Spectacular Gem Crystals: Pegmatite Pocket Formation and Survival

my name is Mai sure if I could remind everyone to please mute your cellphone's if you haven't done so so it's my pleasure to introduce our speaker tonight Tom Campbell and Tom has been collecting minerals since he was 7 so it's been a couple of years he got his BS in geology from the University of Akron his master's and post-grad work at South Dakota School of Mines he then worked at the home state goldmine one of the most productive gold mines in the world currently he is the staff meteorologist for the Arkenstone and it sees some brochures up here they are one of the major sort of fine mineral dealers in the world Tom is also doing independent exploration consulting work for the gold mining industry is a passion for research and interest in granite pegmatite and specializes in their geology and mineralogy what you're going to hear about most of his mineral collection is the Vote it's a common and rare mineral species originating from lithium cesium tantalum type granitic pegmatites he is spent considerable time studying and appreciating brazilian pegmatite and he is on his own describe three new minerals and co described eight others which are new to science in addition he's the co-author of the second edition of the Cyclopedia minerals published numerous professional papers and in professional journals I urge all of you at the end of the talk if you haven't had a chance to look at the this table over here and over here if you feel that some of them have to remain in Jackson in your homes talk to Tom please work call me tomorrow please join me in welcoming Tom Campbell thanks for the introduction Mike and thank you for having me here and I do I appreciate the invitation and Melissa my wife and I were really we're looking forward to being here and Mike and Barb were gracious enough to take us on a wonderful hike today and we love Jackson Hole I've been here several times in the past and just a wonderful place and as far as my talk goes I gave you a little bit of an introduction yeah kind of like what Mike said so I love gold geology and that's pretty much what I do for a living and part of my career in recent years is transitioned into working for Rob Levinsky at the Arkenstone part-time and Melissa helps with that too and it's it's really it's kind of more of my passion it working for him and being able to study pegmatite sand I've studied pegmatite for just as long as I've studied gold deposit which is 30-some years and anyway so part of what I do for Rob just to give you an idea yeah I helped him with sales but the other thing I helped him with respect to mineral acquisitions and that might be maybe traveling to Europe to attend an auction you know maybe an auction house like in Paris or something might have someone's collection a prominent collection for sale so I'll go and represent Rob there and try to acquire specimens for Rob for the Arkenstone evaluating mineral collections and appraising them and then also helping him with shows like the the Munich show which is coming up in in Germany at the end of this month and then the Tucson show Denver show which just happened in September so those kind of trade shows and the other thing that I I do for him which I really enjoy which kind of takes care of a couple things for me is like going to Brazil and so when I go to Brazil I I've been doing that for about ten years both as part of part of my iron ore career which was several years that Melissa and I did which is where I made my initial contacts and then which transitioned into pegmatite s-- actually visiting the pegmatite stone there and making contacts there and so part of that too is visiting people that are now very good friends in Brazil they're good contacts for minerals and also visiting the mines that they own right so being able to evaluate pegmatite and you know that's something that's really different it's something that with a lot of you I know being geologists you know we didn't learn how to evaluate like gemstone bearing deposits you know when we were in college right at least I never did and so that's that's a specialty that I've kind of developed over the last several years so you know we can evaluate like oil and gas resources I can I can evaluate gold deposits and evaluating pegmatite for their gemstone or maybe there are other economic minerals that they might mine right so it's it's a it's a totally different game than like gold oil and gas LEDs name okay so just to give you a kind of a perspective in terms of what I do and how almost kind of specialized that kind of work is which I really enjoy so I'll tell you a little bit some of the stories on my travels to Brazil and whatnot during the course of this but yeah I love pegmatite and I love studying them and my talk tonight in and I like the way I'm not sure who it was they they did a better job on my title than I did they said spectacular gem crystal pocket formation and survival so that's what I should have done right yeah yeah real attention-getter so anyway that's what my presentation is on and see okay do I need to be close or yep oh so I'm doing the pointer well I know I'm doing that right okay so before I really get into it as a preface there are some questions that I thought I'd present and these are ones that I thought I'd try to answer through the course of this talk and number one what are granite pegmatite s' and how do they form what are the differences between a granite and it's related pegmatite what are some of the complex processes that form gem bearing pegmatite s-- how old are these gem pocket pegmatite and what are the minerals that occur in them especially the kind of gem crystals and then how common are pegmatite pockets and do the contents get preserved okay so let's start with kind of a general very general definition of a pegmatite a totally crystalline general generally very coarse-grained light-colored igneous rock derived from a parent granite composed mainly of quartz feldspar and mica and the pegmatite s-- they different composition from a granite by their enrichment in sodium lithium rubidium cesium boron fluorine o h and sometimes beryllium niobium tantalum and tin and to give you an idea the size of crystals in pegmatite this is a outcrop of pegmatite along a road cut in Keystone South Dakota and that's my wife for scale and she's seven feet tall now some of you have met her already and you know that's not true but anyway that the crystals big and no my wife isn't seven feet tall but the other thing to appreciate too is the largest crystals in any kind of a deposit are from pegmatite s-- okay so like at the ED of mine which actually isn't too far from this outcrop that we stopped at years ago there's spot Amin crystal layer that was 14 meters long from the Etta mine okay and the largest pegmatite crystal and actually the largest crystal in the world is from a pegmatite and that was from one in madagascar and it was a burl crystal that was 18 meters long we'll talk a little bit more about that later yeah so 18 meters so that's at least the probably about the length of this room the width of it so pegmatite supply some of the world's finest colored gemstones such as tourmaline topaz aquamarine and 40 other at least 40 other gem minerals and it's their sources of fabulous mineral specimens and crystals and you know that's that's part of this market that the Arkenstone and many other mineral dealers are in and so a good portion of their stock comes from pegmatite s-- okay around the world there are their host to a diverse suite of exotic minerals and they're the only source of many rare minerals and to give you an idea you know Mike talked about discovering three new minerals well one of them was tiptop bite and it's a rare and very complex sodium lithium beryllium phosphate hydrate and that's those little white sprays that are in that particular photograph here so it's these little white sheaves and then it's associated with Rocher right which is another beryllium phosphate hiroba tight another phosphate and it's on whitlock it-- not that these names mean anything to you they're they're very rare and kind of unusual but under the microscope these things are beautiful right and it's too bad they're not like ten times that size but anyway that was the focus a lot of my research but let me tell you a little bit about it because you hear about people you know describing new minerals or use you hear how that well you know 200 and some minerals were discovered last year right well you know and I'm just gonna very briefly tell you how it's done and in in that kind of the process so part of this at least at the the tip-top mine which is in Custer South Dakota it ended up being my master's thesis the work on it and what happened is that there was a old miner in the custer area who decided to go back into the tip-top mine which was mine previously four-barrel right as a source of beryllium and he pumped it out went back in started mining in one part of the pegmatite and you know I I was a grad student then I was running around to pegmatite looking at minerals and seen if there was anything new and interesting right so so I'd stop by and see Vern and see if you had anything new and different that he was uncovering here other than the cool big giant Beryl crystals and it turns out that there were these fractures in the Beryl and in the feldspar and yeah they had these colorful associations in their right and I didn't know what they were and so my my advisor and friend and mentor bill Roberts I don't know if you've ever heard of him or ever got a chance to meet a wonderful man but he he's the one that invited me to work on the encyclopedia with him revision and anyway I I was collecting this material and brought it back to him we we started looking at it under the microscope okay so that's first step and we're trying to identify these things and some things yeah you know it looks like it could be the red things you know yeah looks like could be Rocha right root mineral the white spheres no idea then these you know we were thinking well maybe it's this phosphate maybe it's that one but it doesn't look right and so you know we've got all of our guesses and we're writing descriptions of them and then so the next step is to try to characterize them chemically right and and by even by optical properties and so the optical portion was my forte and I also did a bit of analytical work and so I I did some atomic absorption spectroscopy on these and the the process because you're dealing with very small amounts of material right so they're really kind of micro analyses and so I determined you know like the beryllium lithium and and the phosphate anion and the other part then to is to at least do as much as we could at the School of Mines was to do the optics on it so determine the optical properties of it and just to give you an idea how complex this is I don't know if you any of you have ever heard of this this geologists but you know we've done refractive indices in lab and we've looked at things in thin section and even grain mounts immersion mounts and immersion oils right so there's this method and Bill happen to have this tiny level apparatus called add a taut spindle stage okay so it's almost like a protractor that's bent up and it has almost like a a paperclip running through it okay and it has little angles on there you know marked out on the protractor part of it and you actually get this you you glue one of these two or three millimeter crystals on to the end of this part of the paperclip right and you put it in different refractive index oils until you determine the refractive indices right and so in this case you know we had to do that several times and it's a it was kind of a painstaking thing but it was kind of fun I won't lie and then you've got the the optical properties we had a little bit of initial chemistry and then that's about all we could do right there at the South Dakota School of Mines so contacted Pete Dunn at the Smithsonian and then other scientists like it Canadian National Museum right hey guys you know we've got this these new minerals we've done this much and we can't do anymore you want to help us out right so that's the that's the process so rarely does just one person ever work on a new mineral right it's usually a team of people and they have their areas of specialization you know for the analytical methods so that's what we did and then you end up characterizing it and then you end up publishing on it right and you name it and you can't name it after yourself okay so you have to name it like in this case tip but it was for the mine the tip-top mind pegmatite right and then the other one one other one was paja sabha which is the lakota term for the black hills pasa okay and the other one France away I was someone that I met a day and befriended at a pegmatite conference on during that few France la from the University of liège in Belgium and and his specialization was on primary phosphate minerals and pegmatite so we honored him by naming that mineral after him so that's how that that process goes you know for finding and characterizing these new minerals so that's it's kind of a fun and complex process ok so back to the pegmatite part so they're mine for economic concentrations of rare elements so that would be like the tantalum niobium tin beryllium lithium okay not so much anymore mainly because there's different deposit types other than pegmatite so that are larger volume maybe lower grade that they they can lie but they still do and the other part of it is gem rough and in mineral specimens like these right so part of this process and this is the this is the economic economic geology part of this really is that okay these guys are mining these pegmatite say in Brazil and they're they actually do what they used to do 50 60 70 years ago they stockpile concentrate of certain minerals like the niobium Cannell minerals will go into one pile big black pile right because that's what most of them are they're just kind of black sort of ugly minerals I appreciate them but anyway and then like the lithium so it may be big spa do you mean crystals and then the giant Beryl crystals so they'll they'll sort those out and then if they're lucky if it's a gem bearing pegmatite they'll have pockets right that encounter during the course of mining and maybe they find nice spot I mean crystals in these pockets or tourmaline crystals like that are over here right and aquamarines and whatnot and so that's the other part of the economics for them and so they have the material that can be processed for the the raw material that it is and then they have the the gem bearing material that they can use as and sell as specimens or sell it as rough for gemstones right so that's how this is not just in Brazil this is anywhere that has pegmatite mining so in Brazil South Africa Namibia Pakistan Afghanistan Ukraine anywhere that you have these gem bearing pegmatite s-- as far as the chemical composition of them they're very similar to Granite's they tend to have a higher aluminum content lower calcium content the miura lytic and rare element pegmatite s-- again are often enriched in sodium lithium rubidium cesium beryllium boron fluorine hydroxyl and phosphorus again which are important for gem minerals and economic mining and is something that we'll find out later on some of these rare elements are are concentrated during the fractionation process and during that process they actually when they're in the fluids still are in the melt they change the properties of the melt and that that fluid and we'll talk about that give you an idea okay so I collect rare and unusual echt the pretty you know the aquamarines tourmaline and everything but I also very much appreciate some of the rare minerals and this happens to be a really nice Pulu site crystal and so I don't expect everybody to know what that is but it's essentially a cesium bearing an LC okay which a announcing as a zeolite that you might be familiar with but this is has cesium in place of the the sodium or calcium so this relationship to two Granite's the pegmatite scan be direct products of igneous fractionation from s-type granite so they're the ones that are derived from melting of previous sedimentary rocks that have been metamorphosed and melted and they're the offspring of these granite pegmatite s' and this gives you an idea of what the texture of pegmatite is very coarse-grained this has microcline quartz a little bit of biotite in it and some elbaite and the depth that these pegmatite form are anywhere way below even ten kilometers so maybe 11 12 kilometers up to near this near surface and those are the ones that were going to be interested in as I'll keep talking about here so these two diagrams they're pretty classic Peter journey who was a good friend of mine was a specialist in pegmatite at the University of Manitoba in Winnipeg and so he he he went to a lot of pegmatite fields and he mapped the relationship of pegmatite s-- to the the parent granite and what he found out was that doesn't matter really how you slice it whether you do this in plan view or in cross-section which this happens to be to the zoning starts from the the parent granite here and you get essentially barren but coarse-grained pegmatite s-- either within the granite or the metamorphic rocks essentially adjacent to it and then you grade out into those that are that have barrel so they're beryllium bearing or those that have beryllium niobium tantalum and then you might add lithium and then the channeled niobium beryllium and then all the way up to to cesium so those are the ones that are more fractionated and I'll talk about that a little bit more detail but this gives you an idea in like in the Black Hills I'll give you that as an example because it's close and that's something that's kind of near and dear to my heart the the Black Hills pegmatite surround the Harney Peak granite are very classic in this regard you look at it planned view you have the Harney Peak granite in the center and you have these pegmatite s-- that are found in essentially the metamorphic rocks around it and it is it's zoned just like this you just have to you just have to slice it in plan view and that's what you get you get the distribution of these pegmatite Slatterly out away from the Harney Peak and that's the way it is in most places you go to Brazil Pakistan the the relationships are very similar [Music] biotite muscovite granite so this is a this is something that's a little bit more specific so this is the zoning within the granite itself so it might be a biotite granite at depth bio type muscovite muscovite granite and then more of a peg matific granite up here so here the the grain size you know it might be you know average centimeters in size whereas you get up into here you're talking meters in size of the crystals right you know it is a little bit yes because this material would be a little more dense and this would be less so and that is part of the the process that I'll get into about the emplacement of these yeah yep that's right now so we kind of talked about this so the simple pegmatite s-- our proximal to the granite whereas the the fractionated the volatile barring pegmatite SAR a little more distal which we saw in that last diagram and the rare element pegmatite Syncrude the country rock around the pegmatite and you know this is the evidence for the the link between the pegmatite and that parent granite is is supported by the geochemistry okay which we've kind of talked about age-dating so in most cases you date the granite say example the Harney Peak granite it's one point seven to about billion years old in the the pegmatite s-- that are surrounding the Harney Peak in the metamorphic rocks are just slightly younger than that right so you can use age dating and then you can use fluid inclusion work on the various minerals to to determine the the chemical the micro chemical link between the granite and the pegmatite as far as size and shape no the pegmatite they're very they're variable you can find pegmatite that might be the width of one of these tables and it might extend for 100 meters and you know at depth it might go for another hundred meters whereas other ones are probably the size of this library right and i'm going to give you an example of a pretty spectacular one here in a minute so the the factors that affect the size and shape though are the depth that the pegmatite s-- are emplaced okay the structures of the host rock the structure of the host rock so they tend to follow if it's metamorphic rocks and it's foliated they tend to follow foliation maybe shear zones or fracture zones within the metamorphic s-- okay and then also the differences in with a static versus hydrostatic pressure so what that is so the lithostatic pressure is that load of all the rock above this say this particular pegmatite and the hydrostatic pressure is the pressure that that pegmatite has on its own because it has a certain amount of all littles in it and it has a certain amount of pressure in it itself that hydrostatic pressure that helps it muscle its way into those metamorphic rocks so if that pressure is higher than the lithostatic pressure it will make its way upward and the fact like john was alluding to the it's almost a buoyancy thing to write the pegmatite generally are being emplaced into rocks well they're much lighter the pegmatite sar much lighter and at less dense and they're getting in place and into rocks that are more dense right so there's that oyon c factor so they can rise into those rocks with a higher density and as far as shapes they can be elongate dyke like bodies dike complexes big bulbous masses inverted teardrop shapes and these giant sheets too and to give you an example i put a little time in at the tanco pegmatite at ver Nick Lake Manitoba years ago and to give you an idea of how how big this pegmatite is is one of largest pegmatite s-- in the world it's 1,400 meters long okay 1400 meters long it's 600 meters wide in a hundred meters thick it's huge right and it has been mined for probably close to 40 years now and life of mine is probably another thirty at least and it's been a major source of cesium for the for the mineral industry right and so I'll go back to that one mineral specimen I showed you earlier the the Palouse site that's what a lot of its in so yeah it's huge and then another example this is the Helen Burrell pegmatite in Custer South Dakota and this is really cool because it it really is the exterior the pegmatite here so this is essentially the wall zone that's exposed on the surface and then you have the the intermediate zones but then the inner intermediate zone in the core mined out because that's where all the spa demeaned and the panel of niobium minerals were okay and then again here for scale I have my 7-foot wife there for scale and that's my my son who he was anomalous in size to he was he's 7 years old and he was 4 feet tall yeah okay sorry but gives you an idea okay so how do you classify pegmatite yet you can do it on chemistry but when you're out in the field when you're down in Brazil or you're in the Black Hills and say it was the early days and you come across a pegmatite or a series of pegmatite s' you know you don't have access to do the chemistry right then and there right so you can determine the mineralogy of each one which helps and then the other part too is with the mineralogy is is the textures and so if you come across pegmatite s-- that have absolutely no pockets and all of the pegmatite sin that area don't have any pockets you can definitely assume that they have been in place relatively deep into the crust so we're talking probably say 7 to 11 kilometers at depth so you don't have any pockets at that depth so it's kind of like well I'll make an analogy here in a minute but and then as you go shallower in the crust with more complex pegmatite so you see the the mineralogy here getting pretty complex with the the lithium pegmatite sand those that contain Beryl spudgy mean maybe more albeit and bligg innate and other minerals and then even closer to the surface you get these Neolithic pegmatite the ones that have pockets and they have topaz Beryl spotty mean petal light lepidolite and so and these are the ones we're interested in especially with respect to the minerals over there okay so the classification is a depth classification and a chemistry classification essentially and that's what they they use now and so there was a fellow by the name of Ginsburg in in Russia and an Peter journey and then in recently years it was Dave London and skip Simmons and they keep refining the classification based on a little bit more detailed chemistry okay so as far as depth you know and if you're a mineral collector you know do we do we want this or would you prefer that I'm going with the one on the right okay so as far as the incompatible elements go and we've talked a little bit about some of these you know like cesium and there's a couple groups here that we can talk about the large I and with a file elements that they call lilies and so this includes cesium rubidium barium lead and strontium and the ones we're mostly concerned with in pegmatite is the cesium and rubidium and the high field strength elements which include tantalum niobium phosphorus zirconium for the most part for the pegmatite so we're talking about and the neat thing about it and I don't have visual aids for this but the cesium and rubidium you know they're their atomic size their atomic radii you know it would be like having a basketball okay and it's very large and a plus one charge okay then you have the high field strength elements like Tanel naio being phosphorus or cone IAM and even uranium they're tiny so it'd be like a golf ball essentially okay and very high charge plus five plus four right well those elements don't easily fit into the structure of common rock forming minerals right like like the feldspars or quartz or mikeís right there's a little bit of substitution but they're there they don't form their own minerals with respect to the common rock forming minerals so and even the Pegman peg mattify elements like lithium beryllium and boron so what they do they form their own minerals so they don't substitute they have limited substitution but they form their own minerals like the like the barrels and the the spudger means and tantalite and column bite and that's what's responsible for the unique mineralogy and this is a specimen of wood a knight that I have in my collection from Brazil and so look at the chemistry of this this is the formula so it's a manganese tin tantalum oxide pretty bizarre right and forms its own mineral sorry I had to throw this in there so this whole thing it is it's like a pigma tight soup right you have a lot of the the common rock forming elements as part of it you have silicon aluminum oxygen and potassium sodium and then you throw in all those oddball elements like cesium lithium beryllium barium boron tantalum right and you just really mix things up in this pegmatite soup and you end up forming these gorgeous minerals that are very unusual and like here this is a stiviano light with lb8 tourmaline and some albeit and my wife melissa specializes in garnet and this is a garnet specimen from Brazil it's special team Almondine and some aquamarine from Iran NGO and tourmaline from the mall kam pegmatite it's in Russia so in this chart I'm not going to go through the whole thing but it gives you an idea of the complexity of the the mineralogy in these rare element pegmatite and the the pegmatite so that can have these pockets right then we are oolitic pigma tights and so not only do you have the unusual chemistry that makes these minerals right like Beryl is a beryllium aluminum silicate tourmaline is is a complex lithium aluminum silicate borosilicate and the neat thing about it is you might have just trace amounts of say manganese in tourmaline or in Beryl to give it a pink color right so that trace amount of manganese makes these beautiful colors in the minerals and I've got a neat piece a morganite barrel over there and that's the pink variety and then the pink portions of the tourmaline so there's pink caps on a couple of the tourmaline x' over here it's because of the manganese right just a little bit of manganese in it and then a little bit of fe 2 plus gives tourmaline the green color so like the bicolor tourmaline as you see so it's a kind of a competition for iron and manganese and I'm not going to go get really excited about this stuff so sorry but so maybe during the development of a couple of those tourmaline crystals over there it's green for most of its growth right so there's more iron when that iron gets depleted and maybe there's a little bit of manganese left at the end and no more iron and that's what gives you the pink caps right so just really neat things that happen in a pocket a pegmatite pocket as far as the chemistry goes so there's a bunch of other gem bearing and unusual pegmatite minerals on the site here like Brazil unite Chris a barrel dan berate Hamburg eight pedal light and FINA kite several others just to give you an idea the complexity mineral complexity so this is the diagram that's really good for showing the magnitude of concentration and the fractionation between a parent granite and the pegmatite and i'm not going to talk about this when this is mostly the source area here but i'll let you look at those numbers if you want but what i'm going to focus on this is the the parent granite here that come coming off of this source area and we'll focus on the lithium cesium beryllium boron concentration that's in this parent granite lithium is at 57 parts per million cesium for beryllium for boron 30 and you look over here and this is in the fractionation process so what happens is that these elements along with some other of the oddballs we've talked about they like going into that this vapor phase that has water and a more buoyant melt okay and so as we'll find out later these melts can have up to 12 percent water in them okay and so these elements like that part of the melt they like that vapor rich portion and they get fractionated into it and so you get these concentrations like you see here lithium goes from 57 parts per million up to three thousand 450 parts per million same with cesium to go from four to 2600 beryllium for 270 boron 30 to 215 and that's why you can get spa amine forming in it Orpah lucite or barrel or tourmaline okay it's because those elements are fractionated into that part of the the pegmatite melt and so this is what happens so you have this volatile enrichment that includes these ok I'm not gonna read them off but this is the cool thing so this these are this is essentially what happens due to the volatile x' that are present in this melt so it and I'm not going to read these in order just because it comes from Simmons Adele and what I like to do is start so from the kind of the middle there where it says decreases nucleation rates so what happens is whether it's the pegmatite or you're in a pocket right the these volatile x' what they do is they reduce the number of places say tourmaline for example will form so instead of having a pocket where you have tourmaline crystals growing all over at little ones you have only specific sites where maybe a tourmaline or maybe an aquamarine crystal will grow instead of instead of say thousands of potential sites you only have dozens ok and so that's part of it so it decreases the nucleation rates and it also decreases the temperature at which these minerals will crystallize that's at solidus temperature right and then it decreases the viscosity so no longer do you have this super thick melt it's instead of being like molasses it's more like maple syrup the consistency okay and what that also does it decreases the polymerization so instead of having real complex chains within this volatile melt it really simplifies it so that diffusion can increase so if you have like boron atoms that are trying to make this tourmaline it makes it easy for boron to get to these limited number of sites right and whether it's in a pocket or if it's in the pegmatite it enables these crystals not only to grow large within the pegmatite because there's a limited number of nucleation sites right if it's in a pocket it also enables them to grow large in the pocket but also Jimmie right because they're looking they're growing in this restricted pocket with its fluid filled with a specific chemistry and that's how you get those beautiful crystals forming in there right and you don't have when you look at a pocket I'll show you a picture here in a little bit you don't have like I said thousands of aquamarines or tourmaline is growing and they're very limited number okay so that's what the role of volatile does yeah this is cool this is a old picture from the bumpass quarry in Albany Maine and these are giant baroque crystals so and this was this was not uncommon back in the day when they were mining right so whether it was in the Black Hills whether it was the New England pegmatite where the ones in Madagascar the other giant crystals and so they would mine these crystals and they would send these chunks of giant barrel crystals or spa Janene crystals off to be processed right for as a source of lithium or beryllium right and here again I'm going to talk about that barrel from Madagascar okay we said it was 18 meters in length it was three-and-a-half meters in diameter a diameter right and it weighed 419 tons right okay largest crystal of any kind ever reported so this is kind of a summary so the role of volatiles they dissolved from the melt by fractional crystallization the melt can contain up to 12% water they lower the point at which minerals can crystallize they're responsible for producing gem bearing primary pockets mineral attic cavities and these giant crystals and they're also sort of unfortunately responsible for the corrosion and alteration of primary pockets in their minerals so what I mean by that is so if you have like a crystal of a barrel and you're welcome to come up and look at these these pieces I have over here you can handle all you want these are all examples that I bring around when I I do talks on pegmatite sand there's there's some cool pieces here but so sometimes if you have a barrel crystal forming in a pocket and maybe the pocket ruptures there's a fracture and you have these other hydrothermal fluids coming from elsewhere in the pegmatite come in it will actually alter the the crystals that are in there the previously formed crystals which isn't a good thing because that means you take a pocket filled with these gem crystals and you bring this other fluid in and it will either itch them or alter them and now I'll tell you how that's done and yes this was a segue over to me getting uh getting my water okay so as far as rates of crystallization you know most of us when we were in college we were taught that pegmatite so you know they have this coarse grain size because they took so long to form you know millions of years to to crystallize right that's the way you got these giant crystals right that's that's what I was taught back in the day so it's interesting so within the last decade people like Karen Webber skip Simmons David London they've been looking at pegmatite Segen and they're finding out that the rates of crystallization are much faster than anybody anticipated so they're doing these extensive studies whether it's fluid inclusion work or some of it is kind of common sensical but what they're finding is some of these pegmatite form in the smaller ones days to months and then some of the larger month larger ones maybe decades to hundreds of years okay so it's not the millions of years that we're thinking of maybe in the case of a giant pegmatite like the tanco pegmatite maybe that's thousands of years we don't really know yet but my guess is those guys will probably be working on that at some point too right and the other thing that makes sense is that thin dykes cool faster than the the big bulbous masses right you know the the dike complexes and like the Himalaya pegmatite in California you know they're just you know a few meters to several meters thick and it kind of makes sense there's something like that if it's intruded into the surrounding host Rock which is much cooler it's not going to take thousands of years for that to cool right and when we're talking about those nucleation rates and the viscosity and everything that actually promotes quick crystal growth and you know the dikes probably didn't take as long as we used to think they did to form right so just something kind of interesting that I i thought you´d it's different departure from what we've learned so pegmatite anatomy the simple pegmatite s-- there unsewn generally not very economic consist of feldspar quartz muscovite and they pretty much have like uniform composition and texture right so there's no zoning so it's it's mostly just feldspars quartz and Micah's and the reason I say sub economic is because sometimes those were actually mined for ceramics right you know the feldspars they've mined that the potassium feldspar for ceramics back in the day or like isinglass big sheets of mica to put in the the Front's of the old furnaces and wood-burning stoves and whatnot okay so most of the shallow through intermediate depth pegmatite s-- they do have some kind of internal structure and these internal structures they're subdivided into zones replacement bodies and fracture filling units and this diagram to the right shows the zoning pretty good so you have the border zone which is really essentially the contact with the country rock so it's usually very fine-grained and then you have the wall zone which is just inside that also you know could be variably the grain size could be variable and then you have the intermediate zone but you can have multiple intermediate zones and then you have the core right in the center which a lot of times that's where then I'll get into this that's right at the core intermediate zone margin that's often where you find these pockets in the shallow pegmatite and it's also where you find sometimes find these giant spod Jimena and Beryl crystals - okay the zones they're incomplete to complete concentric shells okay so they don't have to be perfectly concentric like you show like I've shown here you know the the wall zone usually is and then the border zone and the intermediate zones yeah they might be continuous but sometimes not and then these are the fracture filling units here and then the replacement bodies there is just as a diagram so the interesting thing here is that each of these have each of these zones has a specific mineralogy and when these pegmatite s-- they crystallize from the outside in and when that starts happening the the core or the pegmatite may be part of the intermediate zone it might still be kind of a melt or crystal mush right and as that pegmatite schooling like a lot of things when it cools it reduces in size and you get these cooling fractures developed and you might end up getting material that was in the core intermediate zone squirted into a fracture that transects the whole intermediate zone and maybe out into the the wall zone okay so you have something with a distinct mineralogy that is totally different from the host zone it's in right and that's also a place where by the way where you can find jump crystals okay so complex pegmatite s-- there's owned have fracture filling your replacement units they're the ones that have the elevated concentrations of those elements they're foreign from highly evolved all over rich melts the produce pockets lined with these gorgeous gem crystals okay and these are a couple of really good diagrams but the me are oolitic pegmatite s-- the ones that have the the nice pockets they form between about less than a kilometer and a half to three and a half kilometers that's that's the sweet spot that's the the depth we like for these pocket pegmatite s-- and their have their characterized by having pockets or cavities that have gem crystals pods of pegmatite or pegmatite dikes that are located in the upper parts apparent Granite's in the adjacent host rocks so that's the way it is in the himalaya system in california cavities can contain crystals of quartz Beryl tourmaline topaz along with felts bars Lyra silicates and other minerals and these are this is pretty good little schematic where you have essentially a graphic granite very coarse-grained more of a pegmatite at graphic texture and then you have the the open space in here where you get these tourmaline x' and big quartz crystals and other mineral species forming so their mineralogy and i'll try to run through this pretty quickly silicates phosphates and oxides they're the most abundant mineral groups most common silicates include quartz microcline feldspar albeit and muscovite and then you can also get spa Janene Beryl topaz tourmaline and and garnet common in some of these gem magnetites this is these are some examples of the silicates so on the left side my wife has graciously let me photograph her one specimen of cool specimen of spessart een garnet with albite from Pakistan on the right hand side again another one of these oddball minerals petal light which is actually a lot like spa Jeanine it's a lithium aluminum silicate and it is also in or of of lithium in some pegmatite and then in the middle this is actually a pretty spectacular specimen that Rob had and subsequently sold from Brazil and you know I never did get the dimensions on this thing so I just said it's big right sorry um but yeah it was it was this tall and it was it's almost like a polychromatic snowman right with the big albeit base and then a huge it was a huge Elba 8 crystal top on there a really neat piece and then of course you get barrel on the left and this is the the green or yellow green variety Helia door and then aquamarine crystal from Brazil and this is sorry this one's from the Ukraine and that's from Brazil and then the one on the right it's a topaz beautiful topaz crystal front on albeit from Pakistan and then the oxides on the left here we have consider 8 which is a tin oxide on albeit on the right actually this was this is kind of cool neat little sorry little story here I got this on my last trip to Brazil and so this is another one of those cases where I know this family and I actually got to go in and actually map part of this pegmatite the Itachi pegmatite and he needed me to try to figure out the continuity of this zone that carried these Wojo night crystals because again that's part of his economics right yeah the gem crystals it also produces these beautiful tabular aquamarine crystals but this is part of his economics too he needed to try to find the extension of this whoa tonight zone so that he could mine that and use that material stockpile for tantalum or right okay so and that's one of the pieces he had and so I you know sorry I kind of like some of these black ugly minerals that come from pegmatite stew so I bought it you know so anyway interesting little story and then a Chris a burl a six-link twin here in the middle I think those are fantastic that's a beryllium aluminum oxide and then here we have the some phosphate minerals on the Left this is floor appetite on albeit with a little bit of elbow a tourmaline and then on the right this is a gem mana brass site crystal which is about six centimeters really cool then the halides and borates yeah you can find fluorite in a pegmatite and this one's from stock Nala and it's associated with some sure all tourmaline crystals and on the right I don't expect any of you to you know what sometimes I I bring incentives like candy to these things and I ask people what the formulas are I should have done that I'm sorry so anyway I'm gonna ask you anybody know what either be here right or given a toe itis if anybody does yeah I'll tell you what this is my incentive oh boy and don't look at your phones I'll give you ten dollars if you can tell me what either one of those is the formula okay sorry times up so Becky right is a tantalum borate and ski event at oh right is a niobium bori two really rare minerals okay so yeah there's just super unusual things that that form in these pegmatite and yeah you're not gonna believe this okay you know we hear about zeolite you know the ones that come from India or the ones from here whether it's in Wyoming or like up in Yellowstone there's a Z light occurrences up at Yellowstone right and there's if you go to Golden Colorado North and South Table Mountain there's great Z light occurrences there there's some in Washington right and you know you think about those being associated with these lava flows or whatever especially elected to contracts and in India they can form in pegmatite stew and you know it kind of makes sense because why not there are sodium calcium potassium along with other cations bearing aluminosilicates and they just contain water right in their structure so you can find zeolite sand pegmatite s-- and even though unusual and this piece here that we have it's a spa I mean crystal with a little bit of El bite and a big ball of still bite and this one's kind of cool too it's kind of just one of those white minerals but you have fuel indict with bhava Knight which is a beryllium aluminum silicate okay so you have these gem pockets and what happens is you have this residual melt that accumulates and a low-density volatile rich fluid solves that's rich in rare elements and like I already said the pegmatite crystallized from the wall to the core okay and the primary pockets are one of the last features to form during the crystallization of these and they're the ones that containing these beautiful gem minerals right well and this is the interesting thing so yeah I'm talking about this stuff but the size of these pockets sorry I tend to talk too much but anyway the size of the pockets they can be they can be this big or they can be the size of that screen or larger right in diameter right you can walk into them and so that's how spectacular they can be and how large and generally they're found at the intermediate zone core margin they were abundant in the shallow pegmatite but essentially absent in the deeper higher pressure zones of the crust and this is just another schematic of a gem pocket and a lot of times the gem crystals can be preserved in clay in Pocket clay and this can come from two sources so as the crystals form within the pocket you know you get this residual fluid that keeps getting depleted in all of these elements that form like the tourmaline x' or the barrels or whatever the the feldspars right and you just don't have much left in the fluid you have all that material all those elements taken out and all it is you end up getting or precipitating like a mantra Lynette clay there's nothing left right so you just crystallized this kind of a massive gooey clay in the center and that can also happen the second way that can also happen during pocket rupture where you get those hydrothermal fluids come in they break up the crystals and then kind of the same thing you you just deplete the pocket in that material and you just get a clay pocket that's formed that comes in later okay pockets are most common in complex pegmatite but are rare pocket bearing pegmatite that may be pervasive in some pegmatite regions like Brazil Pakistan Afghanistan the midea Ukraine Southern California New England they're still rare okay pockets containing gem tourmaline crystals aquamarine kunzite topaz like the pieces I have over or even more rare you see where I'm going with this pockets are rare in pockets containing preserved gem crystals are a miracle really it it really is and this is a really cool diagram that Wendell Wilson I don't know if any of you get the mineral electrical record but this is a he's a great artist and what he did for this diagram on the left is he took all the information he could from the the Jonas pegmatite pocket and tried to put this together based on history which included not only written history but oral history from some of the people that mined it and owned it and put this together and remember when I was telling you about limited nucleation sites and all those things that volatiles do this is a great example you can see that okay here was a nucleation site for for these big crystals right very limited number it's it's not like the term aleene's were all over they were very specific sites where those tourmaline 's grew and they grew huge and they grew beautiful the tourmaline 's from this pocket were essentially a cranberry color right very unique very gorgeous yeah yep yeah quartz and then this is albeit here sorry yep that's quartz those are quartz but a lot of albeit and maybe some microcline but yeah so the occurrence of gem crystals pocket distribution is erratic right I'm not going to say that when you're mining a pegmatite you know where these pockets are you don't right and so like when these Brazilians which is they're usually family operations for the most part right and they hire a few people they don't know where these pockets are going to occur so they have to mine with keeping the the economic minerals in mind you know like the Tanel niobium minerals the massive barrel spa Jimena and whatnot right and if they happen to hit a pocket that's just a bonus huge bonus for them right but let me tell you this is a sorry another short story so what happens is that some of these families they know how to mine out these pockets are very careful right so they'll take months maybe to mine out this pocket other people other families that maybe aren't so experienced and this is what happened one time when I went down there this dealer gets a call from one of these families says we just hit this pocket it's got all these crystals not all of them are on matrix but we think we can reconstruct them and that's what happens sometimes they do they have to reconstruct some of these but can you send somebody down to evaluate it so I get this phone call Tom can you go to Brazil can you check this out for us and evaluate this claim right and this pocket so I go down there I fly down there great people you know nice family they did have some interesting minerals that we ended up buying and then they ended up sending me out to their their pegmatite kind of out in the boonies right and then I've got a picture of it later but I end up going down on this little electric winch sitting on a log right and going down about a hundred feet and it's about six by six and you go down there and we get down there and it's great you know the great-looking pegmatite they take me over to this place where the pocket was well where the pocket is was and this is where the pocket well this is where we got all these great tourmaline oh okay and you took your time getting them out right well you know we we used a shovel and we used a rake and I just went oh okay and so they take me up we go back to the house and no kidding they had three buckets huge buckets of tourmaline pieces one bucket had all the terminations the nice tips another bucket there were pieces that were a little smaller that were they thought were the middle sections of the crystal then they had another bucket that they thought was the end and then they had all these chunks of rock out here that they thought all of these things was going to be a giant jigsaw puzzle and they were going to be able to put him back onto this matrix right and that's when I had to tell him you know I'm sorry you know it can't be done right and you know it's it's one of those things where it really takes someone with skill and it's an art to be able to extract these crystals out of a pocket like that right because and this is what I told them you know I told them you know as far as gem ruff yeah they might have had a half a million dollars worth of material there right but what I told them was if you would have taken your time and extracted this I said you probably would have had about 10 million dollars and you see the jaws drop right but you know it's an important lesson for them right because next time they're gonna call somebody ahead of time and say hey we hit this pocket what do we do right well it's using diamond chain saws and and being very careful in the extraction process okay so that's part of it as far as the pocket shape and then the mineralogy of one pocket to another may be variable so like the you might run into a pocket say over there where that table is and it might have a certain mineralogy and then you might end up running into a pocket right next door that has a totally different mineralogy maybe that one has tourmaline and feldspar like case bar and albeit in it and this one might have aquamarine and Shore all crystals in it right so real variable mineralogy and so in larger pegmatite s-- the pockets are usually found between that intermediate zone and core area more Dyke like bodies it's in what's known as kind of a a pocket line right in the center of the Dyke like in the himalaya system and these are the pockets are dominated by fells bars courts Mica's and they're the ones that are rooted in the the base of the pocket and then you get the the tourmaline and aqua Marines and other topaz growing out generally on top of those the courts and the feldspars and they like that open space and like I said and as we saw in that one diagram the crystals aren't distributed uniformly within those pockets yeah this is a awesome pegmatite specimen from a friend of mine carl warning on the right from stock Nala and can you imagine so this was another one of those pockets where it was a few meters in diameter and had a limited number of these beautiful polychrome tourmaline in it right and so it was this particular pocket had only a limited number of really good pieces in it but that gives you an indication and then this diagram on the left again kind of shows the relationship here you got big feldspar crystals a giant burl crystal here quartz crystals tourmaline 's growing into the the cavity and then other tourmaline quartz crystals that might might have been later as in just really formed as floaters or maybe formed as part of that pocket rupture process it actually almost whatever you wanted John really I mean you could you could make it you know that say this feldspar crystal here that could be maybe half a meter or maybe it's a meter right but it gives you a kind of an indication of what these pockets might look like reconstructed so again I and I'll just go to this real quickly you know the demise of these gem crystals so when you have a pocket that has these gem crystals like an aquamarine and it gets ruptured during the course of the pegmatite cooling process or some other process going on in the pegmatite maybe that Beryl crystal kind of like at the tip top gets attacked by fluids of a certain chemistry and you end up forming a lot of these secondary minerals like Bertrand ityou clays FINA kite okay and that those might form at a certain pH and might be buffered by certain things so this is how you form these secondary minerals after a pocket ruptures in those late stage fluids attack a barrel crystal and that can go for spa demean or any other of these minerals and here's a good example like on the left it's a elbaite crystal it used to be an el badi tourmaline crystal that's been totally replaced by the lepidolite and it's because of that late stage process right and then on the right it's a Barilla night crystal that big white snowflake on a doubly terminated hydroxyl herder 8 crystal well these are both beryllium bearing minerals and they formed as an alteration product of Beryl right when these late-stage fluids come in an altar or Beryl crystal so as far as the pocket condition summary must have enough volatile zand favorable pressure conditions of all levels promote diffusion limit nucleation sites resulting in the larger well form crystals crystals grow into the open space you have complex fluid chemistry and complex para Genesis especially during pocket formation pocket rupture my internal pegmatite adjustments or maybe tectonic movements might have mixed effects as we talked about and then clay filling may preserve or protect the pocket give you an idea of Ages of some of these pegmatite s-- that have pockets so in general granted pegmatite range in age between about less than thirty five million years and up to about 3.5 billion years so the Afghani pakistani pegmatite s-- about thirty five million years so my pointer won't work over there but there's a really cool pakistani aquamarine over there and also a really nice elbaite tourmaline so they are thirty-five about thirty five million years old okay okay and another example there's a tourmaline crystal that's laying flat on the table up there from pala so that's from california that's about a hundred million years old okay the pegmatite from the iran go region in namibia about a hundred and thirty million the chinese pegmatite s-- in the Altai region about two hundred and twenty the Brazilian pegmatite in general average about five hundred million years old so a lot of the examples that I have over there from Brazil about a half a million or half a billion years old and then I have a heliodoro crystal from the Ukraine over there big Gilead or so the Ukrainian and the Black Hills pegmatite unfortunately the Black Hills didn't produce the big Jimmy helia doors or anything like that but anyway that you that Ukrainian hylia door 1.7 billion years old okay that's the age of those pigma tights and then the tanco pegmatite that we talked about that giant pegmatite 2.6 billion years old okay it gives you an appreciation of the range and age of these pegmatite s-- you know through geologic time and here's some interesting statistics quote-unquote because they really haven't been tabulated but less than 1% of all pegmatite s-- armor oolitic so less than 1% of them contained pockets and less than 1% of these contain gem crystals and well crystallized rare and unusual species and less than 1% of gem crystal pockets survived intact and here's an example of pocket in the Himalaya mine where you know they they were still able to extract the the gem tourmaline zand as single crystals right and some of them were broken some of them were we're miss shaping and whatnot during the kind of the reheating process and late stages that pocket but yeah it essentially fractured the pocket and so all of these tourmaline ended up being embedded in a clay okay and this is kind of cool so what you do you know you can't predict where the pockets are going to be but what you can do is really just do some basic geologic mapping in the pegmatite kind of if you know what you're doing right so you're looking at the mineralogy and you're looking at the textures and sometimes and just very simply so with the albeit you might see albeit in this massive face that you're blasting into kind of like this photo on the right right so you might see whether it's lepidolite or albeit and the albeit changes from white to kind of a pale blue and that's a really good indicator of of pockets okay the other thing is maybe seeing you end up seeing biotite or muscovite and then all of a sudden you start seeing lavender colored lepidolite okay so right there those are - to me when I'm mapping those are two indicators that say okay there's a possibility we might be coming up on a pocket here right so those are the kind of things that you do and and maybe it's changes in tourmaline color maybe from shore l2l by you know the green and pain oh sorry [Music] oh and they are they're mining a tunnel usually about six by six feet right they they drill holes load it with explosives and then they they muck cut out and they're they're looking for you know any signs of crystals well at the bottom of this last round that they exploded there was a small hole right and so what he ended up doing what he was doing was actually enlarging that hole because we could see into it we could see down that it got a lot bigger right and it's not one of those things you just take a sledgehammer to and do it so he judiciously used if you can do that with a small jackhammer opened it up a bit right and then he ended up pulling out big pale citrine so pale yellow quartz crystals out of that pocket so is really cool so that happened while I was there right and so that's what they do and then the other thing through the through the course of this like I was telling you they they use those diamond tip chain saws and so they would use those when they open a pocket up a little bit then they'll start using those just to cut pieces off that have matrix so they'll have like albeit with the tourmaline 's or the quartz crystals on them right and then they'll they'll pack them up and and prep them later but these are some spectacular examples of pocket preservation and extraction right so these are the blue cap tourmaline the famous blue cap tourmaline 's from the tourmaline Queen mine in California really nice himalaya specimen they're in the center and this is herderite crystals on on topaz from brazil and some other very sculptural tourmaline pieces this one on the left is from Dutton gem quarry in Maine and the one on the right is from Afghanistan so those are that's a big spot Jimmy crystal with morganite the paint Beryl crystal so long torturous life of a gem crystal they must outlast the pegmatite and the pocket forming process they have to survive late-stage equilibration fracturing in fluids pocket rupture itching dissolution alteration you don't want that to happen right and then the waiting process will it outlast geologic time right and like I was saying you know say that Helia door crystal over there from the Ukraine 1.7 billion years so that pegmatite was just discovered I don't know five years ago but they've been mining those hylia doors for decades right but that's the that's the thrill it's kind of like breaking open a geode for the first time and seeing the quartz crystals in it right you're the first one to see it so that's the neat thing about this so they discover these and it's been 1.7 billion years and in the making and this person is the first one to see those crystals that are in it right yeah so anyway then will it survive the discovery and extraction process will it persevere packaging and transportation well it persists through the laboratory press prep work and ultimately end up in display or replacement in one of your collections right and here are some of those pictures from some of the adventures in Brazil this is the one where I'm going down on the on the log into this little hole hole in the ground and this is my good friend Jill armando who owns the itachi pegmatite in the aroo compare my tight [Music] okay this one okay this one you're sorry well see if I can get this to play okay so these Brazilians they just blasted into this large pocket and there was several meters long a couple meters high and they were the first ones in there right and so Ronaldo ended up doing a video of this particular pocket so I thought I'd share that with you because it's it's kind of interesting in terms of you know really seeing that initial discovery and then some of the people that are responsible for the extraction process Ramiro wonderful guy the on the right are on the Left Ramiro Sardinia and he has been mining in Brazil for 60 years right ever since he was 20 years old or younger and a wonderful person and he's been in on all the big discoveries down there he was there during the discovery of the kunzite at the Arouca mine the discovery of the the jonas mind pocket many others and then jeweler mondo on the right and of course bill Larsson down there in the lower right and so this is the summary based on the questions that we asked at the beginning gem barring rare element bearing pegmatite sore fractionation products of a parent granite they're enriched in incompatible elements and volatile and able the formation of giant crystals as well as pocket and gem crystals if they're in placed at shallow levels gem bearings pegmatite scan be less than 30 five million years - 3.5 billion years old have a diverse mineralogy ranging from sulfides to silicates pegmatite pockets are rare and finding a pocket mostly intact is a miracle and finding extracting gem crystals from a pocket for collectors is definitely an art and just in closing this is just my comments granite pegmatite Saar an intriguing igneous rock and mineral deposit type and they represent an unusual combination of common and rare elements that combine to form diverse and beautiful mineral assemblages with complex pair Genesis and I study and collect pegmatite minerals for all those reasons and because to me their artistry is manifested in many different ways not just in their appearance it's the chemistry and how these things form and then really above all you know it's it's the people that I've met along the way you know just some wonderful people in Brazil at the mineral shows it's just been a you know a great experience anyway sorry I didn't mean to go so long and but thank you for your time and so I think instead of our usual Q&A I wanted to give people some time to look at the mineral specimens and and Tom will be there to ask you a question we have a small help present a token of our appreciation no and thank you join me in fact [Music] [Music] I realized that this was back in late eighteen hundreds in the jump arm and started speaking on them and turned into these big mines right but the other way too was by plastic flat circle pots so they found tourmaline and the river they actually been looking for him over in that way my wife Melissa great

Channel: Geologists of Jackson Hole

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Id: SS50-WzOjvg

Length: 88min 49sec (5329 seconds)

Published: Fri Oct 04 2019