Mount Torrens Deposit — Drilling Analysis

Scope. Primary focus = the 38 CRA Exploration drillholes inside the Mount Torrens Deposit Area (1976–84) that define the worked-up orebody. Wider EL7127 / regional holes are covered as second-order anomalies. Context from the SARIG drillhole package (now including collar survey), the 50_Geochemistry database, the EL7127 tenement boundary, CRA 1977 reports, and Opal's May 2026 Technical Summary.

Bottom line. Mount Torrens is a sediment-hosted (SHMS/SEDEX) Pb-Zn-Ag deposit in the basal Talisker Calc-siltstone — a single mineralised horizon dipping ~55° E, intersected over ~1.8 km of strike (high-grade shoot ~1.2 km; CRA's worked-up resource ~450 m) within a ~2 km Pb-Cu soil anomaly. The deposit holds all the high grade in the database (to 14.2% Pb, 7.7% Zn, 77 g/t Ag) and all 8 holes deeper than 200 m. The clearest growth is down-plunge — the central shoot is still strongly mineralised at the deepest assays (~260–310 m down-hole) and open below — plus strike along the soil anomaly. Silver is a true co-product; gold is barely assayed (5%) in the deposit and is the main data gap. Figures interpret historical, pre-JORC data — not a JORC statement.

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Opens in a new tab · holes oriented from collar survey · orbit, zoom and inspect every intercept in 3D

01Deposit map — combined metal (AgEq)

The 38 deposit holes, plan view (north up, collar positions), equal scale. Markers are uniform size; colour = peak combined metal as silver-equivalent (Pb+Zn+Ag+Au).

Peak AgEq (g/t): <50 50–150 150–250 >250 · AgEq = 21·Pb% + 28·Zn% + Ag + 80·Au — illustrative metal-equivalent only (assumed prices, no metallurgical recoveries)

02Geology & mineralisation

Discovered 1976 via SADME stream-sediment sampling (2,100 ppm Pb in Dairy Creek). Classified as a Sediment-Hosted Stratiform Massive Sulphide (SHMS) / SEDEX-style Pb-Zn-Ag, hosted in the Basal calc-silicate unit of the Talisker Calc-siltstone (Kanmantoo Group, Kanmantoo Trough). The economic horizon sits at the base of the Talisker Calc-siltstone, beneath the barren Nairne Pyrite Member and an intermediate garnetiferous quartzite, and carries massive to disseminated galena, sphalerite and pyrite. The horizon dips ~55° E; holes were drilled WSW (~250°) at ~−60° to −70° to cut across it.

Metal zonation. Pb-rich (Ag-bearing) upper zone passing to Zn-rich lower zone; Pb>>Zn+Cu zone at the base of the horizon — visible on the CRA long section as a "Pb=Zn" upper zone passing into a "Pb>>Zn+Cu" zone at the base. Copper and the highest Pb-Ag grades are therefore expected to strengthen down-dip.

Galena PbSSphalerite ZnSPyrite FeS₂Chalcopyrite CuFeS₂Ag with galenaCo to 320 ppmNative Au in gossan

03Long section & Opal re-interpretation

The CRA 1977 longitudinal section defines the mineralised horizon and worked-up intercepts (south left → north right). Below, Opal's interactive re-interpretation — holes plotted at their true inclination/azimuth from the SARIG collar survey. Hover any hole for its full results.

CRA longitudinal section of mineralised horizon (1977)

CRA Exploration, Longitudinal Section, Mt Torrens Prospect, Kanmantoo EL467 (1977). Note "Pb=Zn → Pb>>Zn+Cu at base" zonation.

Opal re-interpreted long section — interactive, survey-corrected

<1% / no sig. 1–5% 5–10% >10% Pb+Zn · grey lines = survey-oriented drill traces · vertical exaggeration ≈ 2×

Strike (south → north) vs RL. Traces follow each hole's true inclination/azimuth (projected to the section). Hover a hole for length, Pb, Zn, Ag, Au and orientation.

Hole orientation resolved + horizon modelled. Collar survey (inclination & azimuth) sourced from SARIG and merged into the database for all holes (722/734). Deposit holes were drilled at ~−60° to −70° toward ~250° (WSW). A best-fit plane through the survey-corrected intercepts gives a horizon dipping ~55° toward ~85° (E), consistent with CRA's 1977 mapped dips of 48–77°. The holes were drilled against this east dip, so they cross it at ~63–65° and true widths ≈ 0.89–0.91 × down-hole length. Remaining unknown: down-hole deviation (holes assumed straight); plane-fit RMS ≈ 31.5 m.

04Best deposit intercepts

Down-hole envelopes from flagged samples (>1% Pb+Zn or >20 g/t Ag). True width = down-hole length × sin(intersection angle) using the modelled ~55°E horizon (indicative). AgEq = 21·Pb%+28·Zn%+Ag+80·Au (illustrative).

Hole	From	To	Len (m)	True W (m)	Pb %	Zn %	Pb+Zn %	Ag g/t	Au g/t	AgEq g/t	Hole (m)

Grade by hole (Pb / Zn / Ag / Au)

Pb grade vs down-hole depth

High grade persists to the deepest assays (~260–310 m down-hole) — open below.

05Growth potential

Down-plunge — highest priority

77MTDD 4: ~5.6% Pb / 55 g/t Ag at ~261 m; 77MTDD 1: ~4.9% Pb / 3.9% Zn at ~165 m; DD84KA 1: ~3.9% Zn at ~310 m (all down-hole). The central shoot is not closed off; mineralisation below the deepest holes is essentially untested.

Strike — ~1.8 km mineralised, ~2 km anomaly

Mineralisation has been intersected over ~1.8 km of strike (the high-grade shoot ~1.2 km; CRA's worked-up resource ~450 m), all within a ~2 km Pb-Cu soil anomaly. The host horizon is traceable beyond the drilled envelope; untested ground lies north and south.

East limb — the host contact again, never drilled or sampled

Mapping shows the Backstairs Passage–Tapanappa contact that hosts the deposit folding back up about 2.5 km to the east, inside EL 7127. Opal's October 2026 fits to Hillgrove's 2005 helicopter magnetics put a 150–460 nT magnetic horizon along ~7 km of that contact, top about 90–175 m below surface (the drilled west limb gives 75–370 nT). No drill hole and no soil or rock sample is recorded on the east limb in the SARIG databases.

The magnetic horizon is pyrrhotite in the Nairne Pyrite Member: it shows where the host contact is, not where ore is. The 1:100k map does not show the Talisker unit on the east contact, so mapping and soils come before drilling. Budgeted in the October 2026 draft programme: A$0.08M in year 1 (mapping, soils), A$0.22M in years 2–3 (first RC holes).

$EL 7127 two limbs$

EL 7127 national TMI grid (40 m, high-pass filtered), CRA drilling, surface sample sites and the east-limb horizon. Opal, October 2026; method and limits in the Section 02 target note of the data room.

Geophysics — TDEM led

1970s–80s magnetics tracked barren pyrrhotite; MIP could not separate ore from pyrrhotite. Modern programme prioritises TDEM, supported by gravity, gradient-array IP and airborne magnetics.

In-fill to convert

The orebody rests on ~13 mineralised holes. Tighter in-fill is required to lift the historic inferred estimate to a JORC 2012 Indicated resource.

06Other economic elements

Co-assay completeness (deposit)

% of Pb-assayed deposit intervals also assayed for each element.

Silver — a genuine co-product (peak 77 g/t), reasonably sampled (69%); deeper holes are silver-rich.

Copper — strengthens at the base of the horizon (to 0.7%), consistent with the Pb>>Zn+Cu basal zone.

Gold — peak only ~0.1 g/t within the deposit and barely assayed (~5%); the only in-tenement gold target is a modest NW soil anomaly (see below).

Cobalt — to 320 ppm; minor but worth tracking. Manganese to ~1.1% (gangue). Mo/As/Bi/Sb not assayed in deposit holes.

Gold within EL7127 — second-order target. Restricting to Opal's tenement, the only gold target is a near-surface auger soil anomaly in the NW of the EL (a cluster of ~6 holes, peak 0.46 g/t Au) — a modest, shallow, separate-from-the-orebody signal worth a cheap follow-up. Note: the stronger historical gold occurrences (old Mt Torrens mine tailings to ~2.9 g/t Au, and DH B5 core ~0.9 g/t Au) sit outside EL7127 and are not Opal ground — excluded here.

In-EL gold target	Position	Gold	Style

Source: 50_Geochemistry database (SARIG), filtered to the EL7127 boundary shapefile. In-EL gold is near-surface and modest — a distinct shallow play, not part of the lead-zinc resource.

Gold targets vs orebody & tenement (north up)

EL7127 boundary Mt Torrens orebody drillholes gold target (filled = in-EL, grey = outside EL) · equal scale, GDA2020

Plan view. Only the NW auger soil anomaly (~0.46 g/t Au) lies within EL7127. The mine-tailings and DH B5 gold occurrences fall outside the tenement (shown greyed, for context) and are excluded from the target discussion.

07Data quality & gaps

Collar survey now incorporated: inclination/azimuth sourced from SARIG for all holes (722/734) and merged into the database — holes correctly oriented and the horizon modelled (~55°E).
True widths now estimated (~0.89–0.91 × down-hole) but indicative — finalise with a 3D horizon wireframe and down-hole deviation surveys if available.
Gold under-assayed in deposit: ~5% coverage — the single most cost-effective assay gap to close (re-assay retained pulps/core).
Silver mostly present: ~69% coverage — contained Ag reasonably constrained.
Collar elevations DEM-derived (±1–3 m) for all but 3 holes — re-survey before estimation.
Vintage QAQC: 1976–84 assays predate documented standards/blanks/duplicates; two resource versions exist (below).

08Historic resource & Kanmantoo peers

Historic resource — documented versions

Source	Tonnes	Pb %	Zn %	Ag g/t	Note

Pre-JORC historic estimate; not reported under JORC 2012.

Comparable Kanmantoo Trough deposits

Deposit	Host	Size	Grades	Status

Angas (Terramin) is the closest analogue — a producing SHMS Pb-Zn-Ag mine in the same trough.

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