by Douglas Page©, 2000

Science is going to extremes to find anaerobic organisms able to remediate contaminated soil. Douglas Page profiles one group of researchers who have wandered into one of the most forbidding places on earth - the deep levels of South African gold mines - in search of microbes called "Extremophiles", thought to be capable of surviving conditions of extreme heat and radiation.

The researchers get no special treatment. Ivy League credentials mean nothing here. Dressed in company-supplied orange cotton coveralls, knee-high gum boots and hard hats, they join the miners - and the tension - collecting on the surface, near the 2 Shaft entrance, waiting for the cages. Here they are issued a charged battery pack and headlamp, the only light they will see in most areas of the mine.

The vertical shaft is a concrete-lined silo that disappears below, into the darkness. The cages - surprisingly clean steel boxes not much larger than freight elevators - carry as many as 150 miners at a time. They are most crowded during shift changes. "Sweaty bodies jam in tightly, like a rock concert," says postdoctoral microbiologist Duane Moser, leader of the team of Princeton University researchers entering the deep levels of South Africa's East Driefontein gold mine.

Moser and his team aren't sifting for nuggets of gold, they're sampling the depths for microbes that might manage to survive metal-rich environments of high temperature, pressure, pH, salinity and radioactivity - creatures potentially useful for soil remediation. Since anaerobic microbes are known to exist elsewhere, project leader T.C. Onstott, of Princeton's Geosciences Department, suspected certain mines might yield such life-forms - called "Extremophiles". Onstott arranged access to the South African mines ("an unprecedented and hard-won courtesy"), then enlisted Moser to organize the field/analytical end of a project to see what might be living in the Transvaal's 'carbon leader', a highly mineralized, organic-rich vein that contains concentrations of uranium and the world's richest gold deposits, where the rock temperatures range to 60 degC. With Moser in South Africa is Joost Hoek, a graduate student in geology at the University of Pennsylvania. The study also involves the Kloof, Beatrix and West Driefontein mines.

Moser became involved in the project by answering Onstott's ad in the American Society for Microbiology News, calling for someone with expertise in geology (his undergraduate major at the University of Wisconsin), microbiology and molecular biology. It helped that one of Moser's passions is caving ("I included a photo of me in a cave in Kentucky showing only my muddy boots sticking out of a very small hole."). While earning a Ph.D. in Biological Sciences, he worked coordinating a study of deepwater Great Lakes sediments, mostly studying microbial ecology. He got the interview.

NOT AN ENVIRONMENT FOR 'SISSIES'

"The miners file in and pack ever tighter," says Moser, who grew up on a farm in Wisconsin and always loved the outdoors, seeking adventure whenever he could find it; you don't have far to look in the mines. "Soon, your arms are pinned against your sides." There is yelling and horse-play - perhaps to bleed off anxiety. The miners speak a mixture of languages - Fanakalo, Zulu, Sotho, Afrikaans and English, but they share a common apprehension. This is not an environment for "sissies".

A klaxon announces the inevitable, then, like prison bars, the steel doors slam closed loudly and the gage begins its descent. "In a few seconds all is blackness and invariably one or more of the miners turns on their lamp," Moser says. The cage picks up speed, accelerating to 65 kph, slipping smoothly along the rails that guide its E-Ticket cable-drop to the well-lighted dock at the bottom, 1,800 m below the surface - deeper than four Sears Towers. A complex set of weights moves opposite the cages.

"I was amazed the first time I saw the cages and winders," he says. "They are remarkable examples of engineering and the scale is as massive as a suspension bridge. The mines are proud of them and their safety record." Driefontein has never had a major cage accident. Those who ride them for a living find them safer than driving a car.

Air pressure change can be a concern the first 1,000 m, due to rapid decent. "This is all in a day's work, as it would be for commercial divers," Moser says. "The miners know how to deal with it. If you have a cold and thus might have trouble clearing [your ears], you are strongly discouraged from going into the mine at all."

As the cage comes to a stop, cable-stretch causes it to bounce like a bungee-cord, sometimes 0.5 m or more, says Moser. "The trip takes about 4 minutes." These may be the world's fastest "winders". (Elevator is not part of mining vernacular.)

The mine goes much deeper, but limitations in cable-winding technology restrict the depth of each shaft. After a length of about 2 km, the weight of the cable itself becomes so great its weight-bearing capacity is reduced to the impractical.

Nothing is mined here, at the bottom of 2 Shaft; 22 Level is merely a junction to a second, sub-vertical, cage, which descends to 50 Level, 3.5 km below the surface. In some mines, when the price of gold is right, a tertiary shaft waits in the profound depths at 50 Level to plumb the Transvaal even deeper.

All of the Driefontein vertical shafts intersect Transvaal Malmani Supergroup dolomites on their way to the gold-bearing strata below. These dolomites are actually quite wet, comprising massive aquifers filled with millions of liters of pure water. In order to prevent disastrous flooding, the vertical shafts are cemented aggressively during construction.

Below the dolomites, the mines become arid, although there are exceptions. In one incident, a water intersection was hit about midway through a 3.5 km crosscut connecting 5 and 4 Shafts at 3.3 km down. The shaft is now used only for emergency escape purposes. "Emergency escape routes are well-planned and take full advantage of cross connections between shafts and even other mines," Moser says. "It is said that someone can travel all the way across the West Rand - 100 km - totally underground."

ALWAYS THE HEAT

"The sub-vertical cage seems to descend faster than the vertical cage," says Moser. "The darkness, although complete for the whole trip, is somehow inkier in these depths. And always the heat builds and builds as one goes deeper. You start to sweat. The air is heavy. Breathing is labored."

Finally, the scientists reach the level they intend to sample. "The heat is now quite noticeable," Moser says, with aplomb. "Men are sweating profusely already and the mine is as well ventilated as it is going to be at the shaft." The working faces tend to be some distance from the shafts, however. The carbon leader itself is in a very tight band that tilts away from the shaft like the upper arm of a "K", rising at a 20 - 30 degree angle; thus the deeper levels have shorter walks. Even so, at 46 Level and 48 Level, where the team did most of its work, the hiking distance is 2 to 3 km, a distance over which the team must hand carry its own water supply and gear (hammers, chisels, collection bottles, coolers, and scientific monitoring equipment) - with the realization that the gear will be considerably heavier on the way out when filled with rock and water samples.

Not far into 46 Level the team encounters two huge wooden doors, used to control airflow. "Air is life in these mines and heat and radon build-ups are threats taken seriously by the mining companies," Moser says. "There are legal standards that they try hard to meet. The virgin rock temperature at these depths vary from 48 to 60 degC. These are lethal temperatures for man. All who work in the mines must be certified as heat-tolerant before they go down."

The doors are used to meter airflow to keep the passages livable. Once beyond the double doors the temperature changes dramatically, due to air returning from deeper levels. "An involuntary heat shiver runs through you when you walk into the hot wind," Moser said. Relief is not far away, however. Spot-chillers are installed every few hundred meters throughout the passages, "large, noisy radiators" that transfer the air heat to water, something like "swamp coolers", that blow a stream of cool, wet air down the tunnels.

Plodding onward, he says, with the heat and perspiration sapping your strength, an inconceivable thirst overwhelms you. "Dehydration is a serious threat. Earlier, I carried 2 liters of water and invariably, no matter how I tried to conserve, would run out. Once on the surface, I was so wiped out I had to take a nap, which often amounted to collapsing for several hours. By doubling this to 4 liters and then consuming a salty bag of potato chips and swilling more liters of water on the surface, I found such effects to be largely alleviated. Even with consuming 4 liters, one emerges with a raging thirst."

The mine is cooled by air and recycled service water. "We have found there are a few highly stressed but viable organisms, all mesophilic (bacteria which grow best at temperatures of 20-45 degC), limping along in the service water," Moser says. "This has turned out to be valuable, as the water invariably contains the lipid biomarker signature of oxidatively stressed bacteria (epoxides). These compounds can be detected at low concentrations and have served as a reliable chemical tracer from service water contamination."

At the working face, the team takes samples of water dripping from boreholes, although the major focus of their work is in the stopes - crawl-spaces sliced from the carbon leader so squat you can't stand up in them. "The carbon leader and other reefs (veins) extend outward in an extensive tilted horizontal plane," Moser says, "meaning all of the mining is done on a considerable slope." Here they obtained the first carbon leader samples.

"This is almost pure, black carbon at a depth of roughly 2.3 km," he says. Mine geologists maintain this high-carbon leader is the richest gold ore in the world. Whereas the mine yields typical values of 10 to 12 g/ton, this high-carbon leader grades out at 5,000 g/ton.

At this level, Moser says, there were also many great accumulations of apparent elemental sulfur covering the walls. "The sulfur was always associated with small cracks and fissures in the walls and was often dry and feathery in appearance. When the sulfur was associated with water, the pH was always in the 3 to 4 range."

THE MAZES OF HELL

A few days later, on a subsequent trip to depth at West Driefontein, Moser took samples at a location where water had been intersected 2 weeks earlier at 38 Level in 6 Shaft, 2.7 km down. To get to this tunnel, Moser had to follow the most hellish of mazes, requiring descent down two shafts, then riding a personnel carrier 3 km to a tertiary shaft, taking it to the bottom, then walking another 2.5 km before entering a fissure nearly 12 km from sunlight. "The 'carrier' is a little version of the cage on wheels," Moser says. "It is very low and guys clamber in and sit hunched over on metal benches. The ride is not comfortable, but it sure beats walking."

As if that weren't daunting enough, the region is seismically active. "We were hit with some pretty serious seismicity while in West Drie," Moser says. "The first 'bump', centered somewhere in Western Deep Levels some 8 km distant, hit while we were in the stopes at 6 Shaft. You could hear and feel it approaching for a spookish period of time and then move on. It was like it moved right through you. The sound, more felt than heard, is like a low rumble mixed with elements of opening a peanut butter jar in a toilet."

Faith in its fullest dimension follows miners underground, but when the ground itself moves, all human confidence is suspended. The riveting realization that kilometers of rock rest overhead cannot be driven from the mind, as it must be at most times at depth. There is no escape. The rumble is so loud it transcends the mine's ambient din. The shaker, a Richter 4.1, "shook us up a bit," says Moser. "The drillers all turned off their machines and there was a second or so of eerie silence, then the bump pushed through. The miners could actually feel the rock contract as the bump approached. They all looked at one another and all was silent for another 5 minutes after the shock. Then they all just went back to work."

On the way out, a second shaker hit with a "massive bang", centered in the 6 Shaft pillar where they were waiting for the second lift. Amazingly, very little damage was done to the

mine, he said, although lots of debris rained down from the roof during both. On the way out, the team could see places where rock-burst had taken a section of roof or wall out, but always the heavy mesh retainers, strung for just such events, held the rock back.

West Driefontein, a, shallower, older mine, was largely ruled out for further studies based on indications of service water contamination, borne out by the epoxide data. "The waters that were studied came from areas that were based on distances from other mining activity, and chemical signatures thought to be pure and pristine," says Moser. "This was important because it demonstrated that we could recognize service water with quick and simple techniques in the field so as to avoid wasting time underground chasing unproductive samples."

The majority of carbon leader samples were taken in East Driefontein 5 Shaft 46/48 Levels, collected with ever-improving care and technique. "The sampling in East Driefontein represented a very different situation," Moser says. "No levels are present over the stope here, as only the carbon leader is being mined. It's a new mine. With each blast virgin rock is exposed. No other mining is conducted for at least 4 km in any direction."

The sampling method settled on in the end was to collect a large freshly blasted hand sample with carbon leader cutting across it, to which a variety of chemical (e.g. rhodamine) and particulate (e.g. bacteria-sized flourescent microbeads) were applied. The sample was then blasted in situ with an actual mining hose to simulate treatment it would receive in the mining process. The samples, weighing as much as 15 kg, along with bulk quartzite controls, were then transported to the surface for processing.

"At the surface, the sample was first place in an anaerobic chamber which we set up in our field laboratory," Moser says, "and the outer surfaces were carefully pared away with the powerful jaws of our hydraulic rock splitter, a device made with hardened steel and powered by a 20 t jack." Samples from the outer layers and the resulting putatively pristine internal nugget were taken for tracer analysis and a suite of other studies. "A portion was ground to make a slurry, or chunks were added directly to bacteriological growth media for enrichment experiments," he says. "Subsamples were likewise archived frozen or fixed for electron and light microscopy, DNA extraction, lipid biomarker analysis, mercury porosimetry and geological analysis. Great care was taken to be certain that every surface that touched the precious rock sample had been either bleach sterilized or autoclaved."

In later experiments, the mine provided the team a coring team, Moser says. In this way, tracers were added directly to the drilling water and the miners core directly into the carbon leader from the sidewall. Samples thus collected were then processed using sterile tools.

Thus far in the bedrock ovens, Moser has obtained quality samples that have never before been available to science. "All sorts of obstacles had to be surmounted," he says, "but in the end we have a freezer full of great stuff, a growing spreadsheet of data and isolates that very well may be life from the deep subsurface."

Early indications are a new form of the bacterium, Thermus sp., isolated from groundwater samples, may be anaerobic, radiation-resistant, and appears, at least in the mine, to interact with iron, chromium, cobalt, and uranium - elements common in contaminated soils. -end-

This article appeared in Science Spectra (No. 19, 2000).