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Gibeon Iron Meteorites
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Gibeon Iron Meteorites. Their Discovery, History and Research. By Svend Buhl
Dr. Paul Range - First systematic collection
In 1911 the chief geologist of the colonial administration in Deutsch-Südwest Afrika,
Dr. Paul Range, was advised by the governor to survey the find locations
and to purchase all remaining meteorites of the Mukerop area. Range admits
this was an “interesting enough order” and so he frequently visited Amalia,
Goamus, Kameelhar and other farms in the Gibeon area between 1911 and 1913.
In 1913 he published the results of his survey in the article “Meteoriten
aus Deutsch Südwest Afrika” in vol. 26 of the colonial periodical
“Mitteilungen aus den Deutschen Schutzgebieten”.
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A 77 kg Gibeon meteorite from the collection of Walter Zeitschel. The impressively sculpted
individual shows a characteristic pattern of exaggerated regmaglypts due to soil etching
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Before 1911, apart from the four masses already known to Brezina and Cohen,
several additional specimens had been exported to Germany via the colonial
company Hesselbach. At least three specimens went to the Mineralogical Museum
of the Hamburg University. The two smaller specimens were cut into sections and
used for trades with various museums worldwide, among them the Smithsonian.
The biggest specimen of 420 kg still resides in the Hamburg collection today.
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Another ex-Zeitschel collection specimen weighing 21.4 kg. The pentagon shaped mass with a flat tapered profile shows
the moderate effects of soil-imbedded weathering. The very stable
dark red to brown patina is characteristic for untreated Gibeons
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Together with the farmer Piet van der Westhuizen, who
had already discovered seven specimens, among them the meteorites
exported by Hesselbach, Range explored the wider area on horseback in
search for further undiscovered masses - with success: “On our rides
through the country on various occasions we found the messengers of
another world on the spots where they had fallen onto the earth.”
Range stated that the meteorites are usually found with the bulk of the
mass embedded in the soil, though some of their finds were recovered from
on top of the surface. The soils in the eastern part of the Gibeon district
belong to the Karoo and Post-Karoo layers and are covered by the Kalahari
lime formations. The meteorites found by Range were recovered partly from
Karroo layers and partly from on top of Kalahari limestone plateaus. Because
the latter formation is considered of diluvial origin Range concluded
that the terrestrial age of the meteorites could not exceed these layers.
Range’s research from 1911 to 1913 brought to light 51 meteoritic masses
including those found before his survey. The total weight of these Meteorites
was 15,396 kg. The 37 masses piled up and later caged in in the public garden
in Windhoek originate from Range’s field collection. After several donations
to foreign museums and prominent collectors,
including a 650 kg mass which went to South Africa, 33 masses were left. Of
these 28 are on public display today in Post Street Mall in Windhoek.
Spencer and Citron - extending the strewn field
In the following years additional masses were found and in 1930 the number of
known Gibeon meteorites had risen to 54. Spencer (1941) noted their unusually wide
distribution over an area of several hundred square miles. Based on the considerable
size of most of these masses Spencer concluded that the shower must have been a
“swarm of meteorites rather than a single mass broken up in the earth’s atmosphere.”
In 1967 Robert Citron undertook an invaluable survey of the distribution
of the Gibeon iron meteorites and published the results in his paper On The
Distribution Of The Gibeon Meteorites Of South-West Africa. Citron dismissed
the idea of a swarm of meteorites travelling together in space and suggested
that in fact the Gibeon irons represented a single body that
fragmented in mid air during its flight through the atmosphere. Citron
also provided a new distribution map which
gave the find positions of many of the 65 finds known at his time.
Through his work the extensive dimensions of the strewn field became obvious. Although at
least 53 of the 65 known masses were recovered from a 300 square mile area within 20
miles of 25°10’S and 18°00’E centring around the Bukarros structure, the remaining 12
masses were scattered over an extensive area up to 145 miles away from this position.
The maximum separation between two meteorites reported
to have been found in their original position is 230 miles (Kamkas and Kinas Putts).
Citron also speculated that with Roter Kamm crater he had discovered a
structure that perhaps was related with the Gibeon meteorite. Indeed the crater
was later proven to be a meteorite impact crater, however Dietz (1965) was convinced that
the crater exceeded the terrestrial age of the Gibeon iron meteorites.
Recent research on Platinum-group element abundances and ratios indicate an ordinary
chondritic composition for the Roter Kamm impactor, which definitively rules out the
Gibeon meteorite as the smoking gun. The impact age
for the Roter Kamm crater today is given with ~ 5.1 Ma. (Hecht et al. 2008)
Vaugn F. Buchwald - detailed classification
Buchwald in vol. 2 of his Handbook Of Iron Meteorites gave an
extensive survey of the research on Gibeon and provided another map which also
included many masses for which no precise find locations were conveyed.
Gibeon according to Buchwald is classified as a group IVa polycrystalline
fine octahedrite with a Widmannstätten bandwith of 0.30 + 0.05 mm. The Ni
content is given with 7.93 wt% and the Co content with 0.41 wt% (Buchwald 1975).
As has already been stated by Shepard, some of the Gibeon masses display a
remarkably unoxidized surface. By referring to the 650 kg Lichtenfels mass
(see photo on the next page) Buchwald
noted the occurrence of fusion crust and flow features on several of the
specimens he examined. Because many Gibeon cut sections show heat affected zones
on their rims, Buchwald
argued that only little material was lost to oxidation and erosion.
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