New Shallow Copper Mineralised Zone Discovered

("Tertiary" or the "Company")

17 August 2026

New Shallow Copper Mineralised Zone Discovered: Western Zone, Target A1

Tertiary Minerals plc (AIM: TYM) is pleased to announce the preliminary results from portable X-Ray Fluorescence ("pXRF") analysis of samples from two scout holes drilled to the west of the Discovery Zone at Target A1, Mushima North Project in Zambia ("Mushima North" or the "Project") as part of the recently completed drill programme.

The pXRF results indicate the presence of a shallow zone of copper mineralisation approximately 900m west-southwest of the Discovery Zone (Exploration Target of 15-30 million tonnes at 40-60 g/t silver equivalent) in an area the Company is now calling the Western 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:

Ø The Western Zone is a newly discovered mineralised copper zone approximately 900m west-southwest of the Discovery Zone within Target A1.

Ø Drill intersections include (downhole widths, true widths unknown):

o 25m at 0.38% Cu from 19m downhole (26TMNRC-076).

·   Including: 13m at 0.53% Cu from 29m downhole.

·   And: 3m at 0.75% Cu from 33m downhole.

Ø Drilling at the Western Zone was carried out alongside a larger infill drilling programme at the Discovery Zone, Target A1.

Ø Additional pXRF results from the Discovery Zone and a scout hole at Target A2 are expected imminently.

Ø Certified laboratory results from the drill programme are expected over the coming weeks.

Ø Initial metallurgical testwork is set to commence imminently, followed by the Mineral Resource modelling at the Discovery Zone.

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

"We are excited to announce the pXRF results from the two scout drill holes drilled at the Western Zone, Target A1, which have intersected shallow copper mineralisation, including 13m at 0.53% Cu from only 29m below the surface. These holes are 900m to the west-southwest of the Discovery Zone and indicate the potential for additional mineralisation in a new zone well beyond the Exploration Target boundary at the Discovery Zone where we have recently completed infill drilling aimed at supporting the production of a Maiden Mineral Resource Estimate.

"These results continue to support our wider geological model and belief that the Mushima North Project has the potential to host a much larger mineralised system than has been delineated to date.

"While the current drill programme is now complete, we expect substantial newsflow over the coming weeks. This will include the remaining pXRF results for copper and zinc from the last seven holes drilled, as well as the certified laboratory results from across the entire drill programme inclusive of silver analyses for which our expectations in the Discovery Zone are justifiably high.

"I look forward to updating shareholders on these results as we advance the Mushima North Project with the aim of producing a Mineral Resource Estimate before the end of this year."

Drill Results

The two drill holes at the Western Zone, Target A1 (26TMNRC-075 and 26TMNRC-076) were drilled approximately 225m north of a line of 5 shallow, exploratory Air Core holes drilled in Phase 1. These holes targeted the western part of the Target A1 copper-in-soil anomaly and intersected low-grade copper mineralisation. The new holes were positioned based on our current understanding of the mineralisation within the Exploration Target at the Discovery Zone and its surface expression within the regolith. The pXRF results suggest the mineralisation at the Western Zone is copper only, rather than silver-copper-zinc as intersected at the Discovery Zone but this has yet to be confirmed by certified laboratory analysis.

pXRF results from the remaining 7 holes drilled are imminent and include the last of the infill drilling of the current Exploration Target at the Discovery Zone as well as the first scout drill hole drilled at Target A2. The certified laboratory results will be announced on an on-going basis as they become available.

Table 1. pXRF intersections for copper from the Phase 4 drill programme, Western Zone, 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) 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. Location of the two drill holes at the Western Zone, Target A1, in relation to the Discovery Zone showing the mineralisation 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. Phase 4 drill collars (this programme) are in green and earlier drill phases (yellow).

Drill Programme

A total of 39 holes (for 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.

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.

Target A1 Silver Oxide Discovery

The Company has previously reported a JORC-compliant Exploration Target for the Discovery Zone of between 15 and 30Mt 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 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 not been fully investigated. The potential for the near surface oxide mineralisation to transition to underlying sulphide mineralisation has yet to be tested or the potential of additional mineralisation nearby, 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.

Figure 2. Geological map of the Mushima North Project showing the locations of the priority targets within the licence and their distance out from Target A1 based on 5 km radius rings.

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.