Coffee with Samso – The Discovery of the Prominent Hill IOCG Deposit, Gawler Craton, South Australia - The Discovery that Proved Mineral Exploration for Deposits Under Cover.

Coffee with Samso | Episode 215 | Adelaide Markets | Adelaide | South Australia

Guest: 

• Derek Carter – Managing Director (later Chair) of Minotaur during the discovery period

• Tony Belperio (Exploration Lead) – Exploration Manager

• Barry Van Der Stelt (Contract Geologist) – first recognition of copper

• Peter Reid (Senior Geologist) – senior geologist involved in the Prominent Hill work

Introduction

In this Coffee with Samso episode, I went back to Adelaide to sit down with the people who were there when Prominent Hill was found — the discovery that became one of South Australia’s defining IOCG (Iron Oxide Copper-Gold) stories.

This is not a corporate recap. It is a first-hand account of what actually happened in the lead-up to discovery, how the target was chosen, what the drillers and geologists saw in the core shed, and why a single drilling decision could have changed everything.

The team shared the backstory from the early tenement holders right through to the Uranus prospect becoming Prominent Hill — and the reality is simple: discovery is often a chain of decisions, relationships, and technical judgement made under uncertainty.

1) Prominent Hill Was Not a “New” Area — It Was a Patiently Reworked Story

A key point in the conversation was that the Mount Woods ground had history well before Minotaur. The tenements were originally held by Metals X, who worked the region from the late 1980s onward, focusing on magnetic features and drilling at least one early target. Later, Burmine Limited entered the picture, and then Normandy/Poseidon ran a helicopter-based gravity survey across the area.

Burmine Limited (ASX code: BUR1) was an Australian-listed gold and minerals exploration and mining company active in the late 1980s and early-to-mid 1990s. It was primarily focused on Western Australian gold projects, notably operating the Copperhead mine near Bullfinch.

This matters because it shows the reality of exploration cycles: ground can be worked, tested, and even partly understood — but still not properly unlocked until the right targeting logic arrives.

2) The Technical Pivot: Magnetics Were Useful, But Gravity Was the Key

The story turned when the targeting mindset shifted. Earlier programs were chasing magnetic features — and while they were hitting copper-bearing magnetite breccias, there was a ceiling to the grades being intersected.

The breakthrough came when the team could simultaneously interpret magnetics and gravity, and start looking at where these anomalies were offset from each other. The concept was simple but powerful:

• Magnetic anomaly = something magnetic

• Gravity anomaly = something dense

• Offset between the two can be the clue to a different part of the IOCG alteration system

This is where the conversation became very “real exploration”: data doesn’t tell you it’s mineralised. It tells you where you should be brave enough to test.

3) 3D Modelling Was a “Game Changer” — And It Was New Back Then

One of the most important takeaways was how early this team was in adopting 3D inversion modelling. Today we treat 3D models as routine. Back then, it was cutting-edge.

The team explained how the modelling allowed them to rank targets properly, separate those already drilled from those not tested, and better understand the geometry of gravity and magnetic responses.

In Samso terms: this was one of those moments where technology didn’t replace geology — it amplified it.

4) “Uranus 1” — The Discovery Hole That Almost Looked Like Nothing

The drill hole that changed everything was Uranus 1.

Barry Van Der Stelt described the core and is the kind of detail that explorers remember for life:

• The core was so hematite-rich it was hard to even see textures.

• The team was washing core just to interpret it.

• The operation was low-budget — even the core cutting was done on a basic brick saw setup.

Then came the moment: blue specks appearing after the core had sat for a couple of days.

That blue tarnish was the first real visual signal of copper — and it triggered the call that brought the team running.

This was also a reminder that Prominent Hill echoed the Olympic Dam story: sometimes the copper is not obvious until it’s tested, altered, or routinely assayed.

5) The Numbers Were Bigger Than Anyone Expected

The team admitted they initially thought they might have something like “30 metres of ~1% copper.”

Then assays came back with results that were materially stronger, including:

• a high-grade copper interval around 4% copper over ~30m, and

• broader zones around ~1% copper that they simply could not visually recognise in hematite breccia.

Later, deeper drilling confirmed additional IOCG-style signatures, including:

• copper-gold mineralisation and

• uranium increasing at depth, reinforcing the Olympic Dam-style system interpretation.

6) The Sliding Doors Moment: Drilling the Flank, Not the Core

This is one of the most valuable exploration lessons in the episode.

After the discovery hole, infill gravity shifted the interpreted peak of the anomaly by several hundred metres. The team realised they had not drilled the very centre.

The irony is that drilling into the “peak gravity” later hit barren, intensely altered hematite-silica core, which is now recognised as central IOCG alteration.

The team openly discussed the risk: in 2001, if they had drilled the core first and hit barren alteration, they might have walked away.

That is a brutal truth about exploration: a discovery can be decided by where you hit a system first.

7) The Business Reality: Minotaur Had Only 19% — But It Was Enough

One of the most interesting parts of the conversation was the structure.

Minotaur’s maximum share of the project was 19%, while the major partner (BHP/Billiton through the merger timeline) held the majority position.

Minotaur’s “cost” for that 19% wasn’t cash — it was local geological knowledge and management. The team framed it with a simple idea that still applies today:

Better to own a piece of something real than 100% of something you can’t fund.

This is a proper junior-to-major alliance lesson, and it explains how big discoveries are sometimes possible in down cycles.

8) Capital Cycles Still Matter

The group reminded us that this happened during a period when market attention was elsewhere — the dotcom era, when exploration was not “in fashion.”

And yet, the discovery still drove a dramatic market response:

• strong share price movement,

• heavily oversubscribed shareholder participation,

• major legal/accounting work managing scale and compliance.

The point wasn’t hype. It was showing how quickly markets can change when geology delivers.

What This Episode Really Shows

This Coffee with Samso episode is a reminder that discovery requires:

• Local knowledge (not just imported models)

• Funding and deal-making (alliances matter)

• Technical courage (you still have to drill the target)

• Open-minded thinking (don’t get trapped by one model)

• A tolerance for failure (because near-misses are common)

Prominent Hill wasn’t found because everything was obvious. It was found because the team kept moving forward, making decisions with imperfect data, and backing their judgement.

Samso Concluding Comments

For me, episodes like this are part of documenting the real value chain of discovery.

A lot of people talk about the “next Olympic Dam” like it’s a marketing phrase. This conversation shows what that actually looks like in practice: long lead times, multiple parties, tight budgets, imperfect data, and a team that had the discipline to keep testing.

If you want to understand how IOCG discoveries really happen — this is one to watch.