Mining Volcanoes: Diamonds, Copper and Hot Water

so tonight we're moving on actually for continuing the theme of volcanoes and what I want to talk about is how the volcanoes relates to what I've called here treasures from the deep earth for the the mineral deposits that are formed by the processes linked to two volcanoes we see on the surface we're used to the destructive power of volcanoes but it's incredible energy in a in a volcano and we know from this is a map of the seismic activity around the planet and we know that the earth is comprises a series of tectonic plates the earth is a dynamic system and places where these tectonic plates are moving around we can map seismicity so on this diagram here you can see areas where we have the most earthquakes but the periodicity of the earthquakes being the shortest and you can see lines of these around the globe and these correspond to these tectonic plates and these are testament to the the dynamic nature of the earth we know the earth is a zone from a core to a mantle to a crust and we have an interplay between those parts of the earth the planetary system and a part of that is manifested in the volcanoes we see at the earth's surface so the Earth's tectonic plates are a very dynamic and we see places here this diagram showing you but there are parts of the surface where the plates are moving apart like the mid-atlantic ridge and there are parts of the earth where the tectonic plates are getting are moving towards one another and the western side of the Americas is is one of those zones and so there are parts of the earth where they're getting stretched apart parts that are coming together and being compressed and in those we're going to see tonight that the volcanoes are linked to those but we're also going to see that we can link these these and ore deposits the mineral deposits that provide us with the economic treasures from the earth that feed our modern modern economy so this is just to get you in the mood it's an erupting volcano in Ecuador and you can see the what we're getting out of the top of these are the extrusive products of the of the from the magma that lies below and you can see the initially molten they're flowing but there's also a lot of what we call pyroclastic rocks which are the fragments of the of the consolidated and cooled magma but you can see there's an awful lot of gas coming off these two and those gases are very mixed in composition there's often a lot of water in there there's a lot of carbon dioxide often but the rather gas is like a sulphur dioxide and hydrogen chloride and they're testament to the fact that although their volcanoes that are producing effectively of volcanic rock they're also coming from Magma's that contain dissolved gases and dissolve volatiles and as a result there's a very complicated chemistry link between the evolution to form a silicate melt under and a volcanic eruption and then the the dissolved volatile elements in there and I what I'm going to hopefully show you tonight is how they are responsible for moving some of the metals that we use around and concentrating them but also we're going to talk about some of the more precious minerals that we we use in in our daily lives and how they might be linked to two volcanoes okay so this is just here showing you these this is the solfatara site in in italy where this is a volcano that erupts it's very close to Vesuvius and it has erupted in a human time scale this is a cold era but what we're getting here are the gases that coming off the magma chamber so though there's no eruption there's a lot of volatiles coming off there's a lot of carbon dioxide there's a lot of sulfur dioxide you can see the yellow sulfur being precipitated here and a lot of water as the steam coming off there so this is testament to the the magma chamber losing that some of that dissolved gases and you can see methyls moving around so it's giving you a flavor of part of the rest of my talk later on this is actually another part of the link to to volcanism we get hot spring development so this is a actually water that's not coming directly from the the magma chamber that sits underneath here that feeds the volcano but it's it's it's the result of surface water that is finding its way down into the crust and getting heated up by the cooling magma the crystallizing magma that still remains very hot and what's happening is that that surface water meteoric water is is finding its way down to get heated and coming back up as in the form of hot springs but it's also tapping some of the gases that coming from the magma and so we have a mixed system and you can see it's moving minerals around because we get precipitation in this case there's a lot of silica but we also get some other minerals forming here and we get some metals as I'll talk about a bit later on okay so let's have a look Steve may have covered this in the previous talk but I just want to to to sort of revisit this that there are key tectonic settings so I gave you the plate tectonic story we talked about the volcanoes now I want to try and link the two together and we'll talk about some different geological environments where we have volcanoes and where we can directly link them to the formation of the the mineral deposits that we we mine for our everyday needs so you can see here this is a very simplified cross-section through it's a piece of crust it could be across the Pacific really because what we have in the center there in the blue main blue area we have what we call a mid-ocean ridge and you can see the two arrows and they're pointing to the part of a cross where we're making new ocean crust what we call a mid-ocean ridge and then on the either flank of it we've got places where we're getting the process of subduction you may have heard about this where we have to lose because the earth is not changing its its volume that was a theory a long time ago that the earth may be an expanding earth but the earth is conserved in its total size and so in order to accommodate mid-ocean ridge spreading we have to have the old foam crust returning back into the mantle to be recycled otherwise we wouldn't wouldn't have a consistent planet so we we have places where so at the mid-ocean ridges you can see there's a sort of a red indication there there's some new crust forming and then at the margins we are losing crust but you can see in in the case of the these margins we have these continental arc volcanoes or we can have what we call island arcs on the left-hand side so where we get ocean crust under ocean crust and and so these are the sort of factories where volcanoes are created and then there's one in the middle there which is called the mantle a mantle plume and so there are some very deep mantle processes that we don't entirely understand that give rise to convected mantle so deeply sourced parts of the deeper earth that are rising up to form what we call hotspots and we can get volcanoes related to those Hots boss okay so there they're the the scenarios that we're going to look at and I'm going to take you through those different scenarios look at those volcanoes and then look at the or deposits that relate to those those volcanoes so I'm going to give you a little bit of a talk about the the actual ore deposits themselves so the first thing we're going to do we're going to go and have a look on the ocean floor we're going to go and have a look the places we create new crust on the ocean floor and we create new crust in the form of extrusive volcanic rocks and related to those we can form these giant sulfide deposits and I'm going to talk to you about how they form but just to give you a little taster back in the geological record we can see evidence of very old deposits of this type and this is one that I've worked on in the euros of Russia and it's a giant resource of copper zinc and gold being mined in a very large open pit and that's currently producing about over a million and a half tons of ore per year so it's a big repository of copper and zinc and it actually formed on on the ocean floor and we'll talk about that setting in a minute and they never lead you on to talk about a set of deposits called porphyry copper deposits and these are directly linked to volcanoes that form at some of the destructive margins i talked about those places where we have subduction and where we have arc volcanoes then we have the same environment we form these porphyry copper deposits and I'm going to show you how those two are linked this is actually the chuquicamata porphyry copper deposits one of the largest in Chile and it's got more than two billion tons of ore being mined and it's producing around about 350,000 tons of copper metal each year in a again in a very large open pit and coppers a metal that's essential to modern the modern modern life and its growth in demand is enormous be given the development of countries like China India and so on so increasingly we need to find these types of deposits and the work that we do understanding volcanoes tells us that they're the kind of places we should be looking for new deposits like this one here then I'm going to move on really for something quite quite different and that is to talk about diamond deposits and they are linked to a type of volcano which is very unusual a unique type of volcano it's a kimberlite volcano and we're going to look at that and and then lastly I'm going to give you a little insight into some types of volcanoes that on earth we only know from the very very deep time so these are what we call kamati i'ts so they're a type of lava that is very very high in magnesium it's a very primitive lava and erupted at very very high temperatures and we we can't get that kind of magma to the surface of the earth today it only was able to form back in the Precambrian and we get some very unusual deposits related to that but I'm going to talk to you a little bit about these why they so interesting because there are other parts of the solar system where these types of volcanoes are still probably erupting okay so let's have a first of all before we move on to talk about the the volcanoes and the different settings I want to talk a little bit about water now water is really an important part of this story it's really important for those of us who study of mineral deposits because water when it's heated up is probably the best solvent we have on the planet for moving things around so we can move for just about anything in salty water dissolved if if the temperature is high and we've got different parts of the if we look at the crust in them and the mantle we find water in different environments so we go to the bottom there I've got magmatic water so this is the kind of water that is associated with those intrusive Magnus that we get intruding into the crust and we'll talk a bit about those because they're the kinds of the water or the volatiles that come off into into volcanoes then we cut water obviously it can come from metamorphosing a rock when when you bury a wet sediment like a clay or a sandy sediment it's got lots of trapped water which then gets trapped in the minerals that as they form but that can also be later released and then we've got meteoric water I talked about water coming from the surface we've got sea water and then we've got the kind of water that's in aquifers we call that Khanate water that might be stuck in in sandstone reservoirs or in the deep earth so just bear in mind that water is actually the thing that drives our planet it dries life and I hope you'll go away from tonight to to understand that water is actually driving so many of the geological process processes that we have on the planet okay so the first area that I would want to talk about is that sea floor where we are creating new crust the the spreading zones that we have on the ocean floor and the thing that scientists noticed in the 1970s is that they when they would discover when they went down there with a submarine they found that where we had these volcanoes submarine volcanoes on the ocean floor we also got high temperature vents and this is where very hot water was being circulated and venting out onto the sea floor and it was quickly noticed that they were associated with the precipitation of metal sulphide minerals and that's because these dissolved waters which were heated they're very salty were able to scavenge metals and circulate them around and bring them out out onto the seafloor and form these large metal deposits and then I directly linked to submarine volcanoes but for most part we don't see those volcanoes we do know that they're there because there are parts of the parts of the earth where these mid-ocean ridge spreading zones can be seen on land and Iceland's a fantastic place to go as a geologist it's a geologists dream because the mid-ocean Atlantic Ridge goes all the way through Iceland and so as you know Iceland's very very volcanic the volcanoes often disrupt holiday flights to two parts of southern Europe but they are a response to the fact that the Atlantic is opening we're creating new crust and the the red triangles there are the active volcanoes on on Iceland but as you can see they go out off under the ocean pretty to the north and the south and that's really where I want to take us so you can see on on the surface on the right hand that photograph that is the Rift Valley so that is a place that is actually going apart couple of centimetres every year Iceland's getting bigger and we get volcanism and we get lots of faulting but what I want to do is take us down onto the ocean floor and this is what is happening so it was Fred vine back in the 1960s who was able to show that in this mid-ocean ridge spreading we were getting new crust forming nobody believed at the time the paper got rejected twice before it was then accepted but there what we've we've got we're pulling across the park we're creating new new crust and we know that's the case because we can pick it up they did magnetic geophysics and they're able to show these stripes in the magnetism of the rocks that showed that the the the rocks were growing apart the the continents were spreading and we were creating creating new crust in the middle and if we look down there there are lots of submarine volcanoes and volcanoes can erupt under the ocean floor and you wouldn't see anything I mean this is like a 1 and a half kilometers down off Iceland and we get these basalt lavas erupting into cold sea water but this is so hot and so fluid that they extrude like toothpaste onto the ocean floor and we get something called pillow lavas you've probably heard of pillow lavas and it's where the lava is erupting on to the sea floor getting quenched but as you can imagine there's a lot of heat coming out onto the ocean floor and actually the magma chambers feeding these are not very far below the surface so what is happening there is we're pulling that apart we're getting volcanic eruption but because we're stretching the crust it allows cold sea water to come down into the higher temperature where the magma chamber is and that water gets heated and as a result it's hot salty water is very good at dissolving metals and minerals from the volcanic rocks and it brings it dissolves those metals and it will bring those back up to the surface because hot liquid is less dense it's more buoyant it will come up onto the seafloor it comes up through the same fractures system that we've been developed by this stretching and we we develop a phenomenon called black smokers and this is where that really heated fluid is coming back out onto the ocean floor it's got lots of dissolved metals in there and as soon as it hits the cold seawater those metals come out of solution and they crystallize and that black smoke is actually very very fine-grained at sulfide minerals so it contains copper contain zinc contains goals and so this is happening all the way along those ocean ridges in a in a predictably repeatable set of deposits forming all the way along the volcanic chain you saw that map with the red spots along the along the mid-ocean ridges and that's where hydrothermal activity has been has been detected so I just want to show you a little bit more of a video so this is going to be a little bit of a maybe a minute minute and a half and so this is a submarine it's coming down through the black smoker smoke clouds towards one of these chimneys and these chimneys are composed of the minerals that are forming as that heated seawater with all the dissolved metals is is hitting the cold water and as we get in closer perhaps you can see that there's quite white a chimney quite white and that's because the chimneys covered completely in bacterial mats so there's a whole series of bacteria that are using the hydrogen sulfide gas from the vent for their for their life cycle so this is actually a food basis of a food chain a chemosynthetic food chain so you can see this is down on the deep ocean we've got crabs living down there we've got a whole range of other crustaceans we've got some mollusks and we've got some some worms we've got some annelid worms we're gonna gonna zoom in and see in that white area there there's a whole bunch of you can see some sort of tubular structures things waving around in the warm water that's shimmering and yeah the pink thing on the top right there that's actually one of these Alvin le worms and these guys have got bacteria living on them that are feeding off the hydrogen sulfide and so it's a place of mineral formation but also of a place of abundant life in the absence of of sunlight so really interesting environment and what we have is these chimneys forming and they slowly build up from the sea floor and we have owned minerals forming there now scientists found these and thought well we ought to have a look and find out what they're like underneath and so there's been a whole series of programs some of you may have seen these on television that saw on deep drilling going on on the ocean floor these deposits are forming down more than a kilometer down on the sea floor so you need to have a pretty robust ship to do this so back in the 1990's the the mid-atlantic site called tag was drilled where they discovered some of these chimneys and what they found were that this is just a cartoon diagram done by Mark Hanning ttan you can see the black smoke of chimneys shown at the top of that edifice but what they found when they drilled it is that there was masses of sulfides forming underneath it and these are the the massive sulfides linked the the volcanic rocks and the hydrothermal activity that are forming close to those seafloor volcanoes and actually in parts of the ocean people are now considering mining those because some of them are quite large some of them are of the range of the economic deposits we find upon land and where they're close to land so in Papua New Guinea there's a site that company called Nautilus minerals are looking to exploit using the kind of equipment you see on the right there and obviously these are forming on the surface of the ocean floor and are potentially easier to extract than something found in the in the deep earth but we already are mining these things because I showed you the first picture of the big or deposit the big sulphide deposit in the Urals I'm going to show you some the geology of a small one of these that I've worked on in the Urals so there's a geological map and a geological section and that big red lens is the massive sulfide lens and it formed right at the contact between seawater and the volcanic flows we know that because this is an amazingly preserved sight 420 million years old but what we did when we looked in detail and this is a kind of a reconstruction of that sulfide mound we found all the evidence that people find on the modern seafloor so we found evidence of those vent chimneys we found hydrothermal crusts on the top but more importantly we found evidence of these unusual organisms that are living close to the vent sites so we know that this is an absolute analog to what's happening back what's happening today on the seafloor and so this was happening 420 million years ago so we know exactly this process of formation of deposits that in spreading zones on the ocean floor has been happening since then so that relationship between volcanoes and all deposits is very very strong ok so I want to take you away now we've done the deep ocean we've done where new crust is forming let's go to the places where we are destroying crust so those subduction zones the edges of the ocean where we are pushing one tectonic plate underneath another so what I'm showing you there are the subduction zones and with the red spots in this diagram are where we find giant deposits porphyry copper deposits and you can see there's a uncanny link between the areas where we're getting those subduction subduction occurring and the formation of these giant copper deposits and in fact what we find when we get in closer is there's a very strong link between the porphyry copper deposits and volcanoes this is geological cartoon produced by one of my colleagues at Museum and it's just showing you and I just I don't want you to look at the detail but you can see the green slab coming down here that's the oceanic crust being pushed down or dropping down underneath the the Continental margin and as that goes down deeper it gets heated up and what we start to do is we drive the water off the subducting slab what we call the subducting slab so the lower slab is full of water because it's been on the ocean floor and that water is getting up into the that little wedge of green which is what we call the mantle wedge and it creates melts because water if you inject water into that situation water lowers the melting point of a magma and so what you do is you generate a melt and by its nature it's very fluid it's less dense it wants to rise up through the crust and we get it rising up and you can see the cartoon it goes up from the blue to form the yellow because it starts life as a primitive like basaltic type crust but as it goes up it evolves and becomes a more sticky more silica rich crust silica-rich melts and then it gets up into these crustal chambers a few kilometers below the surface and that's when it starts to generate the ability to feed up to volcanoes so we are linking the volcanic arc directly to this process of subduction and actually when we look at the the copper deposits the porphyry copper deposits we find really clear evidence and this is a geological cross-section at the bottom there from a very large porphyry copper deposit in in the u.s. that the geological reconstruction which is shown on the top would have a large stratovolcanoes sitting right on the top we know that because we can see all the volcanic rocks that are have been laid down around the where the Palfrey deposit is forming and actually the interpretation is these are rather like volcanoes that we we see in that part of the world happening today so there's Garris which is in colombia it's a very very very dangerous volcano very gassy volcano and that's the Sophia Hills volcano in monster at which Steve sparks has worked on very extensively again a very dangerous volcano that is very gassy and is it and these are the types of volcanoes that we would expect to be sitting on top of the deposit forming there in the US and all the way down that arc on the western coast of the Americas we find giant porphyry copper deposits so this is the Lost bronzes porphyry districts in in Chile you can see these very large open pits and we're right in the high Andes and so these are very high-level magmatic intrusion that are linked to volcanoes that would have sat on the top the volcanoes are now eroded away but these deposits are only in the order of up to ten million years old so they're very recent by geological by a geological perspective and in some places that volcanic tops - these are preserved so what's happening are underneath that volcano well I did say to you that these are very gassy volcanoes so there's a lot of gas a lot of water in the silicate melts and a lot of that gets ponded underneath and it's able then to extract metals from the silicate melts so a bit like we're using water on the ocean for to strip metals from the volcanic rocks in this case the water is able to take in because it's quite salty it's able to take in metals and in this case the copper gets taken into the into that the aqueous part so that's the water that is coming off the silicate magma and as long as it doesn't all get lost up the volcano some of that can get trapped to form these copper deposits and we've got good evidence that that's happening because in some of these volcanoes that are gassing we can detect large amounts of copper coming off in the vapor and in fact we find someone like Vesuvius and if any of you've ever gone to the gun look at the Vesuvius collection in the museum in Naples it's a heck of a lot of copper minerals in the volcanic rocks coming off the volcano in Vesuvius and so if we're not losing all the copper we can form these copper deposits so this isn't the last bronze district there's a little quartz vein with some copper in and this is actually some drill core from underneath one of these deposit you can see all that sort of golden colored mineral burr is the copper mineral called choco pie right the copper iron sulfide and this is a really rich deposit it's a two hundred and twelve meters thick running about seven percent copper really very rich or very very high grades and this is actually forming in the intrusive rocks right underneath that volcano and we've got really good evidence that these volcanoes are erupting at the same time as we are forming deposits because we've got good evidence here of lots of oxidized sulfur sulfur dioxide gas probably that is being is coming off the magma because the oxidized sulfur here is forming is up to a purple mineral called an hydrate so it's a calcium sulfate and it forms as the the oxidized sulfur gases are reacting with those wall rocks so the and you can see the rock is very very brecciated this whole thing is a very dynamic system so the magma chamber is probably losing volatiles its erupting and we're forming deposits and there's an interplay between almost like a psychical interplay between those those types of processes and so here we have in the evidence that we had magma in a melt form coexisting with liquid water this is like a big hug in a granite it's called a Meyer oolitic cavity and it forms when we get almost like big bubbles of vapor or water inside a silicate melt it's an a miserable situation where you've got the hydrant the water dominated fluid separating from the silica dominating through it either the melt and when that happens you you get some very interesting textures that are picked up in the in the record and this is showing us that this intrusion is beginning to crystallize and it's beginning to lose its vapor and and water that's stored within it and it's priming its priming that intrusive rock to be able to form a mineral deposit and how do we know that there's lots of water and lots of salt well this is actually a photo micrograph of a fluid inclusion and it's coming from a quartz crystal in one of those mineralized veins and so what that's showing you is there's a bubble which is a vapor bubble and then we've got a cube of halite a little iron chloride and then we've got water around it and that points to the fact this is very very salty water that it's being trapped in this course that has grown at a time when the when the granite is beginning to crystallize and form an immiscible water fluid we've also got good evidence that when these deposits are beginning to forming it coincides with a phenomenon sometimes called magma mingling where the magma chamber that's forming the volcano is getting a new injection of a more primitive magma in at the bottom and it's the kind of thing that would trigger an eruption this kind of event so there's almost showing you the cycle of the volcanic activity the hydrothermal activity that is forming the the ore deposit and bringing in this different magma sources actually supercharges the whole system with regard to sulfur and we know we want sulfur because sulfur helps us to form those sulfide minerals that collect all the copper and put it into one place to make it economic to mine so this is just bringing it all together this is like a cartoon cross-section through a volcanic edifice so we have the intrusive shown as these sort of pink fingers at the bottom that link into a volcano and then just above there we form these very big copper deposits where we are losing the fluid from the being the intrusive melt and that's just to put the thing on the top okay so that's just sort of summarizing things where we have magma is coming up they kind of stall at the base of the crust they then evolve and then we get periodic volcanic activity but we also get all deposits forming as part of that cycle so there's a strong link between the dynamic magmatic processes the eruptive processes and the hydrothermal all forming processes so what we see is a porphyry intrusion linked to a strata volcano we would then get a cyclic eruption we'd start to move some of the the water vapor and the other fluids which would include the gases and things like chlorine so in this in the dissolved with sodium chloride salt solution those things can boil and they can they can form other types of deposit and then what we do is we form the porphyry deposit sort of sitting at the bottom of that volcano but then we also bring in the meteoric water I talk to you about the hot springs that perform at the edge because just like we get in the sea floor we get water permeating permeating down it gets heated up it can then bring minerals back up to the surface so it's quite a complex scenario there and some of these hot springs are pretty interesting they're very useful for geothermal power so this is why rocky a power station in New Zealand and very close to it is the champagne pool in the Rotorua district where we're getting active mineral precipitation and even more interesting is when the geothermal power station took her away they have to regularly clean their pipes because of pipe scale and the right scale in the geothermal pipes is very rich in gold and it contains up to 2% gold in the pipe scale so clear evidence that circulating hot water is also bringing metals and has the the ability to form all deposits okay I'm now going to move to the latter part of the talk we're going to talk about some very unusual atypical volcanoes so I'm going to talk about the volcanoes that are responsible for diamonds back in history diamonds are only known in the alluvial form until the 19th century so lots most of our diamonds would come from India so the you know the crown jewels diamonds a lot of those are coming from from the subcontinent and it was only in the sort of 19th century that was recognized that South Africa had good potential and so this is from the Orange River where they've got alluvial diamonds but it became pretty clear and if this was discovered by the British who found the Kimberley deposit in in South Africa that the diamonds were actually sitting on a rock a very unusual rock they called blue grounds and it turns out of course it's Kimberley which is a very unusual of volcanic rock and we know it take they sent the original sample to the Natural History Museum we have it where the diamond sitting on this kimberlite Rock because people work didn't believe that it was as a new type of volcanic rock people thought these are all in sediments but anyway this is proof and this was some recent drilling done in Canada where a diamond was found in a piece of drill core and you could see it visually so very very rare but we know that they come from this very specific type of volcanic rock very busy diagram but all it remains to be to say is that we know that these diamond diamond bearing kimberlites are only found in places where the crust is really old it's really cold and it's really thick and there's a reason for that and I'm going to come onto that so we find diamonds in South Africa West Africa parts of Russia a parts of South America in northern Canada and there in these areas we call cretons which date right back to the Archaean so they're more than 2.7 billion years old and there is a reason for that and this is a geophysical image of Africa and you can see this is what they call seismic tomography and it's telling us where the crust is very thick and very cold and that's shown in white so this is the deepest thickest oldest parts of crust on the earth and there was in the back in the 1960s it was recognized that only the you only got diamonds in kimberlites that had come through these oldest parts of the Earth's crust so it was an empirical relationship that was noticed in the 1960s and Clifford's rule fitted very nicely to the cat velcro song and and why is that well what we find is that now we can analyze inside the little inclusions that are found in diamonds and we reveal that diamonds actually can form up to 800 kilometers down in the Earth's mantle so diamonds as we know they're a form of pure carbon and they're only stable at very high pressures so they only form deep in the Earth's mantle and they're only stable depths below 150 kilometers so that means in order for them to be stable there has to be conditions where we've got very thick crust and thick cold mantle that will preserve those diamonds at depth and so this is just a diagram to show you that they more or less the golden part for the golden window for finding diamonds is between about 100 and 200 kilometers and that's telling us that that's where they form and that's where they're stable and these kimberlite Magma's so these kimberlite volcanoes are erupting from deeper than that and the studies of these kimberlites show us you only need to go and buy in latina soo to actually to find out me get the geology it's a beautiful stamp and it shows you that what we have with we have a definitely a volcano but it takes the form of what we call a dietary so it's a round structure and inside there we only have volcanic elastic we don't have any flows because this type of eruption is extremely dynamic it's full of gas and actually it breaks up long before it gets to the surface it's an incredibly erosive process and it rips up at supersonic speed through the crust from deep deep down it's coming from maybe 200 kilometers down and you imagine the pressure it's under down there 200 kilometers and it basically fight funnels its way or all the way through the crust and actually by the time it's coming up it's it doesn't really notice what it's coming through and it forms these round structures that are these so-called kimberlite pipes and this is some work that if steve sparks had been giving the talk he could tell you more about this because it's his paper but effectively there's some kind of explosive eruption that's coming up at hundreds of meters a second so that's pretty pretty fast then the whole thing becomes under-pressured and everything falls back in so it's almost like a you know it's a big explosion a rupture and then you get a fall back into the into the crater and then it's like fluid ice so you're getting vapor coming up from the bottom and all the rocks are getting turned around and and abraded and it must be a spectacular volcano when it erupts now the youngest kimberlite we know is about a hundred thousand years old so that's within human memory so if in Tanzania there would have been people living there so I have no idea what they would have thought when one of these erupted as far as we know they haven't stopped erupting they could happen again but would we get warning I don't think so so very very an unusual type of Europe but we get diamonds associated with them and that's that's a kimberlite there with the diamond actually on the on the matrix and so people understand more about these but they come they don't only come on their own they often come in clusters and so these vapors are coming up for very very deep source and are erupting and this is dear Katie mine in northern Canada and there's at least four different pipes occurring together here and it's only been discovered it's very difficult to explore in this part of Canada no rocks exposed but modern geophysical techniques were able to detect these and and so here's a Katty there's four of these pipes there like carrots and they've got different fasci so it's mostly pyroclastic so that means it's it's all Brett ciated and it's coming up as part of a pyroclastic flow and we don't have deep down we've got coherent kimberlite which is shown in red so that's really where it's a it's still a melt and we get a coherent deposit but in these northern Canadian deposits we find evidence of a tree of father actually carbonized tree fragments so these things were erupting up into forests and we're getting full back of of trees into the into the kimberlite Sur pipe okay so the final couple of minutes of my talk I'll talk about some volcanoes that we no longer see on the earth but we might see them elsewhere in planetary systems which can give us a lot of evidences for how they reforms back here on earth so these are things that are probably related to mantle plumes I mentioned those early on we don't we still really don't understand the mantle very well the kimberlites come from the mantle so big discussion as to how the kimberlites formed there very rich in carbon dioxide so we think if there are places where you get large accumulations of things like carbon dioxide which actually stimulate formation of a melt wants to come all the way up to the surface mantle plumes is where we're getting mantle convection it happens in deep earth and we form these hot spots and we get volcano volcano eruptions linked to those hot spots and if we go back into the Precambrian and i'm talking here about 2.7 billion years ago we find these kamati a cloud as I mentioned them to you and they're really hot lavas that erupted at the Earth's surface at about 1600 277 hundred degrees centigrade there's no way a melt could find its way to the surface about temperature now but back in the early Precambrian these melts were able to come to the surface and these eruptions were very magnesium-rich they've got quite sulfur rich and they're so hot that they have a viscosity close to water so these are very very runny lavas they're very hot lavas but are quite dense and so they channelized they form like rivers on the planet's surface and because of that they start to interact with the rock that they flow over and as a result they they they quench very quickly we get these very unusual textures which is called spinifex texture which is testament to a really hot melt quenching very quickly but the other thing that we get and we know this experimental is we get sulphide immiscibility so the sulphide in the melt wants to come out of the melts and form its own liquid and so we get something like oil separating from water and we get those little sulfide blebs separating from the silicate and they they capture all the metals that are in the melt and as a result of that we form sulfide and nickel and copper sulphide deposits and we know those from the Archaean in western australia around that those of you have ever been to calgary campbell the district's some very big nickel deposits there that are formed as a result of these types of lava but they don't exist at all on the Earth's surface today but the thing we do know is there are parts of the solar system where they probably are erupting so this is IO it's one of the moons of Jupiter and this is a thermal image of the surface of Io and they're kind of temperatures and the spectroscopy that we can do on these on these areas using things like the Hubble telescope tell us that these are erupting magnesium-rich lavas very very high temperatures and these are likely to be kamati ayat lavas so they they're forming in a very primitive planetary body elsewhere in the solar system so it's really interesting to study this because this might be one of the few places where we can start to unravel what happened on early Earth and in a similar vein another one of Jupiter's moons has got evidence for other volcanic activity we've got a the surface of Europa is an ice sheet that's crazed like this into sort of fractured surface and that's testament to probably there being a wet ocean a liquid ocean underneath that ice we know because it's so close to Jupiter it's going to be an active planet it's going to have a mantle and it's likely to have volcanoes and it's a sort of thing that we can see that texture that we saw on the surface in Arctic ice sheets like this one here so we've interpreted that to mean there's probably a liquid a liquid ocean underneath the surface of Io and in Europa sorry and in which case the likelihood is that there are volcanoes under submarine volcanoes and that's sort of speculated that there might be hydrothermal venting here so this is their cartoon they've already designed a probe that could go to Europa to go down and have a look for volcanoes and mineral deposits but why are they really interested well because we saw in the modern ocean we see unusual life-forms developed around those two thermal vents so the speculation is this is one of the sites that people want to go and study is this where life might have begun and there are some scientists who who think that these hydrothermal vents associated with volcanoes are where life began on earth okay I'm just going to end this is my last slide and I just really want to end with there are other planets that have volcanoes that are interesting to study venus has active volcanoes I haven't got time to talk about that and and what's going on on Mercury but obviously Mars is under the spotlight because we've got a few missions going there and one there at the moment and we know Mars has had some huge super volcanoes but what seems to have happened in in in Mars is it had a lot of volcanic activity and then it's kind of stopped and they've just put a seismic experiment on Mars which suggests it's tectonic ly a seismic there's no earthquakes and that the first slide I showed you was that our planet is very earthquake rich and this linked to the tectonic activity it links to the volcanic activity so dead volcanoes dead planet maybe so Mars is perhaps disappointing from one perspective but it is a place we can probably go and study what early volcanism looked like on our earth because Mars has almost been frozen in time and what people are hoping is it's kind of frozen in time when it had it's because it did have a liquid water on the surface it had a bigger atmosphere a more dense atmosphere we might be able to see what the early Earth look like as tektites we're just beginning to get going and I guess people are hoping that we'll see evidence of how life might have begun on Mars I think it's highly unlikely that there's any life still on Mars but we might find evidence for that sort of early early start okay so I just really want to sum up these are just some points from from the talk but just really to say that these volcanoes they're a menace station of a dynamic planet but there are also incredible factories for producing metals and minerals that are of interest for us to use I just really also want to point out how important water is for so many of the processes on the earth in fact the entire volume of the ocean gets circulated through the mid-ocean ridges every sort of five to six million years so you can see the amount of activity there and then a lot of that water gets recycled and we won't have arc volcanoes if we didn't have water so water is an intrinsic part of plate tectonics and it's an intrinsic part of the life on Earth and I think what we've seen for Mars is if we go there we might be able to understand more about that that sort of linkage so I'll leave it there but I'm more than happy to take any questions thank you very much [Applause] you

Channel: Gresham College

Views: 11,602

Rating: 4.7468352 out of 5

Keywords: Gresham, Gresham College, Education, Lecture, Public, London, Debate, Academia, Knowledge, natural history museum, volcanoes, mineral deposits, minerals, Natural environment, tectonic plates, fumaroles, diamond mine, Komatiites, Ekati mine, Kimberlite, Clifford’s Rule, Richard Herrington

Id: Swh2nF8Heh0

Length: 54min 20sec (3260 seconds)

Published: Wed May 01 2019