Geology rocks! An insight into the formation of sediment-hosted stratiform copper

My Laidlaw research project has been a long and rewarding experience so far. My research focuses on a major deposit type, sediment-hosted stratiform copper (SSC), specifically one of the world’s largest deposits in White Pine, Michigan. While there is a general knowledge of how SSC deposits form, the energy source for driving fluid migration and the copper precipitation mechanisms are still uncertain. One model that has been devised is the Thermal Lid Model. In this model, black shales act as thermal lids, trapping heat and inhibiting fluid flow. My research aims to test this hypothesis using samples from White Pine.

You may be wondering why I have decided to dedicate 8 weeks of my summer vacation to researching copper, and this is due to the fact that copper ore is fundamental to the global economy. Copper exists in every device that uses or transports electricity. So, you can thank geologists like me for your ability to read this blog post on a computer!

Now, I understand most people have not studied Geology before, which means some of the words I mentioned in my first paragraph may mean nothing to you. I will go through the general idea of my research, and hopefully by the end of this post you will have a new appreciation for rocks and the ground you walk on every day!

My research begins with understanding how the area of White Pine, Michigan formed in the first place. The Lake Superior region of North America is a portion of a failed intracratonic rift (imagine the USA being ripped apart, but not fully, with a big crack running through the middle of it). This crack then gets filled with a sequence volcanic and sedimentary rocks (think of magma, volcanoes, and the erosion of land and mountains).

The best way to think about these sediments is like a layered cake. At the bottom there are the volcanic rocks, which in this case are flood basalts.  On top of this is a layer called the Copper Harbor Conglomerate, which as its name states, is a sedimentary conglomerate rock. Then on top of this layer is the Nonesuch formation, which consists of black shales. These sediments are heavily researched due to their wealth of economic mineral deposits, including the copper deposit that I am looking at in my research. The copper in these sediments formed when cupriferous fluids flowed up through the Copper Harbor Conglomerate, and into the bottom of the Nonesuch Formation. In the model I am testing, the Nonesuch Formation (shales) acts as a thermal lid, trapping both heat and the mineralizing fluids in the system, causing copper to form.

The way I am testing this model is by determining the maximum temperature of metamorphism that the Nonesuch Formation reached. I am doing this using three different methods: X-ray diffraction and Illite Crystallinity, Hyperspectral Reflectance, and Raman Spectroscopy. I am currently in the data interpretation phase of my research, so unfortunately I cannot say at this point what my results are. From what I have looked at so far, I seem to have mixed results in terms of the temperatures I am seeing, which may mean that I will not get to answer the question I originally posed for my research. This point leads me to the final point I will make in this blog post, which is the difficulties of scientific research!

As this is my first time doing research, I was not sure what to expect in terms of how smoothly it would go, or whether I would get any results that I wanted. My project was originally supposed to look at rock samples from both the Zambian Copperbelt along with rock samples from White Pine, Michigan. Unfortunately, my rock samples that had been collected in Zambia were stopped by customs and still have yet to arrive (yikes!)! While I found it really disappointing that I was not going to get the opportunity to study these rocks, I have been working with wonderful samples from the mine in Michigan which I am very lucky to be studying. As mentioned above, another difficulty I am having with my research is with my results that I have received. Although I have not fully interpreted them yet, they do not appear to have the consistency which each other that I had hoped for. While I may not be able to answer my original research question, my results still tell me very interesting things about this area, and are useful for gaining general knowledge about this deposit type.

I still have three weeks left of my research, and I am looking forward to learning what my results have in store for me. I have a lot of interpretation to do and my research is proving to be incredibly intellectually challenging which is everything I had hoped for! What I am researching is not covered in the Geology curriculum here at St Andrews, and I am incredibly thankful that I have had the opportunity to be exposed to different topics through the help of the Laidlaw Internship.

A jazzy photograph of me working with the Raman Spectroscopy gun!

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