Transcript
27: Agnete Steenfelt – From geochemical exploration to a Greenland-wide geochemical map
Based on interviews held on September 26 and October 3, 2019 in Helsinge, Denmark
Note: Polar Podcasts are designed to be heard. If you are able, please listen to the audio, which includes emotion and emphasis that is not evident in the transcript.
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Agnete 0:01
It was very fascinating when you had covered such large areas. It’s obvious that South Greenland is the richest metal province in Greenland. It’s got uranium and gold and zinc and rare earth elements in abundances larger than everywhere else in Greenland, whereas all of North Greenland is enriched in zinc.
Julie 0:22
Welcome to Polar Podcasts, where you’ll hear stories from geologists who’ve spent their careers, their lives, exploring and studying the remarkable and remote geology of Greenland. Why did they become fascinated with Greenland? What were the problems and the discoveries that drove them? And what was it like working in these remote places, where few people venture, even now? I’m Julie Hollis.
In this episode, we hear more from Agnete Steenfelt, emeritus senior scientist at the Geological Survey of Denmark and Greenland, about developing the Greenland-wide geochemical sampling into a regional geochemical map of the whole island – a culmination of over 30 years work.
Agnete 1:09
I want to um, tell a little bit about how this geochemical exploration method turned into geochemical mapping and from starting off with a, an area in East Greenland and applying this to uranium how it developed into being a method and a mapping method that could look at a range of different chemical elements or metals and use them for various purposes.
If you want to track a specific deposit, you suspect that there’s something in a specific area, you can collect densely around this area in the streams draining it and follow the increasing amounts of the metal you’re interested in to the ore, and locate the ore from there. And you do that at a local scale, taking for example, samples at the hundred metre interval along a stream back to where you can see the source is. Or if you go further upstream and the concentration suddenly drops, then you know you’ve passed the area supplying ore elements to the stream system.
Developing this into a surveying method we had to concentrate on systematic sampling at particular intervals because then when you look at the results you have to find out, can you find areas in Greenland that has been particularly enriched in specific elements. And you can do that by systematic sampling over large areas.
It started with a large project in South Greenland. There we used a combination to get the overview, the airborne gamma spectrometry where we flew with a helicopter. And then we did systematic sampling of stream sediment over the entire area. And of course followed up with field work in the most interesting sites.
In order to do this, to make it into an overcomable task, you have to pick samples at a large interval. And with experience from Scandanavia, they had experimented with different scales where you could pick the signal from different kinds of mineralization or ore systems, I decided with that we should use a scale of one sample per five to six square kilometres. And then on from there because we didn’t have the staff or the funding to collect densely, so I decided to do it at one sample per thirty square kilometres from there on.
And the purpose in systematic geochemical exploration, you try to cover large areas with a low density of sampling stations and then you look at regional variations. You can tie the increase in certain elements to the rock assemblages in this area but they cannot pinpoint the individual ore systems or orebodies. If you start with the regional scale, or what we call reconnaissance scale, then you can always go back to the area and then increase your sampling density. And then, if you still find something interesting, you can go back to individual streams and follow up on the first results.
So that was the general plan for the coverage of large areas of Greenland. And over a period of twenty years, we have now covered large areas of Greenland and when you compile these results and plot them on a map, then you can see some variation patterns in the element concentrations that you didn’t know of. So that was extremely fascinating.
You could see something happening that you had not been able to observe because when you were in Greenland then you were on foot, you were always covering a small area for mapping. You don’t see these large scale variation patterns.
So suddenly, by the end of the compilation, and I did that for South and West Greenland, in 2001, I had the results from large areas of West and South Greenland and I looked upon the element variation and at that time we had analytical data for the major elements and for about thirty trace elements. Analytical methods were not always good enough to pick out low values for some of the rare elements – not rare earth elements necessarily but rare elements like gold or arsenic – but we did pick out the high values so that these results can still be used to pinpoint large areas in Greenland where the crust has been enriched in these elements.
Well these are in our language called geochemical provinces. And there’s been a debate over whether such geochemical provinces exist but they do. There are areas of the crust that, by some process or other, have been enriched in certain elements or an element suite. And I compiled the results from North Greenland and from remaining areas in East Greenland and Southeast Greenland. That was covered late in the mapping campaign in 2011.
And when you look upon all this, it’s obvious that South Greenland, for example, is enriched in a lot of elements. It’s the richest metal province in Greenland. It’s got uranium and gold and zinc and rare earth elements in abundances larger than everywhere else in Greenland. It’s looked upon as a regional province, whereas North Greenland in particular, all of North Greenland, if you go from Inglefield Land to Kronprins Kristians Land in the northeast, they are enriched in zinc and barium, and that’s something to do with the mineralising systems on that carbonate platform and the sediments in that geological environment. And that was really a nice example of this dataset when you compile such large areas.
And then also, from that compilation you could pick out areas where you had enrichment in rare earth elements and that became very important at a certain time because of the increasing demand for rare earth elements, particularly, for example, neodymium that is used in these special magnets used for windmills. And also the elements sometimes called high-tech elements er, like niobium and tantalum. They have seen increasing demand. And that has been very nice to say, “Oh, you’re interested in this element. Well, look at Greenland’s stream sediment map – the geochemical map of Greenland. Oh yeah, look for where we have anomalies for this particular element and go there and look for a, an occurrence.” That’s been exciting.
Actually, the stream sediment geochemical data can also be used in future environmental control because they document the natural variation in element concentrations in the surface environment. If high concentrations of arsenic, for example, is measured in soil at a place, it can be pollution, but to know how polluted an area is, you need to know how much arsenic that was produced by nature itself before the suspected polluting activity started. This information you can find in the geochemical map of arsenic. The map shows that some regions are naturally enriched in arsenic and others are not and that is of course important to know if we want to estimate the degree of man-made pollution.
If you want to find out how rocks were formed you need to know their chemistry, but rock samples have not been collected in all parts of Greenland. Typically, the geology was studied along the coasts, where you could use boats to get around, and some inland areas are poorly known because helicopter transportation has been too expensive. However, we have the stream sediment data now and that can tell us what kind of rocks there are – well, not precisely, but our experience is that the chemistry of stream sediment is fairly close to the chemistry of the rocks surrounding the stream. And we have many examples where we have discovered special rock types in places where they were not known before because we had seen some unusual stream sediment compositions there.
Now, that I have retired, I cannot let go of Greenland geology and I continue working with geochemical data to figure out how this wonderful and spectacular part of the Earth was created. But I miss field work, I miss the wilderness, the wildlife, the smell of arctic vegetation, the clean and cool air, the mountain views, the ice, the challenges of field work, perhaps not mosquitoes, all that drove me to go back to Greenland, summer after summer for so many years.
Julie 10:23
I’m Julie Hollis and you’ve been listening to Polar Podcasts.
Julie 10:33
In the next episode, we hear more from emeritus senior scientist Bjørn Thomassen about experiences with wildlife around Flemming Fjord, in central East Greenland.
