Resolution Minerals Ltd (ASX:RML, OTC:RLMLF) has reported what it describes as exceptional surface sampling results from the Antimony Ridge target within its Horse Heaven gold-antimony-tungsten project in Idaho, United States.
The company’s recent rockchip and soil sampling programs have returned the highest grades recorded to date at the project, significantly expanding the known mineralised footprint and reinforcing Horse Heaven’s potential to host a large-scale system.
Horse Heaven Project location plan, highlighting the location of the two current major antimony-gold-silver-tungsten targets, the Golden Gate Target and the Antimony Ridge Target. Also highlighted is the Stibnite Gold Antimony Project, which is only 6kms east of Horse Heaven.
High-grade results at surface
Peak assays from grab samples taken near a historical antimony mine include:
- Sample 730253: 49.8% antimony (Sb), 1,420 grams per tonne (g/t) silver (Ag) and 3.12 g/t gold (Au).
- Sample 730255: 10.35% Sb, 68.5 g/t Ag and 4.43 g/t Au.
Antimony results of rockchip sampling at Antimony Ridge (RML ASX release 11 June 2025) together with two high-grade rockchip sample results from this announcement.
Rock samples collected comprised massive stibnite, the key antimony sulphide mineral historically mined at the site.
A rock sample collected from a historical mine located at the Antimony Ridge Target. The photo shows a single rock specimen comprising the grey-silver coloured metallic mineral stibnite. Stibnite is an antimony sulphide ore mineral, containing 71.7% mol weight antimony. The stibnite in this rock specimen is massive, containing between 75% and 90% stibnite. Coarse to very fine stibnite crystals are visible which form an interwoven mass. Samples similar to this photographed rock specimen have now been assayed; the results are as follows: 730253: 49.8% Sb and 1,420 g/t Ag and 3.12 g/t Au.
Soil sampling has also outlined a broad 1,000-by-700-metre NE-SW corridor of Sb-Au-Ag mineralisation, with peak results of 0.5% Sb, 0.9 g/t Au and 68 g/t Ag. This materially enlarges the target area beyond past producing pits and trenches, while indicating the potential for parallel mineralised zones.
Building on historic work
Antimony Ridge has a history of small-scale production dating back to World War II and the early 1950s, when high-grade stibnite ore was mined from surface trenches and shallow pits. Previous exploration had reported trench rockchip grades of up to 5.9 g/t Au, 19% Sb and 367 g/t Ag, while historical drilling intersected significant gold intervals — including 1 g/t Au over 36.8 metres — though most holes were never assayed for antimony or fully for silver.
Landscape panorama photo of the Ridgetop trench. The rockchip channel sample locations are graphically illustrated in the photo with sample numbers. The two figures below each colour bar are the gold (top) and antimony (bottom) grades as ppm and % respectively.
Resolution says the new soil geochemistry is consistent with known mineralisation exposed in historical trenches, suggesting the system is larger and more continuous than previously understood.
Metallurgy and next steps
The company is now collecting representative bulk samples from stibnite-silica vein exposures at Antimony Ridge to undertake preliminary metallurgical test work, with the aim of better understanding the potential for future processing or even direct shipping of ore.
Follow-up work will include additional rockchip and bulk sampling, mapping and drill target definition, with a Phase 1 drill program planned for Antimony Ridge once permitting is complete.
Meanwhile, Resolution continues its Phase 1 diamond drilling program at the Golden Gate target within the same project, where six core holes (totalling 1,513 metres) have been completed. The seventh hole is currently under way, with initial assay results expected once processing is complete.
Rare opportunity in antimony grades
Craig Lindsay, Resolution’s CEO of US operations, said the results point to a much larger system.
“We are very encouraged with the recent sampling program results from Antimony Ridge, which indicate that the mineralised target is larger than initially thought. As we expand outwards from the immediate area of the historic workings, we look to expand the target even further,” Lindsay said.
“Indeed, Horse Heaven is revealing itself to be a much larger opportunity as we conduct modern multi-disciplined exploration across the project area,” he added. “Its potential as a very significant antimony, gold, silver and tungsten project is crystalising.”
Resolution senior strategic advisor Steve Promnitz said high-grade results of this kind are especially significant.
“Not all antimony is equal,” he said. “High grades around 50% Sb are truly rare — and usually reflect crystalline antimony, potentially available for direct shipping ore as an oxide. This is because high-grade antimony requires limited processing — and is therefore sought after.”
Adjacent to major development
Horse Heaven is located directly next to Perpetua Resources’ Stibnite gold project, a large-scale development with one of the largest known antimony resources in the US.
Resolution says its exploration success at Antimony Ridge reinforces the project’s strategic importance, particularly as the US continues to prioritise antimony as a critical mineral with significant supply chain interest.