Proposed Fundraise and Capital Access Window

(“Tertiary” or the “Company”)

21 September 2026

Proposed Fundraise and Capital Access Window

Following the encouraging results from the recent Phase 4 drilling at the Mushima North Project, Tertiary Minerals plc (AIM: TYM) announces its plan to advance the project further and its intention to undertake a fundraising through the issue of new Ordinary Shares of 0.01 pence each in the Company (the “Proposed Fundraise”).

The Proposed Fundraise is being arranged by SP Angel Corporate Finance LLP, the Company’s joint broker.

The result of the Proposed Fundraise will be announced in due course.

The Proposed Fundraise will be conditional upon shareholder approval at a General Meeting (“GM”) due to insufficient share authorities. A notice of GM will be included in a circular to shareholders to be published following completion of the Proposed Fundraise.

Use of Proceeds

The Proposed Fundraise is intended to provide funding for the advancement of the Company’s flagship Mushima North Project in Zambia, as well as general working capital.

Capital Access Window

Following the recent updates to the AIM Rules for Companies, the Company has elected to utilise the Capital Access Window in connection with the Proposed Fundraise.

The Capital Access Window provides AIM companies with a voluntary mechanism to implement a temporary pause in trading in its securities and the Company has elected to utilise this facility to provide pricing stability during the Proposed Fundraise.

Accordingly, trading in the Company’s Ordinary Shares will enter a Capital Access Window trading halt with effect from 7.30 a.m. today until a further announcement is made detailing the results of the Proposed Fundraise.

Further Information:

Market Abuse Regulation

The information contained within this announcement is deemed by the Company to constitute inside information as stipulated under the Market Abuse Regulation (EU) No. 596/2014 as it forms part of UK domestic law by virtue of the European Union (Withdrawal) Act 2018 (‘MAR’). Upon the publication of this announcement via Regulatory Information Service (‘RIS’), this inside information is now considered to be in the public domain.

Cautionary Note Regarding Forward-Looking Statements

The news release may contain certain statements and expressions of belief, expectation or opinion which are forward looking statements, and which relate, inter alia, to the Company’s proposed strategy, plans and objectives or to the expectations or intentions of the Company’s directors. Such forward-looking statements involve known and unknown risks, uncertainties, and other important factors beyond the control of the Company that could cause the actual performance or achievements of the Company to be materially different from such forward-looking statements. Accordingly, you should not rely on any forward-looking statements and, save as required by the AIM Rules for Companies or by law, the Company does not accept any obligation to disseminate any updates or revisions to such forward-looking statements.

About Tertiary Minerals plc

Tertiary Minerals plc (AIM: TYM) is an AIM-traded mineral exploration and development company whose strategic focus is on energy transition metals. The Company’s projects are all located in stable and democratic, geologically prospective, mining-friendly jurisdictions. Tertiary’s current principal activities are the discovery and development of copper and precious metal mineral resources in Nevada and in Zambia.