Iron, IIIAB, octahedrite
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Found July 1, 2007
53° 59′ 57′ N., 115° 35′ 51′ W. While searching with metal detectors in a forested region near Whitecourt, Alberta, Canada, two local residents, James ‘Sonny’ Stevens and Rod Stevens uncovered four jagged, angular fragments of an iron meteorite. The fragments were located near the partially raised rim of a 36 m diameter, 5–10 m deep, circular impact crater of late Holocene age (<1,130 years old); the Whitecourt Meteorite Impact Crater is recorded in the Earth Impact Database, Planetary and Space Science Center, University of New Brunswick, Canada. The crater is now protected from meteorite hunting under the Alberta Provincial Historic Resources Designation Act. standby for whitecourt photo
Cross section through the crater along 110°
Image credit: R. Kofman et al., MAPS, vol. 45, p. 1434 (2010)
‘The Whitecourt meteorite impact crater, Alberta, Canada’
Calculations by Kofman et al. (2010) indicate that the Whitecourt crater was excavated by an impactor weighing 1,285–16,728 kg measuring ~0.7–1.6 m in diameter. By contrast, modeling conducted by Newman and Herd (2010) indicates a somewhat smaller object weighing 500–800 kg and measuring 0.5–0.55 m that impacted at 8–10 km per second from an angle of 55°. The target material was composed of sediments associated with the advance and retreat of the Laurentide Ice Sheet (Herd et al., 2008; Kofman et al., 2009). The impactor struck at an angle of 40–55° along a trajectory of 60–85°. Within the crater there is a sharp transition from poorly sorted, fine-grained glacial till (heterogeneous pebble diamict) overlying unconsolidated fine quartz sand at a depth of ~2.9 m, and it is considered that this boundary marks the base of the transient crater. Notably, amber-colored glass fragments are found above ~2.9 m (Kofman et al., 2008).

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Simon de Boer standing in Whitecourt crater.
Photo courtesy of Simon de Boer (2010) Subsequent searches of the area have resulted in the recovery of more than 5,000 meteorite fragments, some found a considerable distance from the crater (Kofman et al., 2010; Newman and Herd, 2015). The meteorite fragments consist primarily of shrapnel-type morphologies but rare examples of regmaglypted individuals have been recovered. The smallest recovered fragment weighs 0.1 g and measures <1 cm in size, while the largest individual weighs 31.5 kg; the combined weight of both fragments and individuals is ~230 kg (Herd et al., 2008; Newman and Herd, 2015). It was reported that the largest mass was found at a depth of 61 cm. A 6.51 kg mass exhibiting regmaglypts and fusion crust was found 261 m east-northeast of the crater. In addition, it has been reported that an exceptional mass weighing ~27 kg likely also retaining ablation features was found in the Fall of 2010 and donated by the finders to the University of Alberta in Edmonton. Among other noteworthy fragments found outside of the protected zone is a 1.9 kg fragment that exhibits possible ablation characteristics. Diligent documentation of location, depth, weight, and other data for recovered fragments and individuals has made it possible to construct an accurate strewn field map:
Distribution of meteorites in and around the 200 × 200 m zone protected by the Alberta Historic Resources Law
Image credit: J. Newman and C. Herd, MAPS, vol. 50, #2, p. 310 (2015)
‘Mineralogy, petrology, and distribution of meteorites at the Whitecourt crater, Alberta, Canada’
The crater is surrounded by an ejecta blanket covering 6,000 m² constituting 40% of the volume of the crater. Meteorite fragments recovered from under the ejecta blanket have experienced less oxidation than those recovered from within the crater. It is thought that the crater was excavated during a high-angle, low-energy, hypervelocity impact by a single projectile measuring ~1.1 m in diameter traveling towards the east-northeast (Kofman et al., 2009). It was argued by Kofman et al. (2010) that the evidence was most consistent with a meteoroid traveling 4–10 km per second which experienced a catastrophic disruption upon impact; the lack of size-sorting of the fragments and individuals is consistent with this scenario. Following the recovery of additional regmaglypted samples, some low-altitude fragmentation is considered to have occurred (Newman and Herd, 2015).

Geochemical analyses and structural studies (conducted after etching) distinguish Whitecourt as a low-Ni medium octahedrite belonging to the IIIAB (IIIA) iron group (Herd, University of Alberta). Accessory minerals present in Whitecourt include a variety of sulfides and phosphides, along with rare chromite inclusions and grains of carlsbergite and native copper (Newman and Herd, 2015). The iron meteorite shows some signs of shock and recrystallization, while planar microstructures present in quartz grains located below the transient crater boundary provide evidence for a low degree of shock. This is consistent with the presence of Fe,Ni-oxide spherules and rare samples of partially melted impactor material. The specimen of Whitecourt shown above is a 10.2 g shrapnel-type fragment kindly donated to dweir’s Meteorite Studies by its finder Simon de Boer, via Canadian Cultural Property Export Permit #103306. Pictured below is a Whitecourt slice that was expertly etched by Mirko Graul.

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Photo courtesy of Mirko Graul Meteorite

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See the ‘Meteorite Men’ episode Return to Whitecourt, 12 December 2011, originally broadcast on the Science Channel and now available on YouTube.

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