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The ML rocks are not considered to be archetypal kimberilte and have been variously classified as alkaline ultramafic rocks, hybrid alkaline ultramafic rocks, alkali olivine basalt and basanite; they are difficult to classify because of strong clay alteration that has obliterated most of their original mineralogy.
Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes, as well as igneous dykes and can also occur as horizontal sills. Kimberlite pipes are the most important source of mined diamonds today. The consensus on kimberlites is that they are formed deep within Earth's mantle.
The ML pipes form part of the Northern Alberta kimberlite province, along with the nearby Birch Mountains kimberlite field and the Buffalo Head Hills kimberlite field.They were discovered in 1989-90 just north of Mountain Lake (55.456291n 117.714510w), which lies about 75 km (47 mi) northeast of Grande Prairie, Alberta.
It is generally accepted that the pipe was emplaced about 180 million years ago. The lake Ellen Kimberlite is popular with rock hounds as the classic indicator minerals (pyrope, magnesian ilmenite and chrome diopside) for kimberlite are easily found in the material, though few are of gem quality and size. While there was considerable interest ...
Lamproite pipes operate similarly to kimberlite pipes, except that the boiling water and volatile compounds contained in the magma act corrosively on the overlying rock, resulting in a broader cone of eviscerated rock (the ejection of this rock also forms a tuff ring, like kimberlite eruptions). This broad cone is then filled with volcanic ash ...
Deep beneath the BHH kimberlite field lies a 2.0 to 2.4 billion year old Precambrian craton called the Buffalo Head terrane, which has no exposure at surface.The Precambrian craton is overlain by about 1,600 m (5,200 ft) of Paleozoic and Mesozoic sedimentary rocks, which are covered by as much as 200 m (660 ft) of unconsolidated glacial and post-glacial sediments of Quaternary age.
Since then it has accumulated about 40 metres (130 ft) of water, leaving 175 metres (574 ft) of the hole visible. Once above-ground operations became too dangerous and unproductive, the kimberlite pipe of the Alyrick Mine was also mined underground by Cecil Rhodes' De Beers company to a depth of 1,097 metres (3,599 ft). [5]
The country has the highest concentration of kimberlite bodies in the world—a total of more than 400, including 343 dikes, 39 pipes and 23 blows. Northern Lesotho has an average of one kimberlite body for every 10 square kilometers. In spite of the large deposits, very few sites are mined and research is ongoing into alluvial deposits.