Berkeley has sent written notification to the Spanish prime minister and Miteco, the Spanish ecological transition ministry, complaining of breaches of the internatinal Energy Charter Treaty.

The construction of the uranium-concentrate plant was rejected by Miteco following an unfavourable report from the Spanish Nuclear Safety Council in July 2021.

"Berkeley strongly refutes the NSC's assessment and, in the company's opinion, the NSC has adopted an arbitrary decision with the technical issues used as justification to issue the unfavourable report lacking in both technical and legal support," the company said.

Last week, Argonaut named Salamanca as one of the best undeveloped projects on the ASX.

Berkeley shares closed at A28c on Friday, giving the company a market capitalisation of nearly $125 million.