on lithological – geodomain boundaries, rather than at 1m fixed intervals, following the maximum and minimum thickness criteria’s established in the sampling protocols. Since 2011, sample preparation has been completed at RT Jadar sample prep laboratory located at the core storage facility (rarely in an external ALS prep-laboratory). After weighing, samples were immersed in water for volumetric measurement and then dried at temperature just below 60ºC, for minimum 24 hours, and weighing again for dry density calculation. Samples were crushed to -1.4 mm in two stages, subsampled in a rotary splitter to obtain 200-300g, pulverized to -75 µm (>85 per cent passing) and then riffle split to produce 100-150g pulp for assaying. The unused rifle split pulp is stored in the sample archive. Sealed batches of pulverized samples were sent to the ALS Laboratory for assaying.

Besides Li and B, a standard suit of assays includes: main oxides as Fe2O3, CaO, MgO, Na2O, K2O, MnO and SrO. Additional assays as, C, S, Cl and F were conducted on selected samples for processing tests purpose. Additional assays of about 26 other elements have been conducted on a limited number of batches, including poisonous and radioactive elements, to test for by-products, deleterious constituents and to ensure that neither the mineralization nor its host rocks are abnormally hazardous. Blanks (every 40th) and Jadarite high and Low grade standards (every 20th) were inserted in every batch, as well as sampling, crush and pulp duplicates (every 20th).

Criteria used for classification

The Jadar resource model for the Lower Jadarite Zone (LJZ) has been reported as Indicated and Inferred Mineral Resource categories.

The resource category determination is based on a number of factors:

Drill hole density in the LJZ
Slope of Regression geostatistical parameter
Geological continuity and confidence in the structural model
Grade continuity based on the semivariogram and sectional interpretations

Indicated Mineral Resource estimates are generally based on drill hole spacing less than 100m and Inferred Mineral Resource on drill hole spacing greater than 100m and less than 200 m.

Estimation methodology

The estimation process was completed using the Maptek Vulcan geological modelling and Isatis geostatistical software packages. Mineralised domains and background mineralisation were estimated in 3D space using ordinary kriging with up to four estimation passes to account for the highly variable nature of the drilling density (25m to greater than 200m in plain view). A parent block size of 25m (X) by 25m (Y) by 2m (Z) was used for grade estimation (no sub-celling).

Data was composited to 2m, the same vertical interval as the parent block thickness in the vertical direction, to remove unwanted variability in the vertical direction. Statistical and variography studies were undertaken and confirmed that the geostatistical approach to grade estimation was appropriate.

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Grade estimates were constrained laterally within a boundary polygon that contains the majority of drill holes from the resource database (grade estimates were not extrapolated outside of this polygon). Grade estimation parameters were optimized using Kriging Neighborhood Analysis (KNA) studies, taking into account data density, kriging variance, and minimum and maximum numbers of samples.

Reasonable prospects for eventual economic extraction

Underground mining layouts utilize a variety of underground panel and stope designs for the Jadar Project. A prerequisite for underground mining is that surface subsidence is minimised. As such, stabilised stope fill mining options are being developed. No minimum ore thicknesses were assumed in the modelling of the jadarite mineralisation, given the zone ranges between 3 and 50m thick (average 15 m) and the need to complete stope design trade-off studies. The assessment of internal dilution is dependent on the mining cut-off grade and will be evaluated during the economic assessment of the ore material for underground mining.

A cut-off grade of US$300/t for Mineral Resources has been applied to include only material with prospects for economic extraction from the available mineralised inventory. Sharp hanging wall and footwall grade boundaries preclude the addition of significant thickness and therefore tonnes, unless the COG was significantly reduced.

The pilot plant test-work on bulk samples from LJZ has been successful in achieving the separation of jadarite particles from the fine-grained matrix, then dissolution in acid and refining to produce market-quality lithium carbonate and boric acid products. While costs and recovery estimates are still under development within the current PFS study, it is clear that there is a viable processing route to economically process the jadarite and borate ore from recent pilot processing studies.

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Competent Persons Statement

The material in this report that relates to Mineral Resources is based on information prepared by Jorge Garcia, a Competent Person who is a Member of the EFG and Mark Sweeney, a Competent Person who is a Member of The Australasian Institute of Mining and Metallurgy, both full-time employees of Rio Tinto.

Mr Garcia and Mr Sweeney 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 Garcia and Mr Sweeney consents to the inclusion in the report of the material based on the information that he has prepared in the form and context in which it appears.

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Contacts

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