TAFASSITE CLASSIFICATION

Not long ago the 'Ténéréite Group' was first proposed by Dr. Carl Agee (2020 #2292). Starting from about 2019, a considerable number of abstracts and articles were published discussing these meteorites, especially Tafassasset, NWA 6704, South Byron Trio irons, and the Milton pallasite. Some of the data show that isotopic relationships exist among them (e.g., O, Mo, Ru, W), while others demonstrate some disparities (e.g., HSE). Much investigation and many articles later, the 'Ténéréite Group' has been split into four groups/grouplets representing as many parent bodies, constituting what may be referred to as the 'Tafassite Clan'. A further split of the 14-member Tafassite Group into two separate groups is now a possibility, comprising (1), a 4-member 'Tafassite Grouplet' having low Fa and Fe/Mn values, and (2), a 10-member group lacking a name. This potential split is on par with the findings of Jiang et al. (2023). If it does eventually resolve this way, the new group of 10 will need a type specimen; however, all 10 members were initially purchased from marketplaces in countries of Northwest Africa, and they have all been given NWA-series numbers. An alternative possibility for an eponymous member might be found among the South Byron Trio (SBT) irons if they are determined to represent the core of the unnamed parent body, as could be speculated based on Nicklas et al. (2024). If this is verified, perhaps South Byron would be the appropriate eponymous member, or alternatively, the even older find of Babb's Mill (Troost's).

Through expert analyses we will ultimately learn how each of these meteorites are related to each other, how many parent bodies they represent, whether Tafassasset and three others compose a Low Fa, Low Fe/Mn grouplet, with the SBT irons related to the remainder, and if Milton was formed on the same body as NWA 6704, or perhaps on one of the others. The following articles are some of those which support the classification schemes shown below.

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'Highly siderophile element abundances and 187Re-187Os systematics in the Tafassasset carbonaceous-like primitive achondrite'
Nicklas et al. MAPS vol. 59, #3 (2024)

"All these data, along with the Tafassasset ε95Mo of 1.20 (± 0.05) (Budde et al. 2019 [see Supl. Tabl. 1]), show that it is genetically distinct from CR, CI, CM, CV, enstatite, and ordinary chondrites, as well as from IIC, IID, IIF, and IIIF iron meteorites. However, Tafassasset overlaps in ε95Mo with CK and CO chondrites and IVB irons, but HSE systematics preclude a direct relationship between those meteorite groups and Tafassasset. The ε95Mo of Tafassasset does not preclude a relationship with the South Byron Trio 'grouplet' of iron meteorites (Figure 1), and the HSE systematics of the grouplet plot close to Tafassasset (Figure 4) indicating a possible relationship, although more data are necessary. Therefore, available geochemical evidence indicates that Tafassasset is from a distinct parent body from all major chondrite and achondrite groups, albeit with a possible relationship to the South Byron grouplet, consistent with the conclusions of Gardner-Vandy et al. 2012), and it may indeed be the type specimen of a new achondrite group (Ma et al., 2022)."

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'Genetics, crystallization sequence, and age of the South Byron Trio iron meteorites: New insights to carbonaceous chondrite (CC) type parent bodies'
Hilton et al., GCA vol. 251 (view open manuscript: 2019)

"Milton has identical Mo and Ru isotopic compositions to the SBT, providing permissive evidence of being from the same parent body. The HSE content of Milton, however, cannot be directly related to the SBT by fractional crystallization or any other process we attempted to model. Milton metal was likely derived from a parental melt with relative abundances of some HSE that were modestly fractionated from known chondritic ratios, most likely on a different parent body from the SBT."

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'The Milton pallasite and South Byron Trio irons: Evidence for oxidation and core crystallization'
McCoy et al., GCA vol. 259 (view open manuscript: 2019)