Completion of Phase 4 Drill Programme

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.

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.

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.

Sampling, Analysis and QAQC

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.

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.

Mushima North Project