today's geology lesson of the day hydrothermal deposits I was down in Montana and I thought for sure I have to go to Yellowstone Park to talk about how gold deposits in hydrothermal veins now hydrothermal means basically hot water a hydrothermal deposit is hot Waters boiling up from deep within the Earth carrying minerals with it now why Yellowstone Park well we're better to talk about hydrothermal activity than standing in front of Old Faithful now let's start by talking about boiling water so we all know that water boils at 100° C but that is only true at sea level and if you go up in elevation that boiling point actually reduces if you go down in elevation it increases the higher the pressure the higher the temperature water needs to boil when you go deep deep deep down into the earth when there's billions and billions and billions of tons of Rock The Rock creates this cap of pressure on the water and the water's boiling point increases and it increases a lot the higher the pressure the higher the boiling point and down deep in the earth it is such a high pressure that boiling is basically impossible it creates this super hot fluid that is a brine it's salty it's got things dissolved into it that is under such high pressure and high temperature that it can start doing things that here on the surface we think are impossible things like dissolving glass or quartz dissolving iron dissolving yes even gold this super heated fluid that's way way down in the ground can start dissolving minerals that we would think would never be possible to dissolve and as these fluids get heated and pushed and pressurized and squeezed up through cracks in the earth and start going up in elevation up higher closer to the surface the pressure starts to reduce and as that pressure reduces that fluid that brine starts losing its ability to hold many of these minerals in solution and in fact some of the minerals will start to precipitate out of this fluid and Harden in the cracks the water's being forced into different minerals will deposit at different pressures now the three minerals that we think most commonly associated with a gold deposit quartz iron and gold they all precipitate at a very similar pressure the form of quartz that gets deposited really depends on how quickly it deposits and that depends on where in the elevation how hot it is what the pressure is how quickly quartz deposits now iron will deposit differently depending on what the sulfur content of those fluids are if it's really high in Sulfur it'll create pyrites if it's really low in Sulfur maybe a bit higher in oxygen it'll create oxides of iron like magnetite many other metals will precipitate at that same point we got silver lead zinc copper a lot of metals are depositing at that same time and it really depends on the sulfur levels in that fluid whether they create pyrites or whether they create native metal or oxides of metal now gold does not react with sulfur so gold does not make a gold pyate a gold sulfide it comes out as molecules of gold those molecules of gold are either tied up in the other metal sulfides so they're embedded in the pyate or they combine together and make blobs or pieces of gold what we call native gold now there are a lot of other minerals also dissolved in those hot fluids coming up that haven't precipitated out at that point some precipitate out lower some precipitate out higher the most common is what we see right here that is calcium salts and calcium and a little bit of iron do Contin continue up with those hot fluids until it gets to a point where it can precipitate and often the calcium is the last thing to come out and it doesn't come out until it gets to the surface sometimes calcium will will come out below ground when Waters boil away below ground sometimes the heat isn't enough to boil the waters away until it hits the surface and it leaves these great great calcium deposits even at the surface pressure and 100 ° C where water boils water has the ability to hold some iron some of these hot springs and Geyers do have an iron deposit all around it sometimes they also have a deposit that's red that looks like an iron deposit but it's actually a bacteria a microorganism that thrives in these hot springs and creates these colonies that look like an iron deposit so you can have iron around these hot you can also have these red stains from bacteria growing and then you have these great white pillars and blobs and structures which is the calcium and the salts coming out at the surface and often when the uh hot hot fluids from deep deep within the Earth are pushed all the way up and get to the surface they will boil out on the surface when it loses its final little bit of pressure and it starts to boil at the surface and and creates these hot springs or geysers now geysers usually happen when that final boil happens just below the surface and there's a cap of water on top of it so it creates a bit of pressure before that boiling water can expand and blows that water out the top and that is what Old Faithful Is is one of these hydrothermal fluid structures events happening underground boiling water all the way up and right near the surface it creates a cap of cooler water holding in place until it heats up just enough to boil and then alt once boils and blasts that water out through the top and that should happen any moment now you may ask if the quartz gold and iron and other metals are being deposited so far down underground why are we able to find them here on the surface well that's just other geological activities that is pushing that ground up towards the surface it erodes away on the surface surface eroding those rocks down keeps pushing up mountain building processes and then eventually those hydrothermal quartz veins that hold gold get close to the surface or right at the surface where they can erode away their gold Creeks wash the gold out miners chip the gold out and we can find that gold in those hydrothermal veins once Mother Nature has brought them up closer to the surface and now if there are any geologists out there listening to this they're saying right now Dan you're oversimplifying things and yes really I am the variables in this are huge how much is the acidity the pH of that how hot is it versus how high in the elevation or the strata is it higher up can take cooler waters before it boils lower down be hotter before it boils there are a lot of chemical differences in there what's the sulfur level what's the oxygen level uh there is so many variables in a hydrothermal system that I just can't get into in a video like this but the basics hot Waters deep deep down of the earth under huge pressures dissolve minerals carry them up through the crust to the point where those minerals precipitate out and create these hydrothermal quartz veins those hot Waters can continue on up after they've dropped out their minerals to the surface creating hot springs or geysers just like this [Music] oh my goodness and there you have it today's geology lesson of the day hydrothermal gold deposits hope you enjoyed and I hope I earned your subscription today bye