G11 Resources Confirms Alteration Zone at Zig Zag Hill Next to Restarting Mt Lyell Mine
Key Takeaways
- Drillhole SD2602 confirmed a ~62m phyllic alteration zone with elevated silver, arsenic, antimony, and molybdenum at Zig Zag Hill — the same pathfinder signature associated with the adjacent Mt Lyell Cu-Au orebodies.
- Sibanye-Stillwater approved the restart of the Mt Lyell mine this week with first ore targeted by 2029, directly validating the geological prospectivity of the district where G11 holds ground immediately to the north.
- Three new drillholes are designed and ready to drill from a new pad, targeting the northern extension of the alteration zone and the faulted mudstone/volcanic contact interpreted as a key hydrothermal fluid trap.
- The DHEM survey found no notable off-hole conductive anomalies, meaning the geophysics has not yet confirmed a massive sulphide body — the alteration results remain an exploration signal, not a discovery.
- Diamond drilling at the Sunrise prospect (Linda Project) is temporarily paused due to poor ground conditions, with an alternative rig identified but no confirmed restart date.
Drilling confirms alteration zone at Zig Zag Hill, three new holes planned
G11 Resources (ASX: G11) has received assay and down-hole electromagnetic (DHEM) results from its 2,453m diamond core drilling program at Zig Zag Hill, within the Sedgwick Bluff tenement (EL11/2025) in western Tasmania. The results confirm a phyllic alteration zone with elevated pathfinder element concentrations in hole SD2602, adding geological definition to a prospect located immediately north of Sibanye-Stillwater’s Mt Lyell Cu-Au Mine.
The proximity to Mt Lyell is material context. Sibanye-Stillwater this week approved the restart of the Mt Lyell mine, with first ore expected by 2029. That decision sits directly adjacent to G11’s ground and provides a clear frame of reference for the geological potential the company is testing.
Three new drillholes are now designed and ready to be drilled from a new drill pad at Zig Zag Hill, targeting the northern extension of the alteration zone identified in SD2602.
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What assays from SD2602 revealed at Zig Zag Hill
Assay results from hole SD2602 confirmed a zone of weak to moderate phyllic altered dacite and andesite volcanic rocks over an approximate downhole interval of ~62m. This is followed by weakly pyritic and sodic-calcic altered andesite to the end of hole at 1,201.9m.
The phyllic alteration zone contains elevated concentrations of pathfinder elements, including:
- Silver (Ag)
- Arsenic (As)
- Antimony (Sb)
- Minor molybdenum (Mo)
The key alteration intercepts from SD2602, as reported in Table 3 of the announcement, are summarised below:
| From (m) | To (m) | Interval (m) | Alteration | Pathfinders & Grade |
|---|---|---|---|---|
| 1,115 | 1,130 | 15 | Phyllic | 15m at 1.4ppm Ag with Sb & trace Mo |
| 1,142 | 1,149 | 7 | Phyllic | 7m at 1.3ppm Ag with As, Sb & trace Mo |
| 1,147 | 1,154 | 7 | Phyllic | 7m at 652ppm As with Sb, Ag & trace Mo |
| 1,157 | 1,162 | 5 | Sodic-calcic | 5m at 1,525ppm As |
| 1,191 | 1,201.9 | 10.9 | Sodic-calcic | 10.9m at 1.1ppm Ag with As |
The faulted contact between the black mudstone sequence and the underlying volcanic rocks is interpreted as an important geological boundary that may have acted as a permeability barrier to hydrothermal fluid flow. That contact represents a compelling exploration target and warrants further testing along strike, up-dip, and down-dip from current drilling.
The DHEM survey, completed by GAP Geophysics and independently reviewed by Geokincern Pty Ltd, identified several small, localised anomalies between approximately 1,040m and 1,100m downhole in SD2602. These correlate with intervals of sulphide-bearing black mudstone. No notable off-hole conductive anomalies were detected, though the announcement notes this does not necessarily diminish prospectivity — the alteration and sulphide assemblages observed may be associated with styles of mineralisation that are not sufficiently conductive to generate a detectable DHEM response.
Why the Mt Read Volcanic Belt matters for investors
The Mt Read Volcanic Belt in western Tasmania hosts some of Australia’s most significant base and precious metal deposits. To understand why G11’s alteration results are meaningful, it helps to understand the deposit type being targeted.
Volcanogenic Massive Sulphide (VMS) deposits form on or below the ancient seafloor where superheated, mineral-rich fluids vent through volcanic rocks. As these fluids cool, metals precipitate and accumulate in concentrated sulphide bodies. In the exploration phase, geologists look for the alteration halos that surround these systems — zones of chemically altered rock enriched in pathfinder elements like arsenic, antimony, and silver that indicate proximity to a mineralising system.
The announcement notes that the Mt Lyell orebodies along strike from Zig Zag are associated with alteration haloes of enriched pathfinder elements, generally sitting within or in close proximity to CSAMT (Controlled-Source Audio-Magnetotellurics) anomalies. SD2602 has confirmed exactly this combination at Zig Zag Hill.
The Mt Read Volcanic Belt’s track record of world-class VMS discoveries provides the geological context:
- Mt Lyell — Cu-Au-Ag
- Roseberry — Cu-Pb-Zn-Ag-Au
- Henty — Au
No economic mineralisation has been confirmed at Zig Zag Hill. The alteration results represent an encouraging signal, not a discovery.
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Next steps: new drill pad, refined model, and Sunrise update
G11 has refined its geological model for the Zig Zag Hill prospect through the integration of drilling results, structural interpretations, and geophysical modelling. That refined model now underpins the targeting of the three planned follow-up drillholes.
The two active workstreams are:
- Zig Zag Hill: Three new drillholes designed and ready; new drill pad to target the northern extension of the alteration zone and the faulted mudstone/volcanic contact
- Sunrise prospect (Linda Project, EL6/2024): Diamond drilling temporarily paused due to poor ground conditions; an alternative rig better suited to the terrain and geology has been identified, with the program expected to resume
At the Sunrise prospect, the program is designed to test an untested airborne electromagnetic (AEM) conductivity anomaly in the Comstock Valley, concealed beneath post-mineralisation cover, near the Comstock-Lyell, Tasman, Crown Lyell, and Copper Chert ore bodies that form part of the broader Mt Lyell mine.
Further work planned across the Sedgwick Bluff project includes additional ground-based geophysical surveys encompassing DHEM, MLEM, IP, CSAMT, gravity and magnetics, as well as surface geochemical sampling programs covering rock chips, soil, ionic leach soil, and stream sediment sampling.
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