Cobalt is famous for the abundance of silver veins nearby. This Earthcache focuses on the geology and deposits of silver-rich deposits in the immediate area.
The rocks which make up Canada’s gorgeous landscape contain segments which represent the ocean floor, deep crustal sections, ancient mountain chains, deep sea sediments, and both ancient and modern glacial deposits. The lowermost rocks in Canada are called the Canadian Shield, and they are believed to have formed as the result of plate tectonic processes as smaller continental landmasses drifted together and collided, hundreds of millions of years ago. The Shield extends from the Arctic Islands in the north, to Minnesota in the south; from Great Slave Lake in the west, to the Coast of Labrador in the east. The geologic history Canada dates back over 3.25 billion years.
What made Cobalt so rich? Cobalt is a small mining town in Ontario which is well-known for its large deposits of silver, and has a very interesting geologic history. >The many mines and great silver wealth of Cobalt reflect the occurrence of a dense cluster of small but rich veins near Cobalt. The rocks which rest upon the Canadian Shield in Cobalt are known as the Keewatin. These rocks were formed by basaltic lava flows, interbedded with sedimentary beds of “iron formation” consisting of slate, chert and greywacke.The veins formed during the intrusion of a great molten sheet of magma deep in the Earth 2.2 billion years ago. This igneous intrusion cracked the surrounding rock as it forced its way in, and hot silver-rich fluids filled these cracks and deposited silver and related metals. The flat-lying intrusion, or sill, crystallized to a dark-coloured, coarse-grained layer of rock, called diabase, about 300 m thick.
During the Pleisocene epoch, 2.588 million to 12,000 years ago, great sheets of ice known as glaciers spread out in all directions across Canada, sweeping the rocks clear of their weathered and decomposed surfaces. The upper parts of ore-bodies were carried away, lakes were formed, and Cobalt's landscape as we know it today began to be formed. Erosion has removed much of the diabase sill and only remnants of the original silver veins and diabase remain.
Cobalt as we know it today.
Diagrams are taken from the " Natural Resources Canada and Ontario Geological Survey 2015. Heritage Silver Trail, Cobalt: Road tour of a historic silver mining camp" pamphlet.
Visit the link here to read the pamphlet.
To log a find for this Earth Cache, send me the answers to these questions.
1. Examine the surrounding surface rocks. Are they of:
a) igneous type?
b) sedimentary type?
c) metamorphic type?
2. Given that the vein is 100m long, 60m deep and 0,5m wide, evaluate its total volume.
3. Name the two methods used to extract the silver mineral in this area.
4. If the current price is roughly 16$ /oz and this vein produced 4000 oz of silver, would it be worth mining it today?
5. Optional Photo Assignments: 1. Post a photo of the Silver Sidewalk OR Post a photo of a prominent landscape found within the Cobalt Silver Camp OR Post a photo of mining machinery used by pioneers in the area.
NOTE: You may send answers by e-mail via the link to my profile at the top of the page, without posting them in your log ... otherwise, it could be deleted.