The Prospectivity of the Gawler Craton - Anna Petts - Geological Survey of South Australia

Samso Insight Episode 112 is with Anna Petts, Program Coordinator - Characterising South Australia's Cover at Geological Survey of South Australia.

 

To many people the Gawler Craton is famous for IOCG deposits (Iron Oxide Copper Gold). The most famous mine, Olympic Dam started the rush for these giant deposits. When it was announced that there was this monster of a drill intercept, RD10 with 145m at 2.2% copper together with uranium and gold. This news created a rush like the wild west where everyone flocked to the region.

 

Subsequent to the rush, two other famous discoveries was made and they are Prominent Hill and Carrapateena. However, it was not until 2001 when Prominent Hill was discovered and in 2005 that Carrapateena was discovered. All this action was in the eastern region of the Gawler Craton and this region was named the Olympic Metallogenic Belt or the IOCG Belt.

 

 

 

Figure 1: The Olympic Cu-Au Province in the context of the geology of southern Australia. The main lithotectonic units of the Gawler Craton and Curnamona Province are shown and are interpreted from surface observation and geophysical data. The Olympic Cu-Au Province occurs in the eastern Gawler Craton and also indicated is the Central Gawler Gold Province, a gold-dominated metallogenic province formed during the same early Mesoproterozoic tectonic event that formed the Olympic Cu-Au Province. Inset shows the location of the Gawler Craton and Curnamona Province in the context of major Archean and Proterozoic terranes of Australia.

(Source: Reid, Anthony. (2019). The Olympic Cu-Au Province, Gawler Craton: A Review of the Lithospheric Architecture, Geodynamic Setting, Alteration Systems, Cover Successions and Prospectivity. Minerals. 9. 371. 10.3390/min9060371.

 

The complexity of the surrounding area is not for the faint hearted as they are still arguing about the origins and formation of Olympic Dam. Figure 1 gives a high level summary of the Gawler Craton and its different geological events. There is no doubt that there is no simple answer but what the mineral explorers do know very well, is that their Return On Investment (ROI) here is not high.

 

For this reason, the Gawler remains one of the least explored regions on the Australian continent. Hence, this discussion with Anna Petts is all about the prospectivity of the Gawler and what the Geological Survey of South Australia is doing to help explorers have the edge and the resources to understand and explore the region.

 

Gold Discovery in the Gawler Craton

 

In 1995, there was the discovery of a gold mine in the other half of the Gawler Craton. The more "boring" part which birth the Challenger Gold Mine. This set up a rush to the area, however, till today, there is no Challenger replica. To me, this has got to be one of the mysteries of Australian mineral exploration.

 

If you draw a radius of 100km from the Challenger Gold Mine, there is nothing that is better than a prospect to be found (Figure 2). It will be pretty safe to say that the lack of discoveries is probably due to the fact that the last 20 years of exploration has been few and far in between due to a lack of exploration funding and the historical low ROI in looking for minerals in the Gawler Craton.

 

 

 

Figure 2: The spatial emptiness of big discoveries within the Gawler Craton. The comparison to a typical mining town like Kalgoorlie, there is too many producing assets to count.(Source: Taiton Resource Limited)

 

Why I like the Gawler Craton

 

My first introduction to the Gawler Craton was way back in 2019 when I looked over the Jumbuck project. Figure 2 was the result of that exercise when I was involved in trying to list a company with the project. I could see that there had not been any serious exploration in the region.

 

The conversation that I had with people was that it is hard to make discoveries. The geophysics were not picking anything up. There were not enough data out publicly that companies could use to make discoveries. The lack of success was biting into exploration funding.

 

Imagine a province like the Gawler Craton that still hides major discoveries. Look at the statistical probability of not finding another Challenger. This has to be a great place for the average mineral explorer who has the courage to test their exploration skill. Looking at the western province of the Gawler, the western part of the Stuart Highway, there are no producing mines currently. There are three deposits (Challenger is closed) that exist and two are currently being drilled out to see if they make the cut to become producing gold mines.

 

In one conversation, I was told that while drilling for iron ore, they came across a Gossan. This shows the variability of the area. It was only two to three years ago that the south-western part of the Gawler was identified as a new nickel sulphide area.

 

Samso's Conclusion

 

So what do I make out of this conversation with Anna. What I got out of it is that there is now a flow of fata that is being made public for explorers. The understanding of the Gawler is going to take a magnitude step forward in the near future, if not already. The testing of theories are now being played out with companies such as,

 

• Indiana Resources Limited (ASX: IDA),
• Cobra Resources Limited PLC,
• Investigator Resources Limited (ASX: IVR),
• Petratherm Limited (ASX: PTR),
• Barton Gold Holdings Limited (ASX: BGD),
• Marmota Limited (ASX: MEU)
• Taiton Resources Limited (ASX: T88)

The company that I am involved with is testing the concept that there is a unloved and unrecognised mineral system in between the Olympic Dam Belt and the Gawler Craton gold province, see Figure 3. The concept of a theory like this can be easily considered to be shooting with a long bow, but the recent announcement has made good evidence that there could be some truth to the madness.

 

 

 

Figure 3: The region that Taiton Resources Limited is testing its theory that there is a mineral system in the region (Red) which is now proven to be tapping the same source as the Olympic IOCG Belt (Green). The zircon test has come back with age of 1597.8 Ma, which is atypical of Olympic Dam. (source: Taiton Resources Limited).

 

The concept is that the red region (Figure 3) has been misinterpreted in the past and there lies a mineral system that may be fertile and endowed with mineralisation. This is the postulation and as mineral explorers, we are supposed to be testing the boundaries of believe.

 

The role of the explorer is to come up with the ideas and the concept and of finding minerals when others have missed. The role of the Geological Survey is to provide the tools and the solutions to aid discovery. After speaking with Anna, I feel that the Geological Survey is contributing a lot at the moment. The theory for Taiton Resources came about due to the data release in around 2020. The idea was born and the money was raised to test the theory.

 

As a director of the company and as the person who spoke to the vendor of the Highway project, David McSkimming, I will say that the theory for Highway is the best I have heard. I like the idea that there is a different thinking to understanding the mineral system in this region.

 

What the company has done to date has proven that this theory is still valid. Not only have we proven our original story is valid, we think that we could be on the edge of two tectonic event and that would make us siting on the margin of a major structural feature. We all know that major structural features are the blessing for an exploration project.

 

None of what I had described would not have been possible without the work generated by the Geological Survey of South Australia. Anna has clearly described what the Survey is doing and what datasets are now available. The new datasets will allow future explorers to take on what is potentially the last mineral province that has not been searched with intent for the last twenty years.

 

 

 

Chapters:

 

00:00 Start

 

00:20 Introduction

 

01:51 About Anna Petts

 

02:24 Disclaimer

 

03:04 The potential at Gawler Craton

 

06:07 The cover at Gawler Craton

 

10:39 Uncovering the lack of recent significant exploration stories

 

16:52 The exploration government initiatives

 

20:05 Potential mining hotspots

 

25:17 Understanding the overall complex of the big discoveries

 

29:01 Prospectively at Gawler Craton

 

32:31 All about the Ultrafine+ project

 

44:39 Potential mining location worth looking at

 

46:10 Conclusion