Buffalo Head Hills kimberlite field

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Buffalo Head Hills Kimberlite Field
Location of the Buffalo Head Hills Kimberlite Field in north-central Alberta, Canada.

The Buffalo Head Hills kimberlite field is a group of kimberlitic volcanic pipes or diatremes in north-central Alberta, Canada. As of 2011, 41 kimberlite pipes, of which 28 are diamondiferous, had been identified in the field. [1] They were emplaced during Late Cretaceous to early Paleocene time. [2]

Contents

As of 2014 the Buffalo Head Hills field is in the exploration stage and has not gone into production. The highest grade kimberlite pipe (Pipe K252) has an estimated grade of 55 carats per hundred tonnes. [3]

Location

The Buffalo Head Hills (BHH) kimberlite field is part of the Northern Alberta kimberlite province, along with the Birch Mountains kimberlite field and the Mountain Lake cluster. It is located about 400 km (250 mi) north of the city of Edmonton in the Buffalo Head Hills of northern Alberta. The area lies within the Canadian boreal forest and is sparsely settled. Access is via Alberta Highway 88. [3]

Geologic setting

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. Because of this thick cover of Quaternary sediments and lack of bedrock outcrops, the BHH kimberlite pipes were discovered primarily through interpretation of geophysical data from aeromagnetic and gravity surveys, followed by drilling programs. [2] [4]

Age

According to radiometric dating, the BHH kimberlite pipes were emplaced in two pulses, one between about 81 to 88 Ma (million years ago) during the Coniacian to Campanian Stages of the Late Cretaceous, and one between about 60 to 64 Ma in early Paleocene time. They were erupted into a near-shore setting in the Late Cretaceous Interior Seaway. Marine microfossils in mudstones that are interbedded with some of the kimberlite deposits are consistent with the Late Cretaceous age. [2] [5]

Pyroclastic deposits

Kimberlitic rocks from the Buffalo Head Hills. Display by Alberta Geological Survey. BHH Kimberlite 0264.jpg
Kimberlitic rocks from the Buffalo Head Hills. Display by Alberta Geological Survey.

The BHH kimberlite pipes cover areas ranging from one to 47 hectares (120 acres). [3] They represent maar-style volcanoes which have a vertical-walled volcanic crater of explosive origin, surrounded by a low rim of ejecta and filled with water. Pyroclastic fall and surge are the two volcanic mechanisms of deposition. There are also deposits formed by hydraulic reworking of kimberlite from tephra cones and/or extra-crater fall and surge deposits. [2]

The pyroclastic fall deposits are poorly sorted and massive, while the surge deposits are better sorted, fine grained, and well bedded, with high bedding angles. The reworked kimberlite is well sorted, distinctly bedded, and contains abraded olivine grains. Multiple layers of pyroclastic and reworked kimberlite separated by layers of marine mudstone are present at some pipes. These represent a series of discrete kimberlite eruption events separated by quiescent periods during which the muds were deposited. [2]

Mineralogy and classification

The majority of the BHH kimberlites are diamondiferous, in contrast to those of the Birch Mountains kimberlite field to the northeast which are mostly barren of diamonds. Based on petrography and whole-rock geochemistry, the BHH pipes are classed as Group 1A kimberlites. They have a low carbonate content, low abundances of late-stage minerals such as phlogopite and ilmenite, and a high abundance of fresh, coarse olivine. [4] [6]

Diamonds

Based on examination of more than 700 examples, the BHH diamonds range in color from colorless to yellow and brown, and most are transparent and colorless. The majority are sharp-edged octahedra, but ~45% were dodecahedral due to resorption of octahedra. Inclusions of garnet, olivine, clinopyroxene and rutile were found in a few specimens. [7]

See also

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Churchill Craton The northwest section of the Canadian Shield from southern Saskatchewan and Alberta to northern Nunavut

The Churchill Craton is the northwest section of the Canadian Shield and stretches from southern Saskatchewan and Alberta to northern Nunavut. It has a very complex geological history punctuated by at least seven distinct regional tectonometamorphic intervals, including many discrete accretionary magmatic events. The Western Churchill province is the part of the Churchill Craton that is exposed north and west of the Hudson Bay. The Archean Western Churchill province contributes to the complicated and protracted tectonic history of the craton and marks a major change in the behaviour of the Churchill Craton with many remnants of Archean supracrustal and granitoid rocks.

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The volcanism of Canada is represented by many types of landform including lava flows, volcanic plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes, and maars, along with examples of more less common volcanic forms such as tuyas and subglacial mounds. It has a very complex volcanic history spanning from the Precambrian eon at least 3.11 billion years ago when this part of the North American continent began to form.

Crowsnest Formation

The Crowsnest Formation, also called the Crowsnest Volcanics, is a geological formation in southwestern Alberta, Canada, on the southwestern margin of the Western Canada Sedimentary Basin. It was named for the Crowsnest Pass near Coleman, Alberta. The formation consists mostly of pyroclastic rocks that were laid down in a series of explosive eruptions about 100 million years ago during the Albian stage of the Early Cretaceous epoch. It contains unusual minerals such as melanite and analcime.

The Phoenix pipe is a diatreme associated with the Birch Mountains kimberlite field in northern Alberta, Canada. It is thought to have formed about 75 million years ago when this part of Alberta was volcanically active during the Late Cretaceous period.

The Valkyrie pipe is a diatreme in northern Alberta, Canada. It is associated with a group of diatremes called the Birch Mountains kimberlite field which is thought to have formed about 75 million years ago when this part of Alberta was volcanically active during the Late Cretaceous period.

The Xena pipe is a diatreme associated with the Birch Mountains kimberlite field in northern Alberta, Canada. It is thought to have formed about 75 million years ago when this part of Alberta was volcanically active during the Late Cretaceous period.

The Dragon pipe is a diatreme associated with the Birch Mountains kimberlite field in northern Alberta, Canada. It is thought to have formed about 75 million years ago when this part of Alberta was volcanically active during the Late Cretaceous period.

Birch Mountains kimberlite field

The Birch Mountains kimberlite field is a cluster of kimberlitic volcanic pipes or diatremes in north-central Alberta, Canada that were emplaced during a period of kimberlitic volcanism in the Late Cretaceous epoch. As of 2011, 8 diatremes had been discovered in the field, and diamonds and microdiamononds had been recovered during sampling programs.

K6 pipe is a diamondiferous diatreme in the Buffalo Head Hills kimberlite field of Northern Alberta, Canada. It is thought to have formed about 85 million years ago when is part of Alberta was volcanically active during the Late Cretaceous period. It is typical of melts that originated from the low mantle.

Northern Alberta kimberlite province

The Northern Alberta Kimberlite Province (NAKP) consists of three groups of diatremes or volcanic pipes in north-central Alberta, Canada, most of which are kimberlites and some of which are diamondiferous. They are called the Birch Mountains (BM), Buffalo Head Hills (BHH), and the Mountain Lake cluster (ML), and they were discovered between about 1990 and 1997. Most of the diatremes were emplaced during the Late Cretaceous Epoch although a few are as young as early Paleocene.

K252 pipe is a diamondiferous diatreme in the Buffalo Head Hills kimberlite field of Northern Alberta, Canada. It is thought to have formed about 85 million years ago when this part of Alberta was volcanically active during the Late Cretaceous period. It contains pyroclastic textures and is intruded into Cenomanian and Albian aged strata.

K19 pipe is a diatreme in the southwestern part of the Buffalo Head Hills kimberlite field in Northern Alberta, Canada. It is thought to have formed about 60 million years ago, making it one of the youngest volcanic formations in the Buffalo Head Hills kimberlite field and in Alberta. Unlike many other diatremes in the Buffalo Head Hills kimberlite field, it contains low diamond content.

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.

Volcanism of Western Canada

Volcanism of Western Canada has produced lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, greenstone belts, submarine volcanoes, calderas, diatremes and maars, along with examples of more less common volcanic forms such as tuyas and subglacial mounds.

The Igwisi Hills are a volcanic field in Tanzania. Three tuff cones are found there, one of which is associated with a lava flow. They are one of the few locations of possibly kimberlitic lava flows on Earth.

The Buffalo Head Terrane (BHT) is a terrane in the western Canadian Shield in northern Alberta. It is covered by 1,600 m (5,200 ft) of Devonian and Cretaceous sediments and its centre is intruded by the 88–86 Ma kimberlites of the diamondiferous Buffalo Head Hills kimberlite province.

The geology of Nunavut began to form nearly three billion years ago in the Archean and the territory preserves some of the world's oldest rock units.

References

  1. ↑ Eccles, D.R. (2014). "Northern Alberta kimberlite province: The first 20 years. Alberta Geological Survey, ERCB/AGS Bulletin 65, 116 p." (PDF). Archived from the original (PDF) on 2012-02-25. Retrieved 2014-10-19.
  2. 1 2 3 4 5 Boyer, L., McCandless, T., Tosdal, R. and Russell, K. 2008. Volcanic facies and eruption styles in the Cretaceous Buffalo Head Hills kimberlites, Alberta, Canada. 9th International Kimberlite Conference, Extended Abstract 91KC-A-00367-2, 3 p.
  3. 1 2 3 "Canterra Minerals Corporation: Buffalo Hills, Alberta (Aug. 28, 2014)" . Retrieved 2014-10-11.
  4. 1 2 Eccles, D.R.; Heaman, L.M.; Luth, R.W. & Creaser, R.A. (2003). "Petrogenetic considerations for the Late Cretaceous Northern Alberta kimberlite province. 8th International Kimberlite Conference, Extended Abstract, 5 p." (PDF). Archived from the original (PDF) on 2011-05-26. Retrieved 2014-08-13.
  5. ↑ Eccles, D.R., Creaser, R. A., Heaman, L.M. and Ward, J. 2008. Rb–Sr and U–Pb geochronology and setting of the Buffalo Head Hills kimberlite field, northern Alberta. Canadian Journal of Earth Sciences, vol. 45, no. 5, p. 513-529.
  6. ↑ Eccles, R.D., Heaman, L.M., Luth, R.L. and Creaser, R.A. 2004. Petrogenesis of the Late Cretaceous Northern Alberta Kimberlite Province. Lithos , vol. 76, p. 435-459.
  7. ↑ Banas, A., Stachel, T., Muelenbachs, K. and McCandless, T. 2007. Diamonds from the Buffalo Head Hills, Alberta: Formation in a non-conventional setting. Lithos, vol. 93: p. 199-213.

Coordinates: 57°25′01″N115°55′09″W / 57.41686°N 115.91926°W / 57.41686; -115.91926

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