my name is Andrew Jackson I'm a geologist with global resource investments and I'm responsible for technical evaluations of the mineral companies and their properties that global invests in I put together this all deposits 101 series of talks to help non-technical people understand all deposits talks highlight some of the features of the main deposit types that investors in the resource sector may come across and provides an introduction to the jargon you will find in press releases put out by exploration and mining companies this is the fifth in this series and it covers epithermal deposits if the thermals are a fascinating group of deposits as you can virtually see them forming today simply by visiting hot springs like those at Yellowstone in Wyoming or Rotorua in New Zealand this photo is the poem McCauley low salvation hot springs in Turkey with their beautiful white centre terraces if you like hot springs will love epithermal let's start where we always do in this series showing how epithermal fit into the overall scheme of things you will remember that nature concentrates the metals by a process of partially melting racast rocks at depth letting the melt rise through the crust and cool dumping the valueless minerals such as cells bars on the way and concentrating the useful metals in the remaining magma or hydrothermal fluid cool dump the dull stuff and skim off the useful metals the word epithermal comes from the greek words for nearby heat referring to the fact that epithermal deposits form very close to the surface of the crust by definition within a thousand meters temperatures that these depths are generally somewhere between 100 and 300 degrees Celsius and pressures are much lower than deeper down so the fluids are able sometimes able to boil there are several types of deposits that form in this environment including Carl and gold deposits but this talk will focus entirely on the precious metal epithermal deposits now if the starter must acknowledge the huge contribution from dr. Antonio rebus whose presentation forms much of the basis for this talk during the talk I'll describe the closest ovation of epithermal deposits with nearby porphyry deposits where we find them globally and show why epithermal are economically worth paying attention to the bulk of the talk will cover the different types of epithermal deposits how each of them are for our are formed and our finish up as usual with a short section on how we explore for these deposits and a summary of the key points to take away with you to understand epithermal we really need to recap stuff we talked about in the third of the ore deposits 101 talks which covered for free deposits so please bear with me for a couple of minutes if you have already been through that one for free deposit form in large intrusions that acted as magma chambers feeding active volcanoes you will remember that as the mega magma chamber cools from the outside inwards barren self bars and quartz quartz crystallize out so that the remaining melt becomes enriched in metals and volatiles the volatiles migrate to the top of the chamber and accumulate like the foam in the glass of beer of analogy I used in the first order posits talk elf power crystals take up more space than Sulphur melt and this combined with the accumulating theme and gas builds up pressure inside the chamber until the surrounding rocks can no longer contain it the cool solid Rhine to the magma chamber and the country rock of above at rupture and the volatiles escape upwards carrying their metals with them the metals then drop out of solution as he escaping the fluids cool eventually those fluids reach the surface as hot springs in this talk we're interested in what happens to those foods and how they drop their lower the metals to form a thermal deposits between escaping from the porphyry and reaching the surface epithermal czar both genetically and spatially associated with with poor freeze this is a section through the far southeast and lepanto deposits in the Philippines where this association was first conclusively proven he had geological detective work using isotopic studies and dating showed that the fluids from the far southeast porphyry escaped upwards and laterally to deposit copper and gold along their escape route forming the epithet the Lepanto epithermal deposit he has a spectacular exposure of a poor free and epithermal pair in southern Java the poor free intrusion our Crocs is a small steep island on the right of the image and a genetically related height alpha Dacian epithermal deposit occurs on the mainland on the left of the image note that both here and in the previous cases upon tez CFO thermals are not directly above their porphyry but Lyle actual to it following the path of the arc flowing hoods we will come back to how Apple thermals form in a minute but let me first talk about their timing in a global context although poor freeze and presumably epithermal have formed from the Archaean until today the vast majority preserved epithermal are relatively young tertiary or later ie less than 50 million years again the sounds like a long time ago but if we compress the earth's history into a single year the tertiary would occupy just the last three days of december why this discrepancy between the ages of the poor freezer net the thermals it's all a question of preservation if the thermals usually form in mountain chains and at shallow depths so they're easily and quickly eroded and so there are a few old ones remaining in the geological record so where do we find epithermal deposits well obviously they are generally in the same place that porphyry form in other words above subduction zones and we can narrow down this a little bit more to subduction zones that have been active in the last 50 years 350 million years this means we're looking at the so-called Ring of Fire around the Pacific Ocean or the Alpine Himalayan plate boundary as a map showing the location of significant high and low self evasion epidermal deposits you can see their close correlation with active subduction zones only a few of the deposits associated with older subduction zones such as the Appalachians have escaped erosion you may also note the group of low sulfur Dacian epithermal in Patagonia these include Anglo Gaza Angostura noir Vanguardia xtour a serum Oro and Goldcorp serra negra these are near the Ring of Fire but they're not actually associated with it instead they're due to a mantle hot spot that developed when South America and Africa were torn apart during the opening of the South Atlantic about 150 million years ago these older deposits has survived erosion because they formed in low-lying area that was not subject to higher erosion rates and they're also further protected by layers of overlying volcanics why should we care about epidermal deposits well there are major source of gold providing about 12% of the world's annual gold production in fact they are the second largest producers of gold globally after the Safari front deposits now I've used the term and phrases high self addition and low sulfur Dacian an intermediate salvation in connection with epithermal and it's time that I explained the subdivision because they're very different beasts and you need to understand their characteristics if you come across them in a press release if you understand their geological current characteristics it will help you put the exploration results into context and help you make a better investment decision so what are the differences between low-self addition intermediate self relation and high self addition epithermal x' while the differing sulfa Dacian state of the fluids associated with these deposits results in a very different detailed mineralogy that formed the basis of the definitions but you probably need access to an old microscope or x-ray diffraction laboratory to identify many of these minerals and mostly investor's don't have these so I'm going to speak not spend any more time on this aspect and said I'll try and make it simple by talking about where and how they form there's a very simplified cartoon showing the to end members of the spectrum obviously reality is typically more complex but this works fine as a first stage approximation fundamental genetic difference between high and low self validation is the amount and degree of interaction between the magnetic hood groundwater and host rocks height alpha - deposits form and geothermal systems where hot acidic hydrothermal fluid directly from the intrusion remains undiluted Byam groundwater low sulfur - and deposits on the other hand forming geothermal systems in which the magmatic fluid is called and diluted by groundwater and the pH is neutralized at depth the formation of an epitome of epithermal deposits is all about dropping the gold from solution before it reaches the surface and escapes to the atmosphere or hydrosphere how the z-position occurs varies according to whether the gold is being carried by hot acid foods or cooler neutral fluids first let's look at the high sulfur - and epithermal with a hot acid hydrothermal fluids this is an aerial view of a typical bleached high sulfur Dacian operation zone in the Chilean Andes in highschool predation epified deposits the mineralization is a two-stage process initial alteration followed by all mineralization itself the cartoon shows the alteration stage with hot acid foods sometimes vaporized rising wealth the source intrusion and attacking the country rock as it passes on its way to the surface the rock is progressively leached and altered said that the feldspars break down to clays and these clays are then removed leaving only a silica sponge which is impervious to hydrochloric or sulfuric acid the silica remnant is often referred to as a buggy silica or buggy quartz or Luthor cap the second and third cartoons showed the deep position of the gold this often occurs in two phases against an initial gaseous tri transport of the gold and then as the system cools the gold comes up in a liquid phase in many cases we then get the second stage and we end up with a baron T baron leach liquor cap of advanced or Jellicle of the Drakh here's another cartoon of the same process but showing how the shape of the plume and are of alteration and the mineralization may be affected by local geology and groundwater pathway I promise not to go too deeply into the mineralogy but you may well hear geologists talking about alien 8lu night is a pink alteration product or false Mars and it indicates that the fluids were highly acid its present is indicative of a high sulphur dashing epithermal system active high self additional Hot Springs are not places you'd like to swim there acid and they stink of rotten eggs from the hydrogen sulfide and because the acid breaks down into feldspar the bakes down the feldspar to clay they usually consist of more of mud than of water but how do you know when you're standing on an extinct height alpha Dacian epithermal system the obvious diagnostic features are the presence of Ruggie quartz and abundance of white clays and the minerals al unites injera site which tell us that the fluids were highly acidic and the lack of obvious veins because in these deposits fluid flow relies on the porosity that the LIA acid leaching imposed on the host rocks rather than on faults due to their disseminated cellular mineralization high sulfur - and deposits are generally mind as open purse well-known high sulfur - nepo thermals and cool clued goldcorp selfie soul in mexico barracks Peter Purina and new monster Yanacocha both in Peru this is an old photo of Elsa cells looking south before they started the mining the Wragge silica makes up the cliffs due to its hardness and resistance to erosion the light-colored the drill roads is due to the white clay in the Argyl acculturation in this plan view of the same deposit the mineralized silica is shown in red and the clay alteration is in orange and in yellow in section the buggy silicon red can be seen to have developed in a gently dipping saver ball horizon in the volcanic stratigraphy at P arena in Peru you can clearly see the association of the gold which is the heavy black lines on the image with the solicit alteration in red although it also extends out into the advanced idyllic in orange in the section of pure in Purina you can again feed the way that the alteration has followed a sub horizontal favorable stratigraphic horizon this is the alteration map of the UH Nicosia district the mother of all high self relation of others the alteration system is sixteen kilometers across and covers over fifty square kilometres and again it in Numancia Nicosia is a combination of both flats stratigraphic controls and steep structural controls to the silica alteration so does the size of an alteration zone reflect the size of the gold deposit it looks like having a large dog advance are julik zone is a necessity for significant mineralization but not all big alteration zones have gold probably because they went through the leaching phase but not the later mineralizing clay phase this is critical to keep in mind when reading press releases which extol fix intercepts of alga silica they can still be completely barren okay enough on the high shelf addition assistance let's look now at the other end of the spectrum the low-sulfur Dacian epithermal although there are products of the same igneous system low-self adacia narrow tunnels are very different in low sulfur lucien epithermal the main control for goldman deposition is fluid boiling caused by a drop in the confining pressure as the fluid approaches the surface this is a cartoon of a simple low sulfur Dacian vane system with all its components preserved the fluids flow off a single weld nut up well-defined structures that blossom out near the surface alteration is not nearly so pervasive as in a high self relation system and seldom extends far beyond the structures and this is a permeable horizon and then the fluids may expand the long destruction unlike the muddy acid waters of high self addition systems the low self relation fluids are usually crystal clear and have a neutral to slightly alkaline pH that are good enough to drink but often have high silica mercury and arsenic content along with the gold when the water reaches the surface it flows out and cools allowing the silica to drop out of solution to form hard siliceous sinter terraces low sulfur Dacian veins are usually well banded offering with alternating layers of silica and carbonate and they frequently show brachiation or open space filling more importantly they may show plates of silica replacing calcite which indicates that the fluid boiled this is just what we're looking for as boiling is critical for gold D position as in certain other deposit types the golden low sulphur Dacian epithermal fluids is being carried as a bio complex with sulfur now I've lifted this slide from an earlier tool from green stone shear zone hosted gold where we covered various ways to drop gold from entire complex solution I won't go through this again in detail but one of the key ways was to break the gold sulfur bond by allowing the fluid to boil this is the main way in which gold is deposited in low sulfur Dacian episodes a reduction of pressure allowing the previously pressure constrained fluids to boil the boiling CONUS it is called begins at a certain depth below the water table and they extend up to the water table or die out before then in the zone you'll see this evidence of boiling and this is where the gold will be below the boiling zone the gold will remain soluble and not be significantly deposited above that zone much of the gold has already dropped out of solution and the lack of boiling prevents any remaining gold from being deposited obviously it's critical to the economics of a deposit whether the boiling zone has a wide or narrow vertical extent the width depends upon a number of inputs including the temperature the food's the amount of ground water mixing the rate of flow and the longevity of the system the boiling zones can be anything from 50 meters up to 800 meters thick with an average of about say 300 meters the particular sulphonation deposit in Mexico has been mined for many years so there's plenty of data to build up a picture of the variability of the boiling zone the thick black lines in this image represent the vertical extent of the boiling at various points along the strike at the vein you can see that in this example there is a single boiling zone that averages by 400 meters thick you may hear the word telescope - used in epithermal deposits this means that the boiling zone moved during the life of the system spreading the boiling zone over a greater vertical extent you have a better known low self evasion epithermal that you may have heard of you'll notice that although some of them are typical vane hosted there are some that have developed in more porous rocks and so disseminated rather than vein hostnet controlled allowed Nevada's hike off deposit in in Nevada is a typical example of this the chicory mine and Japan exploits a swarm of quartz carbonate fans mineralization is very recent and hot water is still flowing from the rocks underground he has an underground view of the vein as he Shikari note the high grades typical of this group of deposits this is the sleeper mine in Nevada again although the average grade was low some spectacular gold power pockets were encountered this is one that will be familiar to global investors Esperanza's san luis discovery in peru high-grade gold and silver mineralization occurs in the highlighted series of Amish long veins barracks Purina deposit can be seen in the distance to the east on the ground the quartz carbonate veins looked like this originally resistant and just a few meters wide the total size of the deposit is modest but the excellent grades make up siddhis with an average grade of 22 grams per ton of gold and 580 grams per ton of silver Kinross and Barrett's Round Mountain Mine is a 10 million ounces or body mine from open-pit because of varying host rocks there are both shallow veins and an underlying blanket of disseminated or similar to some of the high self relation deposits a section through the mine shows the all in red developing as veins in the blue velvet tough and as disseminations in the orange pores unwelded tough and purple filaments below the ultimate pizza outline is shown as a red line so much for the low sulfonation epithermal now let's quickly cover the last of the broad groups the intermediate sulfa Dacian epidermis as the name suggests they form part way between the high self addition and the low sulfa Dacian environments with a degree of dilution by groundwater but not to the same extent as in low sulphur Dacian systems they generally form veins and Becher's like low sulphur Dacian epidermal x' but have course of banding however they also contain alienate like high self relation epidermal x' in addition to gold they usually contain significant silver and increasing amounts of leads in the form of Galena and zinc in the form of a light as you go deeper the gold and silver deposition is controlled by boiling base metal deposition is mainly by fluid mixing or cooling because the base metals travelers chloride complexes not the entire pond taxes examples of intermediate sulfa Dacian deposits include mag Silver's one a Scipio deposit in Mexico Kinross is fruta del Norte deposit in Ecuador and la patria in Mexico at one asipi o the veins barely reached the surface forming just the wispy cilicia stones you can see in this photo but some 400 meters below the surface the boiling zone is encountered and the vein balloons up to ten meters wide with well banded and richly mineralized quartz vein filling boiling zone has a vertical extent of 450 meters silver standards / Tahrir depositors in Mexico it was discovered by an excellent exploration team who looked beyond the low-grade and spotty geochemistry results from sampling surface outcrops understanding that these deposits are vertically variable and that they were looking at the barren cap over a large fairly eroded hydrothermal system drilling has proven this to be the case and this section shows how the system balloons out a depth most of the gold and silver mineralization is controlled by a shallow boiling zone but the system becomes more base of metal-rich at depth with lenses of massive base metal sulfides developed 400 meters below surface the future del norte deposit in Ecuador was discovered by the junior Explorer or iliyan the mineralization does not outcrop and was found by drilling below a smaller crop of Unwin realized center hidden in the six tropical vegetation in the 3d model of the mineralisation you can see steeply dipping structures in pink with the multicolored prisms of mineralization in a vertically constrained boiling zone the all is well banded with plenty of salaries and galina crew total naughty has reserves of 6.8 million ounces of gold and 9 million ounces of silver at a grade of just over 8 grams per tonne gold equivalent and a further 4 million ounces of gold and 8 million ounces of silver in resources ok let's move on quickly discuss how we explore forever thermal deposits many of the techniques are similar to those I've you have you described for other deposit types we need to start by focusing our efforts in areas where there is evidence of major felsic to intermediate volcanism as it is this volcanism that drives the epithermal systems we also need to find an area that has not been too deeply eroded wealth any air thermals will already have been removed multispectral analysis for airborne or satellite images may be able to detect wall rock alteration obviously low sulfur vation epithermal veins with their limited water alteration will not be found like this but it's a valuable tool for high sulfur - and epidermis you'll remember these images for my earlier talk on porphyry expiration with expiration for height alpha Dacian systems we're looking for the same sort of alteration as with pore freeze in other words philic are Dilek and an advanced are Jetix elisa fication these show up is the pink spots on the image on the right this is a similar multispectral image over the Goldfield area Nevada a typical high telfa Dacian epithermal system the highlighted areas are where the ground exploration would obviously be focused once the clear area of hydrothermal alteration has been located exploration moves to the ground phase usually beginning with a combination of mapping to confirm the alteration and geochemistry to identify the best targets for drill testing remember that in epithermal we may have a significant verticals the nation so that low grades at surface do not necessarily mean that the system is barren a DEP here's the result of alteration mapping on the left and soil geochemistry on the right over the same area of the bucket edge I'll profited property in Indonesia note how the highest gold geochemistry on the right-hand image roughly corresponds with the presence of buggy silica alteration the hatched pattern on the left hand image because of the limitations of surface geochemistry geophysics may also be used to identify buried or voguing buried value silica or disseminated sulfides that may be associated with mineralization this shows a series of IP travis's at puckateeto with the red high resistivity highlighting the vibra silica in three dimensions the final stage of exploration as usual involves drill testing this is a cord rig drilling at the fruited el norte deposit in ecuador this has been a long talk but it's just about finished only two more slides to go summarizing the takeaway point for epithermal deposits so here are the key points to remember about epithermal they form above or lateral to pour free systems there the roots of old hot springs most are very recent in other words tertiary or say 50 years or yet or less there are three main types and each have their own characteristics firstly the high self addition they mainly gold with - silver or copper they can be very large like Jana culture and they are often t-shaped due to control by its seep structures and flat-lying host rocks the roots may extend to more than 1,000 meters and depth although they're usually less than this and they're generally low-grade with the simulated cellar mineralization so they're likely to be mined by open-pit a low sulfur - sniper thermals are mainly goldrich they have - silver Mercury with them they're usually small though to moderate in size but they're generally high-grade and form relatively narrow steeply dipping veins the depth is limited by a boiling zone which is seldom more than about 350 meters in vertical extent they likely to be mined from underground unless there's a swarm of veins in which case they might become open pit targets finally intermediate self addition episodes are goldrich near the top becoming more silver and then dominantly Ledyard zinc rich at depth mineralization usually occurs in steep veins but it may have flats layers as a patria the veins may be long and continuous silver lead zinc mineralization can extend to significant depths for example at fresney Oh lead solve lead zinc extends from about 300 meters right the way down to 900 meters depth and intermediates alpha Dacian like close operation are generally mined from underground although the flat portions may be open put it as well so that's the end of the this talk on it for thermal deposits in the next talk in this series I'll talk about another group of hydrothermal gold deposit that's formed at shallow depth the column type gold deposits