Tertiary Minerals PLC (AIM:TYM, OTC:TTIRF) has extended a promising silver discovery at its Mushima North project in Zambia, after drilling confirmed that thick seams of mineralisation continue at least 225 metres further north than previously thought.
The company, which is listed on London’s junior AIM market, said the latest drill results from its Target A1 prospect included the highest grades of silver and copper recorded so far at the site.
Silver was found at grades up to 223 grams per tonne (g/t), with copper peaking at just over 1%.
One hole intersected 73 metres of mineralisation starting just 11 metres below surface, with an average silver grade of 32 g/t.
Within that, 11 metres graded at 94 g/t silver, alongside modest amounts of copper and zinc. Another hole found 27 metres at 35 g/t silver.
“These results increase the extent of the thick, near surface intervals of silver mineralisation a further 225 metres to the north of the previous drilling,” said Richard Belcher, Tertiary’s managing director.
He described the latest data as "very encouraging", providing further support for the potential of Target A1 as a primarily silver target.
While the company has yet to determine the precise geometry of the mineralisation, Belcher said the width and grades are comparable with silver deposits that are mined using open-pit methods elsewhere in the world.
Follow-up lab results and metallurgical tests are expected in the coming weeks.
Understanding the numbers
Grades like “32 g/t” mean each tonne of rock contains 32 grams of silver. For context, anything above 30 g/t is considered relatively good for large, low-cost open-pit silver mining, especially when found near the surface, as is the case here.
Copper and zinc values in the reported holes were lower, but Belcher said the data still support a polymetallic model.
The best copper intersection so far returned 1.01% copper over a short section, but most of the mineralisation reported is in the 0.1% to 0.3% range.
The Mushima North project
Mushima North sits about 28 kilometres east of Kalengwa, a former copper-silver mine that was once one of Zambia’s highest-grade copper producers.
Target A1 is just one of several exploration zones within the Mushima North licence, which is being developed under a technical cooperation agreement with First Quantum Minerals, one of Zambia’s largest copper miners.
The mineralisation lies within a type of rock known as a haematitic conglomerate, essentially a mix of sand and pebbles hardened into rock, with haematite giving it an iron-rich character.
The company has observed visible copper minerals, such as malachite and chrysocolla, in drill cores, but the exact form of the silver and zinc is still being studied.
So far, Tertiary has completed two phases of drilling, covering an area roughly 1.7 kilometres long and half a kilometre wide. The first two holes of the latest campaign were reported today, with results from four more holes expected shortly.
The drilling was shallow, the deepest hole reached 90 metres, but this suits Tertiary’s stated goal of targeting mineralisation that can be mined from surface.
What’s next
Laboratory analysis will continue, and the company has flagged that mineralogical and metallurgical studies will soon begin. These are important steps in understanding how the metals can be extracted and processed efficiently.
The company also plans to drill other targets at the Mushima site, where previous soil sampling and geophysical surveys have highlighted zones that may host additional mineralisation.
Tertiary owns 90% of the Mushima North project through its Zambian subsidiary. The remaining 10% is held by local partner Mwashia Resources.