June/July 2013

Elephant hunting

Exploration geologist Dan Wood dishes the dirt on the next generation of discoveries

By Peter Braul

Dan Wood at the top of Mt Merapi, Indonesia's most active and deadly volcano, in Central Java | Courtesy of Dan Wood
As mining companies develop deeper, larger underground mines, exploration geologists are feeling the push to discover suitable deposits. For exploration teams taking on this daunting task, Dan Wood serves as a role model. During his 42-year career in exploration with BHP and Newcrest, he led teams that made some spectacular finds including what are now Newcrest’s Cadia Valley Operations in New South Wales, consisting of a pair of productive cave mines. Wood is happy to impart his wisdom, now that he has officially retired. Last year, as a distinguished lecturer with the Society of Economic Geologists, he spoke about discovering tomorrow’s deeper ore bodies. Currently, he is an independent non-executive director of Highlands Pacific Limited, and he also serves as an advisory board member of the W. H. Bryan Mining and Geology Research Centre at the University of Queensland, where he is an adjunct professor.

CIM: Can you describe the task of visualizing an ore body?

Wood: Well, discovery is an art; it uses science, but to practise this art properly, one needs to combine both good science and three-dimensional thinking. To assist me with achieving the latter, I always walked around with a three-dimensional dart board in my mind. What you’re trying to find is the bull’s eye, which is the ore. Around the bull’s eye, there are various rings, and each of those rings has the capacity to point you in the direction of the ore, if you can interpret what you’re finding in the ring. When you go into an area looking to make a discovery, the chance that you’re going to drill a hole directly into the bull’s eye and the ore is, probably, pretty slim. But you’re likely going to drill some holes that are going to get you into one of the different rings – if an ore body is present.

A porphyry copper deposit is a classic target for this type of approach – although I have also used it to discover a coal deposit – because a porphyry copper deposit might be, say, 500 metres across. But the influence of that ore on the surrounding rocks might be several kilometres. Instead of looking at a space of say 500 metres by 500 metres, you’re potentially looking at a space that’s two kilometres by two kilometres, or three kilometres by three kilometres.

CIM: How do we find the ore bodies that will become the large-scale underground cave mines of the future?

Wood: Ore bodies that are suitable for large-scale underground caving require a regular geometry, and this influences how one explores. If you’re looking for an ore body that occupies a cubic kilometre in volume, for example, and you’re drilling holes 100 metres apart to discover this ore body, well, you’re kidding yourself.

Very early on, you really need to know whether you’re chasing an elephant or a mouse. If you’re looking for something that has a surface expression of 200 hectares, for example, that’s a lot of territory, so you can drill very widely spaced holes during the discovery phase. But then you need a lot of smarts to understand what those holes are telling you, because not every hole will strike ore, and every ore body has barren parts to it and post-mineral intrusions and all sort of things that are not ore.

CIM: Technology is certainly a huge component of the next generation of mines. What is your view on how technology will change exploration geology?

Wood: A lot of people seem to be saying, ‘It’s just all too difficult. We’ve got to have technology discover these things for us.’ Well, it didn’t work that way in the past and a lot of old fogeys like me are saying it’s not going to work that way in the future either, at least for the next 10 to 20 years. As an explorer, you’re still going to have to think.

That said, what’s had a significant impact during my career by way of technology is the availability of remotely sensed data. You can do quality regional geological mapping off satellite images, for example, and also measure different spectra, which gives another insight into the geology. So, in Chile and other desert areas, you can start to map out alteration minerals that have accompanied mineralisation. That sort of technology has had a significant effect on better understanding the geology of an area, particularly of those features of the geology associated with mineralisation.

Another remote-sensing technology that’s still in its infancy from an exploration perspective is LIDAR, which is an airborne laser surveying technique. It lets you look through jungle canopy so you can actually map the topography within a two-centimetre elevation difference. Topography reflects geology, so this technique enables rapid basic geological mapping of jungle-covered terrain.

There is a lot of technology that assists, but in the end, it still comes down to the geologist thinking about what he or she actually sees and records.

CIM: If there are under-explored regions like Brazil, West Africa and Finland, where we haven’t even touched the basic deposits, why are people putting faith in enormous, complex and risky underground mass mining projects?

Wood: Many geologists think most places are over-explored and that is why Brazil, et cetera, may seem more attractive, although the discovery record suggests, somewhat

perversely, that you probably never want to be the first company exploring an area. Occasionally, it has paid off, if you go back to the 1950s and 1960s. Then, if you were the first in the area and there was something that cropped out and was really obvious, there was a pretty good chance you’d find it. However, it is possibly the case that many of the 1950s/1960s-type discoveries in apparently underexplored regions have been found, and that future discoveries here are not going to be any easier than in the apparently over-explored areas.

Subtleties to the expression of an ore body can make discovery difficult, and in these situations it helps to have the results from previous explorers. The case can be made that you probably want to be the fifth or sixth company into an area to have a reasonable chance of discovery – if an ore body is present. A classic case was the Cadia district that we found at Newcrest; it had been explored since 1851. That was 140 years of exploration of one sort or another.

CIM: That’s a great story of persistence. Do you have other examples?

Wood: In the 1980s, the geologists at Goldfields found a gold deposit called Mesquite just the over the border from Yuma, in California. I think they were the 13th company into the area, and all the big names in gold – Newmont, Placer Dome – all those companies had explored there, and for some reason never found the ore body. If I recall correctly, the discovery hole was drilled under an old shaft called the ‘Black Jack shaft.’ The old-timers had been mining gold mineralization there. You’ve got to be careful about saying, ‘An area has got no chance,’ because it probably does if you’ve got the right set of glasses on.

Goldfields found the ore body because its geologists were capable of thinking about what the ore body looked like. And Mesquite is a really strange ore body; it’s structurally controlled, which means that the ore isn’t evenly distributed. It’s in bands. You need to be able to put those bands together and that’s what they were able to do.

CIM: How well do you think young geologists are being prepared to understand what these ore bodies may look like?

Wood: To my knowledge, there aren’t any universities that really train exploration geologists. They train geologists. And then you go out, and depending on the company you work for, you serve an apprenticeship, and you learn how to explore.

But there are so few really successful exploration groups around, that unless you’re lucky enough to get a job with one of those groups, the apprenticeship you serve and the training you get is, probably, less than optimal.

One of the major issues for the mining industry is that the generation I belong to, and 10 or 15 years younger than me, we’re all retiring. Unless young exploration geologists have mentors or have been fortunate enough to pick up some skills along the way, they’re basically going to start reinventing wheels.

CIM: If our university education system doesn’t breed exploration success, what can young geologists do to increase their odds?

Wood: The only way I know to easily enthuse people and make them want to go out and look at what they’ve got in a positive, creative way is by telling war stories. You tell them how ore bodies were discovered. There’s a conference held in Perth every two years dedicated to discovery case histories called NewGenGold. The conference organisers have two days where they invite people to present discovery talks, warts and all – just tell it how it happened, and look at how and why you may not have discovered ore. The conference is quite well-attended. They’ll get 600 or 800 people to a conference, and I think the geologists who go to these come away feeling buoyed that what they’re doing isn’t so stupid.

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