By Charles Pitts
Diablo Resources (ASX: DBO) has completed the acquisition of an 80% interest in the Horn Silver Project in southwestern Utah, giving the Australian-listed explorer control of a district-scale exploration position anchored by one of the region’s historic high-grade silver mines.
The project covers approximately 13.2 square kilometres across 201 claims in the San Francisco Mining District near Frisco, Beaver County. It includes the historic Horn Silver Mine, multiple silver-antimony prospects and copper-gold skarn targets that Diablo plans to advance through mapping, sampling, geophysics and drilling.
The transaction was completed through Diablo’s acquisition of an 80% interest in Antler Resources LLC. Antler holds an option over 101 patented claims and owns 100 unpatented claims that make up the Horn Silver Project. The remaining 20% interest is held by the vendor, according to Diablo’s transaction documents.
Diablo said the acquisition expands its position around its nearby Star Range Silver-Antimony Project, located about 15 kilometres from Horn Silver. The combined land position is intended to support a coordinated exploration program across a historically productive but incompletely tested mining district.
A major historic silver district
The Horn Silver Mine was discovered in 1875 and helped establish Frisco as one of Utah’s major mining settlements. According to the Utah Division of State History, the mine was producing large quantities of high-grade ore by the late 1870s and was shipping about 150 tons of ore per day during its peak period.
Some historic ore reportedly graded between 70 and 200 ounces of silver per ton. The mine generated more than $13 million in production by 1885 and paid approximately $4 million in dividends before a major cave-in disrupted operations that year.
Mining resumed on a limited basis after the collapse, and the property continued to produce silver and other metals intermittently for several decades. Operations eventually ceased in the mid-20th century as metal prices, infrastructure constraints and declining grades reduced the district’s commercial viability.
Diablo’s acquisition presentation cites historical production of approximately 17 million ounces of silver and 30,000 ounces of gold from the Horn Silver Mine. The reported historical production material describes average grades of approximately 604 grams per tonne silver and 1.04 grams per tonne gold.
Those figures are historical and have not been reported as a JORC-compliant mineral resource or ore reserve. Diablo has cautioned that the production data and several historical exploration results require further verification before they can be used in a modern resource estimate.
Project extends beyond the historic mine
While the historic mine provides the project’s principal geological and production reference point, Diablo is targeting a broader polymetallic system.
The company describes the mineralisation as including carbonate-replacement and breccia-style silver, gold, copper, lead, zinc and antimony mineralisation around the Horn Silver Mine and nearby workings. Skarn-style copper-silver-gold targets have also been identified around intrusive contacts in the northern part of the project.
Historical sampling across the broader project area returned results of up to 1,310 grams per tonne silver and 0.2% antimony, according to Diablo’s acquisition materials. These are exploration samples rather than resource grades, but they have helped define structural corridors for follow-up work.
The district’s metal endowment is similarly broad. Historical production records compiled by geologist W.B. Wray indicate that the wider San Francisco Mining District produced approximately:
| Metal | Historical district production |
|---|---|
| Silver | 19.6 million ounces |
| Gold | 44,920 ounces |
| Copper | 44.1 million pounds |
| Lead | 405.5 million pounds |
| Zinc | 46.8 million pounds |
| Tungsten | 892 pounds |
The district’s historical output was concentrated in a relatively small number of mines, including Horn Silver and the nearby Cactus operation. The presence of several metals reflects the district’s complex geological setting, where faulting, carbonate rocks and intrusive bodies created multiple mineralisation styles.
For Diablo, that setting provides an exploration pipeline that is not dependent on a single silver target.
Copper targets add a second exploration track
One of the most significant elements of the acquisition is the copper opportunity at the Imperial and Accrington prospects, roughly two kilometres northwest of the historic Horn Silver Mine.
Previous drilling at the copper skarn system intersected several broad zones of copper mineralisation. Diablo’s acquisition materials cite results including:
- 54 metres at 1.4% copper from 46 metres, including 14 metres at 3.4% copper;
- 34 metres at 1.0% copper from 153 metres;
- 102 metres at 0.58% copper from 194 metres; and
- 6 metres at 1.8% copper from 144 metres.
The company has described those results as historical exploration data. The intervals are reported as downhole lengths, and true widths have not been established in all cases.
The copper targets were explored by earlier operators, including Alderan Resources and Kennecott Exploration, a member of the Rio Tinto group. Their work included diamond drilling, induced polarisation surveys, magnetic surveys and geological mapping. Kennecott ended its option agreement over the broader Frisco project in 2023, leaving much of the accumulated exploration database available for reinterpretation.
Diablo plans to review and integrate this historical information with new mapping, sampling and geophysical work. The objective is to determine whether the copper mineralisation forms part of a larger skarn or intrusive-related system, rather than isolated mineralised intercepts.
The copper focus also places Horn Silver within the wider supply discussion around energy-transition metals. Skillings has tracked the pressure facing copper supply in its copper price outlook and market analysis, where permitting timelines, declining grades and limited new mine development remain central industry concerns.
Drill targets remain open at depth and along strike
At the Horn Silver Mine itself, Diablo is focused on testing extensions below and alongside the historic workings.
The company has identified an induced polarisation anomaly beneath the mine that it interprets as a possible continuation of the known mineralised system. Additional chargeability anomalies at the Gossan and Buckhorn targets sit along the same broader structural corridor.
Diablo has also pointed to historical drilling near the Horn South prospect, where shallow holes intersected silver-gold mineralisation outside the main historic workings. Reported historical results include:
- 6.1 metres at 5.9 grams per tonne gold and 165 grams per tonne silver;
- 12.2 metres at 1.0 gram per tonne gold and 156 grams per tonne silver, including 1.5 metres at 629 grams per tonne silver; and
- 1.5 metres at 268 grams per tonne silver.
The results were generated by earlier operators and are not currently sufficient to establish a mineral resource. Diablo intends to conduct confirmatory drilling and assess the continuity, geometry and grade distribution of the mineralisation.
A key challenge will be separating the mine’s historical production record from the modern exploration case. Historic workings demonstrate that high-grade mineralisation existed, but they do not by themselves establish the size, continuity or economic viability of remaining mineralisation.
Acquisition shifts Diablo toward a multi-target pipeline
The Horn Silver transaction gives Diablo a larger portfolio of targets at a time when the company is seeking to build a more active exploration pipeline in Utah.
The immediate work program is expected to focus on:
- Confirming historical geological and assay data;
- Completing detailed mapping and rock-chip sampling;
- Testing the Horn Silver mine extensions and Horn South target;
- Drilling the Gossan and Buckhorn IP anomalies; and
- Advancing the Imperial and Accrington copper-silver skarn prospects.
Diablo has said the presence of patented claims may provide permitting advantages for some exploration activities, although drilling and other field programs will remain subject to applicable state and federal requirements.
The company raised A$3.5 million through a placement to support the transaction and exploration at Horn Silver and Star Range. The acquisition terms also include deferred equity consideration linked to exploration milestones, including completion of 1,000 metres of drilling and delivery of a JORC-compliant inferred resource meeting specified silver-equivalent thresholds.
For investors and operators assessing the deal, the significance of Horn Silver lies less in its historical production alone than in the combination of established mine workings, a large claim position and multiple mineralisation styles. Silver remains the project’s historical anchor, while copper and antimony offer additional exploration angles.
The next test for Diablo will be whether modern drilling can convert a fragmented historical record into a coherent geological model and demonstrate sufficient continuity to support a formal resource estimate.
Until that work is completed, Horn Silver remains an exploration project with a substantial production legacy: not a defined mineral resource or operating mine.