I have been posting a lot lately about the Yukon. So for a change of pace the photo for this week comes from Australia…about as far from the Yukon as it is possible to get. This is a photo looking down on a mat of stromatolites. They are the round shapes poking up through the limestone.
Fun with PHREEQ at Red Creek
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.
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.
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!!
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
Geology Photo of the Week # 21
The photo of the week today is of a Canadian National Heritage Site. It is located just outside of Dawson City, Yukon and is unassumingly called Dredge 4. Those of you who read this blog regularly will know that I am a huge fan of the Yukon, which is the site of my field work, and love talking about the gold rush history of the region. Very few things embody this history better than Dredge 4…the Discovery Claim may be the only better spot. Dredge 4 really represents the industrialization of gold rush mining. Dredging took backbreaking labour once done by men with picks and shovels and turned it into a truly industrial operation. This method of mining very effectively purged what gold was left in the Klondike district. However, placer mining of this scale had a huge impact on the local environment as some of the other photos will show. However, despite the impact the dredge and its mark are still incredible relics of gold rush history.
The next picture shows a schematic of how a dredge worked. The bare essentials are that the dredge would move along flooding the land beneath it so that it would float and all the while scooping up the gold bearing gravel below it. The gold was extracted inside and the cleaned gravels were “pooped” out the back of the dredge in large piles that litter the landscape today.
![](network/geosphere/files/2013/02/dawson.png)
An aerial view of Dawson from Google Maps. The lines snaking along the landscape are gravel piles from dredging.
Cheers,
Matt
GeoSphere: In Review
After two years of regular geology blogging I was thinking it might be fun to highlight the posts that I think are my best work as well as the ones that have been the most popular…they are not necessarily the same. This just goes to show it is impossible to predict what the collective consciousness of the geoblogopshere or the geotwitterverse will like the best. Some of these posts come from my old blogging home, which is just a regular blogger site so the links will take you there. Others are more recent and were posted on my EGU blog. I hope you enjoy this little blast from the past.
This EGU blog went live on October 1, 2012 and in that time it has had 2,530 visits of which 66% were by unique visitors, who spent on average 3 minutes on the site, which I think/hope means they actually read something. The most viewed pages have been:
Title | Pageviews | ||
---|---|---|---|
1. | 777 |
20.79% |
|
2. | 282 |
7.54% |
|
3. | 211 |
5.64% |
|
4. | 173 |
4.63% |
|
5. | 162 |
4.33% |
|
6. | 125 |
3.34% |
|
7. | 118 |
3.16% |
|
8. | 115 |
3.08% |
|
9. | 114 |
3.05% |
|
10. | 104 |
2.78% |
Entry | Pageviews |
---|---|
10 Reasons Geologist’s are Weird Apr 21, 2012, 13 comments |
3153
|
Apr 11, 2012, 4 comments |
3006
|
Jun 13, 2011, 3 comments |
1910
|
May 6, 2011, 3 comments |
1522
|
Mar 4, 2011, 5 comments |
1406
|
My favourites
My personal favourite posts over the past few years are mostly on the most viewed lists above. It is hard to pick just one that I like the best though and there are a few that I wrote early on in my blogging career that only got a few pageviews, but I think are pretty interesting. Here are my top 5 in no particular order.
The Odyssey and Geology – The Search for Ithaca – this post summarizes a Nature Geoscience paper that surmises the legendary island of Ithaca has been lost in plain sight for the past few thousand years…
The Art of Geology – this was an Accretionary Wedge topic and for whatever reason I felt inspired and feel that I made a pretty solid contribution to this one.
The Media Portrayal of Geologists – This is a funny one….my apologies if not all the videos work…they were uploaded 2 years ago.
Back to Basics on Groundwater – This one is a really simple primer on groundwater and groundwater flow. It has proved to be extremely popular so far…maybe I should write another one…
It’s all about scales – I had been planning this one for some time and I have to say it turned out better than I had expected.
Bonus Favourite: The Wooden Wall – the story of how a silver mine saved the Greeks during the Persian Wars…I enjoyed doing the research and looking a mineral pics.
Things I’ve Learned
By the way, to put some of these numbers into perspective I also monitor a website about a book called Breaking the Vicious Cycle. It was written by my grandmother and is in its 14th printing right now having sold well over a million copies and been translated into several languages. Her website receives between 1,500 and 3,000 visits per day!!! It has gotten 266,125 visits since October 1, 2012 and 1,471,484 pageviews. If I ever get too cocky about getting a measly 2,530 visits I just think about her website and that helps restore me to an even keel.
All in all I am very happy with how being a geology blogger has gone and am extremely happy to be part of the EGU blog network. I think blogging has been an enriching experience that has allowed me to connect with fellow geoscientists from across the globe and expand my network. Not only that, it has allowed me to hone my writing skills, and given me a soapbox of sorts from which to expound my views on geoscience communication and outreach. I certainly intend to continue blogging in the future and I thank any readers who do stop by for your encouragement and support.
Matt