Sentinel Metals’ first diamond drill hole at Montana’s Columbia Project reveals a robust 46.8m intercept averaging 5.5 g/t gold, including a standout 13.5m at 16.6 g/t, confirming mineralisation extends into fresh rock below historical drilling depths.
- Maiden hole DDCO26-001 returns 46.8m at 5.5 g/t gold
- High-grade core includes 13.5m at 16.6 g/t gold
- Gold mineralisation confirmed below oxide zone in fresh rock
- Core recovery variable but no clear bias on grades
- Further drilling and assays underway to expand understanding
Strong Maiden Drill Intercept Opens New Depth Potential
Sentinel Metals (ASX:SNM) has delivered a promising start to its maiden diamond drilling program at the Columbia Gold-Silver Project in Montana, USA. The first hole, DDCO26-001, intersected a substantial 46.8 metres grading 5.5 grams per tonne (g/t) gold from 88.2 metres down-hole, including high-grade intervals of 21.4 metres at 11.1 g/t and 13.5 metres at 16.6 g/t. Notably, this intercept extends beyond the historically targeted oxide zone into fresh rock, a domain previously untested by past operators focused on shallower heap-leach feed.
Gold Continues Below Oxide Boundary with Geological Insights
The drilling confirmed gold mineralisation persists below the redox boundary at approximately 135 metres, with core recovery in fresh rock intervals reaching 95–100%. This fresh sulphide horizon remains largely unexplored, presenting a compelling target for follow-up drilling. Sentinel’s Managing Director Matt Herbert highlighted the dual significance of the results: a robust maiden intercept and confirmation that the system extends into fresh rock, expanding the project’s potential beyond historical limits.
Herbert also noted the program has refined geological and drilling techniques, transitioning to triple-tube drilling to optimise core recovery amid challenging ground conditions. While core recovery was highly variable, particularly in the highest-grade interval (averaging 20%), the company’s analysis found no systematic bias linking low recovery to inflated grades. This suggests the high-grade results are geologically driven rather than artefacts of sampling loss.
Detailed Assay and Recovery Analysis Underpin Confidence
Core recovery ranged from 12% to 62% within the 105.5–119.0 metre high-grade interval, with approximately 10.6 kilograms of half-core recovered from an expected 53.4 kilograms. Sentinel compared similar low-recovery intervals elsewhere in the hole, which returned negligible gold, reinforcing that poor recovery does not inherently inflate grades. The company plans to re-drill the low-recovery interval using triple-tube equipment to verify the results.
Gold assays reported were derived from PhotonAssay, a large-charge technique improving representativity, with fire assay checks pending and expected mid-August. Silver and multi-element assays are also forthcoming, which will provide a more comprehensive geochemical picture.
Geological Context and Future Drilling Plans
The Columbia Project’s gold-silver mineralisation is hosted in a low- to intermediate-sulfidation epithermal system within Eocene volcanic rocks. Mineralisation occurs in steeply dipping vein and breccia sets, with the maiden hole drilled down-dip to test continuity beneath the oxide resource. Sentinel has intersected hydrothermal breccia at depth in previous drilling, confirming geophysical targets and opening avenues for deeper exploration.
With assays pending for holes DDCO26-002 to DDCO26-005, the company is progressing its 21-hole maiden program. Follow-up drilling will target the fresh sulphide horizon between the redox boundary and 218 metres, while deeper porphyry-style targets remain untested. The hydrothermal breccia zone intersected at 288–330 metres, previously highlighted as a conductive body, returned sub-economic gold grades and has been deprioritised for immediate follow-up.
Resource and Metallurgical Considerations
The Columbia Mineral Resource Estimate stands at 21.4 million tonnes at 1.3 g/t gold (920,000 ounces inferred), constrained within a US$2,200/oz gold price shell. The new drilling results, particularly the high-grade core, suggest potential to enhance this resource with deeper and higher-grade material. Metallurgical testwork on oxide material from prior studies indicates strong gold recovery, but no testwork has yet been conducted on fresh sulphide mineralisation, an important next step for assessing processing characteristics.
The company’s cautious approach to low core recovery intervals and pending assay confirmations reflects a rigorous commitment to data integrity. Sentinel plans to re-drill critical intervals and conduct umpire assays to validate the preliminary results.
Bottom Line?
Sentinel Metals’ maiden Columbia drill hole confirms high-grade gold extends into fresh rock, setting the stage for deeper exploration and resource growth, though verification of low-recovery intervals remains crucial.
Questions in the middle?
- Will re-drilling confirm the high grades in low core recovery zones?
- How will pending fire assay and multi-element results influence resource modelling?
- What metallurgical characteristics will fresh sulphide mineralisation reveal?