Completion of Phase 4 Drill Programme

Tertiary Minerals PLC

10 August 2026

("Tertiary" or the "Company")

10 August 2026

 Completion of Phase 4 Drill Programme at Target A1, Mushima North

Results support current near-surface mineralisation and the presence of a higher-grade silver-copper zone

Tertiary Minerals plc (AIM: TYM) is pleased to announce the completion of the Phase 4 drill programme at Target A1, Mushima North Project in Zambia ("Mushima North" or the "Project") and new preliminary results from portable X-Ray Fluorescence ("pXRF") analysis of drill samples.

Not all pXRF results are available yet and while they remain subject to confirmation by certified analysis, the results obtained to date appear to support the previously reported near surface Exploration Target of 15-30 million tonnes at 40-60 g/t silver equivalent and also the presence of a higher-grade mineralised zone.

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:

·   Phase 4 drilling is now complete, with 3,639m drilled over 39 holes.

·   Higher-grade silver-copper zone presence supported by drill intersections including (downhole widths, true widths unknown):

·   15m at 0.53% Cu from 100m downhole (26TMNRC-063).

§ Including: 7m at 0.77% Cu from 101m downhole.

·   4m at 0.68% Cu from 85m downhole (26TMNRC-065).

·   8m at 0.62% Cu from 51m downhole (26TMNRC-073).

·   Infill drill hole results continue to support the wider Exploration Target of near surface silver-copper-zinc oxide, with drill intersections including (downhole widths, true widths unknown):

·   65m at 0.23% Cu from 19m downhole (26TMNRC-069).

·   83m at 0.16% Cu from 19m downhole (26TMNRC-059).

·   Currently reporting only copper and zinc pXRF results in full, as pXRF is less reliable for silver, but the high-grade zone has yielded values of up to 408 g/t silver and the larger exploration target has yielded values of up to 135 g/t silver in line with expectations.

·   Samples submitted to the certified laboratory and results expected in the coming weeks.

·   Initial metallurgical testwork to commence imminently, followed by the Mineral Resource modelling.

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

"We are pleased to announce the successful completion of this phase of drilling, as well as reporting pXRF results for copper and zinc from additional drill holes. The drill holes reported here not only continue to support the mineralisation extent, but also suggest the presence of the higher-grade silver and copper mineralisation previously reported.

"The on-site pXRF analysis of our drill samples has aided a more dynamic drill programme allowing us to not only get early indications on the extent and grade of mineralisation but also to efficiently explore in terms of the number of drill holes and metres we need to drill to support the planned Mineral Resource Estimate.

"With the drilling now completed we eagerly await the remaining pXRF results and the first certified laboratory results. We will also proceed with our initial metallurgical testwork as we aim to announce a JORC Mineral Resource Estimate before the end of the year."

Drill Results

The preliminary results from the Company's internal analysis using a pXRF analyser continues to not only support the current extent of the oxide mineralisation contained within the Exploration Target, and in places to potentially extend this, but also the presence of a higher-grade silver and copper zone within the core.

The potential extent and tenor of silver mineralisation is not yet being reported as the pXRF results for silver are not sufficiently reliable to indicate average grades over known mineralised extents. Certified, independent laboratory analysis is currently underway to confirm silver values, along with copper and zinc and other potential, important accessory metals including bismuth, antimony and gallium.

pXRF results from the remaining 9 holes drilled are expected imminently and include the last of the infill drilling of the current model at Target A1, along with testing for additional mineralisation in the west of Target A1 and at Target A2. The certified laboratory results will be announced on an on-going basis.

Table 1. New pXRF intersections for copper and zinc from the Phase 4 drill programme, Target A1.

Note to Table:

•     Calculated intersections (downhole, true width unknown) are weighted averages based on copper (intervals start and end with ≥0.1% Cu, and the average grade cut-off is 0.1% Cu) or zinc (intervals start and end with ≥0.2% Zn, and the average grade cut-off is 0.2% Zn) and allow for up to 3m internal consecutive dilution.

•    Reported values were produced using a pXRF analyser to test unprepared samples and as such are of a preliminary nature but provide an indication of potential mineralisation.

Figure 1. Cross-section (location on Figure 3) showing pXRF copper results only for drill holes 26TMNRC-051, 26TMNRC-054, 26TMNRC-055, 26TMNRC-066 and 26TMNRC-068 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 pXRF copper results only for drill holes 26TMNRC-061 to 26TMNRC-064 overlaid on the current Exploration Target (silver-copper-zinc) mineralisation boundary (to be updated as part of the Mineral Resource Estimation work).

Drill Programme

A total of 39 holes (for 3,639m) Reverse Circulation ("RC") drilling were drilled as part of the Phase 4 drill programme. Holes were planned as a series of east-west drill lines spaced approximately 100m apart (north-south). Holes were collared approximately 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 preliminary results to support a more dynamic drill programme and the updating of our geological model as new data became available.

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

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 are being initially analysed on site using a pXRF analyser for copper, zinc and silver. Analysis protocol includes 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 is being used as a preliminary analytical technique to provide an approximate quantitative measure of copper and zinc grades.

Samples from selected drill holes based on the initial pXRF results are being 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) will be inserted and 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 zinc (using a cut-off grade of 0.2% Zn) or copper (using a cut-off grade of 0.1% Cu) with up to 3m internal dilution.

Figure 3. 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. Completed holes from this programme (green) and earlier drill phases (yellow).

Target A1 Silver Oxide Discovery

The Company has previously 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 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 (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:

Tertiary Minerals plc
Richard Belcher, Managing Director	+44 (0) 1625 838 679
SP Angel Corporate Finance LLP, Nominated Adviser and Broker
Caroline Rowe/Jen Clarke	+44 (0) 203 470 0470
AlbR Capital Limited, Joint Broker
Lucy Williams/Duncan Vasey	+44 (0) 207 469 0930

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.

This information is provided by RNS, the news service of the London Stock Exchange. RNS is approved by the Financial Conduct Authority to act as a Primary Information Provider in the United Kingdom. Terms and conditions relating to the use and distribution of this information may apply. For further information, please contact rns@lseg.com or visit www.rns.com.
RNS may use your IP address to confirm compliance with the terms and conditions, to analyse how you engage with the information contained in this communication, and to share such analysis on an anonymised basis with others as part of our commercial services. For further information about how RNS and the London Stock Exchange use the personal data you provide us, please see our Privacy Policy.