Dart Mining Hits 3.96% Tin at Walwa Ahead of October Diamond Drilling
Key Takeaways
- The headline rock chip sample WWP002 returned 3.96% Sn and 165 ppm Ta from an in-situ grab of cassiterite-bearing pegmatite at the historic Walwa open pit, the strongest result in Dart Mining's current programme.
- All four samples display a coherent multi-element signature — elevated Ta, Nb, Li, Rb and Cs alongside tin — consistent with a highly fractionated rare-metal pegmatite system, positioning Walwa within the critical minerals narrative beyond tin alone.
- More than 45 years of historical sampling from five independent exploration programmes corroborate the new results, with Union Corporation recording 2.91% Sn at Mt Alwa South as far back as 1981.
- Maiden diamond drilling is scheduled to commence in October 2026, targeting a concealed greisen zone interpreted to sit at approximately 500–600 metres depth beneath the historic workings — a target that could represent significantly larger tonnage than the surface dykes alone.
- Dart Mining holds a 100% interest in EL007426 covering 499 sq km at Walwa, meaning any discovery value accrues entirely to DTM shareholders with no joint venture dilution.
Assay results confirm high-grade tin-tantalum system at Walwa
Dart Mining NL (ASX: DTM) has received assay results for four rock chip samples collected from the historic Walwa (Mt Alwa) tin mine in Northeast Victoria, confirming high-grade tin and elevated tantalum across the project area ahead of maiden diamond drilling planned for October 2026. The headline result, sample WWP002, returned 3.96% Sn, 165 ppm Ta and 197 ppm Nb from an in-situ grab of cassiterite-bearing pegmatite taken from the south-west wall of the historic open pit on EL007426, a tenement in which Dart Mining holds a 100% interest.
All four samples are selective grab samples of visibly mineralised rock and are not representative of the average grade of the dykes. They do, however, confirm the presence of cassiterite and high tin grades within the greisenised and pegmatitic phases of the system.
James Chirnside, Managing Director
“Almost 4% tin in a rock sample taken from the wall of the old Walwa pit is a very encouraging result, and it sits alongside decades of historical sampling that tells the same story: that the Walwa dykes are rich in tin, and associated tantalum and niobium. This gives Dart Mining real confidence as we finalise the deep drilling program designed to test for a larger tin-bearing greisen system beneath the historic workings.”
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Q1 FY27 rock chip results at a glance
The four samples span two locations within the Walwa project area: the historic open pit and the Mt Alwa South prospect approximately 700 m to the south-south-west.
| Sample ID | Location | Sample Type | Sn % | Ta (ppm) |
|---|---|---|---|---|
| WWP002 | Walwa pit — SW wall | Outcrop (in-situ grab) | 3.96% | 165 |
| WWP001 | Walwa pit — pit floor (south) | Float (boulder) | 1.09% | 70 |
| WWP003 | Walwa pit — north of pit | Float | 0.61% | 29 |
| WAS001 | Mt Alwa South | Outcrop (grab) | 0.40% | 24 |
The multi-element profile across all four samples tells a coherent geological story:
- Ta and Nb increase with tin grade, consistent with tantalum being hosted partly within cassiterite and partly as tantalite-columbite
- Tungsten is low in all samples (≤9 ppm), confirming this is a tin-tantalum system rather than a tin-tungsten system
- High Rb (871–2,611 ppm) and Cs (50–156 ppm) in K-feldspar and muscovite are characteristic of highly fractionated, rare-metal pegmatites
- All four samples are elevated in lithium (31–170 ppm), rubidium and caesium, consistent with a highly fractionated, tin-tantalum specialised pegmatite system
What is a tin-tantalum pegmatite system, and why does it matter?
A pegmatite is a coarse-grained igneous rock that forms during the late stages of magma cooling. Because they crystallise slowly from magma enriched in water and volatiles, pegmatites tend to concentrate rare and economically valuable metals that don’t fit neatly into the crystal lattices of more common minerals.
When geologists describe a system as “highly fractionated,” they mean the magma underwent an extreme late-stage differentiation process that progressively concentrated elements like tin, tantalum, lithium, rubidium and caesium. The Walwa dykes display exactly this signature.
Cassiterite is the primary tin ore mineral and the coarse black mineral visible in the pit wall samples. It is the mineral being measured when Dart Mining reports tin grades. The presence of abundant coarse cassiterite in WWP002 is what drives the 3.96% Sn result.
Greisen is an alteration zone that forms when hot, mineralised fluids derived from a cooling granite body react with the surrounding rock. Greisen zones can host significant tin mineralisation in larger tonnages than individual dykes alone. The Walwa geological model proposes that the shallow, sub-horizontal aplite-pegmatite dykes visible at surface are the upper expression of a deeper buried granite system, with the drilling target being a concealed greisen at approximately 500–600 m depth beneath the historic pit.
The multi-element profile at Walwa, which includes Ta, Nb, Li, Rb and Cs alongside tin, positions the project within the broader critical minerals narrative. These elements are in demand for energy transition technologies, meaning Walwa is not exclusively a tin story.
Decades of historical sampling corroborate the new results
Dart Mining’s compilation of historical rock chip data from five previous exploration programmes spanning more than 45 years reinforces the new results. Multiple independent explorers have reached broadly consistent conclusions about the Walwa system:
- Union Corporation (1981): A greisen sample at Mt Alwa South returned 2.91% Sn; a 15 m chip-channel across the dyke on a bulldozed bench at Mt Alwa South averaged 0.096% Sn and 172 ppm Ta
- Tantalum Australia (2001): Sample W021 at Mt Alwa South returned 0.19% Sn with 3,931 ppm Ta; Walwa pit area samples W011 and W013 each returned 0.39% Sn
- Brady (2004–2006): Outcrop samples of albitite dykes at Snake Gully (1.5 km west of the pit) returned 0.44% Sn with mullock samples returning up to 670 ppm Ta; a quartz vein float sample at the Amphitheatre returned 2.7% Sn (as stannite)
- Queensland Gold & Minerals (2008): 167 composite rock chip samples across a 70 ha prospect area — the Walwa pit area averaged 0.23% Sn over 80 samples
A clear zonation pattern emerges from the historical data: tin grades are highest in the greisenised and pegmatitic phases of the dykes at the Walwa pit, while tantalum and niobium are highest in the outer portions of the system at Mt Alwa South, Redbank Creek and Snake Gully. This pattern is consistent with a single fractionating granite source beneath the Walwa pit area, and it forms the core of Dart Mining’s drilling thesis.
The historical results have been extracted from reports lodged with the Geological Survey of Victoria by previous explorers. They have not been independently verified by Dart Mining, and readers are cautioned that the historical sampling was selective.
Maiden diamond drilling set for October 2026
The near-term work programme at Walwa is focused on converting geological confidence into drill targets, with diamond drilling expected to commence in October 2026. Nine proposed drill sites are well advanced in preparation. The conceptual cross-section for the project (Figure 6 in the announcement) illustrates how the known shallow dyke system at surface is interpreted to connect downward to a concealed felsic granite body, with the interpreted greisen zone sitting at the top of that intrusion at approximately 500–600 m depth. That greisen is the priority target.
Three near-term work items are planned:
- Complete drill access approvals and commence the planned diamond drilling programme at Walwa, targeting repeated tin-mineralised dykes at depth and a possible tin-rich greisen zone at the top of the interpreted causative intrusion
- Systematic rock chip and channel sampling of the dykes exposed in the tantalum-enriched albitite dykes at Snake Gully for total Sn, Ta and Nb
- Field inspection and rock chip sampling of the McHargs tungsten and Hall’s gold prospects to confirm historical results
For historical context, Walwa has the highest recorded primary tin production in Victoria, with approximately 97,000 t of ore treated from the open pit during the last phase of mining in the late 1960s. Union Corporation produced pre-JORC estimates in 1983 of 8.64 Mt at 0.163% Sn and 50 ppm Ta₂O₅, and a higher-grade selective zone of 993,000 t at 0.38% Sn and 55 ppm Ta₂O₅. These historical estimates are not reported in accordance with the JORC Code 2012 and are not being treated by Dart Mining as current Mineral Resources.
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About Dart Mining
Dart Mining NL (ASX: DTM) holds 100% owned granted tenements at Walwa (EL007426, 499 sq km), Cudgewa (EL006866, 508 sq km) and Berringama (EL007170, 27 sq km) in Northeast Victoria. The company also holds the Triumph Gold Project in Queensland and is farming into the Coonambula Antimony-Gold Project in Central Queensland.
Beyond Walwa, the Triumph Gold Project has yielded results of its own, with multiple high-grade parallel lodes identified that broaden Dart Mining’s exploration pipeline well beyond a single commodity.
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