Yukon

Tools of the Trade

Matt Herod May 14, 2013

It is already May!! Crazy. Everyone in the department is incredibly busy right now trying to get all of those things on their winter to-do list checked off before it is time to head out to the field once again and re-fill the to-do list for next winter with sample prep, analysis and some interpretation. It is also time to start thinking of preparing for the field. Some of you hard rock folk might think it is a bit early to start prepping since all you need is a hammer, some canvas bags, and….what else do you need? However, for the geochemist it is time to start organizing our MESS aka. Mobile Experimental Sampling Supplies. Yes, I did just make that up, but I think you get my drift.

For real though, there are numerous essential items that every aqueous geochemist/hydrogeologist needs to bring or at least consider bringing into the field and since these type of items often get back ordered around this time of year it pays to start thinking about it early. Otherwise, one could find oneself lacking anything from their new pH meter to bottle caps the day before one leaves. Not that either of these things has ever happened to me…..mistakes are part of learning, right?

Uh-oh! Notice the chipped edges and the crack. These are not good things and this guy ended up in the garbage. (Photo: Ian Clark)

Key parameters that must be measured in the field are pH, Eh/ORP, temperature, alkalinity and conductivity. There are many other parameters that may be measured in the field, but those five are the most essential as they are subject to change once the sample is collected and therefore any long delay in measuring these can compromise the integrity of the data.

The most essential piece of field equipment is probably the pH meter. It is the one completely indispensable measurement that must be taken sitting beside the sampling site. The other four, are essential as well, but if I could only do one, I’d do pH. The reason I am touting pH measurements so highly is simply because in geochemistry so much depends on pH: speciation/redox, dissolved gases, dissolved aqueous complexes, mineral mobility, alkalinity, etc. The list goes on and on. The reason it is so essential to measure pH in the field is because it can often change once the sample is collected due to temperature changes or CO2 degassing. One key thing that must be done before any pH measurements are taken is calibration. It is very important to calibrate the probe at least once each day in order to make sure of getting the most accurate performance.

Our current pH meter and probe: the YSI Pro Plus meter and combination pH/ORP electrode. So far so good, although it has yet to face the rigours of the field. Note the geochemical nature of the background. (Photo: Matt Herod)

The other measurement that goes hand in hand with pH is Eh/ORP (oxidation reduction potential). ORP is a measurement of the oxidation/reduction potential of the water. It measures the electron activity of the water which has a major influence on the specification and solubility of elements and minerals in the water. Eh/ORP measurements are given in volts and often go hand in hand with pH. In fact, many pH probes also measure ORP at the same time so both of these crucial parameters are recorded simultaneously.

Conductivity is another measurement that uses its own probe. Conductivity of a water sample is a measurement of salinity of the water. It is basically a measurement of the ions in solution. Conductivity is not a particularly quantitative measurement in that the numbers that it gives are not super accurate, however, it does provide a very good idea of the relative salinity of different waters. For example a cold freshwater spring might have a very low conductivity whereas a lake after a rainstorm might be very high, due to increased sediment influx from runoff.

A nicer pic of our conductivity meter than I could take. (Source)

Alkalinity is another key field parameter that measures the acid buffering potential of the water sample, which directly corresponds to the concentration of HCO3 in the water, except in rare circumstances, where other species provide the acid buffering capabilities. Alkalinity titrations are a bit of a process, and do take a bit of time, but it is essential to do them ASAP as the loss of CO2 from the water can change the alkalinity. Alkalinity is measured by taking the initial pH and then slowly adding acid using a digital titrator and taking the pH along the way. The keys to this are to know the volume of water being titrated, the volume of acid added and the pH after each acid addition. With those basic numbers the amount of HCO3 can be calculated. The key equipment needed for alkalinity titrations are the pH meter, filtering apparatus, the digital titrator and a flask. By the way, helpful tip: don’t store the acid with the titrator, or make sure the acid is well sealed or else this can happen….and those babies aren’t cheap.

This is what happens when the acid is put away with the titrator. (Photo: Matt Herod)

Other field parameters that can be measured depending on the type of work being done are dissolved oxygen (DO), which is a common parameter in groundwater sampling and ion selective electrode measurements (ISE). ISE’s can provide a guide to the concentrations of certain ions in the field such as Cl, NH4, F, etc. Ion selective electrodes are great, but they often have a higher limit of detection that the mass spec back in the lab. They are very useful for groundwater sampling or contaminated water sites, where the concentration of dissolved ions is high.

So that is the basics on the different things we have to measure in the field, but there is a lot more stuff that has to come out in order to make these measurements possible and take the samples…and it is really, really easy to overlook something. For example, you can have a great pH meter and probes and be ready to go, but it won’t be much use if you forget one of the calibration standards back in the lab a few thousand kilometers away.

The key pieces of this list (if it were mine) include a lot of random, but very necessary, items such as: filter papers, syringes, filter cartridges, DIC/DOC septa, pH standards, AA and AAA batteries, digital titrator tips, acid, de-ionized water for rinsing, instruction manuals, rock hammer, ziploc bags, GPS and many other little things.

The list of stuff that must be brought to the field is dependent on the type of sampling that you are trying to do. The most important part of planning to the go the field is to pick the parameters that you would like to sample for and tailor your gear list, sample collection methods and field measurements to make sure the samples are of the highest quality. Follow these words of wisdom: “Determine what you are analyzing for in advance and collect your samples according to the proper protocols for each analyte! An analysis can be only as good as the sample that goes into the ICP-MS” – Nimal De Silva (ICP-MS legend). Basically, what this means is that in order to ensure good results the samples must be collected properly, in the proper containers and stored the right way until they are analyzed. Failing to do so could compromise the quality of the results.

Thanks for reading and I would love to hear if I missed anything or if anyone else has field methods/gear that they use for other types of sampling. Please comment!

Wishing everyone a productive field season.

Matt

p.s. I forgot to mention the most important piece of field equipment in the geologists arsenal:

Geology Photo of the Week #33

Matt Herod May 13, 2013

The photo of the week this week is of a very special place in Canada. Yes, predictably, it is the Yukon. However, this part of the Yukon is unique. It is a special region known as Beringia, which extends into Alaska and Siberia and it is the only part of Canada that was not covered by kilometers of ice during the last glaciation. Beringia is a special place because it is believed that that first human inhabitants of North America made their way across the exposed land bridge form Siberia into the Yukon and spread west and south. Geologically, Berinia is interesting as it is full of Pleistocene mammal fossils like mammoths, short faced bears, giant beavers and other giant mammals. It is also strange because of the degree of weathering and erosion that the rocks have undergone is like nowhere else in Canada. Piles of talus may not seem like a big deal to people from other parts of the world, but for a Canadian geologist this is a somewhat unusual sight as most of our mountains had a good scraping 20,000 years ago and we just don’t see this level of weathering anywhere else in the country.

Cheers,

Matt

Photo of the Week #27 – Someone’s had a few too many

Matt Herod March 25, 2013

The photo of the week came to me this morning on my walk to school. Yes, it is now warm enough in Ottawa to comfortably walk to school! All the melting ice and the slight smell of spring and undergrad panic in the air got me thinking about permafrost degradation and nights out during my undergrad. An odd combination of thoughts, I grant you. Well, what do these two very separate things have in common? Observe the photos below, particularly the trees in the hillside to find out.

(Photo: Matt Herod)

The trees all look a little askew. This is because they are the epitome of a “drunken forest”. Many of you may not have encountered this amazing term, which I assure you is the real one, for trees that sit on degrading permafrost or ice wedges that become drunkenly tilted as the ice melts. The ground underneath the tilted trees also looks somewhat heaved which is characteristic of melting permafrost terrain. I took these photos just outside of Dawson city next to ongoing placer mining operations. So there you have it. The strange explanation for what links the melting of spring ice to memories of my own spring experiences in undergrad (never now…).

Cheers,

Matt

Fun with PHREEQ at Red Creek

Matt Herod February 15, 2013

Most freshwater on earth is not that highly saturated with dissolved metals or minerals. However, there are exceptions to be found all over the world from natural acid rock drainage to the alkali springs of Jordan. If the concentrations of dissolved metals are high enough the water can be toxic. For example, water draining from gold mines is often very high in arsenic and must be contained and cleaned. It is incredibly important to understand what will happen to these dissolved ions because they have profound implications on the health of the environment and people. Water like this can occur naturally or due to mining, deforestation, or other human industrial activities.

One tool that we can use to understand water and what is happening to the dissolved metals and minerals is the geochemical modelling program called PHREEQC a.k.a PHREEQ (pronounced freak) to those in the business. PHREEQC is pretty much the industry standard amongst geochemists for modelling the composition and behaviour of dissolved ions and minerals in water and every aspiring geochemist has to be familiar with the basics of the program and what the information it provides is telling us. PHREEQC is a quick, easy and free way to do a huge number of tedious calculations really, really quickly. Yep, that’s right, it’s free on the USGS website, which is another great thing about it.

PHREEQC works by taking the concentration of ions in water such as calcium, sodium, sulphate, etc and calculating the concentration of these ions that actually participate in geochemical reactions at certain temperatures, pressure, salinities, pH’s and redox conditions. Once we know these values PHREEQC then calculates how much of these ions and the minerals that they combine to form are dissolved in the water and if they will precipitate out of solution to form actual minerals. It can do a lot more than this as well such as incorporate isotopes, model ion-ion interactions, ion-surface interactions, etc.

For this post I thought it might be interesting to show the PHREEQC output from one of the creeks that I sample called Red Creek and it is a bit of a weird one. Red Creek is located in the central Yukon and the most notable thing about it is the colour of the water and the rocks around it.

A view of Red Creek. Note the milky coffee colour and the red stained rocks. (Photo: Matt Herod)

Close up of a very iron stained rock. (Photo: Matt Herod)

As you can see the rocks around Red Creek are red and black. They are shale and are loaded with all sorts of interesting elements, particularly iron. In fact the iron concentration in this water is about 3 ppm, the nickel and zinc values are 0.3 and 0.9 ppm respectively and the sulphur concentration is a whopping 340 ppm. These numbers are all way out of the ordinary for the rest of the creeks I sampled throughout the Yukon. In fact, the Fe, Ni, and Zn values are at least 10 times higher than anywhere else! WOW…(did I just find a new mine?…I wish)

—————————-Description of solution—————————-

pH = 6.790
pe = 4.000
Activity of water = 1.000
Ionic strength = 1.170e-002
Mass of water (kg) = 1.000e+000
Total carbon (mol/kg) = 2.435e-004
Total CO2 (mol/kg) = 2.435e-004
Temperature (deg C) = 25.000
Electrical balance (eq) = 2.563e-004
Percent error, 100*(Cat-|An|)/(Cat+|An|) = 2.15
Iterations = 10
Total H = 1.110128e+002
Total O = 5.552116e+001

I have included some of the highlights for what is called the saturation index. Basically this number tells us if a mineral is under-saturated in the water, meaning it will stay in solution or over saturated, meaning it will precipitate. If the number is negative the mineral is undersaturated and will not precipitate and if it is positive it is over saturated and will. In Red Creek there are hundreds of mineral species that are undersaturated and only a handful that are oversaturated. I have listed the oversaturated ones below. Some of these numbers are super high such as magnetite and hematite, which are clearly the ones precipitating on the rocks.

Barite — 0.47 — BaSO4

Fe(OH)2.7Cl.3 — 6.54

Fe(OH)3(a) — 1.89

Fe3(OH)8 — 2.35

Goethite — 7.78 — FeOOH

Hematite — 17.57 — Fe2O3

Maghemite — 7.17 — Fe2O3

Magnetite — 18.83 — Fe3O4

ZnSiO3 — 1.12

Red Creek is obviously a pretty wild place geochemically and the PHREEQC modelling opens the door for us to interpret it. There is a lot going on and one has to ask, where did all of the high concentrations of these metals come from? Well, in this case the question is a fairly easy one to answer. All you have to do is look around at the bedrock.

Some nicely bedded, overturned shales in the Red Creek region (Photo: Matt Herod)

The local bedrock is black shale, a rock that is notoriously full of metals due to is high organic content. Red Creek is fed by springs issuing from the shale and the groundwater, which has had moved from its recharge point to discharging in the creek, has had time to leach metals from the rock. The water gets so loaded with metals from the bedrock that it carries them along as minerals in suspension as well as dissolved, which is why the water is that weak coffee colour. Actually, when the spring emerges from the shale the water is not white/red. It is, in fact, black!!! And I mean jet black. This is because it is loaded with reduced iron in suspension. Once the iron oxidizes at the surface it turns red. Futhermore, there is so much sulphur in the water that elemental sulphur often precipitates around the springs and the reduced, and highly toxic form of sulphur, hydrogen sulphide gas is bubbling out of the water as well because of the massive partial pressure difference in H2S in the atmopshere versus the water. What a wonderful place for a geochemist!!

A spring coming out of the shale near Red Creek. Yes, that water is black!!! (Photo: Matt Herod)

Places like Red Creek have interesting geochemical stories to tell. In this case the dissolved metals are naturally occurring and no one lives in the area so no remedial action is necessary to make the water drinkable. However, water like this has major impacts on the life that can survive in the region and in the creek. Indeed, natural places like this are home to a wide variety of life that has adapted to survive and flourish in these harsh conditions that are found in very few places on Earth and we can learn a lot about life on our planet and potential life on others from places like Red Creek. However, if such a water body was the result of mining operations it is absolutely necessary that it be treated lest is thoroughly contaminate the local environment with heavy metals such as arsenic or mercury. It is the geochemists responsibility to ensure that places like this are understood so that when remedial actions are necessary the lessons learned from natural places can be applied.

Hope you enjoyed this geochemical adventure to Red Creek!

Cheers,

Matt

Some nicely stained shale showing the high water mark in the spring at Red Creek. (Photo: Matt Herod)