Atalaya Mining Plc announced new Mineral Resource Estimates, prepared in accordance with CIM guidelines and disclosure requirements of NI 43-101, for its San Dionisio and San Antonio deposits, which form part of Proyecto Riotinto and are located adjacent to the Company's operating Cerro Colorado open pit and 15 Mtpa plant. The estimates will be included in a new NI 43-101 technical report that is being prepared by Ore Reserves Engineering for the overall Proyecto Riotinto property and which will be published in Second Quarter 2022. Since its restart in 2015, all mining at Proyecto Riotinto has been conducted from the Cerro Colorado open pit.

The other known mineral deposits within the Riotinto concession area - the San Dionisio deposit and the San Antonio deposit - have not been mined by Atalaya. The San Dionisio deposit is located less than 1 kilometre west of the Cerro Colorado pit, and was historically mined by the Corta Atalaya open pit and the Pozo Alfredo underground mine, which targeted copper-rich stockwork and massive sulphide mineralisation. The San Antonio deposit is located around 1 kilometre east of the Cerro Colorado pit.

It is an eastern extension of the historical Planes deposit, which was mined in the early 20th century. Mineralisation at San Antonio is characterised mainly by massive sulphides and the deposit is shallow at 150 - 300 metres below surface. In the 1960s and 1970s, an exploration programme at the deposit was undertaken by sinking a shaft, developing two levels and completing 183 drill holes, however, no mining took place.

The deposit can be accessed by a ramp collared at the east of the Cerro Colorado pit.