Great Boulder Extends Mulga Bill East to 1.5km With High-Grade Gold Hits
Key Takeaways
- Mulga Bill East has grown to more than 1.5km of strike, up from approximately 900m reported in July 2026, with the discovery remaining open along strike and at depth.
- Every positive intersection at Mulga Bill East represents potential resource growth, as the trend sits entirely outside the existing 782,000oz Mulga Bill–Eaglehawk resource within the 1.02Moz Side Well Gold Project.
- Top drill intercepts include 2m @ 30.76g/t Au from 133m and 2.64m @ 14.62g/t Au from 292.36m, with structural interpretation suggesting west-dipping veins are continuous between Mulga Bill and Mulga Bill East across a 200–300m gap.
- GBR's total resource base stands at 1.502Moz Au across Side Well and Peak Hill, with the 1,021,000oz Side Well figure not yet incorporating a single ounce from the ~1km-plus of unclassified Mulga Bill East strike.
- A Peak Hill resource update is targeted by end of 2026, while infill RC and diamond drilling at Mulga Bill East is underway in preparation for a formal resource estimation process.
Mulga Bill East grows to 1.5km as high-grade drilling extends the discovery
Great Boulder Resources (ASX: GBR) has announced high-grade RC drilling results that extend the Mulga Bill East discovery to more than 1.5km of strike, up from approximately 900m reported in July 2026. Critically, Mulga Bill East sits entirely outside the existing 782,000oz Mulga Bill–Eaglehawk resource within the broader 1.02Moz Side Well Gold Project, meaning every positive intersection here represents potential resource growth rather than resource infill.
The company holds a total resource base of 1.502Moz Au across two Western Australian projects: Side Well (1,021,000oz) and Peak Hill (481,000oz). With 1,971,131,864 shares on issue, the scale of the exploration pipeline is now a material part of the GBR story.
Drill Highlights — Mulga Bill East
- 2m @ 30.76g/t Au from 133m, including 1m @ 60.9g/t Au from 134m (26MBRC088)
- 4m @ 7.60g/t Au from 60m (26MBRC058)
- 2m @ 5.90g/t Au from 73m (26MBRC080)
- 2.64m @ 14.62g/t Au from 292.36m (26MBRCD006)
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Understanding what “outside the resource” means for investors
A JORC Mineral Resource represents mineralisation that has been drilled sufficiently to be estimated with reasonable confidence. It is a formal classification, not simply the full extent of a gold system — and that distinction matters here.
Mulga Bill East already has an existing resource, but it spans only 450m of strike, mainly at the southern end of the deposit. The remaining ~1km-plus of strike that recent drilling has confirmed currently carries no resource classification at all. Before that mineralisation can be converted to a formal resource estimate, infill and extensional drilling is required to establish sufficient geological confidence.
The investment implication is direct: if even part of the 1.5km Mulga Bill East trend is eventually converted to resource, GBR’s already 1Moz-plus Side Well estimate grows materially. The discovery is open along strike and at depth, so the current 1.5km figure represents the current limit of drilling, not a boundary.
Structural connectivity points to a bigger gold system
The geological interpretation put forward by Managing Director Andrew Paterson is central to understanding the resource growth thesis here.
Many of the high-grade intersections within Mulga Bill East correspond to west-dipping vein-hosted lodes that have already been drilled deeper down at Mulga Bill. In his words, “…many of these results are up-dip projections of veins we’ve already identified.” Mulga Bill and Mulga Bill East are approximately 200m to 300m apart, and the west-dipping veins appear to be continuous across that gap — a structural interpretation now supported by a cross-section (Figure 2 in the announcement) showing potential lode continuity between the two zones.
That continuity has precedent. Previous drilling to the south returned 21m @ 7.24g/t Au from 99m in 26MBRC021 (reported 25 May 2026), demonstrating the southern end of this lode system has already proven up. Mineralisation remains open to the north, south, and at depth.
Andrew Paterson, Managing Director
“The structural continuity and ongoing success in the Mulga Bill – Eaglehawk area continue to support our belief that this is a very significant gold system, with potential to become one of the biggest gold endowments in the Meekatharra field.”
What comes next — resource update pipeline and multi-rig drilling programme
The immediate next step at Side Well is a targeted infill drilling campaign. Further RC and diamond drilling will infill the Mulga Bill East area in preparation for resource estimation, with drilling planned to extend the west-dipping lodes down-dip toward Mulga Bill, and also to test strike continuity of the north-northeast striking en echelon high-grade zones.
Separately, the on-site team at Side Well is currently cutting and sampling the final diamond holes drilled at Mulga Bill and Golden Bracelet, with assay results pending.
At Peak Hill, two RC rigs and one diamond rig are continuing extensional and exploration programmes at priority targets, with a Peak Hill resource update targeted by the end of 2026. The company’s five-rig drilling programme is active across both projects, with a major resource upgrade flagged as pending.
| Project | Area | Current Status | Next Step | Timeline |
|---|---|---|---|---|
| Side Well | Mulga Bill East | 1.5km strike, open along strike and at depth | Infill RC + diamond drilling | Ongoing |
| Side Well | Mulga Bill / Golden Bracelet | Diamond core cutting and sampling underway | Assay results pending | Near-term |
| Peak Hill | Multiple targets | 2 RC rigs + 1 diamond rig active | Resource update | End 2026 |
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GBR’s total resource base in context
The full picture of GBR’s resource position, drawn directly from Table 1 of the announcement, underscores the scale of what is already in the ground — and the potential uplift Mulga Bill East represents.
| Project | Resource Category | Tonnes | Grade (g/t Au) | Ounces Au |
|---|---|---|---|---|
| Side Well | Indicated | 7,025,000 | 2.8 | 626,000 |
| Side Well | Inferred | 9,017,000 | 1.4 | 395,000 |
| Side Well Subtotal | 16,042,000 | 2.0 | 1,021,000 | |
| Peak Hill | Indicated | 7,547,000 | 1.5 | 376,000 |
| Peak Hill | Inferred | 1,838,000 | 1.8 | 105,000 |
| Peak Hill Subtotal | 9,385,000 | 1.6 | 481,000 | |
| Total | All Resources | 25,427,000 | 1.8 | 1,502,000 |
The 1,021,000oz Side Well figure does not include a single ounce from the 1.5km Mulga Bill East trend beyond its existing 450m southern resource block. That makes Mulga Bill East the clearest near-term growth lever in GBR’s portfolio. As the infill drilling programme advances and resource estimation work progresses, the pathway toward a materially larger Side Well estimate becomes more defined. Management’s stated ambition, that this could become “…one of the biggest gold endowments in the Meekatharra field,” is now backed by an increasingly substantial body of high-grade drilling evidence.
The 1,021,000oz Side Well figure itself reflects a major step in GBR’s development, having crossed the 1 million ounce milestone only recently, which contextualises just how significant any Mulga Bill East resource conversion would be on top of an already substantial base.
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