Dowling–Koorabri

Geological setting and mineral system

The prospect occupies the Goodradigbee Graben between the Cowra Trough and the Cotter Horst, where the Koorabri Fault — a splay of the first-order Long Plain Fault — juxtaposes Lower Silurian limestone–chert–shale sediments against the Lower Devonian Mountain Creek Volcanics (Quek 1980a, R00016067). A calc-silicate corridor (clinopyroxene–garnet–epidote–actinolite, locally barite-bearing) of ~3–5 km strike and up to ~80 m apparent (outcrop) width — true width not established — is developed on the fault, hosting galena, sphalerite, pyrite and minor chalcopyrite, and is recorded across the GSNSW open-file series from GS1979/405 (R00016066) to the 1982 final report GS1982/474 (R00009880). The synthesis classifies the system as fault-controlled carbonate replacement, with “distal skarn” retained only as a textural descriptor of the calc-silicate assemblage, not a genetic claim: the nearest mapped granitoids lie 2.5–3 km east of the collars, so a proximal pluton-contact skarn is not supported. Two inferences are stated as inferences: the target horizon at the abandoned DOW-2 site is an interpretation at ~120–130 m — no hole at that site has reached it; and the regional north–south magnetic low along the corridor is an unverified reading from statewide imagery — bespoke reduced-to-pole products have not yet been produced over the corridor.

The grades — what the system has already demonstrated

Headline historical results — GSNSW open-file, verbatim-sourced (the only intercepts in this document)
Result	Confirmation status / resolution path
Gossan rock-chip maxima, corridor — 5.04% Cu · 3% Pb · 1.14% Zn (Quek 1982, R00009880)	Independently confirmed: reproduced in the BHP-Utah 1989 final report (R00006039). No discrepancy on record — the best-supported result in the dataset.
DOW-1, 0.15 m at 110.8 m — 17.8% Zn / 2.20% Pb / 82 g/t Ag (Preussag) vs 8.9% Zn / 0.89% Pb (North Broken Hill) (Table 5; R00009880 / R00015095)	Two-laboratory split not yet reconciled; the column-to-laboratory assignment (including which laboratory carries the 82 g/t Ag) is itself PENDING manual verification (Appendix E). Resolved by the Phase 1 four-acid ICP-MS re-assay of the preserved DOW-1 core, A$12–18k.
Peak soil geochemistry, line 9,400 mN — ~4,000 ppm Pb · ~4,400 ppm Zn (Quek 1980a, R00016067)	Strongest soil anomaly on the grid; the 1980 proposal’s ‘Hole 2’ target — not drilled. Tested directly by designed hole DKD001.
Old-shaft mullock ~300 m N of DOW-2 — 4.4 g/t Au maximum (NBH 1982, R00015095)	Value and locator re-cited to the NBH primary record in v3.0; gold values elsewhere are described as very low. The gold overprint is downgraded — the play stands on base metals.

Exploration history — three operators, documented exits

Three operators, three documented exits — none drilled the corridor to target
Period	Operator (licence)	Model targeted	Departure reason
1979–83	Samedan–Preussag JV (ELs 1196/1206/1207)	Syngenetic VMS beneath the calc-silicate gossans	Concluded on S/Se grounds that the IP sources were barren footwall pyrrhotite and relinquished after DOW-2 was abandoned at 113.0 m, short of target — a laboratory-model conclusion, not a drilled test (Quek 1982, R00009880).
1981–82	North Broken Hill (farm-in; funded the 1982 drilling)	Stratiform base metals; judged the pyrrhotite favourable for Au–W deposition	Withdrew after the 1982 campaign; its own logging read DOW-1 sphalerite as apparently stratiform and possibly syngenetic — genesis contested between the two operators holding the same core (NBH 1982, R00015095).
1988–89	BHP Gold Mines (EL 3198)	Epithermal Au–Ag in the volcanics; skarn-hosted Au	Gold-only BLEG and stream programme directed away from the corridor; recommended relinquishment on the gold case — the base-metal case was not tested (BHP-Utah 1989, R00006039).

Why the grade is still available — in the operators’ own words

Wrong commodity, wrong model. Preussag targeted a syngenetic VMS body and withdrew on a laboratory argument, not a drilled one: its 1982 final report concluded from S/Se ratios (~3,800:1 in the band vs ~82,000:1 in footwall siltstone) that the sphalerite was epigenetic and vein-hosted and the IP anomalies largely sourced from barren footwall pyrrhotite — the principal stated reason for withdrawal (Quek 1982, R00009880; paraphrased). Its farm-in partner disagreed on genesis: North Broken Hill’s own logging of DOW-1 recorded conformable banded sphalerite at 62.08 m and 69.3 m as apparently stratiform and possibly syngenetic (NBH 1982, R00015095; paraphrased) — the model was contested between the two operators holding the same core. BHP’s exit was commodity-driven, and its final report says so: “... the present work in the Dowling area which is in a similar structural setting does not suggest significant potential for epithermal gold” (BHP-Utah 1989, §5, R00006039; verbatim, leading clause elided). BLEG is gold-specific — a Cu–Zn–Ag replacement corridor with sporadic gold would not register — so the base-metal case was never addressed. The 1980 proposal even records a non-technical siting constraint — public sensitivity near Kosciuszko National Park (Quek 1980b, R00000957; paraphrased).

The analytical gap. Historical assaying was warm-acid, partial-digestion AAS (~±10% quoted precision) over a restricted suite, with no standards, blanks or duplicates documented anywhere (Quek 1982, §2.1.1). Partial digestion routinely under-reports refractory cassiterite-hosted Sn and scheelite/wolframite-hosted W — yet the historical series records Sn locally to ~1,300 ppm in chips, and the NBH pit-sampling sheet carries ~83 g/t Ag with ~115 ppm Sn (R00015095; values approximate — the sheet is subject to a PENDING digit-level re-read). The preserved DOW-1 core — 25 boxes, 0–183.2 m, GSNSW Londonderry Core Library — has never been re-assayed by modern near-total ICP-MS. The database audit finding, in one line: the corridor’s pathfinder chemistry has never actually been measured.

The untested target. The 1980 three-hole proposal ranked ‘Hole 2’, north of line 9,400 mN, over the strongest soil response on the grid (4,000 ppm Pb / 4,400 ppm Zn) — it was not drilled (Quek 1980b, R00000957). At the DOW-2 site the synthesis’s formulation is precise: the upper 113 m is tested and barren; only the deeper target horizon (interpreted at approximately 120–130 m) remains not yet tested. The blind IP anomalies in the footwall mudstone (~10,200 mN / 10,100 mE) and on lines 9,800 mN and 9,600 mN have no coincident geochemistry and were never drilled.

The miss, precisely. Three things were never done. The hole on the best four-way anomaly stopped 7–17 m short: DOW-2 was abandoned at 113.0 m in barren cherty mudstone, and only the deeper target horizon — interpreted at approximately 120–130 m — remains not yet tested (NBH 1982, R00015095). The strongest soil anomaly on the grid (~4,000 ppm Pb / ~4,400 ppm Zn, line 9,400 mN — the 1980 proposal's 'Hole 2') was never drilled (Quek 1980b, R00000957). And no sample from the corridor has ever been assayed by modern near-total ICP-MS — the preserved DOW-1 core sits unmeasured at Londonderry. Every operator exit rests on data that stops short of these three tests.

System scale and the 2026 price lens

Footprint — dimensions, never tonnes. Corridor strike ~3–5 km north–south with up to ~80 m apparent (outcrop) width (true width not established); calc-silicate lenses to 80 m maximum thickness, apparently thickening northward; an old-workings zone over ~800 m; three soil anomalies spanning lines 10,400–8,600 mN; true gossans averaging ~20 cm wide. Depth of testing: two completed penetrations on the whole corridor — DOW-1 to 183.2 m and DOW-2 to 113.0 m; the high-grade surface zone is untested below ~7 m (the deepest old working) save for the narrow bands clipped by DOW-1, and nothing anywhere has been tested below 183.2 m. Analogues and price context: Technical Synthesis v4.0 carries no model-class analogue ranges and no commodity-price recharacterisation; this summary does not outrun its source, and none is presented here.

The targets

Primary — T1, the Hole-2 soil anomaly (line 9,400 mN, ≈10,450 mE). The strongest undrilled Pb–Zn soil anomaly on the grid, over calc-silicate. Its technical limitation is stated plainly: chargeability alone cannot discriminate base-metal sulphide from barren sedimentary pyrrhotite — the historical S/Se work raised exactly this ambiguity and did not resolve it for the untested anomalies, and absolute chargeability / resistivity amplitudes have never been read from the Dickson pseudosections. The design answers it two ways: the drill target is the geochemical footprint (soil Pb–Zn over gossan-fertile calc-silicate), not raw geophysics, and DKD001 (220 m at −60°) tests it directly, with the Phase 1 re-assay and pseudosection digitising sequenced first. A NW–SE fault between the 1980 proposed site and its target is recorded in the proposal and honoured in siting.

Secondary. T2 — down-dip / along-strike extension of the DOW-1 110.8 m sphalerite band (DKD002, 260 m). T3 — blind IP / magnetic anomalies on lines 9,600 and 9,800 mN, no coincident geochemistry, never drilled (DKD003, 200 m; DKD004, 180 m). T4 — gossan root zone: the bedrock source of the 5.04% Cu surface chemistry, untested below ~7 m. Beyond the designed programme, the abandoned DOW-2 anomaly core’s deeper horizon (a ~120–130 m interpretation, never reached) remains a candidate for conditional follow-up.

Testing the thesis — gates, kill criteria, cost to answer

Every failure mode is paired with a cheap, pre-specified, binary test
Phase + cost	Scope	Gate & kill criterion
Phase 1a — desktop & tenure, A$5–10k	Georeference the Preussag grid to MGA; verify open ground (MinView) and the Bimberi Nature Reserve boundary; design a licence footprint following the corridor.	Zeroth kill-gate: if a footprint cannot be drawn clear of the reserve, the project stops before any technical spend. Binary — the kill answer costs ≤A$10k.
Phase 1b — DOW-1 re-assay, A$12–18k	~180 one-metre samples of the preserved core (Londonderry); four-acid near-total ICP-MS (Cu, Pb, Zn, Ag, Sb, Sn, W, Bi, Te, Se, As, Mn) with Au by fire assay; CRMs, blanks and duplicates at ~1:20.	Kill test for the pyrrhotite ambiguity at the DOW-1 site (an indirect proxy for DOW-2 and the blind IP — no DOW-2 core was retained). A barren-pyrrhotite result re-frames the play to the narrow remobilised-vein reading rather than the replacement case — binary at ≤A$18k. Also resolves the 17.8% vs 8.9% Zn laboratory split.
Phase 1c — geophysics, A$10–25k	Digitise the Dickson IP pseudosections (lines 10,200 / 10,400 / 9,800 / 9,600 mN) to quantify chargeability and resistivity; reprocess magnetics to RTP / 1VD / analytic-signal.	Gate: a defined chargeability-high / resistivity-low target must emerge from the reprocessing; no target, no drilling.
Optional — surface re-sampling, A$10–20k	Modern multi-element ICP-MS over the corridor and gossans, weather-permitting.	Independently re-verifies the high-grade chip values (including the 5.04% Cu gossan) under modern QAQC. Phase 1 envelope ~A$35–70k to a drill decision.
Conditional drilling — indicative A$590k (incl. 15% contingency)	Designed programme (Drill Design v1.0): DKD001 (T1, 220 m), DKD002 (T2, 260 m), DKD003 (T3, 200 m), DKD004 (T3/T2, 180 m) — ≈860 m HQ→NQ diamond, triple-tube, oriented core; 0.3–1.0 m sampling through sulphide; multi-element ICP with Zn/Pb over-limit and the S/Se discriminant; CRMs, blanks and duplicates ≈1:20 plus 5% umpire re-assay; “four scout holes to a decision gate”, structured to de-risk a JV or grant-supported campaign.	Gated on Phase 1 returning (a) base-metal-bearing sulphide chemistry consistent with the IP response, and (b) a defined chargeability-high / resistivity-low target. Follow-up is contingent on a mineralised intercept — “scope defined by Phase 1 results” (Drill Design v1.0, §5).

Technical Manager: Dr Tim McConachy FAusIMM (1974), Senior Fellow SEG, former Rio Tinto Chief Geologist.

Data room (under NDA): technical synthesis v4.1, Phase 1 drill programme design, source register and figure set.

Contact: Doug Alcock, Managing Director, CAADIA Metals Pty Ltd — dalcock@caadiametals.com.au

No JORC (2012) Mineral Resource, Ore Reserve or Exploration Target is declared or implied. Historical results are compiled from GSNSW open-file (DIGS) records, have not been verified by a Competent Person for public reporting, and are provided for context only. The IRGS / distal-replacement interpretation is a working hypothesis under test; alternative interpretations of the geophysical data exist. Earn-in terms are indicative and non-binding, subject to contract, due diligence and grant of the Exploration Licence.