Iron, IVC, ataxite
(Iron-ung in MetBull)
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Found 1913
51° 3' 30" N., 94° 24' 0" E.

Many flattened, shrapnel-like iron masses having a combined weight of ~210 kg were found along the Chinge stream bed in Tannu Tuva, which at the time was a small independent country between Mongolia and Siberia. A search for an associated crater was conducted in 1963 but none was found as the fall is estimated to have occurred 10–20 t.y. ago. Because the meteorite contains an average of 16.75 wt% nickel, it forms a macroscopically featureless surface structure (micro-plessite). Small inclusions are present, including kamacite spindles, mm-scale troilite, daubreelite, and schreibersite, and schlieren bands occur in the metallic groundmass. Various features of shearing and plastic deformation are related to a violent event in space.

Chinga has been classified by some as an anomalous member of the IVB chemical group (e.g., Buchwald, 1975) based on its low Ge and Ga abundances and ataxite structure. Worsham et al. (2017) and Bermingham et al. (2018) determined that the Mo and Ru isotopic compositions of Chinga overlap with the IVB irons, attesting to the fact that they derive from a common reservoir in a spatial and/or temporal aspect (see top and middle diagrams below). Two distinct reservoirs existed in the early protoplanetary disk—carbonaceous chondrite (CC) and non-carbonaceous (NC). These reservoirs were segregated by the rapid accretion of proto-Jupiter and reflect differences in the contribution (i.e., susceptibility to thermal processing) of p-, r-, and s-process isotopes inherited as dust ejecta from explosive stellar nucleosynthesis (Poole et al., 2017; Bermingham et al., 2018). However, major compositional differences exist between Chinga and the IVB irons, including the presence in Chinga of Si and P, both of which are depleted in typical IVB members, and a highly siderophile element (HSE) pattern that is very different from other IVB irons (see bottom diagram below). It is noteworthy that the ungrouped iron Sombrerete also has an overlapping Mo composition.

CRE-corrected Mo Isotope Compositions of Meteorite Groups
(µ notation denotes deviation from terrestrial standards in parts per million)
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Diagram credit: Worsham et al., Earth and Planetary Science Letters, vol. 467, p. 165 (2017)
'Characterizing cosmochemical materials with genetic affinities to the Earth: Genetic and chronological diversity within the IAB iron meteorite complex'

Mo vs. Ru Isotope Compositions of Irons
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Diagram credit: Bermingham et al., EPSL, vol. 487, p. 226 (2018)
'New insights into Mo and Ru isotope variation in the nebula and terrestrial planet accretionary genetics'

HSE Abundances of IVB and Ungrouped Irons
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Diagram credit: Honesto et al., 37th LPSC, #1374 (2006)

Importantly, Litasov et al. (2018) determined that Chinga shares compositional similarities with six other ungrouped irons: ALH 77255, Alikatnima, Babb's Mill (Blake's), Deep Springs, Onello, and Shingle Springs. In addition, they demonstrated that these seven irons plot between the IVA and IVB groups on all elemental diagrams utilized in their study, and therefore they proposed that these irons be combined together into a new transitional subgroup termed IVC.

Trace Element Distribution
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Classification Diagrams (Chinga is the star symbol)
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click on diagrams for a magnified view

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click on diagrams for a magnified view

Diagrams credit: Litasov et al., Doklady Earth Sciences, vol. 478, #1, pp. 64–65 (Jan. 2018)
'Trace Element Composition and Classification of the Chinga Iron Meteorite'

A sculpture made from an iron meteorite that is petrologically and geochemically consistent with that of Chinga was transported from Tibet to Germany in 1938–39 (see below). This carved figure, weighing ~10.6 kg (3rd largest Chinga mass known), is probably a portrayal of the Hindu (or Buddhist) god of both wealthiness and war, Kubera (or Vaiśravana), but it could also be a deity associated with the 11th century Bon religion of western Tibet. An estimated date for the sculpture is 8th–11th century, but a more recent date cannot be ruled out.

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Photo credit: Buchner et al., MAPS, vol. 47, #9, p. 1496 (Jan. 2012)
'Buddha from space—An ancient object of art made of a Chinga iron meteorite fragment'

Further geochemical and isotopic analyses are required to better resolve the potential relationships that may exist among the members of the proposed IVC subgroup. The specimen of Chinga shown above is a 43.3 g polished partial slice, beautifully photographed by KD Meteorites.