Initial lab results from Phase 4 drilling

("Tertiary" or the "Company")

1 September 2026

Initial certified analytical results from Phase 4 drill programme confirms thick, near surface silver-copper mineralisation at the Discovery Zone, Target A1, Mushima North

Tertiary Minerals plc (AIM: TYM) is pleased to announce the first laboratory analytical results from the recent Phase 4 drill programme at Target A1, Mushima North Project in Zambia ("Mushima North" or the "Project). The results are from five drill holes and confirm both the presence of near surface, thick silver-copper-zinc mineralisation and the higher-grade zone, both of which are part of the Discovery Zone, where the Company has previously reported a near surface Exploration Target of 15-30 million tonnes at 40-60 g/t silver equivalent.

Mushima North is located in the prospective Iron-Oxide-Copper-Gold region of Zambia. Target A1 is a polymetallic, silver-copper-zinc prospect located 28km to the east of the historic Kalengwa copper-silver mine which is currently under redevelopment.

Highlights:

Ø Drill intersections support the continuity of the Exploration Target of near surface silver-copper-zinc oxide mineralisation, including (downhole widths, true widths unknown):

·   66m at 37 g/t Ag, 0.28% Cu and 0.27% Zn (58 g/t Ag equivalent) from 7m downhole (26TMNRC-045).

·   73m at 27 g/t Ag, 0.23% Cu and 0.25% Zn (45 g/t Ag equivalent) from 9m downhole (26TMNRC-049).

·   57m at 38 g/t Ag, 0.20% Cu and 0.31% Zn (55 g/t Ag equivalent) from 34m downhole (26TMNRC-046).

Ø Drill intersections support the higher-grade silver-copper mineralisation zone, including (downhole widths, true widths unknown):

·   7m at 56 g/t Ag, 0.48% Cu and 0.27% Zn (89 g/t Ag equivalent) from 81m downhole (26TMNRC-045).

·   6m at 51 g/t Ag, 0.48% Cu and 0.23% Zn (84 g/t Ag equivalent) from 71m downhole (26TMNRC-049).

·   2m at 16 g/t Ag, 1.48% Cu and 0.13% Zn (107 g/t Ag equivalent) from 89m downhole (26TMNRC-046).

Ø Elevated values of key critical minerals associated with the silver-copper-zinc mineralisation, including:

·   6m at 0.32% Bi, 0.32% Co, 15 g/t Ag and 0.22% Cu from 79m downhole (26TMNRC-047).

·   Highest grade of bismuth (0.53%), antimony (0.11%) and cobalt (0.39%) intersected to date.

Ø Additional laboratory analytical results expected over the coming weeks.

Ø Samples submitted for initial metallurgical testwork.

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

"It is always an exciting time when the laboratory results from the drill programme start to be returned. While these are from only the first five holes, they have not disappointed. These results support the preliminary in-field copper-zinc results, provide the first silver intersections and confirm the near surface, thick silver-copper-zinc mineralisation within our Exploration Target, with intersections including 66m at 58 g/t silver equivalent (0.97% copper equivalent) from only 7m downhole, at the upper end of the Exploration Target grade range. The potential for a higher-grade mineralised zone is also further supported with intersections including 7m at 89 g/t silver equivalent (1.49% copper equivalent) from 81m downhole.

"In addition, these results have returned additional elevated critical metals, including our highest one metre grades of bismuth, antimony and cobalt to date which, while still at an early stage of investigation, could have the potential to be important accessory metals to the silver-copper-zinc mineralisation.

"With additional laboratory results expected over the coming weeks and our initial metallurgical testwork samples now submitted, this is a very exciting time for the Company and we expect significant newsflow over the next few months from Target A1 and remain on course to achieve our stated goal for this year which is to report a maiden Mineral Resource Estimate".

Drill Programme and Results

A total of 39 (3,639m) Reverse Circulation ("RC") drill holes were drilled as part of the Phase 4 drill programme. For the drilling at the Discovery Zone, holes were collared along a series of east-west drill lines spaced approximately 100m apart (north-south) and 50m apart along the east-west lines and drilled to vertical depths of up to 128m. This was the maximum depth capability of the drill rig under the drilling conditions, in particular the higher-than-expected water table and resultant wet samples. Drilling was completed in two passes to allow the updating of the Company's geological model as new data became available and to enable the programme to be more dynamic.

Further information on the planned drill programme can be found in Company's announcement on 8 June 2026.

The results in this announcement are for the first five holes only (Figures 1, 2 and 3), are from the northern section of the Exploration Target and include infill holes to support the work towards a Mineral Resource Estimate, testing of the Exploration Target mineralisation margin to potentially expand the footprint, and also targeting of the higher-grade mineralisation zone.

Accessory minerals such as bismuth, antimony and cobalt are also intersected in these holes as well as being present in previous drilling. While the potential for these metals has yet to be evaluated, they are classified as critical, and in some case strategic raw materials, (e.g. by the European Commission) and if economically feasible to extract along with the main silver-copper mineralisation, could have positive impacts of future economics.

Additional certified laboratory results will be announced on an on-going basis as they become available.

Table 1. Initial analytical results (five holes only, other analytical results from the remainder of the Phase 4 drill programme awaited). Equivalent grades ("Eq") are for illustrative purposes only.

Note to Table:

·   Calculated intersections (downhole, true widths unknown) are weighted averages based on silver or copper (denoted in table by metal in bold). Using a cut-off grade of 10 g/t Ag or 0.1% Cu, respectively. Intervals start and end with ≥10 g/t Ag or 0.15 Cu, respectively and with up to 3m consecutive internal dilution allowed.

·   Silver values rounded to whole numbers.

·   EOH means End of Hole.

·   CuEq (%) and AgEq (g/t) are the copper and silver equivalent grades, respectively, and were calculated assuming commodity prices of Cu: US$4.99 lb, Ag: US$57 oz, Zn: US$1.38 lb and 100% recovery as used in reporting of previous results from Phase 2 and 3 drill programmes. No information on beneficiation recoveries is available at this stage. These are for illustrative purposes only.

·   Gram metres for silver are the silver values (g/t) multiplied by the intervals (m).

Figure 1. Cross-section (location on Figure 3) showing analytical results for silver for new drill holes 26TMNRC-045 to 26TMNRC-047 and 26TMNRC-050, and previously reported holes 25TMNRC-038, 25TMNRC-039, 25TMNRC-043 and 25TMNRC-044, overlaid on the current Exploration Target mineralisation (silver-copper-zinc) boundary (to be updated as part of the Mineral Resource Estimation work).

Figure 2. Cross-section (location on Figure 3) showing analytical results for copper for new drill holes 26TMNRC-045 to 26TMNRC-047 and 26TMNRC-050, and previously reported holes 25TMNRC-038, 25TMNRC-039, 25TMNRC-043 and 25TMNRC-044, overlaid on the current Exploration Target mineralisation (silver-copper-zinc) boundary (to be updated as part of the Mineral Resource Estimation work).

Sampling, Analysis and QAQC

Sampling from the drilling programme was undertaken at 1m intervals and two subsamples were collected from each interval using a riffle splitter: one for potential laboratory analysis, the other for future reference.

Samples were initially analysed on site using a portable X-Ray Fluorescence ("pXRF") analyser for copper, zinc and silver. Analysis protocol included the averaging of two analyses per sample (unprepared sample analysed through a thin plastic sample bag) and the inclusion of Certified Reference Material, blanks and duplicate samples as part of an internal Quality Assurance ("QA") procedure. Given the nature of the unprepared sample and point analysis, this method was used as a preliminary analytical technique to provide an approximate quantitative measure of copper and zinc grades and a qualitative assessment of the silver grades.

Samples from selected drill holes based on the initial pXRF results were sent to the independent laboratory, ALS Global, located in South Africa for analysis for a range of elements using a four-acid digest, method code ME-ICP61 (including silver, copper, zinc, bismuth, antimony and gallium). QA samples (Certified Reference Material, duplicates, blanks) were inserted and will be monitored as part of the Quality Assurance Quality Control ("QAQC") protocol.

Reported drill hole intersection thicknesses are downhole thicknesses and true thicknesses are unknown. Intersections are weighted averages on silver (using a cut-off grade of 10 g/t Ag), copper (using a cut-off grade of 0.1% Cu) and zinc (using a cut-off grade of 0.2% Zn) with up to 3m internal dilution.

Target A1 Silver Oxide Discovery

The Company has previously reported a JORC-compliant Exploration Target for the Discovery Zone of between 15 and 30 million tonnes with an average grade of between 40 and 60 g/t silver equivalent. As currently defined, this 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). The mineralisation remains open to the northwest, southwest and at depth and so the full extent and true geometry of the mineralisation remain to be determined. Further information on the Exploration Target can be found in the Company's announcement on 30 March 2026.

Elevated bismuth (up to 0.53%), antimony (up to 0.11%), cobalt (0.39%) and gallium (up to 40 g/t) are also associated with the mineralisation, but, as yet, have not been fully investigated. The potential for the near surface oxide mineralisation to transition to underlying sulphide mineralisation has yet to be tested. Nor has the potential for expanding the mineralisation based on nearby targets, such as at the Western Zone, Target A1.

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 and does not create any obligation to enter into any further agreement.  There are no commercial restrictions for Tertiary and FQM does not have a right of first refusal over the Project. Further details can be found in the announcement on 15 September 2022.

Target A1 lies 28km 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.

Numerous other geochemical and/or geophysical targets (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 (CGeol, 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 Nevada and in Zambia.