Changes to Argyle Diamonds Ore Reserves and Mineral Resources

02 March 2018

Rio Tinto's 2017 annual report, released to the market today, includes significant changes in estimates of Ore Reserves and Mineral Resources at Rio Tinto's Argyle Diamond mine in the East Kimberley, Western Australia.

The updated 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. Ore Reserves and Minerals Resources are quoted on a 100 per cent basis. Rio Tinto’s interest is 100 per cent.

During 2017, estimated Argyle Ore Reserves decreased by 13Mt from 29Mt to 16Mt. 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.