EL9935 Plumbago Creek: a copper–gold–REE skarn that was assayed for the wrong metals for 87 years

A granite–marble contact in the New England Orogen, worked for iron and then limestone since 1939 — and never once tested for the metals a contact skarn actually carries. The magnetic body at the historic workings has never been drilled. The two tests that would settle it are cheap.

The setup. The Permian Bruxner Park Adamellite intrudes a marble–metasediment sequence and marmorises the carbonate at its contact — a textbook contact-skarn setting. A 1989 NSW Government study independently called the iron bodies here "probably skarns." Modern airborne magnetics resolve a coherent body ~1,000 m × 400–500 m at the old workings that resolves into at least five discrete pods along a NW–SE corridor in the deeper-source (upward-continued) data.

The miss. Across 87 years and eleven operators, every campaign assayed only for the commodity in its brief — iron, then limestone — and left for market or economic reasons, never a negative metal result. No sample from the licence has ever been assayed for Cu, Au, Ag, Pb, Zn, REE, U, Bi, Mo, Co, Te, Sn or W. Nothing at the ironstone has been sampled below about 4 m, and no hole has ever entered the magnetic body — the only historical drilling on the belt tested the limestone, 4–5 km away.

Figure 1 — Schematic cross-section A–A′, SW–NE across strike (interpretive, not to scale). Granite to the SW; the granite–marble contact and the interpreted magnetic body dip steeply NE. All historical sampling of the ironstone sat in the top ~4 m; no hole has entered the magnetic body, and its depth extent is unconstrained. The Terra Rossa alternative — a weathering profile on the marble at the Jurassic palaeosurface — is drawn so the two readings can be compared. One hole collared NE and drilled SW into the contact (≤ ~250 m) would be the first real test.

Why it's a real target, not just a magnetic rock. The reduced-to-pole magnetic body is coherent and survives 500 m of upward continuation — a body at depth, not surface noise — yet there is no coincident gravity high beneath it. That magnetic-with-no-gravity pairing is the signature of an alteration-hosted skarn/replacement system rather than a barren magnetite core. It sits inside a discrete potassium–uranium radiometric halo. And on the ground, manganese climbs 10–80× (to 7.33%) at the southern adit faces — a redox-margin vector outboard of the iron core.

Figure 2 — Airborne geophysics over EL9935 at identical extent. The magnetic body is coherent and persists at depth; the gravity products show no density high beneath it — consistent with alteration-hosted skarn, not massive magnetite.

Figure 3 — Exploration history, 1939–2023. Eleven operators, two commodities, one blind spot: the metals were never looked for, so they were never found.

The honest risk. The preferred model is a contact skarn (Cu–Au–REE), not IOCG — and the leading alternative is that the surface ironstone is a Terra Rossa weathering profile rather than a skarn, in which case the target isn't a mineralising system at all. That is precisely the first question the cheap work answers.

The test — cheap first. Re-assay retained pulps and core for the full Cu–Au–REE and pathfinder suite; re-model the geophysics for a skarn geometry; run a targeted field study of the ironstone. A negative result retires the target for the cost of a few thousand dollars in assays — before any partner-funded spend. A positive result earns a single confirmation hole within JV drill-depth appetite (≤ ~250 m).

Where this came from. The concept is built entirely from GSNSW open-file (DIGS) records, read back against the primary sources and corrected — including the marble tonnage and the geographic attribution of the district polymetallic data. Historical results are unverified by a Competent Person; no JORC (2012) Resource, Reserve or Exploration Target is declared or implied.

Do your own first pass — the data is public. Pull EL9935 on GSNSW MinView and look at the TMI-RTP magnetics, the K–U radiometrics and the gravity over the licence, then read BHP's 1960 assays (DIGS R00028669) and Brownlow 1989 (R00004511). The signature is there in ten minutes.

Then, if the concept holds for you: the full Technical Synthesis — nine sections, the seven-layer geophysical case, the BHP assay dataset, the verification workstream and the staged drill design — is available under NDA, with earn-in JV or option-to-buy terms.

Contact: Doug Alcock, Managing Director, CAADIA Metals Pty Ltd.

No JORC (2012) Mineral Resource, Ore Reserve or Exploration Target is declared or implied. Historical results are compiled from GSNSW open-file records and have not been verified by a Competent Person. The contact-skarn interpretation is a working hypothesis under test; the magnetic-body geometry is a geophysical inference. Terms are indicative and non-binding, subject to contract, due diligence and agreed land access.