Your skin covers your entire body, it is everywhere. Does that mean that when sunlight hits a child’s face at just the right angle, or the bare shoulder of your love peeks into view, that it is uninteresting, or plain, simply because it covers each and everyone one of us?
What about the most common mineral in the earth’s crust? A mineral many consider boring, or unworthy of future study? Well, the same thing applies. Look at the most common things in the world with new eyes, and new light, you’ll be fascinated but what hidden mysteries can be uncovered, and what that discovery could mean for the future.
And if you are Dr. Andrew McDonald, professor of Mineralogy and director of the Microanalytical Centre at Laurentian University’s Harquail School of Earth Sciences, or his former student Elliot Wehrle, you’ll win a medal for it.
Quartz is an easily identifiable piece of Sudbury’s natural world. If a child comes to you with a pretty pebble in their hand, its shimmer catching the light and reflecting in their eyes, most people can identify it for them, and look like the greatest outdoorsperson ever.
But what if you were able to not only identify the treasure that child has brought, but tell them that the quartz is 1.85 billion years old, and largely unchanged since its creation.
“The rocks that we were looking at are old — they're almost 2 billion years old,” says McDonald. “When you want to look at something geologically, if you want to understand what happened 2 billion years ago, you’ve got to look for things that really haven't changed very much, which is that mineral (quartz). So that's what precipitated the study.”
The study he mentions is a journey into the quartz from the Sudbury offset dikes, and the paper that garnered McDonald his third Hawley Medal, awarded to the best paper of the year published in the internationally acclaimed journal The Canadian Mineralogist – he got the hat trick, you could say. But in those previous studies as well as this one, McDonald seems to have a passion for, well, boring.
“My philosophy has always been to understand the minerals, because if you understand the minerals, then you understand the rocks which they form,” says McDonald. “And a lot of times people are only interested in specific minerals. They're interested for example, in chalcopyrite, because it's a copper ore, they're interested in pentlandite, because it's a nickel bearing one. And the rest of the minerals we’re kind of like ‘meh’, and we're not really interested in them, they're boring.”
But in science, boring can hold secrets.
“There's always stories to be told. And sometimes those boring things provide the most interesting stories, and I think this is exactly that's that situation.”
This could also be said of the first paper for which McDonald and a student won the Hawley Medal: pyrrhotite, the most common sulphide mineral in Sudbury. Seeing a theme emerge?
McDonald saw potential in what others consider a ‘garbage mineral’. “It's a garbage mineral because it contains a little bit of nickel, but not enough to mine. The other problem is it has lots of sulfur in it.”
And Sudbury knows the problem with sulphur. Land degradation, and environmental impact.
But if you want to get to the prince – the chalcopyrite, the pentlandite, etc. – you need to get through the frog of pyrrhotite. It’s boring, maybe a bit ugly, but you need to understand how to work with it, in order to move past it.
So, let’s get boring. Two billion years of boring.
Shiny but dull
Quartz may be shiny, but to many in the scientific community, it’s dull. (Sorry.) Though the mineral is exceptionally common, you guessed it: “It’s a boring old mineral, nobody’s interested.”
But it may pique the interest to know a certain fact: the Sudbury mining district is characterized by Quartz Diorite (QD) dikes. Dikes are sheets of rock formed in the fracture of a pre-existing rock body, and are collectively known as offset dikes.
Now for the good part: Quartz Diorite offset dikes can host approximately 40 per cent of the Nickel, Copper and Platinum Group Elements (Ni-Cu-PGE) sulphide mineralization in Sudbury. In other words, that’s where the treasure lies. And if you’re looking for treasure, it helps to be able to read the map.
In the case of quartz, there are very specific clues left along the way. “When I teach minerals or mineralogy, we learn that minerals have chemistries, and we usually think of chemistries as being extraordinarily fixed. For quartz, it's just silicon and oxygen, SiO2. So it's one to two ratio,” says McDonald. “And if that was the end of the story, like a lot of my inorganic chemists might envision that would be a very, very boring story. But the great thing with quartz is that it's SiO2, ideally, but it's never, ever pure.”
It’s an idea that McDonald tries to convey to his students – we want things to be uncomplicated, but they rarely are.
“We learn to think in very simple terms in chemistry,” he says, “but in reality, nature is a dirty, dirty thing. And that makes it great.”
In the case of quartz, the dirty nature of nature is what allows applied mineralogists like McDonald to use even subtle unique characteristics to better understand the mineral – especially its timeline. And that timeline opens a new world of understanding just waiting to be studied further.
Sudbury is an Event
Let’s go back to the Sudbury Event. The shaping of this landscape and the creation of the bathtub-shaped Sudbury Intrusive Complex (SIC) is where we lay our scene.
In the middle, the younger rocks, sediments and minerals that make up wonderfully fertile soil. Around the edges is where we begin to find the QD offset dikes, our main character.
During the Sudbury Event, fractures were created. “When the Sudbury Event occurred, it created these fractures that we call the offset (dikes). These are just basically big cracks,” says McDonald. “If you think about taking a rock and throwing it in liquid mud or wet mud, you get kind of fractures that emanate around them - that's kind of the idea.”
These fractures developed contemporaneously with the Sudbury Event – even as close as an hour.
“In the center of the bathtub, the rocks that were there all melted. There was magma, there was liquid rock. And that liquid rock then flowed like water. More like maple syrup,” he says. “So it (the magma) flowed into all of these offset environments, these pre-existing fractures.”
It’s not just looking at the quartz, it's actually looking at the quartz from the time that the magma was around. Fractures, filled with magma, now mineralized. “If you can understand the conditions favouring mineralization,” says McDonald, “then you have a tool to better understand and to better develop your mines, or to look for new mines.”
So now our Quartz Diorite offset dikes are beginning to have an origin story.
Road to riches
The QD offset dikes are located around the SIC, moving radially and concentrically often for tens of kilometers, and have some names you may be familiar with: Copper Cliff Offset, for one. “The thing that's really important about these offset dikes is that many of them are mineralized. And by mineralized, I mean they have nickel in them. They have copper in them,” says McDonald. “The town of Copper Cliff is built around one of these offsets. So there's economic deposits of sulphides in these offset dikes, and they were developing at the same time the magma was there. So if you can understand the quartz, this boring old mineral, then you start to get insights into the sulphides.”
The study itself examined six offset dikes around the SIC: Copper Cliff, Whistle (once home to one of Sudbury’s oldest mines), Parkin, Hess, Foy, and Trill.
Using an electron microscope, McDonald and Wehrle used a process called cathodoluminescence, (Ca-thoe-doe-loom-in-es-cence. Yes, this will be on the exam.) McDonald compares it to wearing x-ray glasses to change how your eyes interact with an image, or even the last time you went to a club – pre-COVID 19, of course.
It’s the way a black light works.
“Anything white stands out, right? And the reason it stands out is because usually there's phosphorus in the whites. That's why your whites get whiter, phosphorus sticks to it. And that creates a fluorescence effect. So the light from the UV source interacts with your white socks and produces a secondary light effect that we could see as being white.”
Sections or slices of quartz were cut to 30 microns and examined using cathodoluminescence; for reference, a human hair is about 100 microns. What they found was a range of patterns they had never seen before, and it gave them a clue – temperature.
“So then the question was what's causing these patterns, because this effect that we see has to be related to chemistry. Normally, pure quartz wouldn't do anything. It would just sit there and be black. As I mentioned, minerals are very impure, they contain other elements. And it's those other little bits that made the difference.”
In the case of the quartz, it was titanium.
Titanium beads, measured in parts per million, “which is tiny, tiny, tiny, tiny amounts,” is enough to cause a cathodolumiescent response. The team examined previous studies, including one that showed a correlation between how much titanium quartz can hold as a function of temperature.
The more titanium that's present in quartz, the higher the temperature that that quartz formed,” says McDonald. “So we then said, if we can measure how much titanium is in the quartz, then we have a way to measure the temperature at which that quartz was formed. That was really insightful because nobody knew whether there'd be temperature variations in the quartz from the offset dikes, or if there was we had no idea, no one's ever done it before.”
They found interesting trends, one of which is related to the positioning of the dikes around the SIC. “We recognized that a lot of the quartz from the offset dikes in the northern part of the Sudbury Basin, we call it the North range, were quite a bit different than what we looked at in the South range. That's the Copper Cliff Offset. So we knew that the temperatures were higher in the North range, and that these temperatures actually varied within the offset environment.”
With further study, this could mean: “that there may be a correlation between how close the quartz is to the mouth, (contact with the SIC ‘bathtub). So the idea is if you move further away, it might be cooler and if you're getting closer to it, it might be hotter. So there might be a sweet spot for temperatures that correlate with sulfides.” That could mean a new way to find even tiny quartz diorite dikes as well, and therefore, a potential new way to find sulfide minerals.
And while McDonald refers to his study as ‘a test of concept’ and the foundation for further research, it could mean that once again he has taken some boring old mineral, and made it interesting – and worthy of investment.
If rocks are history books, if the study of geology is learning the language of these rocks, then Dr. McDonald feels he’s only added a few words to a chapter on Sudbury. But if you have ever read a great cliff hanger before excitedly turning to the next chapter, then you understand that a few words in a chapter can be quite intriguing as can the potential this study could unlock beneath our feet.
The boring old skin of the earth.
Jenny Lamothe is a freelance writer, proof-reader and editor in Greater Sudbury. Contact her through her website, JennyLamothe.com.