Mushima North - Highest-grade Ag-Cu intersection

Highest grade silver-copper intersection to date at the Discovery Zone, Mushima North: 82m at 107 g/t silver equivalent from 8m depth and ending in mineralisation

Following on from its recent announcement of the best drill intersection to date on 15 September, Tertiary Minerals plc (AIM: TYM) is now pleased to announce the highest grade silver-copper intersection to date 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 new results follow the Company’s news releases regarding the laboratory analytical results on 1, 7 and 15 September 2026 and are from a further four drill holes.

All four holes intersected near surface, silver-copper-zinc mineralisation, with two holes ending in mineralisation and so both increase the known depth of mineralisation beyond the exploration target boundary and confirm that it remains open at depth. These results also include the highest grade individual assay result for silver to date on the Project.

Mushima North is located in the prospective Iron-Oxide-Copper-Gold region of Zambia and is located 28km to the east of the historic Kalengwa copper-silver mine which is currently under redevelopment.

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 at the Discovery Zone.

Highlights:

 Highest grade silver-copper intersection (based on Ag time metres “gram metres”) to date at the Discovery Zone:

 82m at 89 g/t Ag, 0.20% Cu and 0.38% Zn (107 g/t Ag equivalent) from 8m downhole (26TMNRC-066; drillhole ends in mineralisation).

 Including: 37m at 165 g/t Ag, 0.28% Cu and 0.58% Zn (191 g/t Ag equivalent) from 53m downhole.

 Higher-grade, multiple-metre copper intersections, with drill intersections including (downhole widths, true widths unknown):

 5m at 1.01% Cu, 164 g/t Ag, and 0.15% Zn (227 g/t Ag equivalent) from 101m downhole (26TMNRC-063).

 Results include highest silver assay to date of 659 g/t from certified laboratory analytical results on the Project.

 Additional support for continuation of mineralisation at depth and beyond current Exploration Target boundary.

 Additional laboratory analytical results expected in the coming weeks.

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

“We are thrilled to report additional exceptional results for this Project with our highest-grade silver-copper mineralised intersection to date, returning 82m at 107 g/t silver equivalent from only 8m and including silver and copper assays of up to 659 g/t and 0.94%, respectively.

“These results released today, along with the results over the last few weeks, are incredibly compelling for the potential to expand the current known extent of mineralisation at the Discovery Zone. With multiple, shallow, higher-grade silver-copper intersections that extend the mineralisation beyond the current Exploration Target boundary. The true depth extent of mineralisation below the higher-grade zone is yet to be tested.

“Additional laboratory results for the remaining drill holes submitted for analysis are expected in the coming weeks and we look forward to updating our shareholders in due course”.

Drill Programme and Results

The aim of the drill programme is to provide additional drilling data to increase confidence in the continuity of the mineralisation to the level required to report a JORC-compliant Mineral Resource Estimate. Further information on the drill programme can be found in Company’s announcement on 8 June 2026.

The results in this announcement are for four holes only (Figures 1 and 2). Including these four holes, results for a total of 29 holes have now been released from across the Exploration Target. This total includes infill holes, expansion drilling around the Exploration Target mineralisation margin and drilling targeting the higher-grade mineralisation zone.

Accessory minerals such as bismuth, antimony and cobalt have also been intersected in these holes as well as being present in holes in previous drill phases. While the potential for these metals has yet to be evaluated, they are classified as critical, and, in some cases, strategic raw materials (e.g. by the European Commission). If it’s economically feasible to extract these accessory minerals along with the main silver-copper mineralisation, there could be a positive impact on future Project economics.

Table 1. Additional analytical results (four 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 2) showing analytical results for silver for new drill hole 26TMNRC-066 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

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

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