An EarthCache site is a special place that people can visit to learn about a unique geoscience feature or aspect of our Earth. Thus, EarthCache sites do not use stored containers; their treasure is the lessons people learn about our planet when they visit the site. (reprinted from earthcache.org)
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.
The Abitibi Greenstone Belt (AGB) is a 2,800-2,600 million year old greenstone belt that spans across the Ontario-Quebec border in Canada. It is mostly made of metamorphosed volcanic rocks, but also includes granitoid rocks, and early and middle Precambrian sediments. Numerous faults called "breaks" divide the AGB. The Porcupine-Destor and Larder Lake-Cadillac faults are associated with major gold deposits.
The rocks which rest upon the Canadian Shield in this area 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 mineral-rich fluids filled these cracks and deposited gold specks and related minerals. 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 Kirkland Lake'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 gold veins and diabase remain.
What made Kirkland Lake so rich? The many mines and great gold wealth of Kirkland Lake reflect the occurrence of a dense cluster of small but rich veins. The Kirkland Lake-Larder Lake gold belt is located in the southern Abitibi greenstone belt.
Diagrams are taken from the [Natural Resources Canada and Ontario Geological Survey 2015. Mining Heritage Tour, Kirkland Lake: A Century of Mining the "Mile of Gold"] pamphlet.
Visit this link 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. Describe the uniformity in colour of these rocks?
3. Which two of the following methods could be used to extract gold mineral in this area.
a) panning?
b) underground mining?
c) placer mining?
d) sluicing?
e) open pit mining?
4. Imagine you are prospecting for gold in this area in 1910? What clues would you look for to bring you to suspect there is gold at your feet?
5. Optional Photo Assignments: Post a photo of you and your GPS at the plaque OR Post a photo of a prominent landscape found within the KL Mile of Gold 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.