Weaver Mountains - Wedderburn 1295 Figure 1908. Weaver Mountains (U.S.N.M. no. 1427). Kamacite Figure 1909. Weaver Mountains (U.S.N.M. no. 1427). Kamacite grains with schreibersite crystals (S). Duplex, almost unresolvable grains with numerous schreibersite particles, usually in contact with matrix. Etched. Scale bar 50 ll· (Perry 1950: volume 7.) taenite along at least one surface. Etched. Scale bar 40 ll· (Perry 1950: volume 7 .) forms together occur with a frequency of about 600 per mm 2 . The a-phase has subboundaries, but neither Specimens in the U.S. National Museum in Washington: Neumann bands nor hatched structures were observed. 546 g slice (no. 1427, 19 x 9 x 0.6 em) The plessitic matrix appears to be of a bainitic, duplex 167 g part slice (no. 1427, 12 x 8 x 0.3 em) type, but requires electron microscopy for any details to be 60 g part slice (no. 3145,5 x 3.5 x 0.5 em) seen. It appears striped at low magnification, apparently along the Widmanstiitten directions, as defmed by the scattered a-lamellae. The hardness is 300±15 and rather uniform right to the corroded edge of the specimens. Wedderburn , Victoria, Australia Schreibersite occurs as a few, "large" crystals, 40 x 60 Approximately 36°26'S, 143°38'E or 120 x 2011 in size, but most of the phosphides are present as evenly distributed blebs, 1-1011 across. They Nickel-rich ataxite, D. Numerous a-spindles 10±2~t wide. Neumann have nucleated narrow rims of swathing kamacite, but the bands. phosphide blebs are frequently still attached along one or Group IIID. 22.8% Ni, 0.57% Co, 1.5 ppm Ga, 1.5 ppm Ge, two sides to the parent taenite. Because of this, the 0.05 ppm Jr. schreibersite is easily mistaken for taenite and is overlooked. HISTORY Troilite occurs with a frequency of about one per A small mass of only 210 g was found on a road about 15 cm 2 • The individual nodules are small, 0.24 mm across, 1951 by C. Bell, of Rushworth, while he was prospecting at and have frayed edges against the metal. The troilite has a point three miles northeast of Wedderburn. It was been shock-melted and has dissolved part of the surround­ acquired by the Mines Department, Melbourne, where it ing metal; the melts have solidified to fine-grained ( ~ 1 11) was described with four photomicrographs by Edwards eutectics of sulfide and metal. (1953). He found it very similar to Tawallah Valley, and so Daubreelite fragments, 5-50 11 wide, are dispersed did Lovering et al. (1960) who studied the ablation through the melts, and what appear to be tiny silicate or behavior during atmospheric entry. However, as noted glass slivers are also present. The hardness of the troilite below, the structure is different from Tawallah Valley in composites is 235±10. several important respects and rather resembles Follinge Weaver Mountains is closely related to Tawallah Valley and Freda, two other very small nickel-rich irons. Keil which it resembles structurally and chemically. However, its (1960: 269) reviewed the literature. Schultz & Hinten­ hardness is significantly different. Weaver is a member of berger (1967) determined the amount of occluded noble group NB but does not resemble the phosphorus-poor gases, while Voshage (1967) estimated from these data a members very much because, when phosphides are precipi­ cosmic ray exposure age of 100-200 million years. tated, they tend to create blebs of swathing kamacite which conspicuously interrupt the monotonous ataxitic structure. Furthermore, the matrix of Tawallah and Weaver is bainitic COLLECTIONS and optically unresolvable, while the matrix of, e.g., Hoba Geological Museum, Mines Department, Melbourne and Kokomo, is easily resolvable. (main mass, about 100 g), Sydney (17 g). 1296 Wedderburn - Weekeroo Station DESCRIPTION matrix and the taenite rim zones are, as usual, also affected According to Edwards (1953) the mass was a well in the a 2 zone. The taenite etches only with difficulty in rounded monolith with the overall dimensions of 5 x 3.6 x the exterior parts, and the matrix is distinctly decomposed 2.6 em and weighed 210 g. The mass was slightly corroded to a number of differently oriented grains. but showed a regmaglypt and a distinct heat-affected rim Corrosion has selectively attacked the swathing kama­ zone. cite, the fine iron grains of the shock-melted iron-sulfur Etched sections display a very fine structure, interme­ eutectic, and the a-spindles near the surface. diate between Tazewell-Follinge and Freda. No continuous Wedderburn is , in its structure and chemical composi­ Widmanstatten lamellae are present, but kamacite spindles tion, intermediate between Follinge and Freda and is, as occur in profusion, generating a microscopic Widmanstat­ these, a very small iron. While Follinge shows continuous ten pattern. The largest spindles are 10±2 J.1 wide and about but very narrow kamacite lamellae, Wedderburn and Freda 100 J.1 long, and smaller needles and plates occur in all sizes have so much nickel that the lamellae are arrested in an in varying concentrations. A considerable proportion of the early growth stage and are only present as pointed spindles. alpha phase is developed as swathing kamacite around the numerous phosphide inclusions. Where the swathing kama­ cite attains widths of 10-25 J.1 Neumann bands are clearly Weekeroo Station, Mannahill, South Australia visible, at least below a depth of 5-10 1i1m from the surface. 32° 16'S, 139°52'E The plessitic matrix is bainitic-martensitic with the platelets distinctly parallel to the bulk Widmanstatten Polycrystalline coarse octahedrite with silicate inclusions. Band· structure. Very fine precipitates, about 0.5 J.1 wide, occur as width 2.5 ±0.5 mm. Neumann bands. HV 220±15. ve rmicular bodies, that may be carbides. Locally, unetched Anomalous. 7.22% Ni, 0.45% Co, about 0.15% P, 29 ppm Ga, 66 stru ctureless patches indicate retained austenite into which ppm Ge, 2.8 ppm Ir. martensitic platelets project from the sides. Schreibersite is evenly dispersed and occurs with a HISTORY frequency of about 4 per mm2 , in dimensions ranging from A mass of 94.2 kg was found in 1924 by Mr. James 20 J.1 to 400 x 50 fJ.. Many of the crystals have been Lane at Weekeroo Station, Mannahill, the coordinates of nucleated by small blebs of troilite and chromite, generally which are given above. It was discovered on the brow of a only 10-25 J.1 across. Many of the larger schreibersite big hill resting on, and level with, the surface of a quartz crystals are rimmed with 2-5 J.1 wide carbide precipitates, reef. Hodge-Smith ( 1932) presented analytical results of and carbide also appears to be present as 1-10 J.1 blebs in the bulk material, and planimetric measurements of the some kamacite spindles. The schreibersite is enveloped in troilite (?) and silicate inclusions. In addition he gave two 10-50 J.1 wide swathing kama cite. photographs of the exterior and one of an etched section. A Troilite occurs as 25-100 J.1 nodules, often associated photograph of the meteorite seen from a different angle with the schreibersite. It is shock-melted to 1-2 J.1 fine was given by Hodge-Smith (1939: plate 3), and another poly crystalline aggregates which include 1-2 J.1 iron grains in print of a different section was presented by Nininger & a eutectic. Free gold was reported by Edwards ( 1953) as a Nininger (1950: plate 11). About 1928 the mass was, with 250 x 200 J.1 unetching patch near the edge of the specimen. difficulty, cut in the Government Railway Workshops, and The identification appears very insufficient, and could not following this, large slices were exchanged. be supported by this examination. He also reported The silicates of Weekeroo Station have been the object cliftonite associated with troilite ; it may be correct but is of numerous recent investigations. Olsen & Mueller (1964) certainly not characteristic. identified nodules of sodic plagioclase, and clinopyroxene­ The heat-affected a 2 zone extends to a considerable, orthopyroxene aggregates similar to those of Kodaikanal. but somewhat variable, depth beause of the curvature of Mason (1967a) discussed the silicate minerals and found the small mass; compare Follinge. It was observed to range them sufficiently uniform and closely related to chondritic from 4-7 mm in width, and micromelted rhabdites were minerals to suggest that they might represent inclusions of found to be present to half these depths. The martensitic chondritic material which completely recrystallized during WEDDERBURN - SELECTED CHEMICAL ANALYSES percentage ppm References Ni Co p c s Cr Cu Zn Ga Ge Ir Pt Carlos in Edwards 1953 23.95 0.50 0.78 300 1600 Lovering et a!. 1957 22.2 0.63 <I 580 1.8 < 1 Wasson 1972, pers. comm. 22.36 1.51 1.47 0.052 The phosphorus de termination is too high to be a genuine bulk value and must come from an unrepresentative sample. Weekeroo Station 1297 the slow cooling that resulted in the Widmanstiitten This implied that the recrystallization of chondritic mate­ structure. Bunch (1967) and Bunch & Olsen (1968) rial could not have produced the observed aggregates. They examined the fe ldspars with the microprobe and gave their considered the interesting possibility that olivine might detailed composition. Axon & Smith (1970a) examined the have been fractionally removed from a chondritic composi­ metal with the microprobe. tion, and that Weekeroo Station might be a residue silicate A detailed chemical analysis of the silicate portion was fraction. By adding an average amount, 50%, of olivine reported by Olsen & Jarosewich (1970) who found the (85% forsterite , 15% fayalite) to the Weekeroo analysis composition significantly different from most chondrites.