Notice to ASX/LSE                                                                                                                       

Mineral Resources and Ore Reserves updates

19 February 2025

Rio Tinto has today announced to the Australian Securities Exchange (ASX) changes in Mineral Resources and Ore Reserves to support its 2024 annual reporting[1], including: 

·      Increased Proved Ore Reserves and decreased Mineral Resources at the Rio Tinto Aluminium (RTA) Pacific Operations Amrun deposit in Queensland, Australia.

·      Increased Indicated Mineral Resources at the Rio Tinto Copper Winu project in Western Australia, Australia.

·      Increased Mineral Resources at the Rio Tinto Iron and Titanium Quebec Operations (RTITQO) in Quebec, Canada.

·      Increased Ore Reserves and decreased Mineral Resources at the RTA Atlantic Operations Porto Trombetas deposit in Brazil. Porto Trombetas is operated by the Mineração Rio do Norte (MRN) joint venture.

Supporting information relating to the changes of Mineral Resources and Ore Reserves is set out in the Table 1 Release and its appendices. This release provides a summary of those changes. Mineral Resources and Ore Reserves are quoted in this release on a 100 percent basis. Mineral Resources are reported in addition to Ore Reserves. The figures used to calculate Mineral Resources and Ore Reserves are often more precise than the rounded numbers shown in the tables, hence small differences may result if the calculations are repeated using the tabulated figures.   

These changes will be included in Rio Tinto's 2024 Annual Report, to be released to the market on 19 February 2025 (London time), which will set out in full Rio Tinto's Mineral Resources and Ore Reserves position as at 31 December 2024, and Rio Tinto's interests.  

Rio Tinto Aluminium Pacific Operations - Amrun

Mineral Resources and Ore Reserves for the RTA Pacific Operations[2], including the Amrun deposit, are presented in Table A and Table B. The updated Ore Reserves at Amrun reflect a material change in classification. Proved Ore Reserves have increased by 203 million tonnes (Mt) (77%), while Probable Ore Reserves have decreased by 176 Mt (26%). The change in Ore Reserves classification reflects a higher level of confidence in the modifying factors resulting from completion of an access study, and increased confidence in the underlying Mineral Resources as a result of updated orebody knowledge.  There has been no material change to other modifying factors, including governmental, tenure, environmental, cultural heritage or community factors. Mineral Resources exclusive of Ore Reserves have decreased by 41 Mt (5%) at Amrun due to the conversion of Mineral Resources to Ore Reserves, and updated orebody knowledge.

Rio Tinto Copper - Winu 

Mineral Resources for Winu[3] are presented in Table C. Indicated Mineral Resources comprise 63% of these Mineral Resources, which is a substantial increase from the previously reported 31% of Mineral Resources. This change is the result of the implementation of a different classification methodology which uses the relationship between drill hole spacing and orebody uncertainty as determined by conditional simulation of copper grades. The total Mineral Resources tonnage has increased by 19 Mt (2.7%) in comparison to the previously reported estimates.

Rio Tinto Iron and Titanium Quebec Operations

Mineral Resources for RTITQO[4] are presented in Table D. Significant technical work conducted from 2000 to 2024 on the Grader deposit situated 3 kilometres (km) from the main Lac Tio hemo-ilmenite deposit, with over 4,800 metres (m) of drilling, and the development of a new resource model, has resulted in a 26.7 Mt (100%) increase in Mineral Resources.

Rio Tinto Aluminium Atlantic Operations - Porto Trombetas (MRN)

Mineral Resources and Ore Reserves for the RTA Atlantic Operations, Porto Trombetas deposit[5] are presented in Table E and Table F. Probable Ore Reserves have increased by 167 Mt, while Proved Ore Reserves have decreased by 4 Mt for an overall increase in Ore Reserves of 163 Mt (354%). The increase in Ore Reserves is attributed to the issuance of the Preliminary Licence for the New Mines Project by IBAMA (the Brazilian Federal Environmental Agency). There have been no other significant changes in modifying factors, including governmental, tenure, cultural heritage, community factors, or operational aspects.

Measured Mineral Resources have decreased by 178 Mt and Inferred Mineral Resources have decreased by 112 Mt for an overall decrease of 290 Mt (50%). The decrease in Mineral Resources is partly due to the conversion of bauxite from Mineral Resources to Ore Reserves, as mentioned above, as well as to the downgrade of certain plateaus, containing only historical drilling data, from the Inferred Resource category to non-Resource status. The methodology for determining Mineral Resources remains unchanged.