Keynote address
Discovering the next generation of mineral deposits—what are the right questions?
Dr Neil Williams
I trust that you are all fired up to think about searching deep beneath Australia for our new resources. To help get you started, I am going to challenge you in my presentation to think carefully about what are the right questions that we should be asking. In 1946, at the end of World War II, the great Australian geologist Sir Harold Raggatt convinced the then Commonwealth government in Canberra to set up a national geological survey. It was called the Bureau of Mineral Resources (BMR) and in time it evolved into Geoscience Australia (GA). The basis for the government’s decision to set up the BMR was Sir Harold Raggatt’s vision that, with good regional geological and geophysical maps, industry would be able to discover new mineral wealth and Australia would one day be a very wealthy country due in large part to its mineral resources. The animation I am about to show demonstrates just how well Sir Harold Raggatt’s vision has been realised. The animation was actually made by Phil McFadden when he was GA’s Chief Scientist and it shows mineral discoveries year by year from the year 1946 to 2001. You will see a red fl ash when there is a discovery and then that red flash will collapse back into a little yellow circle, which will remain. Very importantly, on the left-hand side, in dollars, you will see export earnings from Australia’s minerals. You will see that they are very impressive.
Were Phil to update the animation, you would see two things. Firstly, you would see that mineral exports now stand at about $75 billion per annum; so it is really a very, very significant part of the Australian economy. Secondly, you would note, if you had a good eye or Phil slowed the animation down, that the discovery rate of greenfields deposits is slowing. We have seen tremendous growth in mineral production over the past few years, but this has come from accelerated production at existing mines, from brownfields exploration within and adjacent to known mineralisation and also from innovations that have improved the efficiency and effectiveness of mining and processing. But we do have a problem in the greenfields area. These are the sorts of explorations where you build new mineral provinces, new mines and new towns – activities that sustain the long-term health and wealth of the industry. This issue of the slowing down of greenfields success in Australia has been troubling. It certainly concerns the Australian Government as well as the state and territory governments. Over the years there have been several inquiries into what is the problem with greenfields exploration. One of the better known inquiries was the Prosser inquiry, which was undertaken by the House of Representatives in Canberra. Like many other reports it highlights the big problem, which is stated here: ‘...as yet “undiscovered” world-class ore deposits are most probably concealed by barren soils or barren cover rock sequences’. This is the challenge, or a good example of the challenge, for all of you—but, to my mind, it is an exciting, intellectually stimulating and economically rewarding challenge to take on. This slide shows the black soil plains of the Barkley Tableland north-west of Mount Isa. The nearest areas of regional outcrop to the spot where I took this photo constitute one of the most richly endowed parts of the Earth’s crust for lead-zinc mineralisation. There is every likelihood that, somewhere beneath these vast, featureless black soil plains, giant lead-zinc deposits will be lurking and awaiting discovery. The question is: can we find them? As a former mineral explorer and optimist, my view is that of course we can —‘Yes, we can,’ as someone else recently said. But the big challenge really is – how do we go about doing it? We know that what we are doing at present in exploration is beginning to fail and we therefore need to think beyond the current exploration ‘paradigm’: we need to think beyond the square and to go about deep exploration in a different way from how we do exploration today in what I will from now on refer to as ‘surface exploration’. Dr Neil Williams Let’s go from northwest Queensland to another equally flat part of Australia. This slide shows the landscape around Woomera near the famous old rocket range in central South Australia. One of the reasons that I am so optimistic about the future of mineral exploration in Australia is based on what has been achieved in exploration in the Woomera region. Where I grew up, in Albury, NSW, the landscape that you see on this slide was called the ‘back of beyond’. It has many other names, few of them flattering. However, for all geoscientists, both here in Australia and all around the world, this place is, or should be, a place of great wonder because lurking 350 metres below the desert’s surface, at a sheep station called Roxby Downs, sits one of the world’s biggest known ore deposits: the super-giant Olympic Dam deposit. Olympic Dam was discovered in 1975 by the then Western Mining Corporation. The WMC team that found Olympic Dam was led by the great Australian mineral explorer Roy Woodall. We have the privilege of having Roy here with us today. Roy is a legendary figure in the world of mineral exploration. I hope that all of you take the opportunity to talk to Roy—because, if ever there was a person to think beyond the square and to ask the right questions and challenge his staff to do the same, it was Roy. Olympic Dam is now owned and operated by BHP Billiton and, on the basis of known resources, it is now ranked as the world’s fourth largest copper deposit, the world’s largest uranium deposit and the world’s fifth largest gold deposit— all of that in one deposit. It is truly a giant amongst giants. That is all the more impressive when you remember that we still do not know just how big Olympic Dam is, as it has yet to be drilled out fully. Furthermore, the deposit is of a type of mineralisation that was previously unknown and is now generally referred to as an iron oxide-copper-gold deposit. I do not like that term; I think it deserves its own name: it is an Olympic Dam type deposit because of its huge size and uniqueness. Olympic Dam occurs in basement rocks beneath 350 metres of relatively fl at-lying cover sediments that are a billion years younger than the 1.6-billion-year-old rocks that host the deposit. The discovery of Olympic Dam provides some fantastic insights into how we might go about future deep exploration, so let’s have a quick look at how WMC went about finding the deposit. In the little time that I have, I cannot do full justice to the discovery, but I will try to capture the key elements of the discovery. Dr Neil Williams 41 The thinking that led to the discovery was developed by a team with diverse expertise. One member of that team was a structural geologist, Tim O’Driscoll, who had discovered that, if you carefully analysed BMR’s national- scale geophysical maps, you could see long linear features crisscrossing the country. This slide shows one of Tim’s processed BMR magnetic maps of Australia. His main lineaments are marked on the slide. This work was, and remains to some, controversial but, without Tim O’Driscoll’s lineaments, I doubt that Olympic Dam would be a mine today. He noted along the way that many of Australia’s big mineral deposits lay on these lineaments and actually, more often than not, lay where they crossed one another. This is Kalgoorlie and here we have Kambalda. The famous giant Kalgoorlie gold system, for example, sits where these two lineaments cross one another. Another member of the team was Doug Haynes; he had done a PhD at the Australian National University. He research topic centred on what sourced the copper in large copper deposits. Based on his PhD research, he developed a sediment-hosted copper exploration model that led to WMC’s copper exploration program to focus on areas of South Australia underlain by particular basic igneous rocks: the copper source rocks that were an important element of the search model and of Doug’s PhD thesis. One such area of known copper mineralisation was at Mount Gunson, well south of Olympic Dam. At Mount Gunson, beneath the known mineralisation, in the BMR’s regional geophysical data sets there was an area with coincident gravity and magnetic anomalies that was interpreted to be Doug’s copper source rocks - basic igneous rocks. Interestingly, Mount Gunson also lay at the intersection of two of Tim O’Driscoll’s lineaments. Another member of the WMC team, geophysicist Hugh Rutter, had identified from BMR’s regional magnetic and gravity maps some other areas of coincident magnetic and gravity anomalism well north of Mount Gunson and these were refined as drilling targets, using Tim O’Driscoll’s lineaments.
Dr Neil Williams On this slide we see these particular lineaments – and indeed these two cross where Olympic Dam was subsequently discovered. I have skimmed across a fascinating story and I am sure that a lot more can be told. Interestingly for me, at Olympic Dam, we now know that the mineralised body is strung out in this direction – the same as one of Tim O’Driscoll’s lineaments. This suggests a strong structural control on the location of this giant deposit and I think it gives additional support to the ideas that Tim put together back in the 1970s. This is a modern-day image of the regional magnetic and gravity data that cover the Olympic Dam region. Magnetics are on the left and gravity is on the right, and the little faint white circles show the position of Olympic Dam. You might ask after looking at the two images: ‘Well, why did WMC drill where they were?’ The answer is: ‘Remember the lineaments’. The point I want to make now is that these data were available through the old BMR to anyone who was interested in exploring for m