43. Let the Rocks Talk - Mineral Systems and Deposit Models in Northern Sweden

Happy 2024, and welcome to Discover To Recovery, where we're being a geoscience tourist from the world of all deposits. This podcast is brought to you by the Society of Agricultural Geologists. Our sponsor, Angla American, is a leading mining company with a diverse level portfolio. Driven by its purpose of reimagining mining to improve people's lives, it provides many essential, featuring heavily metals and mirrors for a cleaner, greener, more sustainable world. Their sponsorship supports the podcast and its ECG. I'm Koray Tashbichan, a PhD student working on our deposits at the Koran School of Mines, and I'm your host for this week's episode. Make sure that you put your codes on because we are traveling to Norden Sweden and it's called there. We talked to two experienced geologists working in Norden Sweden about metallurgyny and the exploration history and culture of the region. A lot of our guests were field trip leaders at the ECG 2022 based precious and pretty good metal deposits of the Paleo-Proterozoic shell-et-a-dustric suite. First, we talked to Dr. Nils Jansson about metallurgyny and diverse mineral curances in the shell-et-a-bexleia and curinamining districts. Our second guest was Mac Person, an exploration geologist from Boliden, Neroz. He shared the exploration history, culture, and challenges in the shell-et-a-dustric in early 1900s. Could you please introduce yourself? My name is Nils Jansson and I'm a associate professor in orgyology working at Luleå University of Technology in Norden's Sweden and besides research I've also been working for the mining company Boliden Mineral in the past, working in mineral exploration, mainly focusing on VMS deposits. It's a very broad question but what is the significance of shell-et-a-bexleia mining district in Norden Sweden? When it comes to the shell-et-a-bexleia, I've been working there in the mineral exploration. I supervise three PhD students at the moment that they're working there and if we're going to say something about the general, erodical outline there is that there are still a lot of things that we don't really know about the district. From one point of view, if it's very well into many of the other Paleo-Proterozoic, circa 5.9 giga annum, submarine volcanic arcs that we know host VMS, such as flin-flon, et cetera, but there are many aspects of the script that we don't understand. One thing is for example that we don't really see the basement clearly, so a considerable part of the little stratigraphic framework of the district is somehow obscured. There's also a lot of uncertainties about the early stages of the erodical evolution like including the deformation, history, the early stages, but I still say that we have made a lot of progress in the latest years in understanding, for example, the importance of early symbol-canic structures in controlling the sighting of VMS deposits and also how to use this knowledge based on the present day erodical outline. One thing is for example that many of the structures that we see, faults, for example, but also faults, many of them can be related to an early history of basing in version where we're in the early symbol-canic or sedimentary normal faults they reactivate to us, reverse faults. And this has been used and it's still being used, this kind of knowledge to find new VMS deposits and I would say that it has been fairly successful, it's a fairly good tool for going back to old areas and using new ideas to find a new mineralisation. Most of the VMS deposits in the area are gold rich. What do you think the reason behind that? This is actually a very good question which I don't think has been sufficiently researched at the moment. It must have to do something with the sore stroke of these deposits because if you look on the deposit stem cells they're not really that exotic compared to many other VMS in the world. So there's nothing weird about them on that point of view except for the fact that they contain more gold. But I think one hint to this is also that we do have other types of gold deposits in the same region like Origenic, quartz, Wayne, Hosegold, the deposits such as Björktal which is operated by mandolin resources. And we also have some disseminated or poufri-like deposits that are in some of the early granitoids that were in place during the early phases of the Sveka-Kurelia and Rajani. Now we know that these deposits cannot be the same age. The VMS deposits they are probably around 1.9, 1.89 giga annum, the poufri deposits are more like 1.87, 1.86 and there's also I ticked much further north at 1.88. And then when it comes to the Origenic gold deposits many of these they are in late structures that seems to crosscut most of the earlier structures of the Sveka-Kurelia and Rajani's. But they are fairly late and all of them they share this gold endowment. And this can of course be fought about maybe as reflecting some kind of long history of remobilization of gold that you have gold rich VMS then you have remobilization of gold. Alternatively it can also be something more fundamental at a large scale such as we have areas with gold and down soil strokes that have been tapped by many different types of meanwhile systems. And I think that one thing that's supporting this idea is that we don't really see the same kind of endowment for example in the south in Bayes-Lagen in another mining district in the deposits that we know they are the same age they are the same origin. They're probably a different arc though but we don't really see the same degree of gold endowment in late quartz veins and similarly we don't see the same level of gold endowment in the 1.9 giga annum Master's Alpha deposits. So what about the Kiruna mining district is gold coming there too? It is I mean but if you go further north to the Kiruna area then you have more in an area that host a lot of copper and gold together like we have epigenetic copper gold deposits that have been included into the ICG family of deposits. I think that maybe something similar going on there with regards to copper. We have deposits that are around 1.8. There is for example one deposit explored by Boliden called Nautanen. That deposits seem to be more a late originic deposit. It seems to be associated with structures that were active after the main phases of folding and deformation for the south end of the left of this district. What is coming out is basically that we see more than one phase of mineralizing events in the second Corilla and orrogeny. We see those that are more symbol canic at around 1.9 and we see more clearly epigenetic deposits forming closer structures that are active at around 1.8 billion years. Most of the deposits that you have just mentioned are confined to a small time interval but some of the genetic deposit descriptions are different than each other. Like you mentioned some epigenetic deposits but we also have some gold rich degenerative deposits which form or mineralize at the same time of the deposition of those volcanic or volcanic sedimentary rocks. Or are they slightly later than the deposition of the host rocks? I would say that this is actually one of the big questions that have been discussed for more than a century. The main challenge that we have with these deposits is that they are affected quite commonly by metamorphism. In general it's somewhere around low-run fiblyte, sometimes even granulite faseous and metamorphism is generally regarded to be polyphase and similarly we have also multiple events of ductile deformation, plus that we have the fact that the deposits have been completely removed from their original tectonic context and they have been basically eroded flat completely and covered with till. So we don't really see the deposits in the same way that for example if you go to Chile and look at porphoris and you somehow know that you are in a way standing on the seduction so we have to somehow try to repeat all of the aspects of the model based on evidence that we see in the rocks. And one of the main complications that we may have is to determine if a deposit deposit originally there to begin with, it's in the genetic war whether or not it's epigenetic because metamorphism and deformation can have a remarkably effect on the textures and the progenesis in the deposits and can make them look epigenetic. And that's why in many of these broken hill type deposits, that's a classic case where you have a lot of debate going on about how these form. They are high grade metamorphosis deposits that are too big to ignore, but they are not straightforward to place into any of the existing categories. And I would say that in the last decades what we have basically been going towards is some kind of reconciliation about the ideas that we have polyphase mineralization. So we have had mineral deposits forming in these successions as they were being built. Like in volcanic successions we had expressions of hydrothermal activity forming mineral deposits either on or below the sea floor, but it didn't end there. We have also had intrusive activity continuing afterwards and we have had also activity that is seen metamorphic or seen tectonic with regards to the main deformation phases and the problem we have is now when we see everything in one place, we can go to district like I don't know the Kiran area where we left the district and we see many different and fundamentally different deposit type right next to each other and we see alteration features right next to each other and it can be difficult to somehow navigate what belongs to what then. But I think that yeah, you could see like the metal endowment of these successions it began to be built at the same time as the successions were being deposited. As an academic mission and an exploration geologist, how do you see the exploration challenges and associated scientific challenges that you have had in those districts so far? I think that it varies a little bit, they are actually quite different. When it comes to the left district I think that you could basically fly in any Canadian or Australian VMS geologists that have been working in one of the older VMS districts like a paleo-protezoic ones and they would recognize what they see, they would feel at home working with those rocks and it would be quite straightforward to grasp the challenges, the metals and what you're looking for. When it comes to bicellargan, things are much more complicated and the reason is that mining has been going on for so long. So first when it comes to looking for mineral deposits, it's super easy, you find them everywhere. That area has something like seven or eight thousand mineral deposits. Most of them are iron oxide deposits, a lot of scorns, for example even bad dry information, even appetite ionos, and then there are some sulphur deposits. Most of them would not be mine today. There are some really spectacular alteration systems, really large, but the mineral deposits associated with them would not be mine today, they are too small, maybe ten thousand, one hundred thousand metric tons at quite bad grades. They work very well as local mines, but being global mines, not really. At the moment we have two big mines in bicellargan, Sinkruvon and Garpen Bay that somehow at least show that there is potential there to find really well-class deposits. Now the problem when going and working down there is that you will be distracted all the time by everything you see. There's a lot of different alteration styles that you see that are not really straightforward to use for vectoring towards mineralization because we don't really know, for example, are these associated with the VMS or other types of basement of sulphur deposits or are there something related to the iron scorns? Really difficult to use them in a diagnostic way, mainly because that the deposits that are down there, they don't really fit into established categories for mineral deposits. That may be a separate question, but I would say that those two kind of parameters, if you add them together it becomes more complicated, that you have so many different deposits, you need some kind of conceptual model to filter out, which ones you really want to focus on. And this is something that you cannot really get from the straightforward scientific literature. You have to go there, you have to design your own models in a way. Then when it comes to nor bottom, this is actually one of the youngest mining districts since Sweden, together with the left of the district, that these two, they were more or less developed, or 121 to 100 years ago. And they have been built a lot around a few big mines, like ITIC and Kiran area. During the last 30 years, there has been a reappraisal in nor bottom about those deposits that we know up there may actually be ISG deposits. And this has, of course, stimulated a lot of the exploration that is going on up there that people come there with other goggles trying to apply ISG models in hope of finding new copper and gold deposits. And I think this is basically where we are now, that we have, for example, mining of appetite iron ore by LKB and we have also ITIC copper ore being mined. The exploration, a lot of that, is being driven at the moment by the perceived potential to find the next world-class ISG deposit up in northern Sweden. So I will follow up with two different questions based upon your answer. When we come to the Berks Lagen and the zinc or polymetallic rich deposits and some iron scorns there, what's so different about them? And the other question would be, how do they not fit into the genetic model? First of all, I should say that by Storganism type locality of scorn, it actually means the next thing in Swedish. But scorn was used in a way as a curse for the hard gang rock. The gang rock that was somehow needed to be mined in order to get to juicey stuff like iron ore or the sulphide ore. And then it was adopted by Ternbum, you could say like sensulato, he was not really referring to a deposit type or anything, he was just using it as a litology. And then it has been, of course, elaborated into a deposit class scorned deposits. And I will say there that it has crystallized into these different types like iron scorn, zinc scorn. And what we have in Berks Lagen, those deposits, they are not really fitting that well into the global categories. So if you take something like the zinc scorns that we have one thing about them is that they seem to have formed more or less at the same time as the succession was being built. So you could think of it in a way that they are carbonate replacement deposits. Those carbonates that they formed in, they formed by a stromatodytic limestone. We were in an environment that we had heavy extension. So quite soon after they had been deposited, they were being buried. And as they were being buried, they were being highly termally altered and mineralized with deposits that look like scorned deposits. And some of them can even be argued that they are metasomatic scorned deposits. Besides the carbonate replacement deposit, what we also see is evidence that the alteration of the volcanic rocks occurred very early, like in a submarine environment. And also we have, in a way, alteration types and alteration sonation that look a lot like those we see around remastered deposits. So we have the same type of serocyte alteration, citerification, chloride alteration, also a couple of string immunization. And if you only consider that then the symbol-canning timing, sure, it looked like VMS. But then the main problem is that the ore itself quite commonly sits in carbonate. And associated with gang minerals that consist of diapside, tremolite, serpentine, etc. Much like scorned deposits. That's a conundrum in a way, depending on where you're looking, you can see what you want. And people have been trying to somehow pigeonhole them into different categories saying that these are all of them are metasomatic, all of them are metamorphosis ininetic. I don't think that's the way to go. Because I think that what we need to do is we need to acknowledge that they are from part of a continuum. Yes, like with the epitomal poultry continuum, we have to recognize that they are different, but both of them exist. And we are exploring in very large, intrusive associated systems, operating in phallic extensional environments. And then we had potential both to have seafloor alteration and high-automal activity driven by modified seawater. But we also had opportunity of having contacts metasomatic processes, depending on where we were and when the deposits were forming. But then if you have that then then you add a layer of amphibolite fascism at the morphism ductile deformation on top of that, then it becomes really complicated to work in that area. So I would easily say the bi-slogen is the most complicated area in Sweden. I may be a bit biased there, but still. No, that's a legit excuse, I'd take that. I'll follow up on this with a more general question. And you said that you need more like a mineral systems approach rather than globally except models. And you said that there's a trend of implementing IUCG models in curinomining districts. And they are looking for a couple occurrences around the giant IOA deposit. So what are the caveats of trying to impose a genetic deposit model based on those genetic models and, of course, their restrictions? I think that the global genetic models, they are of course important for communication and, of course, for targeting, for selecting which areas we think are prospective for certain the positive types. That's all final all that. But I think that once we're working we need to recognize that each of these districts they have their own features, they will always be something unique about them. And I think that one of the dangerous with the IUCG models maybe in the past was that we haven't really been entirely sure about everything, all of the components in it. Like some people have, for example, still fundamental questions of whether or not appetite iron was should be included as a member or a criteria for IUCG, whether or not it's a casual or a delinquent relationship. And those kind of things we have to acknowledge the uncertainties that some or the positive models are more mature than others. And that's why I say that you can take someone from any one, but most of the people working in VMS in Canada and Australia, you can take them to the left district and never feel at home. Because the VMS model is, after all, quite robust, it is quite mature. You can always pick on aspects, but you have to acknowledge that it has been very successful. For the last 100 years, as the VMS model has been built, it has been very successful and useful in the task of locating where to go to find myself at a positive. So even though there are some uncertainties, it has huge predictive power. And I would say the same thing about the pauper model. But when it comes to some deposits like, for example, the IUCG family, this is something that is still quite new, are only two decades. And even more so when it comes to some of these more exotic metals that have become more invoked now because of the demand for critical raw materials, there is a lot of knowledge caps that needs to be filled. And there I think is really important to embrace the fact that we don't really know for sure none of the aspects yet we need to somehow work out still the fundamental, erodical controls on these deposits. We cannot really take them from the book and even if they spend research, we have to somehow question it. We have to try to dissect the systems and you mention mineral systems analysis and I think this is absolutely the way to go. And we see also more and more of the companies are starting to work, are utilizing this approach over here. And we are also using it ourselves in much of our research. So I think it's definitely a very good framework for how to understand these or forming systems and how to apply that knowledge during exploration. Yep. So part of my ignorance here about what's the direct comparison or how would you define the swells or SVA alas deposits in Sweden? Okay. So complicated term but the story behind that is that originally the deposits in by-stocking were guarded to be metasomatic scorned and intrusion related. Then just like in many other parts of the world, when the first black smokers were found on the seafloor, this created a little bit of a paradigm shift. So in the 70s, 80s everything became synionetic and if you add also that people started to apply plate tectonic concept, like plate tectonics itself was discovered, they became natural and order deposits were metamorphosed, like classic papers by Valkt for example in the Norwegian Caledonites. So that became the paradigm that the order deposits they formed on the seafloor and the reason they looked like they do at the moment is because they have been metamorphosed. That was the paradigm shift and that led to that deposits in Sweden, including deposits that were regarded to have been different in by-stocking, came to be regarded as being in a way the same deposit type, just looking different due to different deformation of metamorphic history. But in the 90s there was a seminal work done by Rodney Allen and also people from the Eurorica Survey of Sweden and mining companies, they basically dissected the whole strategy of these deposits and concluded that the deposits are at least two different types, swells and sas they call them, but I'm not going to go into detail about what it stands for, but what they wanted to emphasize is that they were deposits that formed by carbonate replacement, VMS like in many ways, but carbonate hosted and then there are deposits that formed in later post volcanic successions that were commonly not really carbonate hosted, but they were associated with politic rocks, sometimes even graffitic ones. The best example of that is synchruvon and the research that has been done since that, I would say that when it comes to swells deposits these are the ones that I cited as being somewhere in the border line between VMS and SCARN, you could say like there are some marine extensional phthalzic dramatic systems that could form both carbonate replacement deposits at the below sea floor or that could form contact metasomatic deposit deeper, but the sas type deposits, the stratiform deposits, they are more in the border line between VMS and sediment deposits. And for some of the deposits synchruvon, I would even argue that the evidence for that being anything to do with VMS is actually inexistent, because based on most of the illogical evidence I would say that that deposit formed after volcanicism had ended, so that's the background is basically that when they did that paper they didn't want to pigeonhole any of those deposits into one of the categories, they wanted to acknowledge that they are in fact different and they are unique. When you look at those districts, some of the deposits you see that there are some cobalt enrichment associated with some types of sulfides, do you see a similar cobalt enrichment in shell after this trick? And what do you think the reason behind that cobalt enrichment associated with some kind? When it comes to cobalt enrichment in particular, in part of it has to do of course with the composition of the source stroke, like for example, mafic volcanic rocks probably being a better source for cobalt in the first place. Another aspect is the capacity of the hydrothermal fluid to transport significant amounts of cobalt. And this is something that can need to be related to temperature, like high temperature fluids having high possibility to transport cobalt, but it can also be related to redox, with oxidized hydrothermal fluids being way more capable of transporting both cobalt and nickel in solution. In my slide when we see an effect of this, in the sense that the most cobalt and nickel endowed deposits, they are the ones that are most similar to the sedimentals to deposits. And those are also the deposits where we see evidence of oxidizing brines being transport agent for the metals whereas the metasematic deposits, such as for example Garpenberg, we don't see any cobalt whatsoever, it's basically devoid of cobalt. In the head of this district, I would say that it's not really that much cobalt, it's not really, it's not like all the components in Finland, it's not known for its cobalt endowment. Then whatever cobalt we have sits mainly in the pyrite, like a few hundred, few thousand ppm maybe at best, but there's no major cobalt endowment known in any of those deposits. And about deposits for the north, this is simply something that I don't really really dare to say for sure, but I was speculating that having the green stone belts and also having evidence of evaporites and also having mafic rocks that can be stripped of the cobalt, I think that this should be ample opportunities for forming cobalt and copper enrichment in there. I know that there are for example some deposits that have cobalt like Nautanen has a cobalt endowment and I believe also Viscaria has cobalt endowment, but in pyrite. Yes, you're right, cobalt endowment is partition-biting some different satellite phases. So that was a great discussion to give an oral picture about the different type of mineral occurrences in Sweden. Do you have any final comments about diverse mineral occurrences? The common denominator for all of them is that they are related to circa 1.9, 1.89, billion-year-old volcanic rocks. So even though there may be three different arcs on that, this is the common denominator and that it's not just volcanic rocks, but also some marine volcanic rocks. And this is one of the things that is maybe the strongest lines of evidence for that there is definitely some kind of early phase in the build-up of the meta-dendowment here. And in all of these areas it has also been substantiated. We are geographical work that deposits were forming at around 1.89, 1.88 by cross-cutting relationships, and in Kuruna they even have done direct dating of the war or they have been dating circle in the war. So that's definitely a general feature I would say regarding the meta-login. And then when it comes to the 1.8 gigangium event, this is something more new. And it's only like in recent years that it has been maybe going to be realized that at around 1.8 billion years ago there was probably like an event all over this part of the Finnish candy and shield, like all over the circle Kuridan or originally, regarded as being subordinate in comparison to the 1.9 event. But one reason for this may be the preservation of bias, because we think about it, the early synionetic deposits. These are the deposits that are preserved in the sink line in the super-crossed rocks that are somehow, yeah, what we study when we look into the early evolution here. So the deposits that formed in those, they have the same preservation potential as any of the super-crossed rocks. The problem with the 1.8 gigangium deposits is that when they were forming, this was a mountain range. And many of them, they were forming at maybe depths of 5 to 10 kilometers. There was no subsequent deformation that they would downwarp them or down. So I mean, whenever you see a tungsten deposit or an original gold deposit at around 1.8, you have to know that there's something like 5 or 10 kilometer crustal material gone by erosion that you're never going to see. So when it comes to the scale of the 1.8 gigangium event, we never really know. Probably it was much more significant that we see. And it also makes it a bit more tricky to explore for those systems, because you know that what you see at surface. Well, part of it has been eroded away, but you don't know how much maybe. Yeah. Yeah, you are looking at, in a temporal and spatial setting, they've eroded, that's why you see them. Yeah, but it also makes you think about what type of deposits, like what other mineral occurrences have eroded away? So it makes it more complicated to estimate the relative importance of these two main meteregnetic events here. For the younger one, the picture is incomplete because of the erosion of any potential supercressor rock, so shallow parts of the system has been eroded away. Having provided an overview of the metallurgy in northern Sweden, we will now focus more on the Skeleta district. We had the opportunity to speak with Mac Person for a bold lead in mining company regarding the exploration culture and metallurgies employed in this area. Mac, thank you for joining us. Yeah. Thank you so much, Corey. Yeah, so my name is Mac, and I have a very difficult last name to pronounce. But I'm an exploration geologist. I work for the Swedish mining company, Bullied Mineral. I joined Bullied Mineral in 2010, been here now for almost 14 years. I mainly been working here in the Skeleta district in northern Sweden. I had a stint as head of section for the VMS team for almost six years, but today my role is more technical. From Denmark, did my geological training at the University of Copenhagen? And when you do your studies in Denmark, the big thing is to go to Greenland for fieldwork. And so did I, and so I started my career in field exploration as a student assistant for the geological survey of Denmark and Greenland that led to involvement with junior exploration companies in Greenland during the summer period. And that was really what gave me the taste for mineral exploration. And so when I finished my masters, which was also in Greenland, I was fortunate with good timing, booming in the industry and those loads of jobs. And so I landed one with a Danish junior exploration company, Scandinavian Highlands. They're still around. But I was with them exploring in Norway and Sweden, Sweden in particular. And that led to the contact with Bullied Mineral and that's history from there. Now I'm curious about the Greenland. We have to record another session with you on Greenland to you. But let's stick to Skeleta district today. So I know that Skeleta district is very much important for Bullied and you just mentioned there's a town called Bulliedin. So could you just please a little bit explain the significance of Skeleta and Bulliedin for the company Bulliedin in Tauve? Yeah. Oh, absolutely. It's very important. So that you left the district, it's a paleoprolyzoic, volcanic arc succession. And the belt in itself stretches roughly 100 kilometers east west and roughly 10 to 30 kilometers north, south from the town here in Bulliedin out to the west. It's a place, well, it's a mining camp, Christina Burke in the west. And if we just start out with a little bit about the geology, then we can move on to a little bit more exploration history as well. So the most common and most important deposit type here is volcanic massive sulfites. And that's also what has been mined historically and today we have two massive sulfite deposits in operation and a gold deposit as well. And therefore we should mention that the Skeleta district is not only just the MS deposit, it's also a genic gold deposit, copper gold, poufrey and momatic nickel deposits. But the main deposit type is VMS. So and here comes a bit more history is the first mining kind of dates back to the year 1704 when copper was small scale mines are not too far from here and it's been known for a very long time that in the woods up here in northern Sweden there were metals to be found. But it wasn't really until was a kind of modern exploration started in 1915 with a junior exploration company. And it has a very difficult name, but I'll pronounce it. It's central Imhun's Act that was the name of the company and that was formed in 1915 and in 1920 they formed a separate exploration company which was the start of the Bulletin Company as we know it today. So Bulletin started out as a any other junior exploration company exploring the Skeleta district which at that time was basically unexplored. We had these reports on metal in the ground, bolders but there was no real systematic exploration before. The Bulletin Deposit that's just outside the office building where I sit here was discovered in 1924 and it is one of the most significant discoveries in the Swedish mining history. So that deposit was a company builder. Yeah. Maybe just a little bit of details on the Bulletin Deposit but it was more than 8 million tonnes with 15.2 grams per tonne gold. So an incredibly gold rich VMS deposit, quite a lot of copper 1.4% and some silver as well. And with that the Bulletin Deposit was very rich in arsenic. So arsenic oil was also mined with a good profit back in those days. As you just mentioned the history goes back and the old timers were there, unexplored metals, what methods did the old timers use and how they were successful and fit for the area. Yeah. That's a very, very good question. So like I mentioned before Bulletin was first moving into a new district and they were not the only explorers, the state owned or state operated exploration. What we today would call the Swedish Geological Survey is they were also exploring and between the two they were just incredibly successful to say the least. From 1924 to 1960 I was just looking up these numbers the other day they found 27 deposits with economic potential over a time span of 36 years. So if we put that into the perspective of today, how long there is between the discoveries that we do, I mean they were so successful. And maybe going back to the importance of the, she left the district for Bulletin as a company in its heyday we had 12 mines simultaneously in production providing all to two mills today. We have three mines in operation and they produced the all to one central mill here in Bulletin. So that exploration success of the early days in the 30s and the 40s really was the backbone so to say of the economy of the company. And I think several things came together at just this time and now we're back in 1915, 1918 around there when they started out. And the things that came together and I'm listing this now, not in any order of importance to not upset any of my geology or geophysicist colleagues, you know, what was more important geophysics or geology, they were both important. But what they had at the time are very good understanding of the quaternary geology. The process that's involved in how the inland ice sheet that was covering Scandinavia during the last glaciation, they understood how boulder trains of mineralization was being eroded by the ice picking up the mineralization, the alteration around mineralized lenses. So and transporting that in a direction we call it like down ice direction. We have to imagine that mineralized boulders progressively occupy a higher and higher position in the glacial sediment eventually being exposed at surface. So during this time period of great success, Ulyden and SGU had a small army of boulder hunters out in the field season. And the field season up here is from when the snow melts till the snow comes back. So they had like a half a year of intensive work each year. And so when these boulder hunters were out looking for boulders and they found the boulder train, they would start to work their way up ice, so to say. At some point in time it'd be more and more difficult to find these mineralized floats, even though they're digging trenches and pits to try and find them. And when they understood that, they turned to geophysics. And also at this time it was a major technical innovation, what is called the equipotential method, which is an electromagnetic exploration method that was invented by Tugentumeth Hans-Lun Bergen and Harry Nathorsd. And they tested that here in the Schelefthed district for the first time. And from that test, they found one of the most important deposits here in the Schelefthed district, the Christina Berg deposit, which is actually still in operations. Today. And this was back in 1918. They had this geological understanding, the geological concept of looking for boulders. And at the same time, they all of a sudden had a method that could help them find conductors just below the till coverage or the glacial sediments. And so that was really a major breakthrough because the Schelefthed district is more or less covered with till or other outwashed sediments. And so we have roughly maybe 1% of cropped. Another thing that I'd like to highlight, it's a bit of a pet of mine, they did good old fashion mapping. You know, they were out looking at those few outcrops that were there for another presentation that I did on the bouldering deposit. I looked at one of the old geological maps of the bouldering area that was made three years before the discovery of the deposit. They didn't have the geological models or the VMS models that we used today so frequently. But they had an understanding of the importance of the context zone between the mechanics or the meta-volcanics and the meta-sediments. And that map from 1921 actually very nicely nailed the position of what we would today call the VMS "ohorizon". Final thing that they were very good with was that they had a very clear exploration strategy. They really knew what to do and maybe even more important, they knew what not to do. But when you just said like, they didn't know or they didn't have any idea about the models at that time. So that means that they were unbiased. And that probably made them easier to explore the region. So I will go back to this model in question, but first let me ask you this, now you said that you just made a presentation about the old map from the 1920s on the Bouldering Mine. How do you take advantage of the legacy data, legacy knowledge that's been cumulatively transferred to you since the 1800s or 19s? It might be a bit of a cliche by now, but to be honest I think it really is the truth here is that we that work at the exploration office or the exploration team today here in Bouldering. We're really standing on the shoulders of the explorers of the past and you can kind of visualize that we have the pattern right now and we're carrying it now and hopefully we will deliver it to the explorers of the future. The legacy data that we have here is amazing, I would say, they've left us with a significant geological and geophysical database that which we use on a day-to-day basis and just to mention an example of getting out a legacy drill core, one of my colleagues here at the Experian Department, yesterday, she asked the core library staff to bring out a drill core from the mid-80s and they will have it available for us tomorrow and now this was a drill from the 80s but it could just as well as been one from the 1940s but not only here in Bouldering. I should mention also that the Swedish Geological Survey have a very good core archive. As you can imagine that gives us in our target generation of today our workflow is made easy by the fact that we have access to all these legacy holes and legacy data, geochemistry, geophysics. We do of course modern surveys, geochemistry, geophysics, all the lot. Of course we do that but having that, say, rock sack full of data is really good and hopefully like 40 years from now the explorers working here will have the same opportunity and be able to pull out the core that we drill these days and they'll probably tell us that we're all wrong and that's okay as long as they keep finding more. So I was lucky to know that the facilities in Chelapteo, one we did a CG student chapter field trip with New Mexico Tech student chapter to Sweden. With that trip you took us out to the forest and showed us some of the tricks about the more well-canistered different exploration and all the students we all felt the same thing. We were like learning the geology at the beginning again. You mentioned the exploration challenges in the district like the Glacier till and the outburst elements on the cover. So you use walking a significant exploration to overcome some of these challenges. Could you please just explain what's the, what is this concept and how usable it is? I can, I can try. It's, yeah, excellent, excellent question. So actually if we just like look back to what we're just mentioning that we're pulling out a drill core that we're going to look at tomorrow, I realized that one of our mentors, Rodney Allen came to the Chelapte district in the early 90s and made a tremendous impact or say more or less you've revolutionized the way that we were thinking about exploration or how we were interpreting a volcanic stratigraphy and the use of volcanic fascist analysis to guide in exploration. And I loop back to it because the, the drill core that we will be looking at tomorrow actually Rodney also was working in this area in 1992 and I, I just made the realization yesterday that, that the way that we interpret this stratigraphy now is, is the opposite of what he was interpreting back in 1992. So we never stop learning but understanding volcanic fascists. Why is that important and how is it that it guides us and it's, it's important because in the MS exploration you want to try and be close to the vent of the volcano, by studying the volcanic fascists, you can, you can use that as a vector towards finding the vent near fascists as opposed to the distal fascists. So we try to navigate within the volcanic sessions and here we should maybe also mention the concept of a horizon in the MS exploration, the specific stratigraphy horizon that where the deposits tend to form. The challenges that we face today is that we're exploring on the cover and I think that's challenging for the entire industry. And I think it's pretty clear that the future of the Schlefted district lays at depth. Most of the subcropping deposits have, has probably been found by the early explorers. We're looking for these so-called blind deposits that have no or only little surface expression. And here in the Schlefted district we'd say that we probably have around 90 known VMS deposits, of course, of varying size. And to my knowledge, only five or maybe six of the known deposits that we know of today are truly blind. So you can imagine that that is, that is, that is a challenge. The rocks here in the Schlefted district, they're folded, and not always, but commonly very deformed. And of course, therefore, the metal deposits that sits in these volcanic rocks, they're also deformed. You can imagine that when you have 90 deposits known and almost all of them sit at surface or close to surface and you have very deformed rocks, it's not so difficult to imagine that there is a significant potential at depth. And it isn't really a question if there are buried economic deposits here or not. It's really a question whether we're clever enough to find these deposits. That's a quick question. What's the average thickness of the cover in Schlefted district? So if, yeah, so it depends a little bit on when you talk about the cover, do you mean the marine cover or do you mean the, if the cover of, say, hanging wall? Let's say more rain because we talked about the mechanical dispersal in the area that challenges your exploration efforts. So, like, the thickness of the more rain or glacial sediment. Yeah. I mean, there is a bit, on average, I'd say that it's between 10 and probably 15 meters. Sometimes thinner and sometimes a lot thicker. So people are trying to develop new exploration methods using geochemistry and geophysics. But you said that you're also using geochemistry and geophysics in a way that way. But at the same time, with this more chemistry, difficult exploration, if I understand it correctly, what you basically do is that you use the volcanic rocks and their formation environments to trace back to the proximal plant areas. You utilize that method to find the deposits who are not outcropping or who are not exposed. And Roblida Nora was 450 meters below the surface. So that's a very innovative way to use the fundamental geol. This will lead to my next question. So what have you learned from the fundamental geological applications? How do you have improved the models? Yes. So just to touch upon what you just said, you know, today we work in a very geological driven exploration method with conceptual geological modern, so to say, using our VMS training as guide. Yeah. So I mean, what I have learned, at least I'm looking to myself, the more I work, the more humble I really become. So when I started my career almost 20 years ago, things were easier in the sense that an observation that I was making in a core or in the field or something, it was either this or it was that. It was black or white. Today is that I try to understand all the in between, you know, things are not so black and white. And the feeling that the more I work, the less I know is like the experience that I sometimes catch myself in a really important thing that I'd like to stress when it comes to VMS exploration. And maybe and hopefully there'll be some listeners out there that are in the start of their career and this is and this is for them. It's so important that if you're exploring for VMS deposits, probably any other deposits as well. But if you're exploring for VMS deposit, try and have the opportunity to go and look at pristine deposits in pristine environments, so that basically, I mean, no defamation, no metamorphic overprint. And it took me a long time, actually, before I had the chance to go and look at in the field trip to Turkey to look at these type of pristine VMS deposits, you know, and that was a great development for me. It's the geological textbooks that we show students and I see that because we have a lot of summer workers coming through the Boolean exploration team and, you know, the deposits are never ever written on multiple deformed or unconscious and people like faces, mesmer foes, to 1.9 billion year old deposits, it's always on the easy stuff, eh? So a strong encouragement for me would be to, you know, go on field trips, field trips, you know, it's so important to see the rocks and be there on site. Yeah, I totally understand that because I'm from Turkey, as you know, and when I went to Kiruna to work on my master's at Miskaria, copper iron deposit, I didn't understand anything at the first site because everything was super strange, a ton more foes and was super deformed and that's very strange to me, seeing that kind of geological setting for the first time. And I was shocked because the oldest mineralization or oldest rock that I had seen at that time was maybe 200 or 250 million years old. And now I was there looking at the rocks, which are 2.4 billion years old and with the mineralization alteration, a sandwich that is quite debated. Exactly. On an everyday basis, we seldom actually think about that, talk about the rocks as if they were not metamorphosed, but it was a significant eye opening for me having that opportunity. Yeah, maybe this highlights the importance of geoscience communication, and Thompson recorded in the previous episodes of the season 4. And we all have a lot of things to learn from each other, especially those young terrain geologists. They have a lot to learn from the altering geologists. But you have your own exploration models and mineral systems understanding. So how do you have improved the models in the region and how do you apply mineral systems understanding to find the next deposit? Yeah. Boa. Yeah, that's a good one as well. So like I just said, we have a strong tradition working with volcanic faces analysis. And we've had these good and truly world class mentors helping us building the models that we're using. But to be honest, sometimes I find that volcanic stratigraphy can be so incredibly complex. And on my own behalf, I sometimes end up lost with evidence pointing in different directions and it can be maybe a bit of a challenge to take the next step in the exploration program. And therefore I try to to generalize by thinking more genetically or mineral systems way of approaching this oil like the plumbing system as always also mentioned in the oil industry also using this you know that we need to have some kind of like a source of the metals that's transported in a hydrophermal system. So we need to have the fluids that transport the metals and then we need to have some kind of of trap that can focus the fluids to build the ore. And so I myself and those that I work with I try to navigate those two say way of thinking that we have like the genetic say model with more like plumbing system thinking and then we have our maybe sometimes a bit more complicated VMS exploration model. And I kind of try to think of it as two buttons that I can turn up and down on when I'm confused with the VMS exploration model I turn up a little bit on a genetic model and vice versa finding the ore ice and finding the trap sometimes you don't need to make it so complicated. When you are in an area that is correct that you have the you have the alteration you have the metals moving okay where is the traps very populistic way of expressing it but see the forest for all the trees you know I mean you can easily get lost if you if you if you're worried too much about all those little details all the time. So I do have one last question I see that the exploration culture there being too humble and you want to transfer all the knowledge to next generations how do you think that the exploration that you do today or the methods that that you apply today will look tomorrow. Yeah yeah so it's the thing is that there might be a bit of a tendency and I think it earlier in my career I ended up doing that if because you've been associated to a discovery and it's obviously as an exploration geologist that's that's the most thrilling thing that can happen in your professional career because you were successful there you might have a tendency or at least I had to to just take that same say template and use it everywhere and so you're kind of like ending up squeezing geological knowledge through the same mold so to say but it doesn't in my experience really work that way I mean the the next deposit that you hopefully will find might be a little bit different than the one that you found yesterday. So the discoveries of tomorrow there will definitely be similarities between the deposits but there will definitely also be the opposite. So that really means that if you get too narrow minded on your exploration model you might not see the potential that is in in another area and that's a challenge it's super easy to sit here and say it. Speaking about it makes it more clear that we need to allow ourselves to have to let the rocks talk to us so we're we're not blinded by thinking from somewhere else when looking in a new area and that's what we try to accomplish. Many thanks to Nilce Anson and Mac Person for sharing your stories insights and knowledge. Also huge thanks to our listeners we always appreciate you and thanks again to our sponsor Anglo-American. I'm Gorae Tashbichan your host and co-producer for this week's episode. Next week we will still be in northern Sweden and focus on Kirno mining district and we'll be talking about changing mindsets and how they were useful to rediscover the potential within the belt. All the episodes are available at the SEG website on their podcasts and other places that you get your podcasts for. For information on new releases be sure to follow the SEG social media accounts on Facebook, Instagram and LinkedIn. This episode was produced by your host and and Thompson with support from our production team Halicie Will, Britt Blinnell and Maxwell Porter. Our team music is confused by Eastwings. You can check them out at eastwings.pancam.com. See you next week.