14. Tops and Bottoms of Porphyry Deposits featuring Richard Sillitoe

Hi everyone and welcome back to Discovery to Recovery where we bring you Geoscience and technology stories from the world of world opposites. This podcast is a partnership between the Society of Economic Geologists and Sequent. Your hosts for this series are Nicole Dussett, Sequent, Halle Kebel, Cobald Metals and I'm Ann Thompson. For this episode we also have guest host John Thompson, my partner at Petro Science Consultants. This 14th episode closes out the series and we appreciate all of your support. For three months we've covered a diverse range of stories related to order opposites and had the privilege of interviewing a wide variety of people engaged in our business. Today we shift from structural geology to the tops and bottoms of for free deposits and have three great stories with Dixilotone, Stephanie Sacora and Dave Burrose. The first conversation was recorded at PDAC in March 2020 where Dick and John got together to talk about porphy copper deposits, particularly from Dick's perspective having worked on them all over the world for decades. I'm John Thompson and I've had a mixed and varied career between academia and exploration with companies and I've had the good fortune to spend a fair amount of time in the field of my colleague here, Richard Sulton known to most of you probably as Dixilotone, so Dick, tell us about yourself. Well my life I think has been a little simpler than yours John. I mean all I've done is wander around in the field all over the world so never been near academia, never been near business. But just written more papers than most academics in passing. Well that's if you've got all that free time on airplanes you've got to do something. You can't watch films all the time, so. It's been a pretty productive and prolific career I'd like to say. Some of us like enjoy writing I suppose as a bit of a hobby so. But it's a good, actually writing is a good thing because it means you've got to read a lot of stuff that you wouldn't normally read, so there's a big advantage there. And you have to distill thoughts, yeah if you don't write you don't really order your thoughts I think a lot of the time. I suppose it helps. So I'm going to start talking here and we'll see how this conversation goes, but I want to go back here. You're probably best known for your work on porphyry deposits, although you probably worked on virtually every other kind of deposit and written about many of them, but I think many people in the art community would think of you particularly in context of porphyrys. So if you go back to the beginning and your first foray into porphyrys, the tops and bottoms paper which was in 1972 was a 73, so that was a period when people were getting to grips with porphyry. So what did it feel like to be part of that, did you feel you were changing people's views, changing our understanding, leading to new exploration? Well, I'm very, very difficult to say really at the time. I think the thing that was rather than porphyrys that per se that time it was the plate tectonics revolution. Absolutely. So, you know, I was in Northern Chile and that plate tectonics was just starting and being interpreted in all fields of geology and it seemed fairly obvious in a dynamic spot like Chile that there was going to be a relationship to mineralisation, but I was working on porphyrys at the time. So it seemed fairly reasonable, I can remember in a field camp there in Northern Chile lying in my sleeping mug at night with an oil lamp and I had a couple of issues of journal of geophysical research that I managed to borrow in Santiago from a regular magazine. All those initial geophysical papers, journal geophysical research in 1968, so it was hot off the press and so in my sleeping mug I was reading that stuff and I convinced myself that that was the deal with porphyrys, so there was going to be a connection. So that was the plate tectonics aspect on it, but the other aspect was the model. And I'd been working in a rica right on the border with Chilean Peru and I took the evening flight back to Santiago, the sun was setting over the Pacific, I was looking out the window and of course there were all these volcanoes and I realised that the tops of all these volcanoes was all altered, it was all white. These of course were the tops of lithocaps which was an unknown entity back in those days and so we managed to factor into the project and to climb some of these volcanoes to take a look at this stuff. So again it was a bit of a step into the wild blue yonder but it convinced that this had to be the top of porphyry system and then we started to realise we got different erosion levels right down to things that were replaced in equigranial plutons at depth. So I mean the plate tectonic part people were just now, it's just so embedded in us we can't even remember the other people haven't started, I think, it's just a fact of life with the expression and then we get into the subtleties of, you know, is it a flat slab, a steep slab, was there a cessation of subduction and things like that? Exactly, that was really exciting stuff and when plate tectonics was just being formulated at the end of the 60s, very beginning of the 70s and all the old guys of course were resisting it, not all, but a lot, and it was very much some, you know, a sphere of activity for the youngsters and you know that's always the case, whatever the old shit, and always should be probably. Yeah, that's right, so it was very exciting and it's very difficult to transmit that excitement now because plate tectonics is just like the alpha battery, I mean, it's just something that's just the background to everything. But then the model itself obviously, it's got legs and other people were putting out stuff as well and that started to play into exploration, did you aware of that at the time that was starting to change the way people actually explored for this? Well, I think the level in the system, you know, trying to determine where we were in the system was important for exploration because obviously we're in the root most of it's gone. If you're up the top, then potentially it's all below you. And part of that project, as well we realize that the linkage between potassium alteration and the best hypergene minimization, the pyreipur hypergene minimization, and so we had that in 1969 and then we were scooped by Lowell and Gilbert, classic stuff. Yeah, so they're obviously other people than, and I suppose the internal crew at Anaconda were all also, and the Kenny got people near all that, but of course they were not publishing anything, it was all in house, so we had something partially written on that and then, you know, we were scooped by the famous Lowell and Gilbert paper. Yeah, which we had an impact as well, and to me one of their great impacts was understanding the fault offsets and being able to use the zonation pattern there for our exploration. But of course they didn't have the top on it, they missed the top, the whole thing was blind in their model, so they just went up into, essentially, into unaltered rocks. We'll come back to the blind bit in a bit, they didn't get to fly the andes and see you realize what they were looking down on, I guess. So I mean all that then developed, I think there were two developments that came from there. I mean I was working on strata volcanoes, because that's what I'd climbed and what I could see out of the aeroplane window, etc, etc. But then we started to realize that in Northern Chile, when I aged 18 in the 70s, we started to get some potassium argon dating and so I had to realize there weren't really much in the way of volcamics that were actually coevil contemporaneous with the porphries. So then the question started to be asked, well, is in fact there any volcamage linkage at all? Right. So then a lot of doubts came in and then a little bit more evidence came out and we realized that many of these systems probably had very small volume flowed-on complexes over the top of them. And of course by the time the porphry was exposed, those things had been lost to erosion. So that led into the concept of different sorts of volcanic edifices being a top of these systems. And some of them, maybe even just dieteriums and a very small dome or something like that. So whole spectrum. And of course some of them all linked to strata volcanoes, I mean Batohija was a beautiful example and so there's a spectrum and strata volcanoes, of course, got the big volume of volcanic rock. So there's a higher probability of at least the outer parts of that edifice being preserved at the time, the porphry is unroofed. So that was one side of it and then the other side, but the upper parts of the systems really started to develop a lot more the idea of the lithocap as a quite an extensive feature that might in fact cap more than one porphry centre, it might be a coalesced lithocap with several centres underneath it. And then of course the linkage of lithocaps with high sulphuration epithermal mineral solution. And then along comes the gold kind of boom and that's more interesting and exploring those upper parts of the system. Yeah, well that was out my own little personal introduction to that that I was working in Columbia and the project manager was Canadian and this fellow was a real gold bull of the highest or classic. It put all his money into gold and of course in 1970 it was predicting it was going to take off 1979 into 1980, it went through the roof. Absolutely. Crazy. The guy made a fortune, very, very, very, very nice, just to get into his interest. But he kept on to me, he said you've got to learn about gold deposits, this is where the future is going to be. Yeah, as soon as the gold went, the gold price went up of course, bulk tonnage, potentially open pitminable things, became of interest which had never been considered with the previous gold price. So I managed to engineer visits to lots of things around the world that were low grade gold, several of which were high sulphurations in lithocaps. So did you immediately start to connect the dots between those and the porphyrys or that process of understanding those? Yeah, fairly early on, fairly primitive, to start with these massive sulphide bodies which were quite well known in Eastern Europe, Bulgarian, Serbia, Bohr and those sort of things which set the Soviets and mapped as Volcanogenic Massive Selfides. That's right. So many things were. So we were able to change that, well, I mean you were working of course in New South Wales and it was funny. So the two of you were really, that's funny. It's from the order vision thing, trying to look at what it was. Your stuff was very influential to us at that point trying to think of what to call it. I mean, at that point we had all sorts of names of these things. Yeah, then the lithocap thing became, it took off in a big way, people started to understand zoning in lithocaps and then of course laterally the realisation that the porphyrys of those lithocaps are often characterized by intermediate sulphidation epithelm deposits as well. So that was an extra little bit. And then the discovery of porphyrys underneath them, you know, which was. That's right, yeah. Which was kind of sealed the deal. I mean, that was fine. You know, we could go from sort of going from the bottom up. We'd lost the top in some case, but we started from the top and went down now. Yeah, so the zoning became important, if you can do anything with the mineralogy because you wanted to be in the roots of lithocaps. So you drill hold and you have to go through 1,500 metres of advanced agilic alteration. So that was an important aspect of it, I suppose. And then recognising telescoping and overprinting such that you might have this lithocap, but you're not that far necessarily from the porphyry. Yeah. And then laterally of course in these very high uplift terrains and compressive contractual subducting margins or even these sin and post-collisional porphyrys, very, very high uplift rates. So you were eroding off potentially a kilometre of rock as the system was still active. And ending up then with the lithocap completely telescopeed over the upper part of the porphyry intrusions and really reconstituting previous potassium alteration. Yeah. So really, to me, we've gone through, I mean, 40 years now of this period of understanding these systems, the tops and bottoms, lithocaps, the relationships, the zoning and so on. And then there's been all the incredible dating work and we've realised that some of them are multi-phase and some of them are very, very fast and short lived and dynamic. And we have this view now of these things happening, venting to the surface in some case with late diatrine breaches and so on. And then along come in the last few years, this discovery of some very significant porphyry was apparently beneath blind, the sinmin or pre-mineral cover rocks. How does that fit in? Where did that revelation hit you? Well, in a way, I think we kind of knew this for a while. There's a couple of examples one was described by in Soviet times, in fact, in Russia, where the things were blind beneath massive limestone units. Right. And that was quite easy, but as soon as you accept that, in anything that could act as a potential rigid top seal, could play the same role, I guess. So even though these systems are dynamic and they clearly are, they may actually react out or peter out upwards and move outwards rather than upwards. And I think we've realised for a while, the really high grade systems like Grassburg probably are high grade, because the fluids were retained weren't readily dissipated into wall rock. And that's encased in, as you well know, in marble. And there's just a few metres of massive sulphide on the edge of the stock, and you're into potassium alteration with these spectacular copper and gold grade. So, elling everybody, a lot of people appreciated that, but it's been brought home again by this on-todiscovery and that Valle is made in Henry. Happens to have trouble here at the PDAC on show for everybody, for the first time. That's right. I was lucky to get to work on that, so I'd see it in the flesh. Somehow, I'm not surprised. But, yeah, so that's beneath an undesired sill, but to start with, I think, there was a feeling it might be a post-mineral feature. Right. I mean, that would be the natural interpretation room, you'd see less altered rocks at the top, you'd say, oh, it's a post-mineral. Yeah, but when you realise the alteration fades away gradually into the base of it, I mean, you have to accept that the very least, it's synchronous with the mineralisation. Right. If not pre-mineral. Yeah. Fascinating. So, we got through all these changes, and when you look, you've worked with many different companies and so on. Do you think companies have incorporated this into their thinking? So, I mean, it's always a little bit unsatisfactory when you have a very nice model, but then it starts to get more complex over time in its reality, but it makes it difficult for companies to understand. Do you think so, or are they grappling with this? To some degree, I think as time goes by, grappling with better results are there. Yeah. Because the lithocap, the lithocap concept initially, what that meant, people just sat a drill rig on a lithocap and drilled, and then when we drilled pro-political alteration underneath with a sniff of pyreite. Right. And so everybody, I don't know, these things aren't worth anything. It's too hard. Yeah. And so, that's what was happening really, even in the 90s, and well into the 2000s, but now I think that people are understanding them better and there's more discrimination. Yeah. But I think we've got to remember as well that in Arizona, companies had some of these concepts and we were using them even back in the 70s, a sarco for instance, was a real pioneer in drilling these things. Right. They drilled the sunny side system in the Patagonia mountains in southern Arizona. It wasn't a non-economic, but it was a technical success. Right. And then one of the oil companies drilled red mountain, which was also in the Patagonia, is very, very close by, and again, didn't make it grade wise, and of course the sunny side system now has hit the headlines again, because it's got this big tailor or a Moser carbonate replacement deposit hanging off the edge of it. Yeah. I mean, essentially companies, people love simple models, but other times they get to grips with the area they're working for all sorts of reasons. They may understand the model or they may just have an empirical feel or something. And evidence that caused them to drill. So sometimes you feel like we're just regenerating the models, that's all the ideas that were there in the past, but it's because people worked in different ways at different times, I think. Yeah. And the more young geologists now familiarize with the ingredients of the model, so they're able to recognize them and in the early days they're not read about them. They couldn't completely relate it, I don't think, to reality. Right. I think a lot more young geologists are well appraised of what they're looking for. But the thing is, when you're drilling these, these lithocapses as well, they're all these subtle signs. You start to see the odd veinlets start to appear and the alterational change, you might go through porophyllitis, you then come down into ceriside. When you see these zoning patterns and the change in the veinlets, there's normally a geochemical change that accompanies it. You know you're on the right track. No idea what the grade is going to be when you get there. I've just been involved in a programme in Northern Chile and better say where it was. Possibly not. But two kilometre holes discovered really superb stock works, sub-economic grades, but things that would be interesting if they were in outcrops, there's a substantial amount of copper in them, but still not hit the intrusion. Amazing. Yeah. But when you're drilling two k-holes, it's a million dollars a throw. Yeah, it's a big ask. I don't even think about what it's going to mean in the future. Exactly. And the grade, I mean, you need probably going to need one and a half percent copper equivalent down there to make it go. Why don't you, of course, some of these deepest discoveries that have been made in the last 15, 10, 15, 20 years have been high grade, in fact, almost to get the feeling sometimes that the deeper we go, the better the grade is going to get. And although in a way, perhaps those are the only ones we hear of, I think there's a lot of low grade ones that don't make the press. Well, when Hoshard drilled a system there in Chile a few years ago, and they only got three holes, really, into the actual potassium alteration down below, those grades, if they've been in outcrop, that would be an ore body. Right. People need to rate and need it to raise the grade a little bit down, considering it was down at 1,500 meters, but someone will go back and do some more drilling and I'm sure. You know, porphyrys are what, at 60, 65 percent of the world's copper, and people, obviously, they're always worried we're going to run out of copper, but they don't take a new account. It's just exactly that. All these discoveries that are being made at different depths, which, you know, are currently not economic. And if we really need copper, the people will go back. The price will come up, the technology will improve, the more cave will improve, and we'll be back. It's all price linked, there's absolutely no doubt about that, but I think everybody is committed to trying to find something that's high grade, really. Great solves a lot of problems. Always has always worked. I get you through the full economic cycle, anyway, without any panic. I look around the world right now, there's some good interesting discoveries being made, but they are deep, most than most of them do seem to be deep, or deep-pish, so the pressures aren't either make them work or to find better ones close to the surface. Well, I mean, I think in some of the frontier areas, you're still going to find porphyrys in outcrop, I think that's no doubt, but that's still the case. But if you're looking on the cover, I mean, you've only got two options. You look under lithocaps, or you look under post-mineral cover, post-mineral gravels, post-mineral volcanics, and in a way, the lithocap is better because you can use the geology more effective. If you post-mineral cover, unless there's something peeping out at the side, I mean, you've got as geophysics, really, or grid drilling. Exactly. Yeah. So I'll wrap up here. I'm going to ask you a horrible question, so I'm sure you've been asked many times, so the young people are out there just beginning their careers. You're going to go try to find a porphyry now, where would you go? I'll probably go to the central Andes, I think. Yeah. I thought you might say. Yeah. It has delivered. Yeah. And it's not only delivered. I mean, there are five systems in Norden Chile with more than 100 million tons of contained copper metal. Very, very few places around the world that can claim that. So if you are looking for something that's under pre-or post-mineral cover, you just got a better chance of finding something that's big and high grade. Well, we come back for podcasts, too. Maybe we'll then discuss why that is. Yeah. And that's what I would need to think about that one. OK. Thanks, John. For next story, features Stephanie Sacora, and the giant LiHir Gold Posit, a dynamic porphyry epithermal system. We started first with how Stephanie got to work on LiHir. What's your passion in geology? Been interested in Earth science and geology since, well, since before university, growing up in a place like Squamish, Canada, your face is a big rock every day, so it's hard to ignore it. So I've worked as an exploration geologist from Greenfields, Brownfields, exploration, mostly in porphyry copper, with some large companies like Tech Resources and First Quantum. And then I did my PhD in sponsorship with Newcastle, Down in Codes, and some of my career activities have brought me sort of around the globe in terms of working with other different companies and checking out and evaluating different, different prospects. So lucky in terms of being able to see not only a variety of different exploration projects, but also a variety of different people and companies and how people approach geology differently. I just really like sharing Earth science and geology, so I'm a very big advocate of scientific communication and write a blog and stuff, so I find it very interesting to try and decode and share a bit of the really cool science that is geology to everyone. You're early in your career, but you still managed to get to work on one of the world's most incredible gold deposits from LiHir Island. So how did that happen? How did you end up leaving British Columbia? All right, so first I reached out to Codes down in University Tasmania, Australia, and Dave Cook about the idea of pursuing a master's or a PhD. So this is after kind of learns about code's reputation from colleagues I used to work with at Tech. So Codes has really, they have a great collaboration with industry, a lot of exploration in mining companies, and one of which is Newcastle. So civically, Anthony Harris from Newcastle was setting up multiple different research projects with Codes, and one of the things was they're really trying to understand more about LiHir, which is obviously one of their large gold assets that they have. So I ended up moving to Tasmania and starting the PhD on the LiHir Gold deposit in Papua New Guinea. So, you know, here for most people may or may not know, but LiHir is an island off the coast of New Island in Papua New Guinea. It's quite a remote spot and it's a tropical island with this incredible gold deposit on it. So when you landed there, what was it like for you, what was your first impressions of landing on LiHir Island? As he said, it's quite a unique and pretty special place. So actually, it's a tropical island, very humid and hard as you imagine, but what's unique about it is the deposit itself is right beside the Pacific Ocean, so we have the pit and Pacific Ocean for beside it, which obviously has its benefits and also its challenges. Another unique thing about LiHir and the setting the environment is that it's really hot in the sense like, literally, there's an active geothermal system that exists to this day, and that continues to alter rocks, cause fluctuations, and actually carries gold. There's a study Simons and Brown did in 2006 where they looked at the fluids in the geothermal system, and it still contains gold in it. So it's quite a unique place in terms of it's actively geothermal. What's the first thing about the geology that hits you, I mean, was there a key feature that you went, wow, this is an incredible place. Oh, well, so everything's really young. So the island itself that the here, also known as Lattelheim, gold deposits on, is probably formed less than four million years ago in that island chain, the Tavarlah here, Tang and Fannie Island chain, and it's a very complex and dynamic environment. So mineralization or alteration probably formed less than one million years ago to a few hundred thousand years ago. So everything's very young, which is quite unique in terms of an orthoposit, and because it's so young, the volcanic edifice where it is, it's well preserved. So you can see the environment pretty well to the state of where this system formed in the rocks themselves. It's tons of breaches and veins and, I guess, one of the unique things about it is that we have this telescope environment where we had a magnetic hydrothermal system, like a porphyry style environment that was telescope and superimposition with an epithermal, high grade gold realization on top of it. So we combine with, sort of, it's a young dynamic history, it makes it, it was quite a unique place in terms of it's geology. Yeah, no, it's an incredible place in this story of this telescope, and when I tried to dick, we talked about telescoping in the Andes and a superposition over a large amount of time, a million years of losing a thousand meters of rock to erosion and a resulting superposition of a high level alteration system on a deep alteration system. But here this happened in what minutes? And so what was the best evidence that demonstrates this dramatic change of conditions that happened during the telescoping of the year? Well, there's a few evidence in terms of how we know what happened to its current day. And one of the things is, as I was saying, the land form. So it's the island itself, both the deposit, it's this large amphitheater, it's about four by like three and a half kilometers wide, and it's elongated and breached open to the ocean to the northeast. And so it's estimated to be around about a kilometer high previously, and see for mapping offshore, the amphitheater has identified comically topography and marginal levies that extend offshore, and these are features considered to represent offshore debris avalanches related to the sector collapse event, or possibly a couple of events that helped form the amphitheater. Geologically, what we see to kind of help us understand this telescoping is we have this late stage, gold rich, alcalic, low-subdition, every thermal mineralization. So we have high grade refractory, self-idore, so that's gold in pyrate, in this near surface zone. And we have agiolaria, which is a low temperature of polymorphicase, feltbarb, alteration, and illid alteration. So it's epithermosal alteration. And this is on top of this early stage, porphyrysal alteration. So we have secondary bytite, some k-balt malteration, and lots of in hydrate. And other lines, evidence like sulfur-scientimized tropes that say it's an oxidized magnetic hydrolymeral fluid signature. And things like high salinity fluid infotions. But it's on a typical porphyry deposit, in the sense that we don't have A in beavings, as you'd expect. And it's very silica-undersaturated. And it said it's more into the side of an alcalic style, porphyry copper gold deposit, in that sense. So, can you imagine what was it like, do you think, when the top came off this volcano? I mean, did all hell break loose? Do you think everything really did happen instantaneously with brushes and obviously tremendous boiling of fluids? Can you describe what that would look like? Well, I mean, it's hard to know exactly what happened or how long these processes have placed. But we do know that when you have the acyclox, you just release ton of combining pressure. And so you move to, yeah, this totally different regime, an epithermal environment, very dramatically. In this environment, you have lower temperatures, like different pressures. You have an environment where we're going to have more freeotic and hydraulic fluctuations and boiling as opposed to this, the earlier event prior to this acyclox coming off, where we had, you know, more pressures. We had magnetic hydrolymeral brushes, more disseminated style, like neuralization alteration. And we had influence and pressures from the underlying magnet chamber and exhalation of hydrolymer fluids there. So in terms of when the sector collapse actually took place, it's possible that it wasn't the poor environment wasn't going full speed in terms of it went off and we had big sort of frantic magnetic breaches because we do have free automatic breaches, but seem to come even later, not necessarily related just to the sector collapse event. So I think it's a bit dynamic in terms of we had this poor freezer environment with much hard temperatures, much higher pressures. And it was going on and off and then we had a sex collapse events, possibly one event or multiple stage events, and then we earned this acyclox environment where we can get these types of breaches that form. And that led to a lot of gold. I looked at the new crests website and they claimed that there were about, you know, on the order of 25 tons of gold and reserves still to kind of spin in production for 15 years, 20 years now, something like that. I think as of the annual port last year, there's about 50 million ounces of institute gold at we're here. So it's one of the largest gold deposit out there and definitely the largest alcalic. And it'd be there more gold deposit out there. Incredible. So you and then you did research. What did you do? Was there any tools or special things you had to do to work in this environment in order to try and understand it? So my research was particularly focused on this deep-seated porphyryside environment in one of the ore bodies, which is called the Nets. So this early porphyryside activity resulted in magmatic hygiene breaches and lots of associated hygiene rail veins, most of which contain lots of end hydrate. So particularly, I was really interested in looking at the end hydrate, the significance of it and its controls and relationship to gold distribution. How I went about it was there's a lot of detailed open pit bench mapping, looking at geometries and kinematics available in areas you just can't reach. I used the aid of detailed photography and some photogrammetry further away, as well as core logging. And once there's a geological and structural framework, there are other analytical techniques that use backer codes to answer more questions like laser-evolution, LESPMS, like mass-spec, on the pirates to understand gold departments because again, the gold is in the pirate and isotopes, like self-isolped to understand origins of end hydrate. So why is this so much end hydrate? Well, the end hydrate is magmatic, the sulfur and strontium isotopes all point toward that. So it's just the nature of the alkylic rocks that we have in the area, as we were just having much more calcium, much more sulfur in the area. It's also a very young deposit as well, so end hydrate is common in other deposits, like on the property deposits, but it has a retrograde solubility, so as it cools, it dissolves away, and so perhaps isn't as preserved in the other ones, whereas here we have a very young deposit. The rocks themselves are more alcoholic, more rich in elements and we just have a ton of end hydrate related to this early, early porphyry style environment that forms. So I'm imagining you there in this pit, you know, with the tropical weather and the steaming hot and the ground is hot because of the geothermal system, and you're trying to do the mapping, that must have been quite an experience. Yeah, well, sometimes the rocks are just too hot to even touch them, and as a whole area was a potential geothermal outburst zone, because it could potentially have some geothermal outbursts. So yet to be very cautious, there is a lot of safety training involved ahead of time, and of course they also have a team that monitors the geothermal system all the time there. So it made for quite challenging experiences in terms of coordinating around the best times to, and when you are able to get in, and luckily I had a lot of help with all the guys at the site, I'm at the here, particularly the spotters, one of the local guys to come with me, and we'd be in a pit, and then as you go up to the pit well, they have the spot to make sure that there's no rocks going to fall. I don't know, free attic eruptions off the border. Yeah, no free attic eruptions. That's amazing. So I'll ask you this last question, which is the most difficult of a lot really, you know, it's a very special place geologically, it's seen this incredible event and produced an enormous amount of gold, which is spectacular in this nature. Do you think it's a one of a kind, or do you expect to find other, the here islands or equivalent styles of mineralisation, I should say, to the here island, in other places in the world? Well, so yes and no, I would say. So. That's a good key to much. So, yes and no. So one of the key things about the here is it's so young. So we can see evidence for this dynamic telescope environment. I've heard about their prospects that have mineralisation in amphitheater-shaped features, and of course, they'll hear models invoked in these. Typically, they don't have all the same lines of evidence, but in terms of some of these processes like telescoping, it doesn't have to be a large sector collapse, but any sort of dramatic faulting event can lead to telescoping. Like, I think the, maybe you talked about with Silta, the Rzeo porphyry and Chilean mastermen talks about gravitational collapse, the enormous faults, and this accelerated exclamation to help promote telescoping of a high self-adhesion and thermal environments on the porphyry. So we have a new paper coming up in the, in the special, um, SEG issue on gold deposits with Silta, and this will be a cook at all. And then here, we talked about updated model at, at the here and understanding at the here. So instead of just having, uh, sector collapse, there's probably these five different stages in the evolution of the here. So we have this porphyry style environment, where we have trussians, tasegalteration, loss of in hydrate, veins and breaches, and some low-grade gold with that. And then there's a transition phase, which is something that I was looking at quite a bit with my studies, where we have possibly like a, the post-sector collapse or clapsis, where we have lots of evidence for modification and dissolution of in hydrate, which helped create open-space cavities, which were then reutilized when we had the epithermal phase, where we had the most evasion gold, white spread, breaches, lots of power, lots of agiallaria. Then there's diatrine volcanism phase, and then there's a geothermal phase. So there's lots of different phases in, in the history we're here, and here's a great example of a preserved young or deposit that can help us understand how really dynamic these orchids do this. From Papua New Guinea, we go next to Indonesia and talk to Dave Burrows, but an exciting discovery story this year. The announcement in February by Symbolal Timor Mining, a subsidiary of ballet, of the discovery of the onto deposit, a world-class copper gold system, with a total resource of 1.7 billion tons at 0.89% copper, and 0.49 grams per ton gold. But before we talk about onto, I asked you how we ended up in Sudbury as a chief geoscientist for ballet. Where did you start on this journey? I think I was always one of these people who knew I was going to be a geologist ever from the age of about six, and I was especially fascinated with minds and metallic mineralisation, and, you know, just exploration in general. You know, a really long story short. I did underground in Trinity College Dublin, and then went on to do a masters in a PhD in economic geology in University of Toronto, which, as you point out, is where I met you two guys. And then towards the end of my PhD, I attended a student industry workshop, poster session, and the one of the industry reps, he was director of exploration and the ink of the time. I mentioned my poster in his wrap-up, and that it was applied, and this sort of thing is useful to industry. So I sent him a letter and then to follow up and actually landed the job at that time with ink of gold, as a structural geologist. So I was pretty nice set up at the time, and then I became chief geologist at Inco in 1997. And that's a position I essentially maintain, then when I acquired Inco in 2006. Well, that's got history. You know, despite having worked for one company, which is probably relatively unusual these days, very unusual probably, you know, had a really varied career. I always point out that I started in gold, and then got into VMS, and then got it back and, you know, into porphyry coppers in Chile, particularly Turkey. And then back in for a while, doing what Inco did at the time was, which was magnetically full copy of the G's. And then when I joined Valley, I actually took a brief look at Uranium for four or five years, and then eventually got back into copper exploration and porphyrys and I also did. So I had an interesting career, despite being with one company. I had stayed in nickel copper exploration all that time, I would have probably just left. Dave has been involved from the start in the work to define the ontodeposit. John and I talked with him recently, and we asked him to take us through the discovery story. I think the discovery really started in January 2009 when Valley exploration at the time had a big meeting in Jakarta, and we really decided to try and focus our exploration in Australasia in the prolific app environment, which has these large volumes of advanced hydraulic alteration, which typically over live porphyry copper system. And they're known through a lot of Dixilto's work that they've probably related to porphyry deposits and offer cover them, but are difficult to explore them. So we felt they're under-explored, but when you do do exploration in the prolific app environment, you're exploring right in the top of the porphyry deposit, which is probably the best place to be up in this sort of offshore. And there were some better models being developed at that time and some new tools that were starting to merge from various mirror research projects. And actually, the key part is we kept our plans, and then we acquired several property lithocap type prospects and properties, both in the Philippines and Indonesia, and then started to look a bit in South America as well. One of the earliest projects we looked at was Hu Hu Project in East and Sunbao, it was a seventh generation cow, so it had some bandages in terms of the contract was already in place. What really attracted was a very large lithocap with a lot of advanced hydraulic alteration, foggy quartz and solicification, but then a little bit of work in the past with Aberfoil in the mid-90s that indicated that there was at least some potential porphyrys on the project they had intersected some low grade, but not really extensively explored the actual lithocap itself, they'd sort of concentrated around the edges. So we acquired that in 2009, the same year, we sort of had this meeting and some completed at that stage and really pretty standard exploration, we did some soils mapping, 100 space magnetics and radiometrics, and then in 2011, after we'd done that work, we started to test some of the anomalies. The first one we tested was quite a pronounced magnetic anomaly with some associated copper and gold and moly to your chemistry and soils, and that was a place called Pimpalao East, it was approximately 3 kilometers northeast of the eventual Lanter discovery. That was our first discovery, it was a fairly standard pencil shape sort of porphyry with patastic alteration and about 150 meters underneath the lithocap, so, but it ended up being a bit small, mainly because of geometry, and so it ended up being about 50 million tons of 0.5 copper and 0.5 grams per tonne gold, but it did provide us with some sort of strong encouragement to persist. So we then continued to the southwest of that area and we were drilling deep holes, 800 meters, targeting increasingly subtle copper, geochem anomalies and soils and weak magnetic features. In the thought that we were going to just see a very small part of the porphyry beneath the lithocap, because the lithocap alteration tends to destroy the magnetic signature and also tends to make the geochemistry a lot more subtle because a lot of the copper and some of the other elements are leached during that alteration. But then in 2013, the end of that program, so at the end of the campaign for 2013, we drilled whole '34 and that went through 400 meters round the sides and about 100 meters of quartz dickhead and then through about 80 meters in muggy residual quartz and solidification. Not only really, when it got below that down to a depth of about, we think it was downhill as 550 meters and we intersected, once we got it assayed, 287 meters at nearly 1% copper and 1 grams per tonne gold, with some relic quartz fanings, but all the copper was occurring as covalight. We knew right away it was a brand new style of mineralisation we hadn't seen on the property before, and very consistent looking covalight within that zone. I think even at that stage, in retrospect, I think we realised we were going to a big discovery at that time. But we drilled another hole, hole 37, which was about 500 meters away from that zone that we hit and in that we, that was a 1.5 kilometer hole and we hit nearly a kilometer of 1.26 copper and 0.7 grams per tonne gold and I think that was the one that really told us how thick this zone was and how consistent it was. It was still a few skeptics that thought I've just drilled down an arrow fault zone. And then there were two further holes, so nearly a year later, we drilled another 500 meters to the northwest, two holes oriented north and south and then they defined that zone had a width of about 750 meters. So I think that was really the, that was the real cruncher for me, that was at that stage when you were on to a very, very significant discovery because essentially in ten holes we'd outlined what turned out to be several billion tons of copper gold mineralisation within a 1.5 by 1 kilometer deep by 750 meter wide zone. And I would say it's, that's, that's the unique thing about on to, it's pretty unusual to define the outline of a several billion tons copper gold deposit in just ten holes. And it says something else to the sort of consistency of the mineralisation and we haven't really ever gone back and drilled a barren or even a low grade hole within that, within that outline that we define in those ten holes. What governed the ten holes? We were just stepping out to the southwest following some low grade mineralisation. We hit some material that was below the lithocarp and then another hole we drilled thick lithocarp so it was very variable. In the end there was some very subtle copper only anomalies, which Peter Winterburned outlined at the time was sort of interesting, but they had no signature from, from Molly. And they were quite, you know, low grade, you know, 160 p.m. copper and soils. You know, so it was a pretty barren looking area, but what we did have there that we encouraged us to drill it was we had a series of, I think, mainly freeado-magnetic breaches and some of these freeado-magnetic breaches contained little class of covalent, which I don't think we realize the significance of it at the time, but in retrospect, they seem to be little freeado-magnetic breaches that have punched through the mineralisation at depth and then pulled up some of this mineralisation upfaults to the surface. So that was the cause of those sort of low grade copper only anomalies that we saw. And that was one of the fundamental reasons that we gave this hole a bit of a bash. It had a weak mag signature, which in retrospect was the overlying and the sites, which were quite magnetic, this low grade copper anomaly and soils, but then a couple of occurrences of these freeado-magnetic breaches with class of covalent in it. On the question, you've already highlighted the continuity, the second is just the sheer volume of advanced hydraulic alteration, but why is it all mineralised, I mean, that is very unusual. Yeah. And the programme changes, we went along, I mean, initially when we had a lot of advanced hydraulic alteration, we felt now we'll just target the alteration and look for the higher temperature parts and just continue that. Then we drilled a few holes on the south side and on the north east side, where we had great alteration, not quite as strong, perhaps, but essentially, you know, five, six hundred metres of advanced hydraulic alteration and absolutely nothing. So in the end, the poultry part of the system was difficult to recognise it first, but we did recognise even the first hole that was some of poultry-style quartz-a-beaving stockwork. As we went further and further into the programme, we realised that we actually did have to have those intrusions, and that there'd been a lot of remobilisation and marginalisation of that grade around the intrusions, particularly for the copper, not so much for the gold, but without the intrusions, we found once you got more than, you know, five hundred metres away from them, we just weren't getting any grade at all. We've drilled a lot of geotechnical holes down, hydrojology holes around the edges since that time, and none of those have, you know, nothing. I mean, you're either in the alteration and with the poufries and you've got good grade or you can be within the alteration in very little grade, but then outside it just goes into quite ordinary looking chloride, chloride, epidode-alpha-grocks and regional sort of alteration. Yeah, so it changed with time, you know, originally we thought it's all high solidation, we were sort of using that more model, but as it went along we had to creep back and sort of readjust because we realised that we didn't have the poufries, we didn't have the system, and that's why we continue to call it a poufry high solidation system because I think it's, it is very much a poufry system, it's just one hundred percent overprinted. And do you have any sense of the timing in all of that between poufries and advanced tarjolic and that overprinting? Yeah, we've done some preliminary age dating and the volcanic sequence is no more than 850,000 years old to maybe about 650 in the intrusions and they're probably minimum majors because they're not necessarily dating, you know, it's an average of all the zircon dates in it, not necessarily the ones that crystallise as it intruded. But then we've done some reneumosamine dating on the molybdenum and we dated drains with molybdenum, which is typical of a poufry style, which we think is the earliest introduction of copper. And then we dated what we thought would be the very, very latest type of high solidation mineralisation. So very late discrete veins with paride, covalide and some molybdenum in them. And when we dated those, everything came back between 440,000 to 350,000 years ago and really within error all the same at about 400,000 years ago. So we think the poufry portion and the high solidation overprint all formed more or less at the same time within the error of the dating and we've also done some argon argon dating and that again spans that range from the oldest ages actually a bit older, like as old as 1 million. And we have this slight feeling that some of the advanced gelic alteration may have even proceeded the poufry system that we see now. That's the permissible within the dating we have today, but it's very early days and we just did some sort of very preliminary dating to sort of get an idea of the main features of the positive. And so the argon argon dating value nights goes from a million which, yeah, most people consider that pretty, pretty young to essentially yesterday for some of it. So when I chatted to Dick, we talked about telescoping and his first kind of introduction to that of the Andes and his, you know, he was produced some of the early thoughts and of course, he also thought early about what we're here and the potential decapitation and rapid telescoping. So this presumably is another example but it's very, very different than we're here, although essentially the same age as we're here which is interesting. So what happened? How did it get so much large argonic alteration overprinting and unmodulizing the early poufry normalization? Yeah. Well, that's, I'm not sure I know the complete answer to that. The fairly unique thing about Anto is that you can see in the drill holes that you drill into the top of the intrusions. You can see the original cupola with a lot of these sort of wiggly veins and sort of very high temperature veins. We see the top of the intrusions as they sat there and they're based on reconstructing the cone and some preliminary fluid inclusion work we did. We don't think there was ever more than 1.4 kilometers overlying the system. So it formed fairly shallowly. But then since that time, so we had, we essentially, we had, we had some older volcanic undersights and then we had a large diatreme that formed and then that diatreme was capped by a bunch of sediments, sentiential silt stones or kind of plastics and then it was capped by these undersights and the undersights are the ones that are maybe 850,000 years old. But you know, since that time, those undersights on the top have been decapitated a bit and you've probably lost some of them but you can see because the diatreme is in place and the sediments are all in place and you'd think that would have been the major event that might of course some rapid denudation of the of the train. That's all in place and and the alteration is also perfectly still zoned from quartz diasporate to quartz prophylite to quartz alenite to quartz dickite to quartz kale and night to elite smectite as you go up. So the whole alteration system is still in place. I think most people blame telescoping on either very rapid erosion or some cone plaps or something like the case of the here and various other things. So my own feeling is that didn't occur and if you look at the erosion rates to take off, you know, maybe six, 700 meters, they're perfectly normal erosion rates for an arc in this part of the world. So I don't think there was a big event. My own feeling is that we're looking at the very top of the system and we're seeing a unique situation where the acidic fluids that cause the advanced agilic alteration, you know, condensating and then and actually plowing back down into the system and what may have started as a bit of a cover then went back down into the system and perhaps the the diatreme host rock, which is the main host rock, facilitated that process and then the advanced agilic alteration managed to get down for a great distance within that central diatreme, which hosts the, you know, hosts the porphyrys, where you go outside that diatreme, the alteration definitely drops off quite quickly in terms of thickness and intensity. So, you know, that's the basic answer. I mean, I think that whole the whole process gets a bit blurred in on to and I think after another two or three PhDs here and think it'll cause us to change how we think, you know, this porphyry high sulfidase and transition happens. We have quite a bit of evidence, I think that the, well, I, despite being quite late and filling a lot of bug spaces also intergrown with with alinaite and prophylide in many cases, suggesting it's it's early high temperature in some cases and or is forming and getting deposited from the same fluid that's forming the high sulfidation, star mineralization and advanced agilic alteration. As distinct from, you know, a lot of cases where people think that the advanced agilic alteration is just the ground preparation to give you a lot of porosity and form the vogue residual quartz and then a later fluid, a single phase fluid comes in and mineralizes that as is, you know, it's been demonstrated in lapan term, places like that. But here that I think that distinction is very blurred and you don't have a lot of time for any over printing or another phase of, you know, association because it's just not much time. We haven't seen any late, we haven't seen any really late, you know, cross-cutting phases or any even sort of late intraminal phases of that mineralized. Well, maybe that's part of it. You're just seeing a time-slice that normally we don't get to see. This, this part of the system is just rarely preserved, you know, because it's so young and would be eroded in another, you know, 500,000 years and you've missed this top, you know, 600 meters, which is the part of interest. So, do you think it changes how we think about tops and bottoms of porphyry deposits? Yeah. I think it's going to raise some questions in terms of this, often that this thought to be some timing difference, a subtle timing difference, you know, between the porphyry part of the system and forming the porphyry and forming the, the overlying advanced hydraulic alteration and then some later phase of mineralization, you know, mineralizing that advanced hydraulic alteration. I think Anto will change that a little bit and that there's very little time to have too many processes going on and, and the preliminary age dating, you know, on quite a few samples showed that there's no real difference in age between those, between the two styles. As you say, I think it's, we just don't often see this sort of essentially upflow zone off the top of a porphyry, but you know, it's early days, I'm not sure as I said, I totally understand mechanism how this formed and, and the implications it will have, but you know, the other main implication is that it's in a much younger act than we would normally target the porphyry expression. I mean, arcs of this age or even this erosional levels, you would commonly target the high solidation gold type systems, you know, like in Chile or in Peru or something, but you wouldn't, you wouldn't see too many people exploring them porphyrys. So one of the interesting thoughts about Anto, I mean, to me, you're in the, in this advanced hydraulic world and potentially high solidation, and for many people thinking about copper and copper sulfides, that's going to have a nasty possibility of energizing a lot of arsenic. And you, you don't have that. So why is that? Yeah, I mean, Anto in general, I mean, the, the levels of arsenic here around 320, I think it is PPM. And when you produce a concentrate from that, it doesn't actually increase that very much, whereas normally when you produce a concentrate because it's energized, you'll, you'll increase that in the copper. So it produces a very good copper, why no arsenic? We do see a tiny bit of energite, you know, sort of meter intervals where it might grade, you know, 1% copper or something, and, you know, the equivalent amount of arsenic, generally around the edges of the systems and just where we get outside this central dietary, the but hosts, you know, the majority of the porphyrys. My feeling is it stayed fairly hot and the other keep out of this system, it's very oxidized. There's a lot of later sulfur and high solidation state intervals obviously, but quite a lot of barite and energite just wasn't, wasn't very stable in that regime. So we talked to Dick and I started on the porphyry model and tops and bottoms and his immediate reaction was the big thing for him that was happening was play to tonics and the whole understanding of what potentially could control porphyry deposits. Here you are working right in the active, it couldn't be a more active tectonic environment for onto. Is there anything tectonically that you can take away that tells you there's nothing about why on toes where it is? Are we at that stage yet where we've gone from understanding the importance of play to tonics and seduction zones to being able to be more direct and targeting tectonic features in seduction zone and arc terrains? Well, we've done quite a bit of targeting obviously in Indonesia, you know, as well as on toe. I think you can you can do quite a lot in these recent terrains. We've done quite a lot with earthquake data, for instance, looking for these tears and slabs and things like that and you can see major breaks that represent faults, that represent places where there's seduction changes angle or changes attitude in some way and or you're subducting something on the seafloor and it's causing earthquakes later on. So I think in these young arcs you can actually do quite a lot with trying to predict where the more favorable spots are. There's a couple of major faults and we've done some analysis of the recent faulting which has worked out really well in terms of getting the recent stress fields and then working that back into the faulting we see on the ground. So because we're trying to build a structural model as well and so that's been quite useful. So I was actually pretty impressed with what you can do in these recent arcs because you do a minute advantage because the process that's still going on is what's causing these things. So, you know, it's only half a million years old. So there's something directly relatable potentially on the seduction zone that relates these large deposits. So in terms of the overall the story, the people part of the story, how has that developed? I think all discoveries these days are very much a team effort because as exploration these days is very complex as many moving parts. We had a really great Indonesian team, a very dedicated team. I would say the other important thing is that we were given lots of latitude and quite a good budget to complete the planned deep drilling program which is what it was. I mean, 800 meter holes, you know, along the edge of a lithocap is quite a bold strategy. You say people, I think these discoveries, the actual discovery can often be attributed to a couple of key people and I think in this case that was Dave Bert who was the country manager at the time and he poured all over all the data and ultimately spotted all the key drill holes. And then there's Mike Rennison who was the regional manager of a business development and project generation at the time and he was the one that recognized the potential for who cow and got the deals done and then provided a lot of very critical guidance as we went forward. But the only other thing we did really well was in the early drilling we were guided by a lot of very hands-on daily assessments of the logging data and all the downhill data. And I think having all that run hand day-by-day enabled a very small group to make I think very quick and well-guided decisions that led to a very effective drill-out. I think one of the most remarkable things was essentially we had the outline of the posit in ten holes that just blows my mind. Thanks for joining us in this final episode of the series and the SEG Secret Partner Discovery Recovery Podcast. I'm Ann Thompson. My co-hosts are in a cold to set, Halle Keevel and guest host John Thompson. We hope you'll continue to share this series with others in the weeks ahead. You can access them all on scgweb.org/podcasts. As mentioned in this episode, coming soon will be the much-anticipated SEG Special Publication 23 geology of the world's major gold deposits and provinces with lead editor Dick Zilto. Thanks to Dick, Stephanie and Dave for providing their insights and experience. This episode was produced and written by Ann, a huge shout-out to our podcast partner, Sequit, who opened with us every step of the way. And of course, to my co-hosts, you're the best. Our theme music is "Confluence by East Twins." Thanks for listening.