("Tertiary" or the "Company")

25 June 2026

Drilling Commences at Target A1, Mushima North Project, Zambia

Tertiary Minerals plc (AIM: TYM) is pleased to announce commencement of drilling at its Target A1 silver oxide discovery, Mushima North Project ("Mushima North" or the "Project"), Zambia.

Mushima North is located in the prospective Iron-Oxide-Copper-Gold region of Zambia and Target A1 is located 28km to the east of the historic Kalengwa Copper (-Silver) Mine which is currently under redevelopment.

Highlights:

Ø Planned Reverse Circulation drill programme of approximately 4,000m now underway.

Ø Drilling will test:

o  Oxide mineralisation extensions at Target A1,

o  Infill drilling to support the Mineral Resource Estimate at Target A1, and

o  Initial drill testing of Target A1 west and Target A2.

Ø The aim of the drilling is to enable the delineation of a JORC Mineral Resource Estimate for Target A1 where the Company has already reported a JORC Exploration Target of between 15 and 30 million tonnes with a mean grade of 40-60 g/t silver equivalent.

Richard Belcher, Managing Director of Tertiary Minerals plc, commented:

"We are very excited to again be drilling at Target A1 where we currently have a JORC Exploration Target of up to 58 Moz silver equivalent. This is the largest planned drill programme by the Company in Zambia to date with the aim to not only support the definition of a Mineral Resource Estimate at Target A1, but also test possible extensions of the mineralisation.

"Drilling is now underway and we are undertaking preliminary analysis of the drill chip samples on-site with a portable X-Ray Fluorescence analyser prior to submission of selected samples to an external laboratory for independent analysis. Sample batches will be submitted to the external laboratory on a regular basis with the first batch planned in the next week.

"I look forward to providing further updates as the drill programme continues."

Drilling Programme

A programme of approximately 4,000m Reverse Circulation ("RC") drilling is planned as a series of east-west drill lines spaced approximately 100m apart (north-south). Holes will be collared approximately 50m apart along the east-west lines and drilled to vertical depth of up to approximately 125m (estimated maximum depth capability of the drill rig).

The drill programme at Target A1 is designed to:

·    Infill the oxide zone to provide a sufficient density of drilling to confirm the continuity of the mineralisation and enable the delineation of a maiden Mineral Resource Estimate to JORC standards;

·    Test mineralisation extensions to the northwest, southwest and at depth within the oxide zone to potentially increase the tonnage and contained ounces; and

·    Test the current model for additional mineralisation in the west of Target A1 and at Target A2.

The drill programme is being conducted by Ox Drilling which also completed the initial drill programmes on the Project. The drill programme is expected take approximately 6-12 weeks to complete. Samples will be initially analysed on site using a portable X-Ray Fluorescence ("pXRF") analyser for copper and zinc. Selected mineralised intervals will also be submitted for external assaying at a certified laboratory for a suite of elements, including silver, copper, zinc, bismuth, antimony and gallium. These will be submitted in regular batches throughout the drill programme, with the first results expected approximately 6-8 weeks after the initial batch is submitted.

Figure 1. 3D geological model of Target A1 used to help derive the Exploration Target (500m long, 300m wide and 75m thick) located at the northern end of the copper-in-soil anomaly at Target A1. Planned drill holes are shown in green (infill drilling) and red (extension drilling), along with earlier drilling (yellow).

Target A1 Silver Oxide Discovery

The Company recently reported a JORC-compliant Exploration Target for Target A1 of between 15 and 30Mt with an average grade of between 40 and 60 g/t silver equivalent. As currently defined, Target A1 is a near surface, tabular body located within the oxide zone and is some 500m long, 300m wide and up to 75m thick (based on a lower cut-off of 25 g/t silver equivalent). However, the mineralisation remains open to the northwest, southwest and at depth and so the full geometry of the mineralisation remains to be determined. Further information on the Exploration Target can be found in the Company's announcement on 30 March 2026.

The potential for the near surface oxide mineralisation to transition to underlying sulphide mineralisation has yet to be tested. Elevated bismuth (up to 991 g/t), antimony (up to 824 g/t) and gallium (up to 40 g/t) are also associated with the mineralisation, but, as yet, have also not been fully investigated.

Mushima North Project

The Mushima North Copper Project (Licence 27068-HQ-LEL) is held through Group company Copernicus Minerals Limited ("Copernicus"), which is 90% owned by Tertiary Minerals (Zambia) Limited and 10% by local partner, Mwashia Resources Limited.

The Project is under a technical cooperation agreement with First Quantum Minerals Limited ("FQM"), which allows Tertiary to benefit from FQM's historic exploration data in the area, as well as FQM's geological team's extensive experience and understanding of the area's geology. The agreement is non-binding to any further agreement and there are no commercial restrictions for Tertiary, nor does FQM have a right of first refusal over the Project. Further details can be found in the announcement on 15 September 2022.

The Project lies 20km to the east of the Kalengwa Copper (-Silver) Mine in northwest Zambia, one of the highest-grade copper deposits ever to be mined in Zambia. In the 1970s, high-grade ore, averaging approximately 11% Cu copper, was trucked for direct smelting at other mines in the Copperbelt. The Kalengwa Mine is currently under redevelopment and is expected to produce 15,000 tonnes of copper annually.

Numerous other geochemical and/or geophysical targets (A2, B1, B2, B3, C2) are yet to be drill tested, the majority of which are located within a 12km radius of Target A1.

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.

Competent Persons Statement

The technical information in this release has been compiled and reviewed by Dr. Richard Belcher (BSc (Hons), PhD, CGeol FGS, EurGeol) who is a qualified person for the purposes of the AIM Note for Mining and Oil & Gas Companies. Dr. Belcher is a chartered fellow of the Geological Society of London and holds the European Geologist title with the European Federation of Geologists.

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 Zambia and Nevada, USA.