Extremely Deep: Mining for gold

Extremes month continues, and this week we’re going extremely deep into a gold mine.
25 June 2019
Presented by Chris Smith, Izzie Clarke


Image of a pile of gold ingots


Extremes month continues, and this week we’re going extremely deep; Chris Smith takes a trip to one of the world’s deepest mines in search of gold. Plus, in the news, the GM mosquito that wipes out its own population, and would you return a lost wallet if you found one? We hear which is the most honest country in the world, and who’s the least honest.

In this episode

Four adult Aedes aegypti mosquitoes

01:10 - GM Mosquito to wipe out own population

Mosquitoes are the world’s most dangerous creatures but can they be modified to wipe out their own kind?

GM Mosquito to wipe out own population
with Tom Reed, Intrexon & Oxitec

Based on the number of humans killed every year, mosquitoes are the world’s most dangerous creatures, chiefly because they’re the vectors for a whole raft of viral and parasitic infections that they spread when they bite. Indeed, some dub them “flying hypodermics”. Now a US company, called Intrexon, and their UK subsidiary Oxitec, have announced that they’ve come up with a possible solution: a genetically modified mosquito in which only the males survive. Pretty quickly, the targeted mosquito population - and its ability to spread deadly diseases - crashes. Chris Smith spoke with Chief Scientific Officer Tom Reed...

Tom - We have engineered mosquitoes that will pass a gene that will kill all female progeny. So what we've done is we've engineered male mosquitoes that when they mate they pass the gene to all of the male larvae and to all of the female larvae, and only the female larvae die.

Chris - And how are you making that sex distinction?

Tom - There are certain regulatory elements that differentiate between male and female expressed genes, and so we can control the expression so that it will only lead to the expression of the lethality product in the females and not in the males.

Chris - Essentially, a genetic switch, then, that turns on in the females but not in the males?

Tom - That is correct.

Chris - Why does it wipe them out?

Tom - There are certain biological functions that require a use of energy, and so what we've done is we've overexpressed a protein that leads to a great deal of energy use and you burn out the cell's ability to keep up.

Chris - It's a bit like leaving the lights on for too long. You waste loads of energy and they haven't got energy to put into useful things like growing and mating I suppose?

Tom - It's actually the larvae that cannot go to the next level of development because you burn them out before they even go through development.

Chris - Presumably though, you do need a founding population of males to get this process started in the first place?

Tom - Very good question. So our first-generation mosquito was not male selective. You would have to manufacture both males and females and then use size selection to sort the males away from the females. So our second-generation product is one that we are able to actually select only for the survival of the male mosquitoes, and then when we release the male mosquitoes in the population every male child that’s born will then breed and pass that gene until the population collapse occurs.

Chris - Because it's only going in one direction, I suppose, because any female that breeds with one of your genetically altered males, all of the male progeny will survive and will inherit it and they'll go and meet with more females, so it should grow exponentially to start with until you saturate and then the population is just going to be wiped out?

Tom - That is correct.

Chris -  Do you know if this is going to work in the wild?

Tom - We recently gave a press release that indicated the successful use of this in Brazil showing that our mosquitoes suppress mosquito populations in the field at 96%.

Chris - The population falls by 96%?

Tom - That is correct.

Chris - Is this safe in the environment though? Could that not have environmental consequences?

Tom - This is an invasive species. Aedes aegypti is from Egypt, and these day-biting mosquitoes came via shipping to Brazil and there were no natural enemies for these mosquitoes. So we’re not having any negative impact on the wild-type environment, we're actually removing a detrimental organism from that environment.

Chris - And there's no danger the gene could jump ship and end up in a native species, mosquito or otherwise?

Tom - No. Aedes aegypti will mate with Aedes aegypti. And actually for other mosquitoes that carry different diseases we have to create a version of that unique species in order for it to go after other diseases like malaria.

Chris - I'm glad you brought that up because that's what I wanted to ask you about next which is okay, you proved the point with Aedes aegypti which spread diseases like Zika, but they're not the most nasty, dangerous animals in the room because the Anopheles mosquito that spreads malaria probably are. There are hundreds of millions of cases of that around the world every year aren't there? So can this technology be used in them?

Tom - Absolutely. And I'm pleased to say that the Gates Foundation is working with us to develop this technology within the Anopheles species so that we can combat malaria.

Chris - Now the difference there is, though, that the Anopheles mosquitoes they are native to the geography in which they spread malaria, so rather than them being an invasive species  and you being able to say well, what we're doing is removing an invasive from the environment, you're actually going after something that should be there, so this is a slightly different situation?

Tom - Indeed it is. But there is possibility on how you control the releasing and where the releasing occurs that you can start to collapse the population within a defined area.

Woman holding money

06:50 - The honest truth on money, money, money...

If you found a lost wallet, would you hand it in? Scientists explore the most and least honest countries.

The honest truth on money, money, money...
with Alain Cohn, University of Michigan

If you found a lost wallet or purse, would you give it back? To find out how honest people are around the world, Swiss and American researchers intentionally “lost” wallets in many countries to see what would happen to them. They’ve just published the results in the journal Science, and Phil Sansom spoke to one of the authors, Alain Cohn, to get the honest truth.

Phil - Money: supposedly the root of all evil. But can it ever bring out the best in people? Here's a question: if you lost your wallet would having money inside it make it more likely to get back to you or less likely?

I've no idea.

Probably less. I think it will be more tempting for people to want to keep it.

Less. Because there's a lot more money in there and people are not as honest enough as they used to be.

People generally are goodhearted and would want to return it. I hope so.

Phil - Some people think more likely, some people think less likely. Well, according to a new study the answer is actually more likely to get back to you. Surprised? Well, here's one of the authors of the study Alain Cohn to explain why...

Alain - In 2013 we had a bachelor student and he was spending an exchange semester in Finland. We seized this opportunity and asked him to turn in lost wallets at the counter of various public and private institutions, and specifically we hypothesised that higher incentive to steal would reduce the level of honesty.

Phil - That didn't happen did it?

Alain - No. Much to our surprise we observed the opposite effect. Across the board, people were more likely to return a wallet when it contained a higher amount of money. At first we almost couldn't believe it and told him to triple the amount of money in the wallet. Yet, we again found the same puzzling finding and so this was the beginning of a long journey as we wanted to better understand this result. Overall we had 40 countries and 355 cities. We turned in more than 17,000 wallets. We varied the amount of money in the wallets and the wallets were transparent so people exactly knew what’s inside.

Phil - Where did you turn them in?

Alain - Banks, cultural institutions like museums and theatres, post offices, public institutions like, for example, the police station. We hand them over directly to a person working at that particular institution.

Phil - How would they know where to return the wallet?

Alain - The wallet contained three identical business cards that would signal who the owner is. We created unique email addresses for each wallet. Basically every time we received an email we knew exactly which wallet we were talking about

Phil - Wow. You're really covering all your bases there!

Alain - We tried. I mean it was an expensive experiment so we tried to maximise the outcome.

Phil - How expensive?

Alain - About $600,000. The money in the wallets cost us about $135,000. It sounds like a lot but there are other fields where researchers have to purchase equipment and materials like, for example, an fMRI scanner and that can be much much more expensive. And this is one of the first studies who measures honest behaviour in an everyday life situation where people don't know that they're being observed.

Phil - So you did this upwards of 17,000 times, what did you find?

Alain - About 40% of the wallets were returned. Adding a small amount of money, that rate increased to 51%, if we included almost $100 in the wallet that number increased further to 72%.

Phil - Were you shocked?

Alain - We were surprised to replicate the effect across almost 40 countries.

Phil - So what does it mean? Why aren't people just seeing the money and being like no one's going to know, I'll take that?

Alain - There are two key factors that play a role here. The first one is altruism, you don't want to hurt someone else so that can motivate you to return the wallet, especially when there is no many inside. But adding money completely changes the psychology because now there is a second component, people don't want to see themselves as dishonest people. This psychological cost increases with the amount of money in the wallet, so this force becomes stronger the more money there is in the wallet, and this gives this unexpected finding.

Phil - So not only do you not want to be a thief, you don't want to look like a thief? How do you know you won't just measuring what people behind the counters of these buildings would do rather than just like everyone?

Alain - There evidence speaks a little bit against that. So we took alternative proxies of dishonest behaviours such as, for example, tax evasion or corruption of public officials. And so what we find is a strong correlation between our measure of dishonest behaviour and these other proxies, and so this gives us confidence that we capture a more general behaviour.

While we cannot really say whether we measure people's behaviour in their private role or in their professional role, I think both is interesting. They care about being seen as an honest person.


17:19 - A sound way to help distressed animals

Scientists analyse animal calls to help improve the well-being of livestock.

A sound way to help distressed animals
with Michael Mcloughlin, Queen Mary University of London

Old Mcdonald had a farm, and more recently on his farm he’s been shocked to see the declining living conditions of common livestock. More often than not humans are omnivores, which means meat is a staple in our diet. But as the number of humans on Earth grows, so do the demands for food, and particularly animal products. Some estimates suggest that the average meat eater consumers their own body weight in meat every year. And as the demand increases, we need to ask, where is the line drawn between human nutrition and animal wellbeing? At Queen Mary University of London, they think they’ve come up with a “sound” way to solve the problem. Matthew Hall heard how, from Michael Mcloughlin.

Matthew - Suboptimal animal welfare is a widespread issue plaguing farms. While there are some that have taken initiative and provided more open space for the animals, more often than not they are being raised in industrial facilities also known as factory farms. These farms create a breeding ground for bacteria which leads to abuse of antibiotics and an unhealthy battle to keep the animals from getting sick. It's enough to make Old MacDonald turn in his grave. And despite public knowledge, little has been done to optimise the living conditions of our furry and feathery friends. Fortunately, a team based out of Queen Mary University of London decided to take action in a study published in the Journal of the Royal Society Interface where they are discussing the different confinements seen in farms...

Michael - Yeah, you do have different levels of farming. You would have more intensive kind of farms but you also do have some farms out there where they have higher levels of welfare for the animals.

Matthew - That is lead author Dr Michael Mcloughlin who was a bioacoustician, or someone who studies animal noises.

Michael - So, for example, there will be a difference where you could have two types of indoor farming for chickens, for example. If the chickens are kept in a large shed but they are still able to roam around inside the shed. And then you will also have the more infamous ones which would be the battery cage farms, which they stack up on top of one another. Those are two examples of different indoor farms and there's a world of difference between them.

Matthew - The ultimate goal of the researchers is to improve the overall living conditions for the varying types of farm animals without using invasive methods. To do this, the team has devoted the last two years to developing a deep learning AI that is able to analyse the vocalisations or bioacoustics of pigs, chickens, and cattle. But the question is why these animals specifically?

Michael - If you ever go to a poultry farm the sounds of everything happening is just tremendous. Chickens are always making different types of sounds and there's a lot of information carried on these things. And pigs as well, they are quite vocally active as well, they have different types of communications depending on the situations they are in. This is the kind of stuff that's been established through behavioural research already, and biology research. These animals there's loads of information we can be gathering from them.

Matthew - To better understand the secrets within animal vocalisations it is crucial that the team improves upon the technology. Fortunately for the team, the beginning of the solution was being developed by the popularity of automated analysis in voice recognition software...

Michael - When you think of something like Alexa or OK Google, you speak into your phone and it immediately understands what you're saying. These same types of techniques can be used in machine learning but they require having a lot of information about the actual behaviour of the animals and what different calls can relate to. If you were to take an approach of machine listening, the first step is called feature extraction. If you take a raw audio recording and you were to just start throwing it into a machine learning algorithm, there's so many variables and the information is so complicated that you're probably not going to get the best results. So what you want to do is extract the most important information and features in these recordings. In order to do that, the first thing you usually do is something called a fourier transform.

Matthew - A fourier transform is a method used to take complex signals and break them down into a number of much easier to read waves that have their own frequency, phase, and amplitude values. These acoustic values are acquired to interpret our varying pitches and frequencies when we talk, making them the key in human speech recognition algorithms, in a similar fashion to how Alexa understands your varying pitches and sounds.

Alexa: Play the Naked Scientists.

Animals have been found to have similar changes in pitch and frequency based on their current conditions. As an example, baby chicks are able to make pleasure chirps which are short ascending vocalisations, but also distressed chirps which are short descending vocalisations. These differences are known due to the past experiments that have recorded animals in varying environments of arousal, in turn, allowing the team to optimise their software to listen for chirps or squeals or moos that relate to the overall well-being of the animal. There is still one remaining issue though, what classifies good animal well-being?

Michael - Animal well-being is a very broad term and what one person regards as being good animal well-being, another person may very well be like no, it's not good enough, you know. I think it’s really important to look past just that. So I think one of the things our paper does well is we don’t just talk about things like disease in animals, we also talk about their emotions. One of the things I would really like people to take away is talking about this kind of thing, about animal emotions as well as are they dry, are they happy? We want to raise awareness that it’s more than just making sure that they're looked after, you know, in terms of their physical needs you want to actually have them living enriched lives.

Matthew - An animal that is living its best life is not only good for the animal's health, but in the long run for the consumers as well. Healthier animals mean significantly less hazards after consumption, but even simpler than that it means Old MacDonald can finally rest easy.

The image shows a pair of lungs.

23:37 - Mapping lungs and attacking Asthma

A map of every cell in human airways could improve treatments for respiratory conditions.

Mapping lungs and attacking Asthma
with Charlotte Summers, Addenbrooke's Hospital

Asthma is becoming more common. The chest disease can lead to life-threatening breathing difficulties when the airways constrict and the lung tissue overproduces mucus; this is often caused by an allergic reaction that can be worsened by air pollution. But our understanding of what’s going on in an asthmatic lung to cause the condition is still quite limited. But now for the first time scientists at the Sanger Institute near Cambridge have used a new technique to document and examine every cell in lung samples from both healthy and asthmatic patients to discover what’s changing when a person develops asthma. Chris Smith was joined by Charlotte Summers who is an intensive care medicine doctor and lung specialist from the University of Cambridge. She took a look at the study for us, published in Science by Felipe Vieira Braga.

Charlotte - For the first time these researchers took tissue from the nose, from the airway walls, and from out in the peripheries of the lung and looked at every single cell type that they could find at those particular sites, and tried to find out how many types of cells and what kind of cells where there at those sites. And they did this in people who were healthy and people who had had asthma since they were a child.

Chris -  And what did that reveal?

Charlotte - It revealed that there was more than 20 different types of cells in the healthy lung and that depending on the site that you sampled the types of cells that you found were different. But in people who have asthma, they found some pathological cells, so some cells that were contributing to the disease that they didn't find in the healthy people.

Chris - And are there any clues as to where they came from? Are they cells that were born in the lung and they’re there normally at such low levels we can't see them or did they come in from outside?

Charlotte - A bit of both actually. They found what are probably some cells that came originally from the blood that they found, so one of the immune cells that are resident in the lungs with people who have asthma. But that those cells also cause changes in cells that were resident such as the epithelial cells that are in the lung.

Chris - So why did those blood cells come in in the first place?

Charlotte - Well, that's a question that we may not necessarily have really strong answers to, but I think it's to do with the changes in the inflammatory mediators that were present in the lung.

Chris - Would you suggest then that something winds up the lung tissue? I mentioned the beginning often we regard asthma as an allergic reaction, so could it be that that inflammation recruits these cells in and they then start to distort what should be going on?

Charlotte - Yes. So I think, particularly in these patients, they were people who had childhood asthma which we know is much more likely to be of an allergic problem, and the information they found would be supportive of that, but actually that's exactly what was happening.

Chris - And so those cells, these abnormal immune cells come in, how did they in turn then change what the lung is doing? How do they change the behaviour of the lung and make the mucus different?

Charlotte - The immune cells that come into the lung secrete inflammatory mediators, which they think from this study induced a change in one of the epithelial cells from being what's called "ciliated" to being a type of cell that produce mucus too, as well as causing what we knew already to have more mucus-producing cells in the lungs of asthmatics.

Chris - That's quite interesting then isn't it? Because you basically can persuade a cell to almost have a facelift: stop being a cell that would clean the lungs, and become one that makes goo-ey mucus?

Charlotte - Exactly. And gooey mucus is a problem in people who've got asthma.

Chris - Now, given that we have this insight, and that they've got this baseline - because they looked at lots of healthy people, and they also looked at lots of people with asthma - but given that we've now got this baseline of what normal should be, I presume that's going to be really useful because we now understand what we should be like and we can then begin to compare that to all kinds of different lung conditions using the same sort of technique?

Charlotte - Absolutely. So I think one of the most exciting things about this paper is, for the first time, we have a proper map of what normal should look like for all the different cell types in the airway: everything from the nose right the way down to the alveolus of the lung. And from there you can say "well, how is it changing in a whole host of diseases?" - in fibrosis, in asthma, in cancer, a whole host of respiratory diseases, a lot of which don't have any active therapies or things that work..

Chris - And talking of therapies, will this inform how we make drugs?

Charlotte - I think it probably will. I think part of the reason the researchers did this work - as part of a collaboration called "Open Targets" - is to try and look at what's actually going wrong in respiratory disease so that we can have better, more efficacious therapies that actually target the mechanisms.

Chris - So understanding what causes the disease in the first place you can then work out better ways to treat it?

Charlotte - Exactly.

Chris - And you can work out if your drug actually works because you know where you're trying to get to?

Charlotte - Yeah. You've got to have a target to aim your therapy at. If you don't understand what's going wrong, you don't have a target...

Chris Smith speaks to miners and geologists deep underground at the driefontein mine in South Africa

28:57 - The depths and dangers of digging for gold

Chris Smith dives into one of the deepest gold mines in the world.

The depths and dangers of digging for gold
with James Wellsted, Len Zore & Karel de Langer, Sibanye-Stillwater

Throughout June, The Naked Scientists have been bringing you science at the extremes. And this week, Chris is going extremely deep by exploring one of the deepest gold mines in the world with members from the company, Sibanye-Stillwater.

Chris - This is seriously fast already though. My ears are beginning to go.

Len - Yeah. It's because you're dropping from sea level to below sea level at a high speed. Make a few yawns so that your ears can pop open.

Chris - People pay a lot of money for a ride on a fairground though!

Len - Yeah, we go on a merry-go-round everyday.

Chris - Today I’ve been lucky enough to descend into one of the deepest working mines in the world. It’s operated by the company Sibanye-Stillwater, in the Witwatersrand gold basin near Johannesburg in South Africa, one of the world’s richest sources of gold. In fact, about a third of the world’s entire gold reserve is thought to reside in South Africa, sitting beneath the surface. But why is that? Well, it’s because about 3 billion years ago, this area - in what’s now the northeast of South Africa - was an inland ocean. And surrounding it were mountains built from gold-rich magma brought to the Earth’s surface by volcanoes, and then eroded and washed into the sea by rivers, where they formed a gold reef, as Sibanye-Stillwater’s James Wellsted explains...

James - The Witwatersrand gold basin was essentially an inland water body, or lake, or sea, that had a number of rivers flowing into it. It was in quite a volcanically active period where you had a lot of old granites that had been produced from volcanic activity. The rivers were eroding those granites with the gold that was contained in those granites, and then as these rivers ran into the ocean you've got these big alluvial fans forming. And obviously you've got a river rushing into a still body of water, the water starts to slow down, and what happens is that the heavier and bigger particles drop out first. So in the early part of the fan you get a lot more gold concentrated, and it’s associated with conglomerates which are the bigger rock particles or rock pebbles. And then in the distal parts obviously you get the finer gold, which is probably at a lower grade, and that's what we’re finding over time: that the grade is getting less as we get deeper and deeper.

Chris - Are those sort of fans at multiple depths? In other words, have there been a succession, over millions of years, of deposits; and therefore you just dig through each of them to get to the gold in each case?

James - Yeah. There would have been a number of periods of, you know, dryer and wetter periods over the thousands of years that it took to deposit these ore bodies. So what you would have had is the inland water body growing and shinking. And as it did so obviously you got different phases: of more active deposition, and less active deposition. So you get stages where you’ve got the reefs, which tend to be conglomerates and associated with high fluvial activity; and then the more still periods which are dryer, where you get more muds and things being deposited, which don't have gold associated with them.

Chris - And what form is the gold in, in those deposits? Is it tiny particles? Are we talking nice big nuggets? What does it look like?

James - It's not nuggets like we find in some of the typical gold deposits overseas. Because they've been in river streams, they eroded, and they’re quite rounded particles. In some instances you can't see them with the naked eye at all, in fact most instances. So the typical grade of the ore bodies in South Africa is about 5 to 7 grams a ton - which, you know, that’s 5 to 7 grams of gold per ton of rock. It's not as rich as some of the big nuggetty ore bodies that you find overseas, but certainly it’s much more consistent and over a much bigger area.

Chris - So if I give you my wedding ring for a second, assuming I can get it off...I'm not asking you to marry me or anything. There you go, a wedding ring. How much do you reckon that weighs? That's 18 carat gold.

James - You tell me! That's a couple of ounces of gold, I guess.

Chris - And how much rock would you need to move in your plant to make that?

James - You'd have to move a couple of tons of rock to get this.

Chris - It's a lot isn't it?

James - It's very labour intensive work, capital intensive, dangerous work. So yeah, the price of gold is that for a reason.

Chris - It's worth its weight in gold even?

James - Indeed.

Chris - And with that, I went to explore this incredible setup. There are literally hundreds of kilometres of tunnels below ground, and I met James’ colleague, Len Zore, who accompanied me down. Now this is a very dangerous industry, although thankfully very few accidents now happen because safety is taken incredibly seriously. A poignant reminder was someone training me to use a rebreathing apparatus that would hopefully keep me alive for a while if we got buried. Then, kitted out in our hard hats, boiler suits, and boots, we stepped forward to await our ride - or as it turned out, near-freefall - down into the mine.

Len - We are now standing on the bank waiting for the conveyance to arrive. It is a vertical shaft that drops about 1 1/2 km, and you'll see the conveyance moves quite fast. It's not like a lift in a building, it's like 12 metres a second.

Chris - These are just sort of open cages, aren't they really?

Len - There's four compartments. You get your man winders, and you get your rock winders on this side. This we use for people and material; the other side is for rock.

Chris - We were joining one of the mining shifts heading to work, and this was the first of a number of lifts that descend into the mine, which extends kilometres down into the ground. In fact, it’s so deep - it’s the third or fourth deepest mine in the world - that the men working in the farthest depths take more than an hour to reach their destination. And that’s despite the dizzying speed of the descent...

Chris - This is seriously fast already though. My ears are beginning to go.

Len - Yeah. It's because you're dropping from sea level to below sea level at a high speed. Make a few yawns so that your ears can pop open.

Chris - People pay a lot of money for a ride on a fairground though!

Len - Yeah, we go on a merry-go-round everyday.

Chris - Once our stomachs caught up with us, we emerged from the lift at one of the main underground stations where the rock walls were painted a very tasteful cream colour. Now this area is big, and it's got a train track running through it to bring piles of rock containing the gold from the faces where they're being drilled and blasted out, so they can go back to the surface. Tunnels like this come off horizontally at different levels of the mine. They are called crosscuts and they're intended to intersect the gold reef, as it's known, on what would have been the floor of that ancient ocean way back in time. Pretty quickly though, the tunnels narrow down to just a couple of metres, and Len and I followed a team of miners out to where they were extracting ore from one part of the reef.

Len - We're standing here now at an 8 metre reef and the other side is 12 metres high. And in this reef you can see the various rocks that were transported with the sediment where you get your gold in.

Chris - Oh, I see. So you can use the fact that in amongst this, it's almost like a cake with raisins in, isn't it. Those are the pebbles - that tells you this is a layer which must've been washed into this primitive basin by the rain?

Len - That's it, correct.

Chris - And the geologists know what sort of configurations go with where the gold is?

Len - Yes, yes they do. Also with past experience, as the mines have started mining 50/60 years ago, they intersected the top bands of reef first, which is this one we’re talking to now, VCR. As you go lower down, you get your main reef and you get a carbon leader, carbon meaning it's heavier, so it's much deeper, which is a much older reef. You talk about older - this is millions of years of difference between the reefs. But the carbon leader is the one that's most richest, it’s got the most gold in it obviously, because gold is heavier than most substances. This VCR one has also got lots of reef in it, but you have to mine much more of it to get the same amount of gold as you would mine carbon leader.

Chris - Now this is of course a working mine and before I could ask Len any more questions, a gentleman turned up with the most incredible drill, more than a metre long, and he began to make holes so he could plant charges to blast out more ore for processing...

Chris - But how do the team know where the reef is and how to get to it? I walked a bit further along the tunnel with company Vice President Karel de Lange…

Karel - We do a lot of drilling beforehand, so we anticipate, we know already beforehand, how far we are from the reef; and we will know exactly when we intersect reef as well. The drilling goes ahead, so we all know within 150 metres exactly where the reef is, although we've already got delineation of the reef body through surface boreholes that we've drilled previously.

Chris - So the team know where the reef is, but because the deposit is sloping, they need to extract it in a series of manoeuvres that progressively remove more material each time, and eventually open up a larger space, one of which we were standing in…

Karel - In this instance - what we're looking at here - we’re actually right on the level and we mined into the reef on the level itself. So the mining that we do here, we actually mine from the crosscut, we mine into the reef and we've got these wide excavations. So we’ll take a top cut first, install our support in the hanging wall by means of long tendons, long anchors, and they will start to dredge down, so we will start to take it out. Eventually we'll have this wide open excavation of about 10 metres which we are standing in.

Chris - Between these opened up “paddocks”, as they call them, the team initially leave supporting pillars of rock to prevent collapse. But once the ore has been cleared from each paddock space, the open area can then be re-filled with processed ore tailings, which are brought back from the surface and mixed with cement; and then the pillars, which still contain gold ore, are themselves removed…

Karel - Now we don't take out the large excavation either, we run about 10 metres wide paddocks, and then we leave a pillar and we take out another paddock 10 metres further, and so we carry on. And then we will fold these open excavations by means of cemented tailings, and once these have settled and hardened we will come back and we will take out the pillars in between these cemented back fold paddocks.

Chris - Oh, I see. So you use the waste from the mining, cement it back together, shove it into the hole you've made, and then the bits you had to leave behind before, you then take those out. So you really do clear out the area and then fill it back in.

Karel - Exactly, exactly like that. We try to optimise the resource.

A droplet from a body of water

38:54 - Managing water in mines

When you drill a hole in a mine, water from natural underground sources wants to flood in. How do you stop it?

Managing water in mines
with Johannes Wagner, Water Consultant at Sibanye-Stillwater

Wherever you drill a hole, water from natural underground sources wants to flood in. And if you don’t keep an eye on this, it could impact on the water source for those living in the area; either depleting it or contaminating the drinking water with dangerous material or toxins from the mines. This is a situation that water consultant, Johannes Wagner, works to avoid...

Johannes - Well in this particular mine we're putting into the environment an average of 70 megalitres, that's a million litres per day, but we pump almost 100 or 110 megalitres per day.

Chris - Why the difference?

Johannes - The rest is being used in the plants. So we use our underground water also for processing, for mining, and for doing the gold, as our main transporter and the surplus water we keep clean and that’s suitable for disposal into the environment.

Chris - It's no mean feat to pump that mass of water up to 3 kilometres to the surface?

Johannes - Well, that’s actually a major part of our costings. So what we do is we have very big pump stations, obviously at the lowest points. At certain places we also do underground treatment, put the water into settlers, separate out the slush and the mud. The mud goes to the plant because there's also gold in there and then the rest we pump out through these huge pumps all the time, so it's a continuous process.

Chris - So where does all this water come from?

Johannes - Well the sources of water is mainly rainfall recharge, but also leaks in the system. You know, for example, the local municipality has got a 60% water loss, so their leaking pipes is actually also going down the mines. And then we have old sinkholes where, if there's a lot of rain, the stormwater runs directly into the mine workings that we've got to pump. So in the wet season we actually pump a lot more water than in a dry season.

Chris - So when you say 'leaking' pipes, are we talking freshwater or are we talking wastewater - sewage?

Johannes - We're talking both. The infrastructure is quite old of the municipalities and the course of the soils are moving in these dolomitic areas and that causes breaks in the pipes, and then because of that it leaks.

Chris - So you're pumping someone else's sewage out of your mine?

Johannes - We are. In fact, quite an amount. We estimate that almost 20 megalitres per day, 20 million litres per day at one mine of municipal water and wastewater we're pumping, which is not our water.

Chris - Is that not potentially a health risk for your miners?

Johannes - We have analysed this up to this point and so far we haven't detected anything. What we think is happening is because it goes through the wetted zone, the dolomitic areas act as a sand filtration system, so we pick up little bits of nitrates, you know nutrients but not really bacteria on anything. We do sample and monitor the situation though.

Chris - So what about when you don't want to work here anymore? Once this is worked out, you don't want to leave all these tunnels here and you can't presumably just let them flood because there will be consequences, wouldn't there? Have you got some kind of managed retreat strategy?

Johannes - Absolutely. Because a lot of people think we will create another acid mine drainage disaster, we did extensive planning and modelling and testing and we have a plan to close this mine in such a way that when it's done it will be almost as normal. In other words, the salt pollution will stop and it will return to the normal clean water situation.

Chris - So what is an acid mine tailings disaster that you mentioned, what is one of those?

Johannes - Well, what is happening on the centre of the Johannesburg area is, because of pyrites in the rock still left, and water and air and bacteria causes acid forming. The geological structures in that area is very much different from here. We don't expect, if we close the mines properly, any of that to happen here.

Chris - So what is the strategy? How will you do it?

Johannes - At closure, we will basically install plugs in the shafts, in the lower lying shaft areas, then carefully flood the mine in a controlled fashion with basically pressure relief valves because you don't want to create a pressure cooker by filling it up.

Chris - Oh, I see. Because the rock is so hot here, if you just let the water go in and seal the shaft off you going to have a high pressure buildup behind your plug?

Johannes - Just simply, if you fill up a tank you will have air on the top, and the air pressure will build up as you fill it up, so you've got to relieve the pressure because what we want to be doing is we don't want plug flow. We can fill up the mine and there's no water running through the mine, we won't have any pollution. So the whole thing is we fill up the mine up to the hot rock lavas, we plug it with concrete in a controlled fashion and then we let the normal recharge through to restore the situation, and that's basically the plan.

Chris Smith interviews microbiologist Kay Kuloyo who is looking for extreme bacteria living kilometres underground in gold mines

44:27 - Extreme life lurking underground

While teams continue to search for gold, others are looking for something quite different; life.

Extreme life lurking underground
with Kay Kuloyo, University of the Free State,

Some of the water in the mine has been trapped down there for millions of years, seeping through cracks in the rocks. And while the team continues to search for gold, others are looking for something quite different; special forms of life. Scientists have found life in some bizarre and extreme conditions in the past like around deep sea vents, and in our continuing search for life on other planets, the extreme conditions inside our own planet may provide clues as to how life like this might survive? Chris Smith met with Kay Kuloyo, formerly from the University of the Free State and now at the University of Calgary, who is looking for life deep underground.

Kay - In 2010, there was a paper that was published about a worm found in fissure water in one of the mines. This is one of the biggest discoveries to date because before that we only found smaller life like bacteria and in this case it was a nematode, which is an even higher order microorganism. So that gave an indication that there could be different levels of life in extreme environments.

Chris - When we say extreme environments, where were these organisms found growing?

Kay - This was in a 2.3 kilometre depth mine in fissure water, probably about 30°. So when we talk about extreme environments we’re talking about in the deep mines where there is very little nutrients and the temperatures can go as high as 70°C.

Chris - So to find complicated life growing at those extreme temperatures, in very nutrient poor environments, says there's something pretty special about those sorts of organisms?

Kay - Yes. It means that these organisms have genes that can help them make the kind of food they need. In the absence of sunlight and other sources they can actually use the chemicals and the minerals in the elements to make their own food and survive these conditions.

Chris - How did they get here?

Kay - Well the theory is that over millions of years ago, as the water gradually seeped down into the surface of the Earth, and when you had seismic activities, and the water was going down some of these microorganisms came down with the water and they became trapped here for so long, and over time they have been able to adapt to the conditions here.

Chris - How do you know that's how it happened and that, for instance, they didn't just arrive with the last rainstorm washed in from above?

Kay - Okay. Well, we do isotope analysis of the waters for carbon-14 dating to determine the age of the water. That tells us that some of the water samples that we’ve taken here are millions of years old, and sometimes even up to billions of years old.

Chris - So if the water’s that old, the organisms must've been in it for at least that long?

Kay - Yes.

Chris - So why are you down this mine today?

Kay - We never pass a chance to take one or two samples because you never know what you find.

Chris - And how are you doing that?

Kay - We have sterile Falcon tubes with us that we always carry, and that's to grab samples. If we find a seepage in the rocks, we can take some of the water samples or if we find biofilm growing around the rocks, we take that and then we culture in the lab and see what's in there.

Chris - Because there’s some water dripping down over here, is this of interest?

Kay - We we think it might be fissure water, we need to ask the geologist to confirm that. But if we see water coming out of the rock surface like this it is properly old water that is seeping out. And then what you see on the surface of the rocks like the brown colour and the black colour, we think that’s microorganisms that are growing on the rock and also using the nutrients from the water to survive. So over time, they form a film on the rock of different colours; black or brown or white or pink, depending on the kind of nutrients that they are using. So for us, this is easy for us to collect and understand what the micro biodiversity is.

Chris - Do you have a lot of contamination from microorganisms brought here by us?

Kay - Yes. Because there's a lot of human activity, mining activity around here and especially the places where there's been a lot of development, then most times we find microorganisms that have come from human activities, even sometimes microorganisms like E. coli. We find them in these water samples so we have to be really careful what we say is originally from the mine and what's from the surface.

Chris - Shall we grab a sample?

Kay - Yes. Even very little water samples can yield a lot of information about the microorganisms. So I’m just going to scrape some of the brown colour. I don't know if you can smell a little bit of hydrogen sulphide?

Chris - It does smell a bit sulphurous, yeah.

Kay - I'm going to scrape some of the black colour because we think that could be sulphate reducing bacteria.

Chris - And why do you think the sulphur is important?

Kay - Because usually what you find in goldmine's is a lot of pyrites and sulphates as well and, you know, that's also associated with the gold.

Chris - So the bacteria are using the sulphates as a food source, because they're obviously not able to rely on energy coming from the sun, they have to get their food chemically?

Kay - From what's around them, yes. You find some of them use the sulphates, some use the iron as well and some use perhaps the nitrates.

Chris - What are the implications of this discovery?

Kay -  Well, because of the conditions that we are finding some of these microorganisms in. For instance, the ones we find in high sulphate areas in the goldmines we are able to use some of these microorganisms for cleaning things up, like acid mine drainage agents, things like that. Also use them for green technologies, taking away more chemicals and using biological agents.

Chris - As a vice president of the company has just pointed out, can you not discover a strain of organism that will eat gold and then poo it out in the right place and make their job a lot easier.

Kay - Well, that some of the research that we are doing where we have microorganisms that can bioaccumulate the gold, and then we can extract the gold from the microorganism. As one of them pointed out that in places where they cannot really reach or it's so dangerous is it possible for us to use microorganisms, that's the next level that we’re looking at. We do have some bench scale applications of this where we've seen it happen, with not just gold but copper and some other minerals, so taking it to bigger levels and really showing that it can work is what we're looking at now..

Chris - Can it be scaled industrially to match what these guys do with drills and diggers?

Kay - Well, that's going to take a lot of time. Microorganisms work at their own pace. Over time we can use it for small-scale applications but right now it cannot match what these guys are doing, but give us some time and we might be able to apply it to those processes.

Gold bar

50:33 - Gold: Turning trash into treasure

SPOILER: Mining for gold isn’t like what you see in films...

Gold: Turning trash into treasure
with Ricardo Barker Cooke, Grant Stewart & James Wellsted, Sinbanye-Stillwater

With the rocks collected and hoisted to the surface, it was time to go back up to ground level to see how the gold is processed because, unfortunately, this isn’t like you see it in the films. There are no shiny hunks of gold waiting to be pulled out of the walls of a tunnel. Instead, tiny particles of gold are locked up with the rocks alongside other useful materials, like uranium and copper, and there’s also a huge amount of waste in there, things like pyrite or fool’s gold. The first stage in getting the gold out is to break up - or mill - the material to liberate the gold particles, as Ricardo Barker Cooke explained. Chris Smith then caught up with Grant Stewart and James Wellsted about further gold processing.

Ricardo - The gold is situated in your finer particles and you need to actually grind it to get to the extra gold.

Chris - And how do you smash up the particles?

Ricardo - Currently we've got six mills. So basically what happens is your feed goes into your mill and it's basically the steel balls that is crushing your material.

Chris - So the steel balls bouncing around inside the milling machine, and as the slime goes between the balls it gets crushed?

Ricardo - That's correct, yeah. It's basically just crushing but on a much smaller scale.

Chris - And how much stuff is going through these mills every minute or two?

Ricardo - Okay. We pushing 400,000 tonnes a month. We're talking about doing about 550 tonnes per hour.

Chris - That's a lot isn't it?

Ricardo - It is a lot.

Chris - Next, the excess water is removed, leaving a pulp. And then stage three involved something I wasn’t expecting…

Ricardo - After thickening we get to a section which we call the leaching section. And in the leaching section is where we add cyanide.

Chris - Say that again, you use cyanide?

Ricardo - Cyanide. Sodium cyanide which gets used for gold dissolution.

Chris - The milled ore is mixed with cyanide, and that pulls the gold out of the rock and into solution, and then you add carbon to soak it up...

Ricardo - Carbon is a reagent which has got pores,  and that will absorb all the gold onto the carbon. The gold is not in its purest form yet because it still has all the other impurities which is within the slurry. Then the carbon gets taken to the elution process where we expand the pores of the carbon and then we take the gold out back in to the solution form.

Chris - So having now separated the gold from the carbon, which is done using sodium hydroxide and a very high temperature, they use electricity to pull out the gold in a system called an electrowinning cell…

Ricardo - And that solution gets circulated through the final stage which we call the smelt stage whereby it circulates the electrowinning cell and that's where we produce our final product. Still not in its purest form and that gets dispatched to rand refinery three times a week.

Chris - What they then send off by helicopter is about 88% purity. And after the final clean up at the refinery, you’re left with about a 99% pure gold bar.

The current process tries to minimise the waste that it produces. Indeed, once the gold has been extracted, the mine is backfilled with that waste. But it hasn’t always been like that. Across South Africa there are huge piles of waste material - known as tailings - which have built up since gold was first discovered in the country in the late 1800s. But techniques have improved a lot since those days, meaning that the clean up process can now actually pay for itself. Grant Stewart heads up the gold retreatment facility that’s handling the old mine waste from years gone by…

Grant - One of the fundamental objectives of this programme is an environmental and socially responsible objective, and that's to take all the nasty tailings dams which exist over 40/50 kilometre radius to a central deposition site, thereby taking away the dust pollution, freeing up available land for development and obviously there's a benefit from a gold and uranium and a sulphuric acid perspective that would make it economically viable.

There's around 795 million tons of material that we have available for immediate processing and that would obviously be processed over a life of around 30/35 years. But that, essentially, contains about 150 odd million pounds of uranium, and I think it was about 7.1 million ounces of gold. So there's a substantial amount of economic benefit from being able to extract and process these tailings.

Chris - So literally a case of trash turning into treasure.

And with my day in the mines nearly over, it was time to catch up once again with James Wellsted and we considered the scale of South Africa’s contribution to the world’s gold supply…

James - I think I've heard numbers of around 40% of all the gold in circulation, of which most of it is still in circulation because gold doesn't tend to get used up in any processes. In terms of reserves, if you look at resources that still lie underground and that potentially could be unlocked through new technologies, there's still probably as much as what we've mined in the past, so significant amounts. Much more than, I think, any other country in the world. But the problem is it’s depth  and the cost of extraction which makes it difficult too, so that's why it's likely to possibly lie there for quite some time.

Chris - So next time you go walking past a jewellers, you can safely assume that over a third of the shiny stuff in the window probably came from here, near Johannesburg but a very long way down. I’m not sure if this programme qualifies us for the world’s deepest radio programme or podcast but it should certainly make us all think deeply about how we reach and how we use the world’s resources; and, as I drove back to Johannesburg away from the deafening drilling, mining and processing noises, I experienced something else golden - silence...


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