Tertiary Minerals plc (AIM: TYM) is preparing to commence its first diamond drilling programme at the Mushima North Project in Zambia, targeting extensions to the existing silver-copper-zinc discovery and the potential for higher-grade primary sulphide mineralisation beneath the near-surface deposit.
The company confirmed that mobilisation to Target A1 has commenced, with drilling expected to begin early next week as exploration activity accelerates towards a planned maiden Mineral Resource Estimate before the end of 2026.
The programme will comprise up to four diamond drill holes totalling approximately 1,000 metres, with each hole expected to extend between 200 and 250 metres.
The drilling is designed to investigate mineralisation to a vertical depth of approximately 200 metres, significantly deeper than the existing exploration target, which extends to around 95 metres vertically.
The latest campaign follows more than 3,600 metres of reverse circulation drilling at the Discovery Zone, where Tertiary has progressively improved its understanding of the mineralised system.
Mushima North currently hosts a JORC-compliant Exploration Target of 15 million to 30 million tonnes grading 40 to 60 grams per tonne silver equivalent, representing a conceptual exploration potential of up to 58 million ounces of silver equivalent.
The Exploration Target relates to a near-surface mineralised body measuring approximately 500 metres long, 300 metres wide and up to 75 metres thick, based on a cut-off grade of 25g/t silver equivalent.
Importantly, the target is not yet classified as a Mineral Resource, and further exploration is required to establish the tonnage, grade and continuity of economically recoverable mineralisation.
Recent Phase 4 drilling has identified a higher-grade mineralised zone extending across a surface area of approximately 400 metres by 150 metres, with mineralisation encountered down to a vertical depth of 125 metres.
The system remains open at depth, raising the possibility that the existing oxide mineralisation could transition into underlying primary sulphide deposits.
The new diamond drilling programme will specifically test this geological possibility, while providing more detailed structural information and core samples for metallurgical investigations.
The company believes improved geological understanding will help refine future drilling targets and support technical studies assessing the deposit’s development potential.
Tertiary is also investigating the presence of additional critical and strategic metals associated with the Discovery Zone.
Previous exploration identified elevated concentrations of bismuth up to 0.53%, antimony up to 0.22%, cobalt up to 0.39% and gallium up to 40 grams per tonne, although the wider distribution and potential significance of these elements remain under investigation.
Samples from the new drilling programme will undergo preliminary portable X-ray fluorescence analysis for copper and zinc before selected mineralised intervals are submitted to an independent laboratory.
Laboratory testing will assess silver, copper, zinc, cobalt, bismuth, antimony, gallium, germanium and rare earth elements, providing a broader geochemical assessment than previous programmes.
The drilling campaign is expected to take approximately four weeks, with initial laboratory results anticipated around six to eight weeks after the first sample submissions.
Meanwhile, the final assay results from Phase 4 drilling and initial metallurgical testwork findings are expected imminently, potentially providing further information ahead of the planned resource estimate.
Managing Director Richard Belcher said the company was pleased to resume drilling at Mushima North following substantial progress during the current exploration season.
He highlighted the importance of the first diamond drilling campaign in testing whether mineralisation continues beneath the Discovery Zone and whether a deeper primary sulphide system exists.
Belcher said the remaining Phase 4 assays, metallurgical results and new drilling programme positioned the company for a productive conclusion to the 2026 Zambian field season.
The Mushima North Project is located approximately 28 kilometres east of the historic Kalengwa copper-silver mine, within Zambia’s prospective Iron-Oxide-Copper-Gold geological region.
Kalengwa was historically one of Zambia’s highest-grade copper operations, with some mined material averaging approximately 11% copper during production in the 1970s.
Tertiary holds an effective 90% interest in the Mushima North project through its Zambian subsidiary, with local partner Mwashia Resources holding the remaining 10%.
The company also benefits from a technical cooperation agreement with First Quantum Minerals, providing access to historical exploration information and regional geological expertise.
The agreement is non-binding and does not give First Quantum a right of first refusal over the project.
Beyond the Discovery Zone, Tertiary has identified additional exploration opportunities, including a shallow copper-mineralised area approximately 900 metres west-southwest of the main discovery.
Known as the Western Zone, this target remains open following initial scout drilling.
Several other geochemical and geophysical targets, including B1, B2, B3 and C2, also remain untested within approximately 12 kilometres of Target A1.
For investors, the upcoming diamond drilling programme represents an important exploration milestone, offering the opportunity to test whether the existing near-surface silver-copper-zinc mineralisation continues into a deeper and potentially higher-grade sulphide system.
However, the presence of a commercially significant sulphide deposit has not yet been established, and the current Exploration Target should not be confused with a defined Mineral Resource or reserve.
Attention will now turn to the commencement of drilling, outstanding Phase 4 assay results, metallurgical testing and the planned Mineral Resource Estimate before year-end, as Tertiary Minerals works to establish the scale and potential economic significance of its Mushima North discovery.
