Changes to Ore Reserves and Mineral Resources

RNS Number : 5154G

Rio Tinto PLC

02 March 2018

 

Changes to Ore Reserves and Mineral Resources 

2 March 2018

On 2 March 2018 Rio Tinto announced to the Australian Securities Exchange (ASX):

·     increases in Ore Reserves and Mineral Resources at its Pilbara iron ore operations in Western Australia;

·     a decrease in Ore Reserves and an increase in Mineral Resources at its Boron operations in Califorina;

·     a decrease in Ore Reserves and a full write back of Mineral Resources at its Argyle Diamond mine in Western Australia; and

·     a full write back of Ore Reserves and an increase in Mineral Resources and at the Simandou project in Guinea.

These announcements were made in accordance with the Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves, 2012 (JORC Code) and the ASX Listing Rules.

A summary of the changes are provided below. Copies of the full announcements are available on Rio Tinto's website at www.riotinto.com/reservesandresources. Rio Tinto's Ore Reseves and Mineral Resources are set out in full in its annual report released on 1 March 2018.

Ore Reserves and Mineral Resources are quoted on a 100 per cent basis.  Mineral Resources are reported exclusive of Ore Reserves.

Pilbara Ore Reserves and Mineral Resources  

During 2017, estimated iron Ore Reserves increased by 165 Mt after depletion from mining. The increases have been delivered as part of the ongoing resource development drilling programs, with associated technical social and economic studies, designed to maintain Ore Reserves coverage ahead of mining depletion rates. During the same period, estimated Mineral Resources increased by 508 Mt.

	Ore Reserves	Mineral Resources
Brockman South Marra Mamba	First reporting of Ore Reserves for Brockman South Marra Mamba Deposits O, Q, & R has added 55 Mt to Brockman 4.
Robe Valley	First reporting of Ore Reserves for Mesa B, C, & H has added 253 Mt to the Robe River JV Robe Valley Pisolite ore.
West Angelas	First reporting of Ore Reserves for West Angelas Deposit C and Deposit D has added 100 Mt of Robe River JV West Angelas Marra Mamba ore.
Howard's Well		First reporting of Mineral Resources for Howard's Well has added to the Robe River JV: ·      332 Mt of Brockman ore; ·      286 Mt of Brockman Process ore; and ·      13 Mt of Detrital ore.

Ore Reserves are reported as dry product tonnage, Mineral Resources are reported as dry in-situ tonnages in addition to Ore Reserves.

Boron Mineral Resources and Ore Reserves

RTB Boron Ore Reserves have decreased by 6 Mt, from 22 Mt to 16 Mt. Accordingly, RTB Boron Mineral Resources exclusive of Ore Reserves have increased  by 8.5 Mt, from 0 Mt to 8.5 Mt.

The reduction in Ore Reserves applies to the body of calcium borate ore types at the site.  This decrease in Ore Reserves reflects a reassessment of the study support level of processing assumptions following independent technical review, leading to updated asessments of processing flowsheet options, and likely economics. The  sodium borate Ore Reserves, being majority of the Ore Reserves at the site, are unaffected.

Following this write back of Ore Reserves the operating life of RTB Boron has been reduced by 7 years and is anticipated to run until 2042.

Argyle diamonds Mineral Resources and Ore Reserves

During 2017, estimated Argyle Ore Reserves decreased by 13Mt from 29 Mt to 16 Mt.  This decrease includes depletion of almost 5Mt due to production activities in 2017.  The balance of the reduction results from a more conservative view on future production performance, grade and economic shut-off criteria.

The remaining reserves underpin the operation until 2020, with opportunities to increase reserve estimates and extend the operational life subject to technical and financial performance.

Following further reviews of resource development potential, and with the reduction in the Argyle Ore Reserve and the limited remaining mine life, the other mineralised deposits at Argyle do not demonstrate economic prospects and are not scheduled for production.  As such, Argyle Mineral Resources, exclusive of Ore Reserves, decreased from 15Mt to 0Mt. 

Simandou Mineral Resources and Ore Reserves

On 28 October 2016, Rio Tinto and Chinalco signed a non-binding agreement to sell Rio Tinto's entire stake in the Simandou project, in Guinea, to Chinalco. The Heads of Agreement (HOA) set out the proposed principal terms of the sale with the aim of signing a binding agreement.

Considering current uncertainties in timing of development and potential variations to project scope under future project ownership, the project Ore Reserves have been written back to Mineral Resources.

Accordingly, estimates of Mineral Resources at Simandou have been increased, compared to the previous estimate in the 2016 annual report.  The Simandou Mineral Resources have increased by 1922 Mt, from 835 Mt to 2757 Mt.

Tenure under the Simandou Mining Concession is held by Simfer SA, which is owned jointly by Rio Tinto, Chinalco and the Republic of Guinea. The Concession duration is 25 years, renewed automatically for a further period of 25 years followed by further 10 year periods in accordance with the Guinean Mining Code, provided Simfer has complied with its obligations under the Amended and Consolidated Basic Convention entered into with the Republic of Guinea, dated 26 May 2014.

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