Birch Mountains kimberlite field facts for kids
The Birch Mountains kimberlite field is a group of special ancient volcanoes in north-central Alberta, Canada. These volcanoes are called "kimberlites" and they are known for sometimes containing diamonds. They formed a very long time ago, during the Late Cretaceous period. By 2011, eight of these ancient volcanic sites, called "diatremes," had been found here. Scientists have even found diamonds and tiny diamonds (microdiamonds) when they took samples from these sites.
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Where are the Birch Mountains Kimberlites?
The Birch Mountains (BM) kimberlite field was first found in 1998. It's about 430 kilometers (267 miles) north of Edmonton. It's also about 135 kilometers (84 miles) northwest of Fort McMurray. This field is part of a bigger area in Northern Alberta where many kimberlites are found. Other similar areas include the Buffalo Head Hills kimberlite field and the Mountain Lake cluster.
These ancient volcanoes are found within layers of rock called shales. These shales formed in the ocean during the Late Cretaceous period. This means the volcanoes erupted when the area was covered by a large ancient sea called the Western Interior Seaway. Today, thick layers of loose dirt and rocks, some over 150 meters (492 feet) deep, cover the ground. Because of this, scientists mostly found these volcanoes using special airplane surveys that measure magnetic fields (called aeromagnetic surveys). After finding interesting spots, they drilled into the ground to confirm.
How Old Are These Volcanoes?
Scientists have used special tests to figure out the age of the Birch Mountains volcanoes. These tests show that the volcanoes formed about 70 to 78 million years ago. This was during the Campanian to Maastrichtian stages of the Late Cretaceous period. Tiny fossils found in the rocks around the kimberlites also agree with this age.
What Are These Rocks Made Of?
The rocks from the Birch Mountains kimberlite field are mostly volcanic rocks that exploded out of the ground. They are made of different layers, some thick and solid, and others with coarse bits mixed with finer dust.
These rocks contain small pieces of volcanic material called "lapilli." They also have crystals of a mineral called olivine. All of this is held together in a grey-green material. This material is made of minerals like serpentine, carbonate minerals (like calcite and dolomite), and clay minerals. Other minerals found here include phlogopite, oxide minerals (like ilmenite), apatite, and pyrite.
The most exciting part is that diamonds and microdiamonds have been found. These precious gems were recovered from samples taken from two specific volcanic sites: the Phoenix and Legend pipes.
List of Volcanic Sites
Here are the names of the different ancient volcanic sites, or diatremes, found in this field:
- Phoenix pipe
- Dragon pipe
- Xena pipe
- Legend pipe
- Valkyrie pipe
- Kendu pipe
- Roc pipe
- Pegasus pipe
