Monday, May 28, 2012

Volcanoes at Night

The following exchange is typical of the sometimes unusually informed questions we can receive from young children. In the exchange that follows, the Mom (Jo) wrote to Ask-a-Geologist for her daughter, Samantha, because Samantha wasn’t allowed to have access to the internet yet. Samantha was just 3 at the time these questions arrived!

I am writing to you because I promised my daughter I would send Jeff Wynn the Volcanologist from one of her volcano books an email. The books I read to her every night are Volcanoes! (National Geographic) for Kids, The Best Books of Volcanoes, by Simon Adams, and Time For Kids: Volcanoes.

Not in a million years would I think that my 3 year old daughter would be so obsessed by volcanoes but she talks about them every day at school and always mentions tectonic plates, lava and magma. This phase of hers has lasted since December. :-)

Anyway, questions she had was why does the Volcanologist always have a stick?
==Jo L.

I have not seen volcanologists use sticks except for leveling rods for surveying.  In some cases it would be wise to use hiking poles so you don't fall and do a face-plant in the glass of a recent flow. When we sample some active magma we usually use a piece of wire trolled through an active (glowing red) lobe, or use a trowel to dig out a blob – the hot lava is dense and very sticky (not to mention HOT). It is VERY hard to collect a useful sample, even with heavy gloves.

Can you really walk on hot lava?

Yes you can walk on hot lava, but I don’t recommend it. The human body is a bit more dense than water, but typical basalt lava has a density up to three times this. I've walked over Kilauea magma lobes as they were moving downhill into a forest, and were swelling in thickness – but only after an initial gray crust had formed. The problem is that even the crusted lava is so hot that they will melt your boot soles rather quickly. Cold lava will destroy your boots also - but mainly because cold lava is solidified, crusty glass, and the abrasion tears the boots up at a phenomenal rate. The other problem with walking over hot lava is that the air temperature above it is suffocatingly hot - without a thermometer to say for sure, I would estimate the air temperatures above some flows I've walked over southeast of Kilauea were up in the 120F - 140F (50C – 60C) range. You can't stay in that for very long at all, and if you are downwind you can't stay there either - so in several occasions I had to walk across a new flow just to get out of the heat and back to my helicopter. Helicopters can’t get adequate lift in those high temperatures, which means the pilot could not rescue me unless I moved away from the hot zone.

Why the Pompeii guys not use their cars to get away from the Volcano?

They didn't have cars in those days (79 AD), and I'll bet all the donkeys had already taken off running on their own. The REAL problem with Pompey was that many of the people were likely killed by a rush of hot gas (called a nuee ardent) that roared down the volcano's slopes at high speed - and then they were engulfed and covered by pyroclastic flow debris. This is extremely hot ash and pumice that rained down on the survivors faster than they could run, and engulfed, suffocated, and burned those not already dead. It must have been a fast death, but a very painful one.

Don't know how long she will be so interested in this topic but I try and get books and watch videos of volcanoes as much as we can.

Keep feeding her books, and then just stand back in awe at what you have made.

Have a nice day!

You too.

Hi Jeff Wynn, Samantha was thrilled to hear from you and took your email to share with her class at the NW Montessori School. They all enjoyed hearing about volcanoes. You have a fan!
Samantha has another question.
She always calls Mount Rainier the "Dormant Volcano" but she wants to know why it is a dormant volcano.

And another.
Why do volcanoes erupt at night? I tried to tell her the erupt during the day as well but she is fascinated on how bright they are when she sees pictures of volcanos erupting at night.

Jo L., Mom of Samantha (future Volcanologist?)

Dormant is a fuzzy word. Volcanologists will call a volcano "dormant" after it has been quiet for a long time. How long you would call "long" is still being argued, but generally is up to the individual geologist. She must weigh when the last eruption took place, and what the previous eruptive history was. Mt Rainier had its last "classical" eruption (ash and pumice flew up and out of it, or lava built domes or flowed down its flanks) several thousand years ago, but a big water-and-debris flow called a lahar (the "Electron” flow) roared down into what today is Tacoma, WA, only ~500 years ago. Thus that "dormant" characterization is even fuzzier.

Volcanoes don't care what time of the day it is - no one has ever been able to get a statistical correlation with tides - the Sun, the Moon - for instance. So volcanoes erupt as often in the daytime as in the night-time.  Samantha is probably impressed with some Strombolian activity photographed at night. Glowing yellow-red cinders flying out of a volcano look spectacular in night-time photography, but aren't nearly so in daytime images. 

Samantha is unusually precocious. We usually don’t see questions this sophisticated until kids become teenagers. Keep feeding her books. We need people like Samantha to be the next-after-next generation of leaders in science.

Friday, May 18, 2012

Putting it All Together: Finding the Bacon

As a graduate student at the University of Arizona, I somehow wangled a summer job with AMAX Exploration, a mining company related to the Climax Molybdenum mine in Colorado. Like Bear Creek, Kennecott, Placer Dome, and Rio Tinto, this was another exploration entity focused on locating another billion-dollar mineral deposit.
My assignment for a summer: travel all over remote southeastern Arizona and southwestern New Mexico and make gravity measurements. I was given a 4-wheel-drive vehicle, a gravimeter, a credit card, a $400 cash advance, and a set of maps with broad circles on them where there were no gravity data. I was basically a free agent: leave Monday morning, and return Friday evening, and collect as many gravity stations as I possibly could - in a remote region where you could have a vehicle break down and find yourself 40 kilometers from the nearest human being. This sounds like the ultimate freedom, doesn’t it? Well yes, but it had its drawbacks. For one thing I would push myself to work 12+ hour days, because I missed my little family - and wanted to collect as much data as possible to make sure I kept this job. For another, it meant that when I had a vehicle breakdown, it could be potentially life-threatening because I was so isolated. This happened to me several times during that first summer working for AMAX.
You may ask why was gravity data so important?  Amax was looking for another porphyry copper deposit like the billion-dollar monsters found all over southern Arizona and northern Mexico. All the porphyries exposed to sight had been already found, so that meant that we had to search areas where others could still be hidden. A major potential target area was where valleys in the Basin and Range province (that included Arizona, Nevada, parts of Utah, and Mexico: they were covered with recent sediment weathered off the surrounding mountain ranges.
We all knew that dirt, sand, and gravel - basin and valley-fill material - are less dense than a magmatic porphyry body; the porphyry should show up in gravity data, then, as a denser “bulls eye” on our final corrected map.
I also spent a day working with a geochemist, and another day I spent working with an economic geologist from the project team. I learned more in those two days than I did in a month in school.
Again, it all goes back to the deposit model thing. If you’re looking for something, you need to think out carefully where it might really be, how it got where is is, and what it looks like… or you will be wasting your time. I think of the story of the lady looking for a quarter under a street lamp; when asked by a friend where she dropped it, she gestured towards the dark street hundreds of meters away. "But there's better light here."
The porphyry-hunting team had sat around a table to think these things out – and how one might logically go about looking for a "blind" (buried) porphyry. They realized that all the exposed porphyry copper deposits were already being exploited – and in fact they had been largely found far back in the 19th Century. The trick was to find those that were hidden: covered by later volcanic flows, or debris flows, or soils. There are huge basins in Arizona: bathtubs filled with dirt, as one geologist put it. Fully a third of the state has never been looked at for blind porphyries.
The objective required a cooperative effort that was also sequential. My compiled gravity maps showed several possible interesting anomalies - places where the basins were not smooth gravity lows. Typical of the real world, however, they were never neat bulls-eyes – because the gravity meter picks up density changes at all different depths beneath it. It could “see” the edges of ancient canyons buried beneath the valley fill, and other density contrasts, which would complicate the interpretation of any final result. The geophysicist I worked for, however, was very smart, had been around, and had thought a lot about what the data showed. Frank picked several areas that could use some follow-up. He also had convinced AMAX management to pay for an aeromagnetic survey in narrow areas of the team’s focused interest: those flat-looking basins. 
The team now had TWO sets of geophysical maps.
I was encouraged to go out with the geochemist one day – the company encouraged this sort of cross-pollination. The thinking was that if we each understood what the other was looking for, we could help each other – or report interesting things that the other guy might want to follow up on. The geochemist was working from my gravity maps – with certain areas circled by Frank, the project geophysicist who had hired me.  The geochemist would drive his own 4WD vehicle cross-country, looking for large Mesquite bushes in those areas. He would then fight his way in past the green vegetation and clip off thumb-sized chunks of stem, collecting them in a sample-bag which he carefully labeled. These he took back to his lab in Tucson, where he reduced them to ash and then did a chemical analysis for trace levels of copper, arsenic, silver, and 17 other elements. A 20-element suite cost only a bit more than a 3-element suite, so it was more cost-effective if you also hoped for a pleasant surprise.
I asked him why he was doing this? He told me that after the first white men entered the region with all their cattle, the native grasses had been largely eliminated. The Mesquite bush, freed of water competition, survived and with cactus was pretty much all that remained because it had such deep roots. How deep? Miners, he told me, had encountered Mesquite roots in tunnels they were digging underground in the Bisbee copper mining district. Anecdotal word of mouth suggested Mesquite roots reached deeper than 30 meters (100+ feet). THAT’S how you become the dominant surviving plant species in a desert!
The geochemist contoured a set of maps for the region in southeastern Arizona where the project team had started to focus its interest… one map for each element from his chemical analyses.
Now we had TWO different SETS of maps: geophysical and geochemical. The gravity showed areas with a higher-than-usual gravity field (greater density of rocks under the gravimeter) and the magnetic data showed anomalies that might or might not be caused by a porphyry intrusive. Less than half of these porphyries in Nevada, after a long and careful inventory, had turned out to be magnetic, so by itself the mag data were not diagnostic. We also had “pops” here and there of copper and other metals from the Mesquite geochem sampling.
The exploration team gathered in Tucson and went over the geophysical, geochemical, and surface geology maps. There were several areas they all agreed were possibilities. But a single drill hole, 300 meters deep, would cost at least $50,000. Hmmmm. More proof is needed to justify this kind of expense to corporate HQ.  
The geophysicist suggested another type of geophysics – more expensive per area covered, but they had already narrowed down the areas they would use it on. This kind of geophysics was electrical in nature, called induced polarization or “IP” for short (for obvious reasons). It turns out that if you inject electrical current into the ground and hold it steady for a second or two, it would “charge up” certain kinds of minerals immersed in groundwater deep under the ground. Pyrite (so-called “fools gold”) was one of these minerals, but no one was interested in pyrite – it was just iron and sulfur, and they were everywhere already. But pyrite was often associated with certain copper minerals, for instance gold-colored chalcopyrite, bornite (so-called “peacock ore”), or black covelite, a copper oxide. THESE were what they were looking for. Any excess pyrite found might just prove to be a halo around a big, hidden copper deposit, where all sorts of metals were concentrated by the hydrothermal process described earlier.
In IP survey was contracted out, and the operator sent a report back on his interpretation of the rather cryptic results. He saw polarization layering: the deeper the IP system looked, the stronger the apparent induced polarization effect was. This was a well-known geophysical version of fools gold called electromagnetic (“EM”) coupling. This phenomenon was often seen in conductive groundwater environments like Arizona had in abundance – always getting stronger with depth - as the transmitted electrical current at the surface of the ground set up eddy currents of electricity deep in the ground that acted just like disseminated pyrite “lighting up” with an electrical charge.
The contractor’s summary: I am seeing just EM coupling, nothing of interest.
The project geophysicist, however, pored over the maps for a long time. He noticed that the apparent EM coupling was NOT perfectly layered like EM coupling, but had a slight shift below where the geochemist had gotten a copper “sniff” in his mesquite chemical analyses.
Now comes the serendipity part of this story. I mentioned that this particular geophysicist was different than other geophysicists. Frank was an iconoclast: he thought differently than other people. I learned later that he had negotiated his AMAX salary with a “rider” on it. Every year the company would allocate one drill hole to be drilled on one of his hunches. I had never heard anything like this before or since, but it must have appealed to the intrigue-bone in some senior AMAX manager somewhere.
The company was about to abandon this particular target area, located near Solomonville in the Safford Valley of southeastern Arizona. Frank called for his annual “hunch hole.” Now keep in mind that the faint anomaly he was looking at was probably at least 200 meters (600 feet) deep, and Mesquite roots could not possibly reach down that far. Perry, the project geologist, told him he was crazy, but Frank insisted. The first drill went through 200 meters of sediment… and then intersected 15 meters of pure massive sulfide ore, almost all pyrite. BINGO. It was an astounding success. I saw a chunk of that drill core on the conference room table: it looked like a thick bronze bar. The target property was now even given a name: Sol.
AMAX formed a consortium with Phelps-Dodge corporation to help cover the cost of another 30 – 50 drill holes. The countryside around the discovery hole was quickly claim-staked and then grid-drilled. But after all that work the consortium kept the results to themselves. There was a clue, however: no infrastructure was ever built. It must have been a “bust” even after all those sulfides were found.
By that time I had gone back to school for the Fall, and it wasn’t until nearly a year later that I saw Frank again, and asked him what had happened. Knowing it was considered proprietary information, but knowing also that I had poured a lot of effort into the project, Frank paused. Then he said “We successfully outlined a porphyry sulfide stockwork.” He watched my face for comprehension… and then winked.
What he had NOT said was a “porphyry COPPER stockwork.” In other words, lots of pyrite, but not enough copper, silver, and gold in it to justify a mine development effort when the price of copper had sunk to below $1/lb ($2/kg).
Technically, this was an elegant, successful exploration effort. AMAX recognized that they had a brilliant team in their Tucson office, and kept funneling resources to them for many more years. But while Sol was a success, it was not an ECONOMIC success.

Wednesday, May 16, 2012

Chromite Geophysics

At this point I'm going to move into more direct applications of geoscience. We will start with this chapter on geophysical methods and why they are immensely useful. Simply put, geological mapping covers the surface of the earth and makes inferences about the third (buried) dimension from this. Geochemistry is similarly two-dimensional, but inferences can also be drawn from these data about the third or buried dimension. Geophysics, on the other hand, directly images that third dimension. That sounds wonderful, on the face of it, but there are limitations that one must always be aware of. For one thing, if there is significant topographic relief, it complicates any interpretation. For another, the deeper you want to "see" the less resolution that you will have; a pipe buried at 1 meter depth is visible to a surface electromagnetic system, but not if it is buried at 100 meters depth. This is just like trying to read a sign a meter away vs the same sign at 100 meters away.
I belong to a specialized group on LinkedIn where people ask and answer questions related to mining geophysics. One question came in recently about podiform chromite deposits. Chromite is chrome-iron-oxide ore, typically an extremely dense black rock. I have a small 25-kg (55 lbs) sample on our back deck – it’s only about the size of a jogging shoe. However, its density is over 7 g/cc, so if you try to pick it up, you find you can't - until you reposition yourself and straddle it first.
To help you follow the explanation below (which was aimed at an experienced geologist), I need to add a few explanations. An “Ophiolite” is a piece of ancient seafloor that has been rafted up onto a continental margin by a plate-tectonic accretion process. Think of shoving a sheet against a pillow – part of it will end up on the edges of the pillow for the same reason that some ocean-floor ended up on the Oregon-California coast. The rock-type we found there, called “Harzburgite” is a weird, dun-colored ultramafic rock; this means it is quartz-free, and mostly made up of manganese-iron minerals. This rock has distinctive green olivine crystals in it that come from the Earth’s Mantle, and which don’t weather as fast as the rest of the rock, so they stand up from an exposed surface in points and edges. From personal experience, these will shred your skin if you fall on it. “Serpentine” is a highly magnetic, water-and-heat-cooked mineral assemblage usually found in fracture zones in Harzburgite. The expression “podiform” simply means that the chromite is typically found in massive, dense “pods” 10 – 20 meters (up to 60+ feet) in diameter in the host rock, not unlike raisins in raisin bread. A “gravimeter” (or gravity meter) is a sophisticated device with a spring and balance that is extremely sensitive to tiny changes in the pull of the Earth’s gravity. These devices are so sensitive that changes in where the Moon and Sun are located in the sky will appear as large changes in your repeat measurements in one place as a day goes by. Gravity measurements are also strongly affected by changes in latitude and elevation. All of these things must be corrected for – subtracted out of your measurements – before you can get meaningful numbers out of your gravity survey. “Resistivity” is a measurement of how well some material conducts electricity – the greater the resistance to electricity, the greater the resistivity, which is just a volume-independent value. Metals and some sulfide minerals have a lot of free electrons, so they conduct current easily and therefore have a low resistivity.
 So you will see from what follows that for anything to work, everyone has to learn to talk with each other - the geophysics is useless without an understanding of the geology, and vice-versa.
What is the best and most effective geophysical survey method for Chromite deposits exploration?"
--Yildiray K.
I did some research years ago on podiform chromite in the Josephine Ophiolite in northwestern California. Before I went there, I did some homework first. One gravity survey reported in the scientific literature by the USGS in Cuba (during the pre-Castro era!) had a weak correlation between gravity anomalies and podiform chromite bodies in Camaguey Province. Only about 10% of the anomalies were unequivocally caused by chromite pods, but those discoveries made the survey technically economic: more value was discovered than was spent in the effort searching for it.
There are two problems with gravity surveys that have to do with the sensitivity of the gravimeter and the relatively weak anomalies we are looking for. Think about this: the gravimeter is measuring the effect of all the Earth below you, but you are only interested in the tiny fraction shallow enough to be drilled or mined.
One major difficulty with gravimetry is that you must get a precise elevation for where you are making the measurement. You must correct for even tiny elevation changes to get useful numbers. If the gravity meter is just a meter lower, it will place you closer to the center of the Earth, and the effect of gravity will become significantly stronger – modern gravimeters are that sensitive, and the anomalies being searched for are that weak.
There is another major difficulty with gravity measurements: terrain corrections. If you are on the side of a mountain, the part of the mountain above you to your left, say, will effectively pull upwards against your gravimeter. That part of empty space below you to your right will also contribute – in a negative sense of NOT pulling against your gravimeter. That means that terrain effects are doubly-additive. To correct for these, you must mathematically subtract out the contributions of the different elevations in concentric rings around each gravity station measurement. Typically these corrections are done out to 167 kilometers (100 miles) from each and every station. Ugh.
Because of this, gravity terrain corrections often prove to be the weak link with this kind of survey. In both Cuba and northwestern California, the corrections were far larger than the anomalies caused by the chromite pods - because the terrain we were working in was so rugged and steep. Because of this, the gravity only worked reliably for finding shallow chromite pods.
Podiform chromite deposits tend to be very self-contained (like raisins): there is very little external indication or halo that you are even close to the chromite body in most cases. In my experimentation in the Josephine Ultramafic Complex, a microgravity profile could readily detect pods we already knew existed, and even suggested several others.
Magnetic surveying only showed us where the serpentinite was best developed in the Harzburgite ground mass. This could be construed as an indicator of stress on the Harzburgite by a dense nearby chromite pod during the Ophiolite emplacement process. Basically, the massive chromite pod beat up the surrounding rock as the whole mass was emplaced, and that lead to much faster weathering and serpentinization close to the pod. It’s sort of like having a jug of milk packed in the same grocery sack as your bread and chips. If you brought several sacks of these things home, you could tell right away which sack held the milk jug - by which sack of chips had been turned to powder.
We also experimented with refraction seismic methods. We pounded with a sledgehammer on a steel plate laid out on the ground. With sensitive geophones strung out in a line over the terrain, we measured the arrival time of the sound impulse. We found that yes, there was indeed a significant velocity increase when the sound waves passed through the chromite vs. the surrounding serpentinized Harzburgite groundmass. However, this velocity advantage was offset by the complex 3D terrain we were working in, and was difficult to interpret data if we did not already know where the chromite pod was.
Finally, we experimented with resistivity and “Complex Resistivity” – the change of resistivity with transmitter frequency -  in both the field and the laboratory. There was no strong amplitude change over the frequencies we tried, but there was a subtle time-delay (phase shift) that we believe was caused by Kemmererite. This is a deep reddish mineral caused by alteration (hydrothermal “cooking”) of the chromite over time. It shows up as a thin red rind in a microscope thin-section, surrounding each blob of chromite, and behaves differently in a number of ways from the chromite. The resistivity of the chromite itself is significantly higher (acts less like a metal) than for the beat-up and serpentinized Harzburgite. Again, this small advantage is marginalized by other difficult-to-fix variables including terrain effects and localized serpentinite veins.
The bottom line: geological mapping doesn’t work very well to find buried chromite orebodies. Geophysical methods, especially when several are combined to reduce ambiguity, CAN find these things – but only if they are relatively close to the ground surface. Rough terrain makes it much harder to interpret any results, however.
As a final, odd anecdotal aside, we made several excellent plaster casts of some huge, stream-side footprints that we found in this extremely remote and inaccessible area. These footprints were ~40 cm (at least 16 inches) long, with five toes and a heel-width of ~10 cm (4 inches). Several times, over two separate summers, we even heard the deep hooting sounds of the creatures that apparently made these footprints. The field evidence suggests they were two-legged, very large, and not human - and not bears, either. 
From these hints, can you attach a name to these BIG footprints?

Tuesday, May 15, 2012

Exploration Geochemistry, Part 2

The US Geological Survey at one time carried out a mineral resource inventory of most of the United States and Alaska. This was done by organizing teams of geologists, geochemists, and geophysicists to gather data and evaluate a quadrangle. In the Lower-48 a quadrangle was a one-degree-by-two-degree, 1:250,000-scale topographic quadrangle, typically 100 km x 160 km (60 miles x 100 miles) in size. This was called the Contiguous United States Mineral Appraisal Program, or "CUSMAP" for short. In Alaska it was done slightly differently: it was called "AMRAP", and the quadrangles were one degree by three degrees in size - pretty much the same surface area, but the 3-degree size was necessitated by the convergence of the lines of longitude as one got farther and farther north.

My first introduction to Alaska involved the usual training in handguns and "long guns", the purchase of rubberized rain suits and X-traTuff boots - "cane cutter boots" with an Alaskan attitude. At first I wondered about all the gear, but I soon learned why "Southeast" is famous for two things: bears and rain. The average rainfall in Craig, Alaska, where we first motored to for our work, is 12 feet of rain per year. That's 365 cm of rainfall. It seems like rain every day, all the time. I've seen bumper-stickers in southeast Alaska that say "The Bright Yellow Ball is the Sun."

We started work that first year at the docks of Ketchikan, a small city in the southeastern Alaska Panhandle, where we boarded the R/V Don J Miller, a 35-meter (116-ft), 80-year-old vessel that had been refurbished - outfitted with a map-room and a helipad above it, in lieu of a back deck. We were taught how to drive a skiff - a 5-meter (17-foot) aluminum boat, or in later years this became an inflatable "Zodiac" of about the same size. We were also taught how to make emergency repairs, and how to anchor such a vessel on a coast line. This is much trickier than you might think - this is a region where the tide could shift the sea-level up or down by as much as 10 meters (33 feet or more) in just 6 hours. You do NOT want to tie off your boat, climb up a Devil's-Club-infested creek to collect your stream-sediment sample, and then come back to find your 200-kilo (440-lb) transportation is:
(a) floating out in the fjord a stone's throw away, or
(b) stuck on rocks a stone's throw from the water's edge...
...and thus unusable in either case for up to 12 hours.

Doing an "overnighter" in these circumstances is actually worse than the discomfort of trying to sleep hungry in the cold rain all night. You had to face your buddies sheepishly the next day when they stopped all their own work to come looking for you.  Or for your gnawed bones.

I should mention that the R/V Don J Miller was named after a USGS geologist who died while working in Alaska. By an amazing coincidence this man's daughter, also a geologist, was actually working on that ship with us that summer.

Here were my working parameters: If the cloud cover on any given day was high enough, I would fly out in the helicopter and collect gravity stations. I used a $25,000 gravimeter that could detect changes in the pull of the Earth's gravity field down to  0.0000000001 - that incredible sensitivity is why the thing cost so much. There will be more on geophysics in subsequent chapters.

However, if the cloud cover was below 125 meters (500 feet), our airship was grounded - the pilot sat and read novels and drank coffee all day. Since we couldn't fly, I would instead go out and help the geochemists (I read slowly and I don't drink coffee). As I mentioned, we would motor to an area that we had no data for, then climb up through Alaska's nastiest weed (the thorn-infested, and aptly-named Devil's Club) to a point where we were well above the highest ocean tide. There we would collect several shovels of sediment, crudely sieve out the larger rocks and pebbles to reduce what we had to transport, write field notes on the location, and return to the skiff.

Repeat this 15 or so times a day, with a brief stop at an unforgettable viewpoint somewhere for lunch. Any single stream-sediment sample we acquired was then representative of the entire drainage area to the highest peaks above. We didn't have to crawl through the whole thing to know what might be hidden there. Southeast Alaska's rain brought it right to us.

This process might sound straightforward, but in practice it is truly arduous work. Getting just a single shovel of sediment in a stream bed made up almost exclusively of rocks the size of your head is one issue. Bucking through the Devil's Club is another. Watching the Tide Tables closely enough to ensure that you are tying off your skiff at the right place is another... and timing your climbing and sample-collecting so that you get back when you planned to is yet another. Humping around a .45-70 carbine or rifled-slug-loaded shotgun - and keeping alert for mother bears - is yet another.

Why did we do this?

The geochemists explained to me that when gold, or sulfide minerals like copper, lead, silver, or molybdenum, are deposited somewhere, there are a lot of other minerals frequently associated with the process. For instance, you may not see "puntos" of gold a mile away from the core of a gold deposit, but you could very well detect a higher-than-normal level of arsenic a mile away. Hydrothermal mineral deposits are concentrations of something you want, something you value. Nature has gathered these minerals from a vast volume of surrounding rock and concentrated them in one place for you. This gathering process is caused by water being circulated through an immense volume of older rock that was already there. The engine driving the wateris driven by a heat source - say a granite or monzonite intrusive punching up from the Earth's Mantle. (A monzonite is like granite, but with less quartz and more calcium in the rock). This hot, usually acid water circulation system picks up gold and sulfide minerals in distant rock and concentrates it in the vicinity of the hot intruding body - seemingly like how moths are drawn to a light.

Early on, miners noticed a haloing effect. As you moved outward from the center of a primary mineral deposit, you would see roughly concentric rings of other minerals. You could see different sulfide minerals as you progressed outward. You would also see "alteration": clay minerals like aluminum-bearing feldspars that had been cooked to a powdery, grungy form by hot, acidic water - close in to the deposit. You may also see greenish-looking rock - less-strongly altered or less "cooked" rocks, but still with some extra chlorine in them - farther out from the center.

The geochemists would collect as many samples as they could during the summers, driving themselves to do 14-hour days while they had the chance. The wild beauty of wilderness Alaska was a nontrivial reward, I might add. They would then spent the cold winters in Denver doing the tedious sample grinding, sieving, and chemical analyses. By the time they were ready to come back for another, perhaps final field season, they would already have preliminary contoured the results. THIS island has copper on this side but not on the other side, while THIS peninsula is just glowing with lead sulfides. So we can look at a map of the stream drainages and get a sense of the area we are talking about in each case - each area being represented by one or two stream-sediment samples.

The economic geologists, thinking through their various deposit models, would then begin to make resource estimations of yet-undiscovered resources. It seems counter-intuitive, but this is surprisingly easy. With time they had gathered enough examples of grade and tonnage that they could even begin to make some realistic predictions of undiscovered resources. Example: You will generally find primary (as opposed to placer) gold in regions with "Greenstone Belt rocks" - chlorine-tainted, "cooked" volcanic rocks. These are usually ancient volcanic island arcs that continental drift has slammed into the edges of the early continental crusts as they were forming. There are areas in Colorado, in California, in Canada, and in Australia where they have really, really, searched and mapped thoroughly. It turns out that there is a consistent pattern: you statistically have a 0.06 chance per square kilometer of finding a gold deposit in Greenstone Belt rocks. Any Greenstone Belt rocks. That means you can - more or less - count on one deposit per every 17 square kilometers.


However, when we got to Venezuela the first thing we noticed was that everything was covered with jungle. Where are the Greenstone Belt rocks in all that jungle? Well, Greenstone Belt rocks are usually pretty magnetic. Along with the metal sulfides that formed with the ancient volcanoes, there is a significant amount of iron. Some of it is in the form of pyrite - "fools gold" - but some of it is also in a form called magnetite. We therefore searched until we could find the old aeromagnetic data collected in the 1950's when US Steel was working in Venezuela (hint: they were looking for banded-iron deposits). We converted those data into a form where the magnetic anomaly showed as a high right over the magnetic source rocks, and used that magnetic data to then figure exactly where the Greenstone Belt rocks were. We could then calculate area. We multiplied that area by 0.06 and got how many deposits must be there. We subtracted out the few known gold deposits, and were left with what must still be there waiting to be found. Using the grade and tonnage curves from North America and Australia, we could also then calculate, through something called Monte Carlo simulation, exactly how many tons of gold were hiding there.

I did this calculation for a quadrangle in Venezuela called NB-20-4; this was the Venezuelan name for a 1-degree-by-1-1/2-degree quadrangle that happened to include a known mining district in one corner called Bochinche. Our Venezuelan counterparts thought they had mapped the quadrangle and found no sniffs of gold, so were preparing to move on and start looking farther west. I showed them that a bit more than seven tons of gold were not accounted for by the known mining district... and our host agency reprogrammed their efforts to continue searching in the NB-20-4 quadrangle.

So science (and an enormous amount of very tedious data-gathering) again actually paid dividends here.


Monday, May 14, 2012

Exploration Geochemistry, Part 1

Exploration Geochemistry.

Sounds vaguely like an oxymoron, right? Or, perhaps more like apples and oranges?

Bear with me, because this is an important one. The wonders of modern chemistry reach far wider in your life than that extra-body shampoo you used this morning. I referred earlier to a bumper sticker seen in Tucson, Arizona, during a huge environmentalist vs. mining company political fight years ago. The bumper sticker said in large, 5-cm (2") letters: "BAN MINING."  In smaller letters beneath this were these words: "Let the Bastards Freeze in the Dark."

Yes, a bit extreme (on both sides) but it points out something. If you banned mining, then you WOULD freeze in the dark. No matter how much you may dislike mining corporations (or oil corporations) on principle - and there are people who don't and people who do - then you should at least think of the consequences:
  • ALL your electricity (and maybe your heat, too) gets to you via copper wires.
  • MOST of the car you drive is made of iron.
  • ALMOST ALL of your heat comes from coal, oil, or hydroelectric dams.
  • THAT computer you are typing on is full of Rare Earth Elements. And copper and aluminum.
  • ANY light you see by, if it doesn't come from the Sun, required mining.
In other words, any comfort you have in your life - even if you were a Clatsop tribal member who met Lewis and Clark on their 1805 visit - came from natural resources around you that had to be harvested. That includes any shelter you live under.

So mining is an unavoidable consequence to living a comfortable life. And geochemistry is as essential to mining as breathing is to you and me.

Years ago I led a US Geological Survey mission to Venezuela. I started the mission and ran it for three years. Our task? to map the southern half of Venezuela - the jungle-covered half. At the time, Venezuela was just completing the first road down the east side of the country to connect with Brazil. The only way into the interior was by dugout canoe or helicopter. From personal experience I can tell you that you don't just "walk" through the jungle. You have to cut your way through it... and for this reason it was almost totally undeveloped when we first arrived. The northern half of Venezuela held all the oil and farm lands - so who needed the dark green southern half, anyway? It was full of snakes! Actually, so was the rest of Venezuela...

We went, paid for by the Venezuelan government, to affect a technology transfer: teach the Venezuelans all that the USGS had figured out in economic geology, exploration geochemistry, and geophysics. Again, from personal experience, I will tell you that we learned at least as much from the Venezuelans as they learned from us. 

Case in point. We arrived in a mining district named Piston de Uroy late one Fall. That was in the days before we figured out how dangerous helicopters really were, and we arrived via helicopter... 

We were directed up a path to a clearing, where a "casita" had been set up. This is, literally, a little house. Actually a frame of a house, with plastic sheeting tied across the top, and hammocks hanging from the frame. This was to be "home" for the next several weeks. I set up my hamaca (Hammock) and the Venezuelan geologist offered to take us to what may have been the biggest gold-bearing quartz vein on the planet Earth: 11 meters thick, and hundreds of meters long. If you recall the last chapter, that had to be a very wide crack that hot fluids passed through until precipitating minerals clogged it off and it became a mineralized "vein" in mining parlance.

"How did you find this thing?" asked the economic geologist among us.

The Venezuelan party chief smiled patiently and noted that we were uphill from a huge gold mining operation centered on where these creeks we were standing on emptied into the Chicanan River. The gold had to come from somewhere... how about uphill from there? Duh.

Then he offered to show us how they had found the Piston vein. We walked down to the mining district, and an obrero (worker bee) threw a batea (a conical-shaped wooden gold pan about 75 cm or a bit over two feet across) into the creek at our feet. With a small shovel he dug into the creek and loaded the result into the batea - which stopped floating in the water. With some practiced rocking of the batea, he threw out the big rocks on the top and let the water lift the lighter material and float it away. After only about a minute, the bottom of the batea had only black sand in it... and some "sparklies." The party chief asked the obrero how many "puntos" (points of "flash" - gold flakes) he counted.

9 puntos...

We then machete-chopped our way up the stream to just above a tributary and repeated this exercise. 

16 puntos.  We hiked farther uphill to just beyond another tributary coming in. 

0 (zero) puntos

We then backed down and went UP that tributary we had just passed. 

26 puntos. With only about an hour's effort, we were standing at the base of the Piston Vein this way.

I would call this a primitive - but stunningly effective - example of exploration geochemistry. It works!

Next chapter: Exploration Geochemistry, Part 2 - How to use halos to home in on the bacon.


Friday, May 11, 2012

Deposit Models

Beginning shortly after its founding in 1879, the USGS pioneered sophisticated studies of mining districts - and all the mining company geologists pored over these elegant "Professional Papers" to learn everything they could... so they could find more billion-dollar mining districts. 

These Professional Papers pioneered a new idea - the first rudimentary mineral deposit models. That is, if we are looking for gold, or copper, or platinum, or diamonds... well, how do they form or get concentrated in the first place? Do you find diamonds on mountain tops? Do you find gold in pastures?  If not, then, why not?  If you can codify this mineral formation, concentration, and deposition process, then you create a model of these deposits. If the model is good enough - correct enough - then you can use it to find other similar deposits.

Deposit models are based on a few basic assumptions, the first assumption being that you can even describe them as a class in the first place. Among other things, can you carefully work up a description of:
  • what the host rocks must be like,
  • what the source of the mineral of interest might be,
  • is it close enough to where it will be deposited?
  • then what is the transportation and concentration process, and
  • what "clue" minerals are associated with the one you're specifically looking for?
The USGS has actually produced a whole BOOK (called a "Bulletin") of mineral deposit models:  (by Dennis Cox and Don Singer). It keeps evolving and expanding as more examples and data are added to the huge mineral resource databases.

Behind this dry, tabular format is an incredible amount of raw effort to gather information on just about every single ore deposit known to man (at least at the time this Bulletin was initially published). LOTS of information about each one. 

Here are a few simple rules (just part of their model descriptions) for some different types of minerals:

Tungsten is always found in granite bodies, that is, a slowly-solidified magma mush with a lot of silica in it.

Platinum (and the related platinum-group elements like palladium and rhodium) form in layered ultramafic rocks, that is a slowly-solidified magma mush withOUT much (if any) silica in it.

Bottom line: don't look for platinum when you're looking for Tungsten. They won't be in the same place.

Diamonds are formed by extreme heat and compression applied to carbon. The "normal" square sheet-like lattice of carbon graphite (that's why pencil lead smears on paper) must be made much more compact. Making it much more compact makes it (a) denser, and (b) harder.

The kind of monstrous pressure necessary to form diamonds means that they had to form at least 50 - and more like 100 - kilometers deep inside the Earth - in the upper Mantle. Well, OK. But that means that they must somehow get to where we can lay our hands on them. There must be some sort of mechanism that transports them to the surface. Experience says that these are narrow pipes - filled with material that shoots up from the mantle in an extremely violent fashion. The minerals dragged up along with the diamonds are not what you would usually find on the Earth's surface (things like chrome spinel), and in fact these rocks have a distinctively bluish color. They don't look like anything you will see anywhere else (well, almost anywhere else) on the planet. These rocks even have a name, derived from where they were first found: Kimberly, South Africa: Kimberlites. It turns out that this blue stuff is highly conductive - so an airborne electromagnetic survey can theoretically find a covered-over Kimberlite by simply looking for small, bulls-eye circular conductors. I'm not making this stuff up. There are geophysicists in Canada who make a living out of this.

Potash is a salt - actually many different kinds of salt, sometimes mixed with manganese, found in diluted form in the sea. Potash is one of the three critical elements necessary for the Green Revolution: you know, why 8 billion people on this planet have enough food to eat. Rice requires fertilizer to grow well, and there is just so much human feces that you can throw into a rice paddy. To be effective, a fertilizer must have nitrogen, phosphorus... and potassium. Get the German language involved here - most of Germany is underlain by potassium deposits - and you get the word potash. Actually, some of the first potash was obtained by burning certain kinds of vegetation into an ash. Potassium + ash = potash.

It's not economic to mine potash from the sea - it's not concentrated enough. So geologists look for where a natural process has already concentrated it for them. It turns out that an excellent way to do this is when an smaller sea gets closed off from the rest of the world ocean... and then evaporates. Near the end of the drying-out process (a process that results in thick, layered salt beds), the potash salts will be nearly the last to precipitate out, so they are higher in the stratigraphic column. Potash salts are typically distinctive - pink or even red - which makes them easy to see and pick out in a salt mine. There is a dried-up ancient sea that now extends from west-central Canada all the way down into North Dakota. This is called the Elk Point "deposit", but that word is used loosely here, because this "deposit" is HUGE, and has many different evaporite layers in it - many different seawater incursions followed by evaporation. Seawater first got into a great continental depression near modern central Alberta in the middle Devonian epoch. The entry was then blocked, the sea dried up, and formed a layer of salt with some reddish stuff at or near the top. This happened over and over again: the ocean breaches again, fills the salt-flat basin, is blocked, and the cut off arm of the new sea dries up yet again.

You'd think it would make nice layers that you could mine from Alberta to North Dakota. In many cases, the potash salts ARE rather nicely layered. But salt has a habit of easily deforming. Under pressure, it behaves like plastic. Salt can thus slowly pour itself into places where the overlying rock pressure is slightly lower - that's why we have all those salt domes in the southeastern US and the Gulf of Mexico.

This up-welling process is very much like making a batch of bread dough, letting it rise in the pan, then putting your open-fingered hand down in the center: the dough oozes up like little walls and plugs between your fingers. In the case of salt, this is called "diapirism" or "halokinetic" (salt + moving) behavior. When salt pushes up through a weakened zone, past sediments laid down later that are now lying above it, it bends them. Then oil found in one layer will start oozing up along those sediments gets blocked by the salt plug (or salt dome, or salt diapir). Salt has very low density, so a gravity survey will "see" these salt diapirs and salt walls as gravity lows: they typically look like bulls eyes on a county map in Texas or Sascatchewan. The trick is to not drill the center, but to drill around the edges, because that's where the oil has been trapped. Finding the potash is even harder - you need to figure out where the layers have flowed.

Copper: there are at least two ways copper gets concentrated into an economic deposit: (1) As fluids squeezed out of sedimentary rocks, leaching the small amounts of copper out of them and concentrating them in layers above them. The Central Africa Republic and the eastern Congo have an enormous resource of copper that formed and was concentrated this way. (2) As fluids associated with hydrothermal cells that form when granite and similar monzonite bodies extrude up from the Earth's mantle. The intrusive body heats up the groundwater (which is pretty much everywhere if you recall earlier chapters). This water starts slowly circulating, and it leaches out copper from surrounding rock, and concentrates it in fractures created by the crystal mush (still-fluid granite or monzonite magma) punching upward into the Earth's crust. These are called "porphyry coppers" because of the way some crystals form as it slowly cools... and then the thing breaches the Earth's surface and what's not yet formed into crystals quenches quickly, too fast for the rest of the crystals to form. These rocks are cool-looking: typically white crystals of feldspar in a gray groundmass of quenched magma. One of them in Arizona has the unusually descriptive name of "Turkey-Track Porphyry".

Well. That may be the shortest single paragraph summary of copper deposits ever written.

Gold: But I know you're just waiting for the gold deposit model, right? Unfortunately there are a number of very different gold deposit models. There is the Carlin Trend "no-see-um" gold deposits in central Nevada, and the Comstock placer gold deposits that led to the California Gold Rush of the late 1840's, and the low-sulfide quartz vein gold deposits... In fact, I have a thick book on my shelf titled simply "GOLD" that tries mightily in ~300 pages to make some sense of all the different gold deposits in the world. For a long time, some of the most brilliant minds in economic geology actually despaired at ever getting any gold models articulated. This is because every gold deposit is different - like bears. Or like humans: each one has a different "personality" if you will.

But if you apply brilliant human minds at a problem long enough - especially to a problem that could pay handsomely in a brilliant yellow-orange metal - then you will eventually succeed. Several of these gold deposit models are described in that USGS Bulletin 1693. The "low sulfide quartz vein" gold model was developed from cataloging hundreds and hundreds of small gold deposits in the Canada, Western Australia, and California. This model turned out to apply almost perfectly to the gold deposits we were finding in southern Venezuela. They are found in ancient rocks. They are found in association with somewhat younger intrusives like granites or quartz monzonites. They tend to concentrate the gold in ancient volcanic rocks... because those rocks rather nicely fracture. The gold then precipitates out as the fluids move through those fractures to the cool, low pressure surface of the Earth.

There was one exception to the LSQV gold in Venezuela: there was no ARSENIC found in concentric halos around these deposits like you found elsewhere in the world. The reason for this dearth of grandma's favorite rat-poison was because the particular ancient continental crust  - the Guayana Craton that popped up out of the primordial Earth under what is now southern Venezuela - just happened to be an arsenic-poor crust. No one knows why; it's like the Fine Structure constant of physics: it just is that way. Oddly, the Guayana Craton WAS loaded with beryllium, however, so we learned to look for little "wire stars" of dark-green tourmaline crustals in the quartz veins.

You've heard probably that gold is a "noble" element - that it doesn't dissolve in acids or oxidize. Don't believe it. While it won't indeed oxidize like iron, if you can get the ground water just a bit acidic with carbonation, it will slowly collect and concentrate the gold from many kilometers away into the fractures around the intrusive body. Carbonation! Think of soaking the rock with Pepsi - and ever so slightly it WILL move and collect the gold in the rock it seeps through. The water will reach the intrusive, get hot, and rise. As it approaches the surface, the pressure and temperature will quickly drop... and all sorts of things will precipitate out into the fractures. Eventually all those precipitating the minerals - mostly quartz but also a cream-colored carbonate called anchorite - clogs up the fractures until they are plugged. The fractures then  become the light colored "veins" you see in many beat-up old rocks. But there is a much higher concentration of gold these veins than the surrounding rock.

I wrote in considerably more detail about Venezuelan gold and diamond deposits in a book I authored with my wife called "2 Worlds, The Real Venezuela: Living on the Edge of the Jungle and the Rise of Hugo Chavez". That cute blondie on the cover is our 16-yr-old daughter holding a monkey that likes to eat flower petals from your hand.

Something I haven't really addressed here are secondary deposits. The diamonds found in Venezuela are not generally found in Kimberlite pipes, but are found in placers: where they have been weathered out and washed down to some secondary place where they are concentrated with other heavy minerals like titanium oxides. In fact, the diamonds in southern Venezuela  have been washed yet again out of paleoplacers into a third generation of deposit. The ancient placer concentrations have themselves been broken up, washed down to somewhere else in modern rivers like the Caroni where they are again being concentrated or trapped by clay from weathered-out diabase dikes. Most of the gold mined in Alaska and the California Mother Lode is found in placer deposits.

Too many words. This is supposed to be the easy way to learn geology, so I'll leave it here. This is a whole lot shorter than that book on "Gold" however.


Tuesday, May 8, 2012

Economic Geology

In order for the following chapters to be more understandable, I need to first explain a bit about Economic Geology, and then in a subsequent chapter explain a bit more about Deposit Models.

Economic Geology is the study of ore deposits and mines: 
  • why are they where they are, 
  • how did they form, and 
  • how can I find more?

There are "no-see-um" gold mines along the so-called "Carlin Trend", in north-central Nevada, where gold and mercury are produced. However, the gold is incredibly fine - in the angstrom range - and very low-grade. I talked once with a mine-manager there who told me that he had never once seen a single flake of gold in any rocks from in "his" mine! Yet each of the mines along The Trend were worth literally billions of dollars. There was not much of a grade there - maybe an ounce or two of gold per ton of rock - but there were a LOT of tons of rock. If the average gold grade fell below a certain value - or the claimed deposit proved to be below a certain volume of that low-grade ore-rock, then the mineral concentration there would no longer be an "ore deposit." It would literally, then, not be economic to mine it. If it cost more to get the gold out than you could get ever paid for it, then the whole effort of exploration, development, and production was a bust. 

That's called a losing bet. And you no longer wonder why the fluctuating price of gold matters... 

Therefore the term Economic Geology.

As a graduate student and new father, I helped my family make ends meet by "claim-staking" on weekends for Bear Creek Mining Company. At the time I was working 100-hour weeks supporting a wife and two small children, including working on my PhD thesis in my spare time. Bear Creek was looking for people to go out onto Federal lands in Arizona and New Mexico - lands that their geologists thought might have the possibility of hosting an ore deposit - and stake their claim on the land for them. 

They were following the rules of the US Mining Law of 1872: stake a claim to a piece of federal land up to 600 feet by 1,500 feet in size, and pay $100 to the federal government... and as long as you kept working on it, you could keep it. 

The company geologists sure weren't interested in doing this - staking claims is very arduous physical work, and they figured their college degrees told them they didn't need to do this anymore. That's where slave labor came in: hungry graduate students! We would typically be dropped off by the Bear Creek land manager in remote, always-rugged country somewhere, and hike and survey our way along straight lines all day. Every 1,500 feet (about 500 meters) we would pound a 2-meter (6-foot) stake into the ground. We would then put a piece of paper, describing that sequentially-numbered claim, into a plastic bottle nailed to the top. Then we would pick up our canteens and sledge hammers and the other 19 or so remaining stakes and march another 500 meters over steep hills and evil cholla cactus infested ground to the next pound-it-in exercise.We would do this for an average 12-hour day for two to five days at a time. It was usually so hot that we couldn't eat more than an orange or two during the day. 

Mining companies had to first stake claims to the territory they were interested in, sometimes even before they dared pour any money into geochemical or geophysical surveys (see subsequent chapters) or exploratory drilling. It was such a competitive business that we would quietly drive in and start in the pre-dawn darkness... and still before the first day was over we would see people walking in from seemingly nowhere to try to figure out where the boundaries of this new Bear Creek claim were. 

Bear Creek was a subsidiary of Newmont Mining Corporation, and they were funded for 10 years to do only one thing: find just one more bonanza gold or copper mine. All the salaries, all the equipment, all the chemical analyses, all the geophysical surveys for 10 years were just a huge corporate bet. That bet was that if they put smart people on this task, they could reasonably hope there was a better than 50-50 chance that they WOULD find a new, undiscovered ore deposit. I think they found several during this 10-year period. However, mining companies are notoriously secretive, so that the competition can't "jump" their claims before they can lock up a property and start their drilling program. The drilling program would become far more expensive than the geophysical surveys or the claim-staking exercise, and might itself prove to be a bust. Perhaps there was a "sniff" of gold or copper there, but just not enough to be economic. The company would then just walk away from a property that they had already sunk millions of dollars into.

The claims would then be abandoned, and after a certain amount of time with no work done to "prove" the deposit, another company might come check it out, and stake that land again. They might even then claim the same precise area themselves. This claim-then-drill-then-abandon process would sometimes repeat several times. If the price of copper or gold jumped up and stayed up, then the 3rd time might be the charm.

However, if the drilling program was positive, then the company would start investing in the mining infrastructure. This consisted of, at a minimum: new roads, a mill, a processing plant, perhaps a smelter, distribution and transport infrastructure including huge Euclid ore trucks, etc. It might require five years just to build the durable facilities on the land where they felt there was an ore deposit. That exercise would be predicated on an expected mining-life of 20 years. During that 5-year start-up period nothing - absolutely nothing - would be produced. It was all just investment, a huge bet. The company could easily lose a billion dollars before the first d'ore (mostly gold) or copper brick was even poured in the smelter. If the price of gold or copper took a nose-dive on the international market during that time, they could blow away that much investment money and see nothing for it.

That's actually not a bad business model - because a single producing mine can be worth multiple billions of dollars. 

How important is the price of a commodity? I know that a drop in the value of copper below a benchmark dollar per pound in the 1970's cost some mining companies so many billions of dollars that some went bankrupt. This was caused by a perfect storm: a drop in value brought on by over-production of copper in Chile, and a world-wide recession that slowed down demand. 

I once talked with a little old man missing most of his teeth deep in the Amazonas Territory of southern Venezuela. He was wearing only nylon shorts and rubber boots, wore a home-made straw hat, and was carrying only a machete and a home-made back-pack made out of palm fronds. This pack was full of food and other supplies. When I asked him, he said he was hiking out to "mina nueva" - the New Mine. When I asked a bit more, I found he could tell me the market close on the price of gold... from the previous evening at the London FTSE on the other side of the planet. He could tell me that price to a cent.

Commodity prices are that important. 

The next chapter will be about deposit models - why companies would even make these sort of billion-dollar bets in the first place. Yes, it's more than faith... but sometimes it seems like just barely.


Saturday, May 5, 2012

Water Stinking

When I returned from a four-year assignment to Saudi Arabia, I found myself back in the US Geological Survey’s National Center in northern Virginia, initially without much to do. Rather quickly I got a call from a geophysicist friend in our Denver office, who had just the opposite problem. He had been asked to help solve a pollution problem in Arkansas, and was overloaded with too many other responsibilities. Could I help? Sure.

I quickly found myself at Fort Chaffee in Western Arkansas. This fort had been used during World War II to house German Army prisoners. Part of the Fort area was still being used to train tank battalions - we would hear truly unnerving sounds from the other side of tree stands that separated us from their training areas. I finally understood the point of tanks.

We were working in a section that the US Army wanted to turn over to the State of Arkansas for a park. However, since the turnover would involve transferring liability, the State of Arkansas wanted to be assured that the former camp’s landfill was safe, and not polluting the local ground water. Uhhh. What landfill? No one knew where the old landfill was - it had been covered over and forgotten 50 years earlier.

By looking at old records the hydrologists had narrowed down where this old landfill might be, and we began a survey using an EM-31 unit – you guessed it, and electromagnetic device that could map conductivity down to about 6 meters (20 feet). 

Our survey was a success - at least insofar as we were able to locate the old landfill - but we also detected a conductivity plume slowly leaking out of it (see figure). Feeling very satisfied with our success in just one day of surveying, we finished and headed back to a motel. “Meet you in 30 minutes for dinner,” I asked?

“Make that at least an hour,” both hydro-techs said at the same time... “and be sure to take off all your clothes and check every square inch of your skin for ticks.” I had inadvertently been working in the Galactic Center of ticks in the universe. I found 19 ticks on me - seven already dug into my skin. Geophysics, for me, is ‘way easier.

A conductivity map of part of Fort Chaffee, AK, with red representing the seeping pollution plumes from the World War II German POW camp landfill.  

Bad Water

Everyone has probably heard of towns in the eastern US where the tapwater suddenly starts smelling like gasoline. Or perhaps you remember the headlines where the entire population of Minneapolis was told to NOT drink their tapwater "for a few weeks," because it was loaded with Clostridium. That’s short for Clostridium dificiles, a nasty bacterium that among other things causes gas gangrene and really bad diarrhea. Been there, felt that.

Water quality has become so important that the USGS even has a dedicated website for toxics in surface and groundwater: “Toxics” as used here can include biological contamination and chemical contamination. Sometimes contamination can be at barely detectable levels - but if this includes endocrine-interrupting chemicals or dioxins, then we are talking about some very dangerous stuff. Things like these in our drinking water could potentially have life-changing consequences on entire communities.

These are just some examples of groundwater contamination - plumes of foreign material moving through an aquifer, ruining it. Mitigating (fixing) something like this can be a real problem, and sometimes requires just shutting down an entire well-field. If it’s a bacterial contamination, geophysical methods won’t help you track it. If it’s something like gasoline, or oil - technically a NAPL (Nonaqueous Phase Liquid), then geophysical methods CAN help map and track it.

NAPL's come in at least three main flavors: 
  • "DNAPL" is a Dense NAPL - one of a group of organic substances that are relatively insoluble in water and more dense than water. DNAPLs like bunker oil tend to sink vertically through sand and gravel aquifers to the underlying layer.
  • There are LNAPLs - Light NAPLs, such as gasoline and benzenes.
  • And finally PAHs - Polycyclic Aromatic Hydrocarbons, like chlorinated solvents. The Nose Knows right away when you encounter any of these. 
Did I mention that many of these are known carcinogens? Trust me, you do not want ANY of these, in ANY quantity, in your drinking water.

River Water

I love rivers. Before I moved west to the Cascades, I used to kayak in the Potomac River - that was, until parts of it became so clogged with discarded Cabomba (an aquarium-plant that became invasive weeds) that I could sit still in the kayak and not move downstream. The weeds held me still unless I paddled hard.

I also have kayak'd in the Columbia River that separates Washington from Oregon. Once I received a phone call from the Acting Scientist-in-Charge that there had been another eruption at Mount St Helens. I stopped paddling to talk with him on the chief scientist cell-phone, and noticed that I was drifting upstream. 

"Uhhh, Willy. I'm in my kayak, but I'm drifting upstream," I said. 

"Oh, that's because ocean tides are felt all the way up to Bonneville Dam," he replied. Later the up-coming tide and the down-going current met at a log boom protecting a marina near Interstate-205... and formed a terrifying whirlpool, at least two meters across, that nearly got me.

As I said, I love rivers - but you never know what kind of surprises they may have in store.

There is one other form of groundwater pollution, and like E. coli or endocrine-interrupting chemicals, it is not easy to detect. I’m talking here about mercury and radioactive isotopes. Some of these may be dangerous while not readily detectable (even with radiation counters).

I currently work in Vancouver, Washington, adjacent to the Columbia River. As the chief scientist for volcano hazards - the senior manager in the Cascades Volcano Observatory at the time - I once received a package from the USGS headquarters office of the Water Resources Discipline. The cover letter asked me to take samples of water from the drinking fountains in our building and send them back. The cover letter, however, also asked that I report the source of that water. Intrigued, and having a rare hour of relatively free time on my hands, I called around and got the Clark County Water Utility District. They told me that the water came from a well-field in volcanic basalt in the northern part of the county.

“Why,” I asked? “We’re right next to the Columbia River!"

The reply startled me. I was told that there was a huge mine in Canada whose tailings drained mercury into the headwaters of the Columbia River - which then ran past the Hanford Nuclear site near Kennewick, Washington.

I always carry bottled water when I kayak. “So?”

“So there are chemical pollutants from all the mines and old industrial facilities located along the river’s length over the past century - and at one time there was even measurable plutonium in the Columbia River.”

Plutonium. Microgram for microgram, this may be the most toxic metal on Earth. After an immensely expensive Super Fund cleanup of the Hanford Super Fund site near Kennewick, the Columbia River is a lot safer today than it was even 15 years ago.

From my life experience, however, I have a permanently heightened awareness of water pollution, and now understand why so many of the human population living on the planet does not have access to safe drinking water.

For me, water quality has become personal.