Tertiary Minerals Hits 121m Silver Intercept at Mushima North

Tertiary Minerals’ Phase 4 drill campaign at Mushima North has returned its strongest silver-copper intersection to date, and the mineralisation now stretches beyond the boundaries of the established exploration target, raising the floor on what this Zambian project could ultimately hold.

That boundary matters. The exploration target was drawn to capture a defined volume of ground, and drilling that punches through the edges of that envelope points to a resource model that will need to grow rather than shrink. The project sits in north-western Zambia, roughly 28 km east of the historic Kalengwa mine, and is run through Copernicus Minerals, a joint venture 90% owned by Tertiary Minerals (Zambia) with the remaining 10% held by Mwashia Resources. A technical cooperation agreement with First Quantum Minerals supplies the strategic backdrop, granting access to historical exploration datasets.

Here is where the project actually stands today, what remains unresolved, and which milestones will tell investors whether the trajectory holds.

Phase 4 drilling delivers its strongest results yet, and the deposit keeps growing

The anchor number is a big one: 121 m at 78 g/t silver equivalent from 4 m depth, including a 52 m run at 130 g/t and a 10 m core at 238 g/t. Near-surface, thick, and high grade. That is the intersection that reset expectations for Target A1.

Around it sit several supporting hits that fill in the picture:

• 52 m at 99 g/t silver, 0.41% Cu and 0.43% Zn from 39 m depth
• 22 m at 90 g/t silver, 0.13% Cu and 0.44% Zn
• 10 m at 1.01% Cu, 165 g/t silver and 0.78% Zn

The highest individual silver reading came from the certified lab release dated 15 September 2026.

Standout assay A single sample returned 471 g/t silver, the highest individual silver assay reported so far, per the certified lab results released on 15 September 2026.

The company has delineated a higher-grade zone measuring roughly 400 m long and 150 m wide, sitting inside a broader mineralised footprint of about 450 m x 400 m. Accessory minerals including bismuth, antimony and cobalt were also identified during the programme, though their commercial value has not yet been evaluated.

The programme ran 39 RC holes for 3,639 m, and by mid-September assays had been released for 29 of 39. Here is the detail that matters most: many of those holes ended in mineralisation, meaning the drill bit stopped before reaching the bottom of the mineralised interval. The deposit has not been closed off at depth. For you as an investor, that changes how to read any future resource number: a figure built on open mineralisation is a floor, not a ceiling.

A second copper discovery 900 metres away raises the project’s lateral scope

The second story of the campaign is not a footnote to the first. On 17 August 2026, Tertiary announced a separate copper-mineralised zone, dubbed the Western Zone, sitting roughly 900 m west-southwest of the Discovery Zone boundary at Target A1.

Scout hole 26TMNRC-076 returned the following preliminary numbers:

• 25 m at 0.38% Cu from 19 m depth
• Including 13 m at 0.53% Cu from 29 m
• And 3 m at 0.75% Cu from 33 m

A copper zone that far from the main target hints that the prospective ground here is bigger than a single deposit. But before you fold that into any view of the project’s value, one qualification needs to land clearly.

What pXRF results mean, and what they do not confirm

Those Western Zone numbers come from pXRF, not certified laboratory assays. A pXRF, or portable X-ray fluorescence device, measures the elemental signature of rock in the field and delivers a rapid but approximate grade estimate. Tertiary itself describes silver readings from the tool as “semi-quantitative.”

That is a field screening result, not a confirmed grade. Laboratory assays are required before any of these numbers can feed into resource work, and certified assays and true widths for the Western Zone both remain pending.

pXRF data quality is shaped by calibration protocols, matrix interference, and sample preparation standards that vary significantly across field programmes, which is why laboratory assay confirmation is required before any field-screening result can feed into formal resource work.

None of this is a warning sign. Flagging that lab confirmation is still needed is standard practice for a scout hole. But it is a material qualifier, and it means the Western Zone belongs on a watching brief rather than in the confirmed column. The zone adds optionality to the Mushima North story; it does not yet add to the project’s demonstrated resource potential.

What comes next before a maiden resource estimate is possible

Tertiary has set a firm goal: a maiden mineral resource estimate for Target A1 before the end of 2026. A maiden mineral resource estimate is the first formal, code-compliant statement of how much metal a deposit contains and at what grade. Management reiterated the year-end target in a late-September 2026 interview.

The JORC Code resource classification framework establishes the standards that govern how Inferred, Indicated, and Measured mineral resources are defined and publicly reported, with independent competent person sign-off required before any maiden estimate can be disclosed to the market.

Three work streams sit between the current position and that estimate:

1. Certified assays from the remaining 10 Phase 4 holes, with roughly eight anticipated in the near term per the 15 September 2026 RNS
2. Metallurgical testwork, which the company has explicitly flagged as required before the estimate can be finalised
3. Full resource modelling to convert the drill data into a code-compliant figure

A maiden resource is a milestone, but it is worth being precise about what it does and does not represent. It establishes a defined volume and grade. It does not constitute a reserve, a feasibility study, or economic confirmation that a viable mine exists. Those come later, through a separate sequence:

1. Mining studies to test how the deposit could physically be extracted
2. Processing flowsheet development to establish how the ore would be treated
3. Economic modelling and, eventually, a reserve declaration

Analyst view SP Angel initiated coverage with a buy rating, noting that the shallow exploration target “hints at open-pit potential” and that “the numbers are not trivial.”

The estimate will be measured against the existing exploration target of 15-30 Mt at 40-60 g/t silver equivalent. That target is the frame, and here is the tension for you to hold: the year-end date gives a concrete milestone to track, but the step from exploration target to maiden resource is precisely where many junior projects get revised downward. Watch the timeline and the uncertainty together.

Where Mushima North fits in the north-western Zambia exploration landscape

North-western Zambia has become a magnet for exploration capital, and the clearest reason is who else is in the neighbourhood. First Quantum’s technical cooperation agreement at Mushima North gives Tertiary access to historical geological datasets. It is important to be exact about what that is: a data-sharing arrangement, not an earn-in and not an equity commitment.

The region’s pull is easier to understand alongside First Quantum’s own moves. In April 2025, the major took a 15% equity stake in Prospect Resources’ Mumbezhi Copper Project, roughly 25-30 km from its Sentinel and Enterprise operations. That is the sharpest regional precedent for a major backing a junior’s early-stage ground, though the distinction matters:

• Technical cooperation (data-sharing only): Mushima North with Tertiary, and the earlier Ntambu licence with Zamare Minerals
• Equity participation (capital committed): Mumbezhi with Prospect Resources

Underpinning all of this is Zambia’s national ambition to produce 3 Mt of copper a year, a policy backdrop that makes government support for pushing the mining frontier beyond the traditional Copperbelt relevant to every junior in the region. First Quantum’s scale gives a sense of the stakes: the company contributed $3.46 billion to Zambia’s economy in 2025, including $2.14 billion in procurement and $389 million in salaries, and its Kansanshi operation is described as the largest integrated metallurgical processing facility in Africa. Additional targets within a 12 km radius of Mushima North remain undrilled.

Zambia’s copper production ambitions extend well beyond the traditional Copperbelt, with the government’s 3 Mt annual target requiring new project pipelines in frontier zones like north-western Zambia where Mushima North sits.

First Quantum’s presence and its established habit of technical cooperation make the Mushima North partnership strategically logical for both sides. What it does not signal is an imminent transaction or committed capital.

Jurisdiction risks and what they mean for junior explorers

Zambia carries specific risks worth registering. Fiscal and regulatory exposure, including VAT receivables and evolving tax structures, can affect project economics and cash flow timing. Funding and dilution risk is typical of any pre-resource junior running capital-intensive drill campaigns.

Jurisdiction risks in Zambia have a political dimension that extends beyond fiscal and regulatory exposure, with the country’s 2026 elections introducing potential policy uncertainty around mining taxation and investment terms that could affect project timelines for any operator in the country.

First Quantum’s operational depth offers useful context for the risks any operator faces in this jurisdiction. It does not imply that a micro-cap like Tertiary has anything like the same capacity to absorb them.

Milestone map for the months ahead

The most immediate catalyst is straightforward: certified assay results from the 10 outstanding Phase 4 holes, expected in the near term from September 2026. Those confirm or adjust the numbers already reported on a pXRF and preliminary basis.

Metallurgical testwork follows as the next sequential milestone, explicitly flagged by the company as a prerequisite for the resource estimate. The year-end maiden estimate then anchors the forward view, with the 12 km radius targets remaining unscheduled and firmly a 2027-or-later prospect.

Share price context TYM:LSE traded around 0.08p as of 21 September 2026, roughly 119% above its 52-week low of 0.0365 GBX, against a 52-week high of 0.14 GBX. Market capitalisation sits in the low single-digit millions of pounds. Source: Financial Times data.

The catalysts cluster into a compressed late-2026 window, which cuts both ways for you. It promises an information-rich few months, but it also carries sequencing risk: if assays or metallurgical results slip, the year-end estimate date moves with them, and for a stock this small that delay is itself a material event.

Assays, metallurgy, and a maiden resource: the three steps that matter now

Strip the project back to its current position and it reads plainly. Tertiary Minerals holds a pre-resource silver-copper-zinc project with confirmed high-grade mineralisation that runs past the established exploration target boundary, an early-stage copper discovery to the west, and a defined path toward a maiden resource. Proactive Investors has called it “one of the more compelling small-cap silver stories on AIM,” and SP Angel’s buy rating remains the sole named analyst view on record.

Set against that are the open questions. True widths for every reported interval are still unknown. Certified assays are pending for 10 Phase 4 holes. Metallurgical testwork is outstanding, and the Western Zone copper grades rest on pXRF alone.

Experienced practitioners in evaluating junior mining deals apply a consistent checklist that includes management track record, jurisdiction risk weighting, drill result interpretation, and the sequencing of de-risking milestones, all of which are directly relevant to reading a pre-resource story like Mushima North.

So the story here is about trajectory and de-risking, not a defined asset. Three things will tell you whether the project is moving the way the current results suggest:

• The remaining certified assay results
• The metallurgical testwork outcome
• Whether the maiden estimate lands before year-end, and at what scale relative to the 15-30 Mt exploration target

The next three results events are the signal. Calibrate your interest to those, not to the exploration target as it stands.

This article is for informational purposes only and should not be considered financial advice. Investors should conduct their own research and consult with financial professionals before making investment decisions.

Past performance does not guarantee future results. Financial projections are subject to market conditions and various risk factors. These statements are speculative and subject to change based on market developments and company performance.