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Mountain Lake cluster
The Mountain Lake cluster consists of two diatremes or volcanic pipes in Northern Alberta, Canada. It was emplaced during a period of kimberlite volcanism in the Late Cretaceous epoch.
Although they were originally described as kimberlite or kimberlitic, the Mountain Lake (ML) rocks were later reclassified as alkaline ultramafic volcanics,〔 hybrid alkaline ultramafic rocks,〔 basanite or alkali olivine basalt. Due to extensive clay alteration that obliterated much of their original mineralogy, the question of their proper classification remains unsettled.〔Skupinski, A. and Langenberg, C.W. 2002. Petrography of the Mountain Lake pipe, Grande Prairie area, Alberta, Canada. Alberta Geological Survey, Special Report 15, 39 p.〕
==Location and Geological Setting==
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, which lies about northeast of Grande Prairie, Alberta. The ML south pipe measures by , covering an area of , and the north pipe measures by , covering an area of .〔8th International Kimberlite Conference: Selected Papers: Volume 1: The C. Roger Clement Volume, Elsevier Science, 2004, p. 437 - 440 ISBN 0-444-51775-8 (accessed via Google books)〕
The ML pipes are hosted within the nonmarine sedimentary rocks of the Wapiti Formation and were erupted onto an inland alluvial plain. The uppermost strata of the Wapiti have been removed by erosion in the area, and most of the bedrock is covered by glacial and post-glacial sediments of Quaternary age. The ML volcaniclastic rocks are more resistant to erosion than the surrounding Wapiti Formation rocks, so the ML cluster forms a small hill.〔Leckie, D.A., Kjarsgaard, B. et al. 1997. Geology of a Late Cretaceous possible kimberlite at Mountain Lake, Alberta – Chemistry, petrology, indicator minerals, aeromagnetic signature, age, stratigraphic position and setting. Geological Survey of Canada, Open File 3441, 202 p.〕
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