11 August 2025

Tertiary Minerals plc

 ("Tertiary" or the "Company")

 Completion of Phase 2 Drill Programme at Target A1, Mushima North

Preliminary results extend the wide intervals of mineralisation previously reported

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

Mushima North is located in the prospective Iron-Oxide-Copper-Gold region of Zambia. Target A1 is a polymetallic, silver-copper-zinc prospect.

Highlights:

·   Phase 2 drilling is now complete, with 1,116m drilled over 16 holes.

·  Extension of known mineralisation. Additional silver, zinc and copper mineralisation identified, extending the known mineralisation approximately 350m to the north and over a width of approximately 300m. Mineralisation remains open to the north and at depth.

·   High pXRF silver values of up to 377 g/t and broad intervals (>20 g/t) in line with previous pXRF results (the pXRF analysis for silver is semi-quantitative and so these values are indicative only).

·  Currently reporting only copper and zinc pXRF results and the certified silver results to follow laboratory analysis.

·   Drill intersections include (pXRF analysis for zinc and copper only, downhole widths, true widths unknown):

·   53m at 0.73% Zn from 19m downhole. Hole ends in mineralisation (24TMNAC-028).

§ Including: 8m at 1.95% Zn from 56m downhole.

·   49m at 0.33% Zn from 22m downhole. Hole ends in mineralisation (24TMNAC-026).

·   57m at 0.24% Cu from 21m and 39m at 0.26% Zn from 39m downhole (24TMNAC-025).

§ Including: 10m at 0.54% Cu from 64m downhole.

·   58m at 0.27% Cu from 7m and 18m at 0.21% Zn from 47m downhole. Hole ends in mineralisation (24TMNAC-038).

§ Including: 8m at 0.79% Cu from 58m downhole.

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

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

"We are excited to report the pXRF results for zinc and copper and highlight the preliminary indications of associated silver mineralisation from the recent Phase 2 drill programme. Results indicate the continuation of mineralisation to the north from the previous drilling for at least 350m, over broad intervals and with a continued width of approximately 300m.

"Higher copper values than previous results, such as 58m at 0.27% copper from 7m downhole, including 8m at 0.79% copper are particularly encouraging. Silver results from the pXRF analyser, while only indicative, do suggest the continuation of the silver mineralisation identified in the previous drill programme to the north.

"The mineralisation remains open to the north and at depth, and while the drill holes further to the south returned only anomalous values of zinc and copper, a selection of these will still be tested for the potential continuation of the silver mineralisation in this direction. 

"Target A1 is a polymetallic target and as such we eagerly await the independent certified laboratory assay results, particularly for silver, along with potentially other important accessory minerals. Drilling last year identified anomalous values of bismuth, antimony and gallium.

"With the drilling now complete, I look forward to updating shareholders on the laboratory results in the coming weeks and our plans to further advance this target."

The preliminary results from the Company's internal analysis using a pXRF analyser indicate the continuation of mineralisation for at least 350m to the north of the previously reported drilling with significant silver, zinc and copper values. Mineralisation has also been intersected deeper than previously, to a vertical depth of approximately 82m on drill line 8506925N. Drill holes to the south (lines 8506650N, 8506360N and 8505650N) returned anomalous values of zinc and copper, but below the Company's reporting cut-off grades of 0.2% and 0.1%, respectively. However, the potential extent of silver mineralisation in this direction is unknown at this stage 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 copper and zinc values and to ascertain silver values along with other potential, important accessory metals including bismuth, antimony and gallium.

The preliminary results indicate a current extent of mineralisation over a footprint of approximately 350m by 300m and to a depth from near surface to 82m. However, zinc and copper mineralisation remains open-ended to the north and at depth, whilst the potential extent of silver mineralisation remains to be determined.

Target A1

Target A1 is a large copper-in-soil anomaly (3.1km by 1.7km) with copper values up to 350ppm (via pXRF analyser) associated with a 1.7km by 0.5km zinc- and coincidental 1.3km by 0.3km silver-in-soil anomaly. Phase 1 drilling in 2024 over the silver- and zinc-in-soil anomaly (drill line: 8506925N) identified wide and thick silver mineralisation associated with low-grade copper and/or zinc mineralisation. Elevated bismuth (up to 991 g/t), and the critical minerals antimony (up to 824 g/t) and gallium (up to 40 g/t) are also associated with the mineralisation.

Table 1. Significant Phase 2 pXRF intersections for zinc and copper at Target A1.

Note:

·   Calculated intersections (down hole, true width unknown) are weighted averages based on 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 dilution) or copper (intervals start and end with ≥0.1% Cu, and the average grade cut-off is 0.1% Cu) and include up to 3m of internal dilution allowed).

·    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.

·    Holes 25TMNAC-030 to 25TMNAC-037 and 25TMNAX-039 to 25TMNAC-040 contained anomalous copper and zinc values but below the Company's reporting cut-off grades of 0.2% zinc and 0.1% copper.

Drilling results from the Phase 1drilling programme undertaken in late 2024 included:

·    65m at 23 g/t Ag, 0.14% Cu, 0.27% Zn from 9m downhole (24TMNAC-005).

o  Including: 5m at 73 g/t Ag, 0.16% Cu, 0.31% Zn from 69m downhole.

·    66m at 26 g/t Ag, 0.13% Cu, 0.26% Zn from 13m downhole (24TMNAC-006P).

o  Including: 20m at 40 g/t Ag, 0.21% Cu, 0.40% Zn from 23m downhole.

·    57m at 25 g/t Ag, 0.2% Cu, 0.16% Zn from 14m downhole (24TMNAC-004).

o  Including: 26m at 36 g/t Ag, 0.20% Cu, 0.20% Zn from 45m downhole.

Mushima North Project

The Mushima North (silver-copper-zinc) Project (Licence 27068-HQ-LEL) is held through Group company Copernicus Minerals Limited, which is 90% owned by Tertiary Minerals (Zambia) Limited and 10% owned by local partner, Mwashia Resources Limited.

The Project lies 20km to the east of the Kalengwa copper 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% copper, was trucked for direct smelting at other mines in the Copperbelt. The Kalengwa mine is currently under redevelopment and is expected to produce 15,000 tonnes of copper annually.

The Project is held 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 to any further agreement and there are no commercial restrictions for Tertiary, nor does FQM have a right of first refusal over the Project. Further details can be found in the news release of 15 September 2022.

At the end of the summer 2024, Tertiary completed an initial (Phase 1) 25 AC drill programme (1,274m) to test parts of geochemical (copper-in-soil) anomalies at Targets A1 and C1. This limited and shallow drilling indicated wide downhole intervals of largely coincidental copper, zinc and silver mineralisation at Target A1.

Numerous other geochemical and/or geophysical targets (A2, B1, B2, B3, C2) are yet to be drill tested.

Drilling Programme

A programme of 1,116m combined Air Core ("AC") and Reverse Circulation ("RC") has now been completed, with a series of east-west drill lines spaced approximately 250m apart (north-south). Holes were collared approximately 100m apart along the east-west lines and drilled to bit refusal depth (average hole depth 70m).

Sampling, Analysis and QAQC

Sampling 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 have been initially analysed on site using a portable X-Ray Fluorescence ("pXRF") analyser for zinc and copper. Analysis protocol included multiple point (three) 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 procedure. Given the nature of the unprepared sample and point analysis, this method is used as a preliminary exploration technique to provide an approximate quantitative measure of copper and zinc mineralisation only.

Samples from selected drill holes based on the initial pXRF results will now be sent to the independent laboratory ALS Global 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 QAQC protocol.

Reported drill hole intersection thicknesses are down-hole thicknesses and true thicknesses are unknown as the geology of the drill area is still uncertain. 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.

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.

Figure 1. Location map of Target A1 showing soil sample results for copper and the collar locations for the 20024 and 2025 drill programme.

Figure 2. Drill cross-section (8506925N; location on Figure 1) showing assay results for copper and zinc. Reported weighted average grades from laboratory analysis from Phase 1 drilling (see press release 25 March 2025). See Table 1 notes for further information.

Figure 3. Drill cross-section (8507150N; location on Figure 1) showing assay results for copper and zinc. See Table 1 notes for further information.