54. The Bushveld - Decoding a Mega-magmatic Mineral System

[Music] Hi everyone and welcome to Discovery to Recovery, where we bring you geoscience stories from the world of order posits. This podcast is brought to you by the Society of Economic Geologists. Our season sponsor is Verify, creator of Dora. The world's first AI assisted mineral discovery platform. I post the pair of AI in the hands of geoscientists. With Dora, AI doesn't have to be a black box. Instead, it empowers exploration teams to uncover new insights that lead to game-changing discoveries. I am Maxwell Porter, a current master's student at the Merino Reposit Research Unit. And I am your host for this episode. On today's episode, we will explore the complexities of the giant bushfeld complex joined by two great guests who will share their perspectives on what makes the bushfeld complex one of Earth's most important and fascinating mineral deposits. Our first guest is Wolfgang Meier, professor of geology at Cardiff University. Wolfgang Meier completed his PhD on the bushfeld complex at Rose University in South Africa in 1992. He taught igneous patrology and economic geology at the Universities of Port Elizabeth, Pretoria, Kudemy, University of Western Australia, and Aaloo. He is now professor for all geology at Cardiff University in the UK. Wolf's research deals with petrological and geochemical processes that may fit to ultramathic igneous systems that contribute to our understanding of continental magnetism, mantle evolution, plate tectonics, and the formation of magnetic order deposits, including PGE, Neococopper, Chromium, Venadium, Titanium, Iron deposits. Nice to see you again and nice to talk to you about the bushfeld. Always nice to talk about the bushfeld, of course. My favorite subject, as you know. So, yeah, I'm an economic geologist at Cardiff University in the UK. I work on magnetic order deposits largely, although I believe it or not. I've recently started a project on the Port Phrycopper deposit in Colorado. The PGE rich one, of course, as you might, as you might suspect. But mostly, I work on magnetic order deposits in the context of crustal and mantle evolution. So, I am an igneous patrologist into your chemist and so I'm also interested in broader issues of crustal and mantle evolution, including actually also asteroid impact. Oh, fantastic. And, I mean, you have an extensive background in PGE research. How did you come across, you know, the bushfeld and PGE research in general? So, you did your PhD at Rhodes, right? And focus on the bush, right there? Yeah, so I did my Masters in Munich at Munich University, Ludwig Maximilian's at the University of Munich. And my supervisor for my Masters was a professor named Clem. And he worked on a bushfeld, he had connections on bushfeld, although my master project was on abandoned information in South Africa. My supervisor had connections to the bushfeld. And when I, after I finished my Masters, I went to him and said, I want to do a PhD. But I don't want to do it in Germany. I want to do it anywhere else because I wanted to see the world, you know, like many expression geologists. And so, yeah, I told him, I want to do a PhD. Anywhere in the world, I actually don't mind on what or where. And so, this is something, you know, when you tell it to many of my colleagues, my other professors, they sort of roll their eyes because there seems to be the idea in academia very often that our students, they should already know very clearly what they want to do before they approach us to do a PhD. So, you know, I, in my case, that was totally different. And so, I'm a little bit, I'm a little bit, what's the word, you know, doubtful whether that is actually the only really, the only right approach to expect from the students that they know already what they want to do. Yeah. And so, this guy, my acclaim, he knew where he used, Professor Euse and at Rhodes University in South Africa. He wrote him a letter and he used offered me a PhD. That's how it, that's how it started. And was this more of a field-based approach to the bush-failed complex and focusing on one of the horizons there? No, it was a geochemical approach. My PhD was on a characterizing the interval between the main, you know, interval between the UG2 chromatite and the marine's grieve sort of that key interval between the two main PGE reaves. And on strike, actually. So, I worked on Drillcore because in the western bush-failed complex, certainly there's very little outcrop. There is outcrop in the eastern bush-failed complex. And so, in subsequent years, I did field work and field-based studies too. But in the western bush-failed where our project was initially focused on, there is so little outcrop that the, all the research has to be based on Drillcore. What were your visits like to the bush-failed for those that haven't had the chance to, you know, go and do field work? Oh, I mean, the bush-failed is an absolutely fantastic, amazing place geologically, of course. And particularly in the east, as I said, that's where the outcrop is. So, you have these iconic field exposures, you know, that have been described initially in detail by people like Cameron from Wisconsin University in the 1960s and 1970s. And many others, absolutely iconic exposures of cyclic units and the reefs and their football and hanging wall rocks. And so, almost, you know, with the exception perhaps of Scaregarten and some of these intrusions up in the Arctic, unparalleled field exposures. So, I can only recommend any economic geology student. If you have the opportunity and chance to get to the bush-failed once in your life, then you must, then you must grab it. Hopefully you want to field trip around of these great conferences in the upcoming years. Yeah, absolutely. So, I was hoping you could maybe elaborate a bit more on the overall geological setting of the bush-failed, but elaborate on why we should care about the bush-failed. As a few people know, it's one of the richest, if not the richest or deposit on Earth in terms of metal endowment. Could you give some insight into the commodities that we have at the world? For sure. So, you know, I mean, is this a very large magnetic event, one of the largest magnetic events on the planet? And we believe that we could sort of current thinking and all the positive research is that to form large or deposits, you need a lot of heat flux energy flux into the crust. So, a bush-failed, of course, is one of the largest magnetic events on the planet. The largest layered intrusion on the planet, for sure. More than 100,000 square kilometers subsurface exposure. And so, it hosts 80% of the world's platinum group elements, probably around about that same proportion of the world's chromium and benedium resources. Additionally, lots of tin. There is copper and nickel as byproducts and some cobalt tool. There is gold as byproducts in the PG mining and probably forgot other things. There is dimension stones. There is there is magnetite. So, it is really in terms of mineral resources, you know, an unparalleled belt of deposits, probably in terms of value, the largest one. So, and of course, in addition, the importance of this sort of deposit is that the main other deposits for similar metals are located in Russia and Zimbabwe and Kazakhstan. And so, you know, it's, of course, when we think about mining and when we look for deposits, then it's not only the grade of the deposit that is important, but also, of course, its accessibility and polydigestability and so on and so forth. So, that adds to the importance of the bush-failed complex. All the competitors, of course, currently are in math places that are perhaps not quite so attracted. Yeah, that's right, especially in the current world. Yeah. So, I think one of the most interesting things about the bush-failed is perhaps the ongoing controversies and debates about the geological model. And there's a lot of interesting questions around the bush-failed. Where do we get all these PG-rich sulfides compared to other ultramaric-mapic intrusions forming the plattery for the flat reef? We also have this great mass balance problem that will be great to get into. Maybe could you comment a little bit on, I guess, how we start it and how our thinking's involved through this? Yes. So, by the way, you asked about the tectonic setting. I forgot to answer that question. So, the bush-failed sits within a cratonic, with inter-cratonic essentially, like many large-layered intrusions, they tend to be located within cratons, archaeon cratons, and possibly that's largely actually a result of, or for preservation, more than anything else. You know, these things are 3 and 1/2 billion years old, and so they have been affected by relatively little deformation and processing, reprocessing of rocks. And that may be the main reason why many of these old layered intrusions are located on cratons, but it may not be the only one. But, yeah, when it comes to the metal budget, so the bush-failed has, of course, it is by far the largest PG resource on earth, and people have speculated for a long time whether you can explain the large amount of PG-E simply by means of the magma that is present in the body, in the intrusion, in this event, or whether it requires that PG-E budget, whether that requires actually entrainment, or PG-E rich sulfites, with the magmas from some lower staging chamber, where there may have been some pre-concentration. But, when you look at the mass balance actually carefully, then I think there is not a major mass balance issue. For example, when you consider the parent magmas of the bush-failed complex, they have approximately 30 parts per billion PG-E platinum and palladium. To form a one-meter layer of PG-E enriched layer with about 5 grams per tonne like the merensky-E, we can calculate we need a magma column of about 150 meters. So that's, you know, that's perfectly doable. And if you take all the PG-E reefs in the bush-failed, all the chromatized, there are 13 of them, and the merensky-E reef, then you come to about 10 meters at an average, perhaps, of one parts per million PG, and that requires about 300 meters of magma column. So, you know, entirely doable. I don't think there is a major mass balance problem. The only exception, of course, being in the platoon, we have intersections that run at about up to 4 grams per tonne over 100 meters. And if you do the mass balance there, you would need about 15 kilometers of magma. So there we're beginning to run into a mass balance problem. But my personal opinion is we can do. We can do all this by, you know, internal concentration of PG-E in, for example, in crystal slurries where sulfides and chromates are sorted and concentrated at the bottom of these crystal slurries. That's my personal view. And in generating, I mean, PG-E, how do you think warrock incorporation plays a part into the formation of our reefs? Like, how do you think self-assertuation is controlling metal enrichment in the various layers in the bush-failed? Yeah. Yeah. So I think this must be important. And most people who work on the bush-failed view, that is important, because for a start, the most enriched, the most PG-E and sulfide-enriched portions of the intrusion in the northern lobe in the plattery, we have ample evidence for crustal assimilation in the form of numerous country rock fragments, stainless, the isotopic signatures of, for example, sulfa isotopes and near-demium and strontium isotopes are extremely enriched and crustal. So there the reefs are sitting right next to the right on top of the floor adjacent to the floor. So, most researchers feel that cannot be a coincidence. But on top of that, when you go to the rest of the bush-failed, there too we have a strong enriched signature that most people feel is a crustal signature. So they in addition to that local crustal contamination with the warrocks, we almost likely will have also crustal contamination already in the peter system in the staging chambers. And, you know, that is my feeling. Okay, and I think one thing that people aren't that unfamiliar with the bush-failed is this separation between the main bush-failed complex and, of course, this northern limb component of the bush-failed complex. Would you be able to clarify for our listeners, I guess what the differences are between each of the limbs and how the focus is kind of shifted over time between the limbs? Yeah, so the bush-failed, we generally identify about four limbs, major limbs in the bush-failed, a western and eastern and northern and a far western limb. And, you know, I mean, the whole intrusion you have to imagine as perhaps some kind of a soup dish. It has the shape of a soup dish, you want? And much of the center of that soup dish is not exposed. It's set to depth of more than kilometers, even ten. We only really see the edges, the margins of that soup dish, and also not continuously. So in the west, in the east, in the north, and in the far west, the margins of that soup dish are exposed. And in most of these limbs in the west, east and far west, the margins are the intrusion is sitting on a quartzite. And in the north, the intrusion has eroded down far deeper onto into the transfer supergroup hostrocks, so that it sits directly on the, in places, even the arching basement. And in other instances, sitting on very sulfide-rich trails of the transfer supergroup. So the hostrocks are very different in different parts of the bush-failed. And I think that must control the different, you know, PG and metal and sulfide amount in the different, in the different parts, in the different lobes. So different exposure, different, the different lobes are heavy-roaded down to different depths into the hostrocks, and that, I think, controls the metal endowment. And regarding the replacement of, you know, these very PG-rich trails and horizons, what's the thinking in terms of the aid relationships between each of the horizons? Do they follow similar ages? Or are they distributed through time? Yeah, this has been, of course, in the last 10 years or so, a major issue of contention. So about 10 years ago, or nine years ago, there was a paper by Jim Manguel from, I think, at that time he was the Toronto University, who suggested, based on, you know, geochronology, that the different layers in the critical zone would have been, their ages are out of sequence, so to speak. So in other words, he suggested, based on his data, suggested that some of the upper layers are older than some of the underlying layers. And so he explained that then by a model whereby some of these layers, if not most of these PG-bearing layers, were in place as sills of crystal slurries sourced from some feeder staging chamber at depth. So, you know, this, this kind of model, and there have been, to be fair, there have been others who proposed this model previously already decades ago, in fact, but with the less, you know, less quantitative evidence, perhaps. But so this model has been around for some time, and it remains very contentious, and partly because the field evidence is not always consistent with this model. We see that some of these layers that Manguel and others have proposed are older than their underlying layers. We see that these layers actually are cross-cut by other horizons that cut down into them, so-called potholes. So, you know, layers that are supposed to be older, cutting down into layers underlying layers that are supposed to be younger in terms of geochronology. So this kind of field evidence seems to be in direct contradiction of the geochronological results. And so, you know, we are puzzling what this might mean. Do we not completely understand yet the potential errors in the method, or is it possible that, you know, fluids, late magmatic fluids, percolating through this pile, for a long time, and crystallize, you know, precipitate zircons that in layers that are much older, crystallize zircons in these layers that give us younger ages. So, long story short, we are not at this stage. I think we are not sure exactly how to interpret these geochronological results. Yeah. I mean, I guess a lot of different groups have tried to age date bushfowl, and a lot of that came with, I guess, improved geochronology. C-A-I-D-Tims was a big revelation, you know, resolving uncertainties. Where does the current thinking set? Is there a lot of groups pushing for a particular age at the moment? No, not really. I mean, you know, one of the professors in your own school, James Goetz, he was another one who did the data chronological work on the bushfowl complex. And I think he basically confirmed Mangel's results, although I can't remember now whether on each of the layers, whether they looked at the same layers and whether, you know, whether they found the same results for different layers. But certainly he confirmed the basic idea that the layers are in place out of sequence. So, you know, that would make you think that surely there must be something in this model. But as I said, the field evidence in cases seems to be contradictory to it. So, I'm personally undecided what to think of this. I decided, basically, this needs more work. This needs more research. I am not prepared at the moment to completely put my head on the block there. No, that's fair enough. It seems like quite a field to get into. A lot of strong academic ideas. What are your thoughts somewhere other areas in the bushfowl that were kind of lacking in understanding? Where do you think research in the next few years could take us in what particular areas are you yourself interested in pursuing? Yeah. So, another idea that has been around for a long time is a reactive porous flow. This one, I think, initially proposed by MacBernie. People like MacBernie. Ellen Boudreau has been working on this. He's a student, I think of MacBernie. If I remember correctly, Ellen Boudreau has been working on this for 20 years and even longer, 30 years. Proposed this idea. There are others too. Admitey who proposed it. And, you know, so the idea is that the complex, the cumulative pile remains partially solidified, partially liquid. In other words, a marsh for a long time to considerable depth during the crystallization of that marsh. In the deeper levels, you produce relatively volatile rich residual mails, perhaps also, you know, volatile phases that migrate in a nearly solid cumulative pile. These volatiles and volatile rich fluids, they may, when they percolate upwards through the crystal pile, of course, remalting, partial melting of the overlying incompletely solidified cumulates and recrystallizing these. And one of the effects, for example, is if you introduce volatiles into that cumulate pile, you stabilize phases such as olibene and chromite and destabilize phases such as pyroxenes. And so it is possible. These authors have proposed that during this reactive porous flow, it is called the cumulate pile completely recrystallized. And so that many of the layering, much of the layering that we see and the rock types that we see are the result of recrystallization, essentially. So, you know, so this is another field that remains very, very contentious. And there are many, just as many, if not more authors who are strongly debate and criticize this more. But I personally have come to believe, you know, certainly come to understand in my, I've been on the bush for about 30 years. In the old days, when I was a student, certainly, and also some for some time after that, I, as I think many of us tried to do when, when, certainly, when we are less experienced, we tried to explain all the positives and geological features phenomena by, ideally, a single idea, a single model, you know. We want to, well, the big, overreaching model explaining everything. Be it in my days that was magma replenishment, or perhaps magma mixing, or something like this. But I'm increasingly coming to understand that in a large body, particularly in like the bush that cools over, you know, perhaps I don't know. 100,000 to 100,000 years, very, very slowly, that most, more likely than not, there will be an numerous, you know, late-stage, magmatic processes happening that. So I'm beginning to think that perhaps the budro and others, others, other proponents of reactive porous flow that they have a point. And I'm beginning to look into this and then I certainly feel that in things like an author's side, that I can see evidence for such reactive porous flow and re-crystallization of humans. Okay, great. And I think in terms of mining practice at the bushfeld, of course, these are quite narrow targets, you know, you might be able to comment more on exact thickness and how that varies across across the bushfeld, but you're looking on the meter scale in terms of your targets. What are some of the exploration techniques that, you know, explorers are doing at the bushfeld, you know, using the ideas from academia to help target these, you know, very, very restricted targets. Yeah, that's a good question, of course, you know, the value of academic research in terms of exploration in a well-understood or province like the bushfeld, where is the value? And so my perspective is, and perhaps this may be surprising to many of your audience, is that this is the world's largest or belt, really, and in terms of value also. And yet, we only have one profile, one single profile through the entire geochemical, pathological, stratigraphic profile, well-characterized profile, through the intrusion, through the entire seven-kilometre intrusion, you know. And then we, of course, lots of drug or data through the narrow Merensky Refugee two horizon. There is hundreds of boreholes, many of which are actually accessible, have been studied by people, due to the academics. So not all of it confidential. So we have a lot of information available on the Merensky Refugee two-kilometre. But on the rest of the intrusion, we know very little. And what we also know very little is actually, apart from the actual Merensky Refugee two-kilometre. We don't know much about the lecture variability in geochemistry and patrology. And on top of that, of course, we know almost nothing of what happens down dip into the center of the intrusion, you know. So the deepest mind, northern mind goes down to about, I think, 1800 meters or something like that. And that is just a few kilometers from the edge of the intrusion. So we don't know what's happening in the center. Do the reefs become thicker, richer? If one could argue, and this is something we proposed years ago, that if indeed these reefs form by granular flow of crystal slurries, then one could argue that they would be rushing towards the center of this subsiding, you know, subdish-like intrusion. And if that is the case, one could argue that there are, you know, there's potential for much thicker and richer reefs in the center of the comb. And we have in fact, intrusions elsewhere in the world like in Finland, the Kemi intrusion, where we have, because of its deformation, we know exactly what's happening from the margins into the center and back into the margin on the other side. We see that chromatide seams there become thicker from a few, in fact, millimeters and centimeters at the margins to up to 100 meters in the center. So I have the strong feeling, you know, that we may be looking at similar things in the bushfield, whether we will ever know for sure that's the other question, because certainly with current drilling, you know, techniques very costly, very time-intensive, we are simply not able to drill down there into the guts of this body. But perhaps in the future, you know, with new developments in drilling and implying different costs. And we may be able, and interestingly enough, even how, actually, even how mine's at the moment is drilling into one of the major gravity, normally it's in the bushfield complex in another loop, hoping or speculating. It's a hypothesis that, you know, this might be the side of a major feeder zone to the complex. So they're drilling into this. It's under, it's in progress that that borehole, I think, the plan is to drill up to 2.3 kilometers, they're sitting at about a kilometer at the moment. So, you know, we will see what happens there. This is quite exciting. It's a company who is prepared to, you know, to invest a lot of money to follow up on on this clearly high-risk exploration target. But, you know, that is, that is, of course, a really exciting stuff. So, yeah, to come back to you then, you know, the question, what can academia contribute to exploration? I think the main thing is that we, you know, try to reach and always better understanding ever in an improved understanding of the architecture of that body. And, and, and, you know, particularly in view of the fact that so far we know so little about it surprisingly. After a hundred years of research, as I said, only one continuous geochemical, you know, stratigraphic profile. And that is just, you know, that means that our knowledge really of the intrusion is still surprisingly, you know, incomplete. And I would argue, you know, that in successful exploration, you need to have a really good understanding of the architecture of the stratigraphy of a body. Right. Okay, thanks, Wolf. That was a great conversation. Well, just like to say, thanks for taking the time today to, you know, give us an overall understanding of the bush felt, controversy, is a bit of future research. That was really great. It was a great pleasure, Max, and also great to see you again, and very happy to see that you're doing so well. And did you enjoy BC or the nice place? Second guess for today is Dr. Aaron Thompson. Dr. Aaron Thompson has recently completed her PhD at the University of Leicester, which focused on constraining the magmatic controls on nickel copper mineralisation in the world-class plat reef deposit, located in the northern limb of the Bushville complex. Her research was funded by Anglo-American as part of the northern limb research consortium, which includes researchers from across the UK at the University of Leicester, Cardiff University, and Cambourne School of Mines. She is now applying her background in magmatic processes and geochemistry in her new role as an exploration geologist. They're excited to talk about some of the work you've done in the northern limb. Thanks for halving me. Yeah, it's a pleasure. But I think, first of all, it'll be great to hear a bit about your background, what you've been getting up to these last few years, and perhaps how you got interested in geology and some of your research. Well, that's a really good question. Yeah, so my name's Aaron, and in the past couple of months, I've just completed my PhD at the University of Leicester in the UK. And as part of my PhD, I was studying the magmatic controls on nickel copper PGE mineralisation within the northern limb of the Bushville complex, so studying the plat reef deposit. I got into this because actually, in terms of my undergrad on my masters, I was very vulcanology focused. I'm from Northern Ireland, so I grew up with landscape like the Giant's Causeway, the Moore-Noitins, things like that, all very historical vulcanic landscape. So that was the side of geology that I really wanted to get into growing up. But as I came towards the end of my masters, I decided I wanted to do something a bit more applied, and I thought the economic geology space would be great to get into. So the PhD project that I fell into was actually the perfect way of balancing my background of geochemistry and igneous patrology, but with our economic geology as well. So it worked out rather nicely. Excellent. And maybe some context for the project. So it was on the Bushville to more specifically the northern limb. Maybe you could set up the context of the northern limb in general. So why is it economically important? And we know the Bushville is, you know, the largest mythical traumatic layered intrusion on Earth and hosts, you know, significant proportions of PGE, but maybe more focus on the eastern and western limbs in the past, which gets talked about. So what makes the northern limb special? Yeah. So historically, the northern limb hasn't received anywhere near, among the same scientific research. It was actually discovered a rowing the same time as the Morensky-Ray for the UG2 of the eastern and western limb. It was discovered the year after Hans Morensky made the initial discovery of the Morensky-Ray, which is now in the eastern Bushville where he made the discovery. And mining operations didn't begin in the northern limb until about 1992. That was whenever Anglo-American who funded my PhD opened up their first open pit mine in the region. And so because the mining has typically been a bit more limited in the northern limb, we really didn't know as much about it. And even after doing my PhD in plenty of other research being done on the northern limb, we still are only just getting to grips with its complexities and how it differs quite significantly from the eastern and western bushfeld complex. So just to give a few examples, in terms of the overall stratigraphy of the bushfeld complex, we have the same lower zone or critical zone, which typically hosts our mineralisation, which is called the platwraith in the northern limb, and we have our main zone and our upper zone. But in terms of where the mineralisation sits, in the northern limb within the platwraith, instead of the PGA being hosted in stratiform reefs, such as the Morensky-Ray on the UG2-Ray, our greatest and said disseminated throughout tens of meters of pyroxenetic rocks. So we typically have gradients which are the same if not higher, in some cases a lot higher than those that are found within the Morensky-Ray. And because they're spread out in much greater thicknesses of rocks, it makes that deposit potentially a lot more attractive and also suitable for open pit mining, which is what Anglo-American has been doing since the 90s. Right. Is that because in some locations of the bushfeld, the PGA mineralisation is a little spotty and, you know, maybe not continuous? So is that the same at the platwraith? Is there a consistent, you know, distribution of PGA's? That's a very good question and that is actually something that my PhDs set up to try and look up. So in terms of the magmatic stratigraphy of the platwraith, past studies have shown that it was likely in place in a very episodic manner. So multiple cells of magma being in place. And sometimes these magmatic units are very rich in PGA and sometimes they're completely barren. And what remains to be understood very well is the magmatic control and where the mineralisation sets. So are there certain units that when present are always mineralised? And can you trace these along the entire length of the Northern limb or does this vary? So that's something that my PhD research has been looking at very closely and hopefully shared a little bit of light on. Well, I'd love to talk about some of your experience. Perhaps, you know, it was during COVID. I assume the PhD and for a lot of projects, it was hard to get out into the field. I'd just like to hear a bit of your context, maybe what it was like doing, you know, your work during COVID. Were you able to get out to the field? I guess a lot of lab-based work. Maybe you can give some insight into the methods you used. So I was one of the very lucky people who began their PhD right in the midst of the COVID-19 pandemic. So I moved over to Leicester in the UK, which actually was one of the worst hit places in the UK in terms of COVID. We never really came out of lockdown in that first year. We were in lockdown continuously for about a year and a half. I had to wait about nine months to get on to campus to actually meet people that I was going to be working with and see the labs. And then it took about another year and a half. I think it was, I've began in September 2020 and it was about April 2022 that I was actually able to get out and do field working collect samples from the bush felt. So there was a lot of things up in the air. I had to change around my project quite a lot, but we caught there in the hand. I can imagine, but awesome that you you did get out there. What was the field work experience like? I'm working on site. Yeah, the field work was great. So we were able to do a little bit of mapping out in the field to support some of the remote mapping I'd done during lockdown. And then at the vast majority of the field work, although that was core logging. So with the project geologists in the Magalekwena mine and the resource geologists, they have working there for Anglo-American. We were logging core alongside them and got to bounce ideas off the different geologists we were talking with throughout the day, which was really good. And then in terms of lab work, I got to go out South Africa again and do some lab work in the isotope lab at the University of Wittswaterstrand in Johannesburg as well, which was really good. So I'm lucky that I got to go out to South Africa a few times during my PhD. Well, yeah, some great travel there. Quite a lot different to the UK. Very different. The weather is much nicer. Yeah, we're not blessed with the sunniest weather in the UK, are we? No, snow. Okay, awesome. So maybe if you could just take a second just to frame the context of the research. So we're looking to understand the magnetic controls of Neckocopic PG immunization. If you could summarize some of your higher level research aims, and then we can maybe get into discussing them. Yeah, so the higher level research aims was exactly that to try and examine a magnetic stratigraphy and understand is there a consistent stratigraphy throughout the Northern limb? Can we trace these units from different locations in the Northern limb? Typically, the Northern limb and the bush fell to split into different locations called farms. So as part of my PhD research, I examined two farms in great detail. So that was Tui Fontaine, which is the southernmost portion of the land that Anglo-American owns, and the sound slit. So, sound slit had an open pit mine operating from about 1992. It's not operational anymore, but Anglo did begin some broadened field exploration in that area within about, I think, in the past four or five years. And so then a large part of my PhD was to understand this newly discovered deeper extension of the plot reef at this sound slit area, and understand what are the controls on mineralization? So are they purely magnetic? What are the contaminants? Are they playing overall? Because a very big difference between the Northern limb and the Eastern and Western limb to the bush fell complex is our mineralized horizon, the plot reef directly contacts with our metacetamentory country rocks. So we have a vast range of country rocks. We have dolomites in the Malmani group underneath sound slit. We have the arcane basement. We have calcareous shields and limestone. So what are the roles that do different contaminants having on our mineralization as well? So how did you observe different levels of contamination through your work between the two different sites? Are they quite different? Yes. So what was really interesting about the two in-depth studies we did on sound slit at Tui Fontaine? Is there actually right next to each other in terms of geography, they are right next to each other? There is one large wall structure known as the dolomite tongue, which is sort of a large protruding dome of dolomite, which sticks out into the plot reef magnus that separates the two locations. And the country rocks beneath the plot reef magnus at these two locations are different as well. So at Tui Fontaine we have the penge formation, which is a banded iron formation, and after sounds that we have the Malmani dolomites. So there was very different contamination signatures, and actually where our grid start was also very different within these two locations as well. Right. So I guess a big topic in Neckelcopper PG work is the models and Bechfeld has some competing models for sure. So is the dolomite here is interpreted to be a key component of reaching sulfide saturation at the deposit? Maybe you could just shed a bit of light on the role of contamination of this dolomite in particular. Yeah, there's been a lot of debate in this in the past. So lots of previous studies agree that the highest grades within the plot reef, which in a lot of cases are the highest grades within the Bushfeld altogether are located at Sandslit above where the plot reef sits on this Malmani dolomite unit. And whether this is simply correlation or if there's a causative impact on this is still up for debate and was actually a big part of two of the papers I published throughout my PhD, in this deeper section of the plot reef at Sandslit, we show that the grades are even higher than the shallow proportion at Sandslit. And there is a very strong association between where the grid sits and the contamination from the Malmani dolomite. I think the mechanisms by which the contamination of the dolomite may upgrade the deposit are still up for debate. It could still be a pre-emplacement process that RPG tenors in the sulfides have already been enriched. The four emplacement was in the Malmani dolomite and this is simply a post-emplacement contamination. Or could there be some role of devolatization of the Malmani dolomite, the potential role of fluids in transporting PG and concentrating them at certain horizons? That is something that is still very up for debate and was definitely included very much in detail in the areas for future research area of my thesis. Yeah, that's really interesting. This idea that nickel-couple PG deposit some of them, some of the PG-10, it might be through remobilization due to hydrothermal fluids. I guess it's not primarily a focus and not to go off topic, but did you see evidence for those type of textures, you know, in some patrography or anything that might be indicative of remobilization? Yeah, potentially. So at Sandslit, there was a very strong correlation between our high grid sulfides and lots of hydrothermal mineralization. So things like lots of spentanization in terms of the PG-M assemblages, I wouldn't be the expert to speak on this. We had another PhD student called Kate Cannam, who was looking specifically at the mineralization, but she also saw evidence both within the plot rave and actually within the lower zone in the northern limb actually, that there is some form of interactions between our sulfides and fluids and carbonates potentially produced from the Malmani dolomite. So the correlations are there. I think a lot of a lot more work needs to be done on the chemistry of the Malmani dolomite and interactions of magma with that country rock grip before we come to any sort of more definitive models on that. Okay, so much more good work to be done still. Indeed. Well, something that was really, really cool to see one of my augmenters. I guess a mental we have similar EM McDonald, perhaps I encourage this. Really cool idea around niggly numbers. So it's a tool that to me and myself, I'm not too familiar with and I'm sure a lot of listeners may not be familiar with as well. So I'd love you to, you know, sell me the idea of niggly numbers. So are they underutilized? What do they do? I assume a big part in assessing contamination in your work. So you gave us a quick overview. Yes, no problem. So niggly numbers were developed by a mineralogist named Paul Negley, hence the name, who was from Switzerland and sort of was most prominent in the 1920s and 1930s. But since then in McDonald, one of my PhD supervisors at Cardiff University is on a mission to resurrect them, bring them forward to the geological community and show why they can be useful. And what they are is a way of classifying rocks based on the molecular proportions of your major element geochemistry. So you can take your major element geochemistry and convert it through a series of sums and calculations into niggly numbers. And the way these niggly number functions are constructed is they actually reflect the mineralogy and sort of substitutions that go in and out of mineral lattices far better than just major element oxide geochemistry alone. So we find that can actually reduce the spread of our data and it's much more easily to trace changes in mineralogy using niggly numbers as opposed to oxide data. They're also really good in that they remove some of the problems around the closed sum problem. So we don't need to have all of our major element oxides things like if we're missing silica from the data that's not a problem we can still calculate our niggly numbers and we also don't have to worry about the volatile content of our samples or the oxidation state of elements such as iron. So what they could potentially be really useful for is every companies are sat on a lot of historical ass idea that they've just got major elements they don't quite know what to do with it. If you plot niggly numbers with them you might be able to get a few more insights. Not also in terms of contamination which is what I've done as part of my project but they're also useful in terms of identifying different hydrothermal assemblies and things like that. So Ian published a paper last year which came out in chemical geology which went really in depth to sort of explain their uses why they're good and give a couple of really useful examples and how they could be used. And then I published a paper at the beginning of this year which looked more in depth at how they can be used to identify contamination within the context of the plot race. Awesome. Sounds like a sounds like we got a bit more reading in homework to do. The community after this. So maybe yeah I'd love to hear a bit more about the context in your work. So high and low you know values of niggly numbers what is that indicating higher and lower levels of contamination? Yeah so we can use different niggly sums and different niggly constants to look at different things. So for example niggly C is a value which corresponds to higher carbonate contamination so that was one that I used a lot as part of my project. You can plot lots of different niggly graphs using these niggly sums which are actually available at Iogas. Now I off the back of this work that Ian has done. So then I want to take and look into these see all these lots of different graphs. I think I used three different types of niggly plots as part of my paper but there are many many more that cannot be accessed on Iogas and honestly the best way to get hang of them is just to get in and plot your data and visualize what different things are doing in there. But I specifically was looking at the impact of carbonate contamination and dolomite contamination. So using values like niggly C and niggly MG highlighted really strongly that the most well mineralized portions of the plot rate at sanslick were very strongly contaminated by dolomite. Right so it's really nice you can make that direct correlation and sounds really underutilized in general maybe it's not something I'm very familiar with at all. So yeah lots of homework for us after. Yeah well I myself had never heard of them until Ian brought them to one of our consortium meetings about three or four years ago. No so I was also guilty of not knowing anything about pole niggly. Oh well good to hear he's getting a little more famous after this now. Okay awesome I'd like to talk a little bit about some maybe of your other geochemistry and isotope work. So used a lot of isotopes in your thesis. Could you could you convey how how powerful they were and maybe you on the implications for source in the deposit? Yeah no problem so another large debate in terms of the bushfeld as a whole but also in terms of the plot rate given the plot rate did lack a significant amount of radiogenic data was what are the source controls on the mineralization is there a certain magma or parental magma that lends itself to higher amounts of mineralization so as part of my project I set out to do more of a broad suite of radiogenic isotopes looking at the specific magmatic units I had previously identified at twiefontian in sanslick so we already had that predefined magmatic stratigraphy we knew what units were mineralized we knew which units were contaminated based off our mineral geochemistry and our bulk rock major and trace geochemistry so what could we see more using the isotopes so I looked at half name strontium lead and the adenium isotopes for think about 23 24 samples and I'm not going to lie it was difficult getting good data out of that many samples for that range of isotopes especially given a lot of the samples were very heavily contaminated very heavily altered what we did say and sort of in agreement with past studies on the plot rate is that the plot rate is much more contaminated compared to the eastern and western bushfeld complex as we would probably expect given its close proximity to the country rocks and whenever we looked at magma source controls on grid unfortunately we didn't say any strong correlation either way between those units which are mineralized and those units which are completely bad and there was no strong trend towards maybe a more enriched source or maybe a more austenospheric source unfortunately so the jury's still out on that one but there is a lot more work to be done in that space my thesis was the first to look at half name isotopes within the northern limb so there's a lot more work to be done in that space and I think it was only the second to look at lead isotopes as well so there is a lot more work to be done in the northern limb in terms of isotope geochemistry where would you say we kind of sit like the current understanding in terms of how many sources they could be or maybe what the leading leading model is after some of your work I'd say the leading model is that there is probably a mixture of austenospheric and more enriched potentially SCLM related sources I think a lot of the literature does argue that the reason why the plot reef magmas and indeed the bushfeld magmas as a whole are so enriched in PGA is because there is some sort of enriched SCLM component in there however there is still a lot of debate in the literature so I'm not going to lean too much either way I don't think I don't think the community as a whole is fully decided right okay gotcha yeah there's I guess it has a long history of not non fierce arguments but lots of lots of strongly aligned parties on different models right yeah I would agree I would agree okay maybe you could frame some of this work into the context of exploration applications so what is some of your work linking some of the work with niggly numbers and identifying contamination occurring in different horizons maybe you could give a lens on how this could reshape different exploration strategies in the north limb yeah unfortunately I suppose nickel and PGA globally right now is not in a great place so there may not be that much active exploration happening within the northern limb right at this moment but I think the hope is that the work coming out of our research consortium and L4 day will hopefully guide exploration whether it does restart within the northern limb so my research as a whole and we utilize niggly numbers for the first time which has not been integrated into iogas and anglomeric and we're starting to use that to process and sort of gain further insights from their data one of the really exciting things with niggly numbers is actually it cannot be automated very easily it can be incorporated into machine learning algorithms and actually Ian McDonald has another PhD student at Cardiff University not I who is now looking at the machine learning applications of niggly numbers so watch this space for that and in terms of an overall exploration framework for the northern limb one of the main outcomes of my PhD is that any exploration model within the context of the northern limb needs to have a really nested approach we've seen two forms geographically right beside each other twee fonty and and sand slit actually can have very different magmatic stratigraphies and the grid itself is hosted within very different lithological packages so one of the main outcomes of my PhD was to give an exploration framework to anglomeric and where we show the different processes that need to be considered at different scales right down from our entire northern limb scale down to our farm scale and our micro scales and how we should be considering all of these processes at different locations taking into account the different settings the different country rocks the different orders of emplacement and the different numbers of magmatic units within the platform we're going to inflome our exploration criteria there okay how does exploration look is it would you say I was optimistic is there potential for a lot of new brown fields discoveries around the plat reef does that expand over to the eastern and western limbs do you think just love to hear your thoughts yeah so within the context of the northern limb I think there is a lot more potential for discoveries so it was only in 2007 that Ivan who discovered the flat reef in the southern sector of the northern limb and this was the dawn dip extension of the plat reef at this location and the reason it's called the flat reef is because the dip shallows so we go down dip from the plat reef and we we deepen and we get flatter and we form the flat reef so that was a really exciting discovery and I think the reports Ivan who reported that they went to PGA within that deposit equates to over 10 years of the global supply of PGA so it's a massive reserve within the northern limb itself and then the the literal language was completed by Anglo-American during my PhD also discovered a dawn dip extension at San Slip which is incredibly enriched in PGA and also interestingly contained a nickel rich horizon which we termed the base metal zone so I think that's only two locations where that deeper drilling is taken place to the north the acne project is another dawn dip extension on the farm swarthontian so I think the drilling that's being done shows that there is the potential for dawn dip extensions which are typically thicker and better mineralized and the shallow replat reef to be discovered up in dawn the northern limb you have context for what are the kind of leading tools making these you know extension discoveries is it is it mainly a geochemistry drive are they using a lot of you know trace element work or is it a lot of geophysical work that they're kind of leading I don't know if you have any context on that yeah I'd say geophysical work would be helping quite a lot but I think just the fact that our shallow plat reef deposits are open ended we know they dip to the west and deeper drilling is really the only thing that will reveal what's down there so I think there's very few places where we've sort of drilled and got to the end of where the plat reef is for all we know it might extend further out to the west and actually some geophysical work coming out from I think Janine Cole past couple of years has suggested that the northern limb might actually be much thicker and it might actually increase the entire area of the bush fell complex much more than what we know and what is constrained already on the surface okay well this is great to hear your thoughts on you know the future we'll see we'll see how PGEs do and you know in the coming markets maybe closing out here maybe a bit more of a lighthearted question above to hear potentially one or two highlights from your work what comes to mind from some of the some of the best experiences maybe it could be a field one maybe a really enjoyable one in the lab oh I would have to say I think my two probably most enjoyable experiences were the second time we went out to do field work in South Africa we were presenting to all of the geologists who'd been working on the core and logging it they'd been doing it for months and we had a knowledge exchange workshop or myself and Kate the other PhD student and our supervisor Dave went out and sort of presented what we thought was going on obviously we needed to check it with the geologists who are logging at day and day I know it better than anyone and that was such a fruitful experience it was so nice to get there understanding of it and confirm that we weren't thinking of something that was completely different to their models that was really nice and then I think the other highlight was probably getting to do lab work in Johannesburg in the wiggle lab but that's that lab had only been open for a couple of years at that point so getting to be one of the first people to do like a full suite of isotopic analysis in that lab in Johannesburg was really really nice as well awesome south such a cool experience and I think there's a lot of really cool work around the Bushford and Jamal right in terms of academia and do you think there'll be a lot of you know in the context of future work a lot more questions around the Bushford and Jamal to be asked yeah definitely I think so there's still a lot more work to be done I know there is a lot of research being done within South Africa at South Africa universities like the University of Joeburg the University of Vets as well so there's a lot of work going on there and there's a lot of collaboration going on with researchers from the UK in Australia and America as well so I think there's a lot more to come from that in the near future awesome and if if listeners want to you know tune into some of the great work you've done how can they do that yeah so I published two papers so far from my research the first one is the neglect umber paper which was published in chemical geology earlier on this year and our in-depth study on the plot ref at twiefontein was published in economic geology earlier on this year and actually as of today Kate can't um her first paper from her PhD has also been published online in economic geology as well and that was a study looking at mineralization within the lower zone of the northern limb and again that's another reason why the northern limb is different to the eastern and western limb we don't typically get mineralization within the lower zone in the eastern and western limb but Kate showing that we do in that paper oh nice okay we could be the homework for us to indeed I hope this won't be too much no we get we get awesome okay well thanks Aaron really enjoyed the conversation here and best of luck with your new venture yeah thanks are helping me marks thank you for joining us on the discovery to recovery podcast and a huge thank you to our guests Wolfgang Meyer and Aaron Thompson I am Maxwell Porter one of the hosts of this podcast series you can access past episodes on scgweb.org/podcast and most other places you get your podcasts make sure to tell your friends and colleagues about discovery to recovery and share our posts in social media you can also follow scg on linkedin and other social media channels to get notified when the next episode comes out this episode was produced by your host with support from our production team and Thompson Halle Keevel, Britt Blumel and Corey Tachon our theme music is Confluence by East Swins from their album Confluence you can check them out at eastwins.bandcamp.com thanks for listening to today's episode and stay tuned for the next one