Cape York: The extraordinary mineralogy of an ordinary iron meteorite and its implication for the genesis of III AB irons.

Abstract

A study of accessory minerals in the Cape York iron meteorite has been carried out with the electron microprobe. Phases analyzed include chromite, sphalerite, two closely related potassium-bearing sulfides, silica, and native copper. In addition, four phosphate minerals were found: One chemically similar to buchwaldite, but rather rich in iron, one corresponding to terrestrial maricite, and two more, which seem to be new minerals on the basis of microprobe analysis. Evidence from the composition of accessory minerals as well as texture elucidates some details of the fractional crystallization of the group III AB parent melt. A modification of the fractional crystallization model is therefore proposed. We suggest that sulfide nodules have originated as droplets of an immiscible sulfur-rich liquid that continuously segregated from the parent melt during crystallization of the metal. The modified model also explains the Ni/Cr anticorrelation and the high abundance of sulfur in group III AB irons which could not be satisfactorily explained by previous models.

Sahara 03505 sulfide‐rich iron meteorite: Evidence for efficient segregation of sulfide‐rich metallic melt during high‐degree impact melting of an ordinary chondrite

“…Anhydrous Fe,Mn,Na, Ca,Mg,K,Cr phospates are reported as small spherules (2-8 µm in diameter) within the metal-troilite inclusions of the severely shocked Yanzhuang (H6) chondrite (Chen and Xie 1996); in addition, these phases may occur in magmatic iron meteorites, particularly IIIAB irons, where they are often found in association with troilite and nearly stoichiometric FeCr 2 O 4 spinel (Kracher et al 1977;Olsen et al 1999). Very small (5-20 µm) particles of metallic Cu occur, with a frequency of ~0.1 per mm 2 , within troilite or at the metaltroilite interface (Fig.…”

Mineralogy of the planets: a voyage in space and time

“…Ga, Ge), a similar redox state, and exposure ages indicating a major collision at -6.5 x Io 8 yr. Detailed study of the huge Cape York iron revealed many trace minerals (Kracher et at., 1977): four Nabearing phosphates (including buchwaldite NaCaPO4), six sulphides (daubr6elite, chalcopyrrhotine, djerfisherite, another K-rich sulphide, sphalerite, Fe-alabandine), chromite, copper, carlsbergite (CrN), and a silica mineral. The main group of pallasites (next section) is chemically related to the high-Ni IIIAB irons (Scott,I977a ,c).…”

Iron and Stony-Iron Meteorites

“…llAB irons are medium octahedrites, often heavily shocked (Buchwald, 1975;Steffler ef al., 1988), and have uniform exposure ages and cooling rates. They have the by far highest abundance of phosphates, suggesting formation from relatively oxidized material (Kracher et al, 1977;Olsen and Fredriksson, 1966;Olsen ef al., 1999). Silicate inclusions are documented in only two members Kracher et al, 1977;Olsen et al, 1996).…”

“…They have the by far highest abundance of phosphates, suggesting formation from relatively oxidized material (Kracher et al, 1977;Olsen and Fredriksson, 1966;Olsen ef al., 1999). Silicate inclusions are documented in only two members Kracher et al, 1977;Olsen et al, 1996). Observed compositional trends can be broadly matched by numerical models for fractional crystallization of a common core U1ff-M0I1er, 1998;Chabot and Drake, 1999;Wasson, 1999;Chabot and Drake, 2000).…”