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.

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 75 km (47 mi) northeast of Grande Prairie, Alberta. The ML south pipe measures 400 m (1,300 ft) by 650 m (2,130 ft), covering an area of 29 hectares (72 acres), and the north pipe measures 250 m (820 ft) by 350 m (1,150 ft), covering an area of 8.75 ha (21.6 acres).

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.

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