Mushima North Phase 4 lab results

(“Tertiary” or the “Company”)

15 September 2026

Best silver-copper intersection to date at the Discovery Zone, Mushima North: 121m at 78 g/t silver equivalent from 4m depth and ending in mineralisation

Tertiary Minerals plc (AIM: TYM) is pleased to announce additional laboratory analytical results from the recent Phase 4 drill programme at the Discovery Zone in Target A1, Mushima North Project in Zambia (“Mushima North” or the “Project). The results follow the Company’s news releases regarding the laboratory analytical results on 1 and 7 September 2026 and are from a further thirteen drill holes.

All thirteen holes intersected near surface, silver-copper-zinc mineralisation, with several holes ending in mineralisation and thus extending the mineralisation at depth, including the best silver-copper intersection to date on the Project.

Mushima North is located in the prospective Iron-Oxide-Copper-Gold region of Zambia. Target A1 is a polymetallic, silver-copper-zinc prospect, where the Company has previously reported a near surface Exploration Target of 15-30 million tonnes at 40-60 g/t silver equivalent, and which is located 28km to the east of the historic Kalengwa copper-silver mine which is currently under redevelopment.

Highlights:

      Best silver-copper intersection to date at the Discovery Zone:

      121m at 56g/t Ag, 0.26% Cu and 0.37% Zn (78 g/t Ag equivalent) from 4m downhole (26TMNRC-053; drillhole ends in mineralisation).

      Including: 52m at 99g/t Ag, 0.41% Cu and 0.43% Zn (130 g/t Ag equivalent) from 39m downhole.

      And: 10m at 165g/t Ag, 1.01% Cu and 0.78% Zn (238 g/t Ag equivalent) from 80m downhole.

      Depth extent of mineralisation increased with multiple drill holes ending in mineralisation.

      Drill results provide further support and increased confidence in the Exploration Target of near surface silver-copper-zinc oxide mineralisation, with drill intersections including (downhole widths, true widths unknown):

      51m at 67g/t Ag, 0.16% Cu and 0.38% Zn (83 g/t Ag equivalent) from 28m downhole (26TMNRC-065; drillhole ends in mineralisation).

      Including: 28m at 102g/t Ag, 0.20% Cu and 0.28% Zn (118 g/t Ag equivalent) from 50m downhole.

      60m at 32 g/t Ag, 0.08% Cu and 0.41% Zn (44 g/t Ag equivalent) from 39m downhole (26TMNRC-068).

           Results include highest silver assay to date of 471 g/t from certified laboratory analytical results on the Project.

           Additional laboratory analytical results expected imminently.

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

“We are thrilled to report our best silver-copper mineralised intersection to date on the Project, returning 121m at 78 g/t silver equivalent, a further 24m longer than the previous Project record at 97m at 85 g/t silver equivalent. Even more impressive is that this new intersection starts from only 4m below the surface, with the hole ending in mineralisation at a vertical depth of 125m.

“This intersection along with the other drill holes results released today continue to deliver not only higher-grade silver intersections, with individual assays of up to 471 g/t silver, but also several impressive multi-metre copper intersections averaging over 1% copper, notably 10m at 1.01% copper from 80m downhole.

“We believe these results continue to support our bulk tonnage, open pit silver exploration model and the potential significance of this Project for the Company. Additional laboratory results are expected soon and we look forward to updating our shareholders in due course”.

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 drill programme can be found in Company’s announcement on 8 June 2026.

The results in this announcement are for thirteen holes only (Figures 1, 2 and 3). Including these thirteen holes, results for a total of 25 holes have now been released from across the Exploration Target and include infill holes to increase confidence in the continuity of the mineralisation to the level required to report 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. Additional analytical results (thirteen 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 0.1% 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-052, 26TMNRC-053 and 26TMNRC-074 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 silver for new drill hole 26TMNRC-065 (along with previously reported drill holes) overlaid on the current Exploration Target mineralisation (silver-copper-zinc) boundary (to be updated as part of the Mineral Resource Estimation work).

Figure 3. Plan view of 3D mineralisation model of the Discovery Zone 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. Completed holes from this programme (green) and earlier drill phases (yellow).

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 0.22%), 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.