Rio Tinto : Update to Ore Reserves and Mineral Resources at Jadar

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Notice to ASX

23 February 2022

Rio Tinto updates Ore Reserves and Mineral Resources at Jadar

As a result of the Government of Serbia in January 2022 cancelling the Spatial Plan and revoking all related permits, Rio Tinto has decided to no longer report an Ore Reserve for the Jadar lithium-borates project in western Serbia. Accordingly, the Mineral Resources estimate has been updated to incorporate previously declared Ore Reserves, as well as additional drilling data. This data was collected up to the end of 2021 and prior to the Government cancelling the Spatial Plan, and has resulted in an updated geological model, and reclassification of significant tonnage from Inferred to Indicated Mineral Resource category. This change has been made to reflect the current status of the project.

Rio Tinto remains committed to exploring all options and is reviewing the legal basis of the decision by Government of Serbia and future implications for our activities and our people in Serbia.

The Mineral Resources comprise 85.4 Mt of Indicated Resources at 1.76% Li2O and 16.1% B2O3 with an additional 58.1 Mt of Inferred Resources at 1.87% Li2O and 12.0% B2O3

The changes in Mineral Resources and Ore Reserves 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. Supporting information relating to the changes is set out in this release and its appendix. Mineral Resources are quoted in this release on a 100 percent basis.

These changes will be reflected in Rio Tinto's 2021 Annual Report, which will be released to the market on 24 February 2022, and which will set out in full Rio Tinto's Mineral Resources and Ore Reserves position as of 31 December 2021, and Rio Tinto's interests.

Rio Tinto committed $2.4 billion of funding to the Jadar lithium-borates project, in July 2021, subject to receiving all relevant approvals, permits and licenses and ongoing engagement with local communities, the Government of Serbia and civil society.

The proposed project consisted of an underground mine, sustainable industrial processing and waste facilities as well as associated infrastructure. Production estimates included approximately 58 kt of battery grade lithium carbonate, as well as 160 kt of boric acid (B2O3 units) and 255 kt of sodium sulfate as by-products per year1.

1 These production targets are underpinned as to 54% by Indicated Mineral Resources and as to 46% by Inferred Mineral Resources. The relevant estimates of Mineral Resources are as set out in this report and have been prepared by Competent Persons in accordance with the requirements of the JORC Code. There is a low level of geological confidence associated with Inferred Mineral Resources and there is no certainty that further exploration work will result in the determination of Indicated Mineral Resources or that the production target itself will be realised.

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Jadar Ore Reserves and Mineral Resources update

A full tabulation of the Jadar Ore Reserve and Mineral Resource is provided in Table A and Table B.

Table A	Jadar Mineral Resources as at 31 December 2021
Classification	Tonnes (Mt)		Li2O (%)		B2O3 (%)
Measured		Previous		Current	Previous		Current	Previous	Current
	-			-	-		-	-	-
Indicated		55.2			85.4	1.68		1.76	17.9	16.1
Inferred		84.1			58.1	1.84		1.87	12.6	12.0
Total		139.2			143.5	1.78		1.80	14.7	14.4
Table B	Jadar Ore Reserves as at 31 December 2021
Classification	Tonnes (Mt)		Li2O (%)		B2O3 (%)
Proved		Previous		Current	Previous		Current	Previous	Current
	-			-			-		-
Probable		16.6			-	1.81		-	13.4	-
Total		16.6			-	1.81		-	13.4	-

Figure 1 Jadar Project location map

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Summary of information to support Mineral Resource reporting

Mineral Resources are supported by the information set out in the appendix to this release and located at Resources & reserves (riotinto.com)in accordance with the Table 1 checklist in the JORC Code. The following summary information is provided in accordance with rule 5.8 of the ASX Listing Rules.

Geology and geological interpretation

The deposit occupies a continuous area approximately 3.0 km west-east by 2.5 km north-south at depths from 100 m to 720 m below surface. Mineralisation is present in three broad zones containing stratiform lenses of variable thickness hosted in a much thicker gently dipping sequence mainly composed of fine-grained sediments crossed by faults. Economic grades in the Lower Jadarite Zone (LJZ) occur from depths of approximately 300 m in the south, dipping at about 10 degrees to the north where they exceed 720 m in depth. From a stratigraphic point of view, it is observed that sedimentation in the basin is associated with a low energy environment for large periods with widespread distribution of stratigraphic units in the basin. There were periodical influxes of coarser clastics that are interpreted to be sourced mainly from the slopes of the basin to the north and northwest. Contribution from the west-southwest seems to be important during certain periods of basin fill.

Jadarite, LiNaSiB3O7(OH), is a mineral unique to the Jadar deposit that was previously unknown to science. Its composition was determined by the Natural History Museum in London and was accepted in 2006 as a new mineral in the literature by the International Mineralogical Association (IMA) Commission on New Minerals, Nomenclature and Classification Faculty of Earth & Life Sciences Vrije Universiteit Amsterdam De Boelelaan 1085, 1081 HV Amsterdam, Netherlands. The new mineral was named after the Jadar River.

Jadarite consists of rounded micro-crystalline grains, nodules or concretions. On a larger scale the jadarite occurs in stratigraphic lenses that appear as bands of higher and lower lithium and borate grades in core. At the scale of the project area, jadarite mineralisation can vary from 1 to 2 m to over 50 m in thickness. The mechanism for nucleation of the jadarite particles remains problematic, but it is hypothesised that individual jadarite grains grew either at the water-sediment interface, or within the soft sediments. As the jadarite crystal grew it pushed aside other fine-grained minerals, to the extent that these formed a coating to act as a barrier to prevent the particle from coalescing with adjacent particles. Consequently, in high-grade bands the rounded character may be deformed as the particles changed shape to account for the limited space, forming a mosaic texture. Based on drill hole core observations, there appears to be a range of jadarite crystal textures, sizes and shapes. This proposed mode of deposition of jadarite rich sediments has resulted in the harder jadarite crystals hosted within a matrix of softer sediments ranging from fine mud to marls, carbonate rich sediments, clays and siltstones.

Drilling techniques; sampling and sub-sampling techniques; and sample analysis method

Geological exploration of the Jadar deposit has been completed using HQ3 and NQ3 angled diamond drill

1. holes. Total drilling within the Jadar deposit includes 518 diamond drill holes having drilled a total of 204.7 km. Core recovery in Jadar deposit is generally excellent, with an overall recovery of 98.8%. In addition to the drilling undertaken, a 3D seismic program has been completed over the deposit that has increased confidence in the geological model and location and orientation of the modelled higher grade mineralisation.

Logging and sampling of core is undertaken at the core facility. In the earlier holes mineralised and unmineralized core as sampled and assayed. In the later holes only core intervals containing visible jadarite or borate mineralization were sampled after better understanding of the lithium and boron grade distribution.

The HQ3 core is sampled by quarter-core, generally 1 m length quarter core is processed, with the remainder being retained for later submission as duplicates, re-assay etc. Sampling from NQ3 intervals is half core. All cores are cut by diamond saw.

Both lithium and boron are assayed as elemental percentages, but for processing and estimation are converted to oxide percentages of Li2O and B2O3 by multiplying with factors 2.153 and 3.22, respectively. For a smaller group of samples, a broad suite of elements was analysed by analytical method is a Na2O2 fusion

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followed by ICP-AES, with major oxides determined by XRF including possible hazardous or radioactive elements such as As, Hg, Pb, Tl, Th and U, with no elevated grade values observed that would be considered hazardous.

Estimation methodology

The geological and resource modelling for Jadar was generated using the Micromine geological modelling software. The LJZ grade model consists of 13 domains, global estimation parameters were used in unfolded space for grade estimation in the mineralised LJZ domains and transformed back to real space for resource reporting.

The Isatis geostatistical software package was used for geostatistical input to the grade estimation process including statistical analysis, variography, kriging neighbourhood analysis, and block model validation and global change of support studies. Grade estimation was undertaken in Micromine using Ordinary Kriging (OK) for all economic variables, dry bulk density and other variables using a parent block size of 20 mN x 20 mE x 2 mRL, with sub-celling down to 5 mN x 5 mE x 1 mRL.

Cut-off grades and modifying factors

The grade model used for reporting Jadar Mineral Resources is based on LJZ grade domains defined using a US$300/t contained (Li2O and B2O3) cut-off grade (COG), with the lithium oxide and borate dollar values based on 2020 internal pricing forecast and projected operating costs. The US$300/t COG represents a natural break in the grade distribution between the modelled and reported higher grade jadarite mineralisation and lower grade background material.

As jadarite is a new mineral to the mining industry, it was important to demonstrate that the ore can be processed economically. Significant processing studies have been undertaken and it has been demonstrated from pilot plant studies that the jadarite can be processed economically with high recoveries. Thus, the JORC requirement for "reasonable prospects for eventual economic extraction" can be reasonably justified.

Criteria used for classification

The Jadar Mineral Resource category determination is based on a number of factors including, confidence in the resource data, drill hole density in the LJZ - with Indicated Mineral Resources having drill hole spacing less than 150 m, geological continuity and confidence in the structural model and grade continuity based on the semivariogram and sectional interpretations. Currently only the LJZ has been classified as Mineral Resource based on completed studies.

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Competent Persons' Statement

The information in this report that relates to Mineral Resources is based on information compiled under the supervision of Mr Mark Sweeney, member of the Australasian Institute of Mining and Metallurgy (MAusIMM), and Mr Jorge Garcia, who is Member of the European Federation of Geologists (EFG). Both have sufficient experience that is relevant to the style of mineralisation and type of deposit under consideration and to the activity to which they are undertaking 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".

Both Mr Sweeney and Mr Garcia are full-time employees of Rio Tinto and each of them consents to the inclusion of Jadar Mineral Resources in the Report based on the information compiled under his supervision in the form and context in which it appears.

The information in this report that relates to Ore Reserves is based on information compiled under the supervision of Mr Allan Earl who is a Fellow of the Australasian Institute of Mining and Metallurgy (MAusIMM) and has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity to which he is undertaking to qualify as a Competent Person as defined in the 2012 edition of the "Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves".

Mr Earl's assessment is supported from a metallurgical perspective by Mr Gary Davis who is a Member of the Australasian Institute of Mining and Metallurgy (MAusIMM) and has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity to which he is undertaking to qualify as a Competent Person as defined in the 2012 edition of the "Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves".

Mr Earl is full-time employee of Snowden Mining Industry Consultants Pty Ltd working as a consultant to Rio Tinto while Mr Davis is a full time Rio Tinto employee, and each of them consents to the inclusion in the report of the matters based on his information in the form and context in which it appears.

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