Enigmatic super-reduced phases in corundum from natural rocks: Possible contamination from artificial abrasive materials or metallurgical slags

Litasov, Konstantin D.; Kagi, Hiroyuki; Bekker, T. B.

doi:10.1016/j.lithos.2019.05.013

Cited by 35 publications

(28 citation statements)

References 61 publications

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“…Ishimaru et al (2009) described iron-titanium silicides in mantle peridotite xenoliths from beneath Kamchatka (Russia), whereas Pankov and Spetsius (1989) and Shiryaev et al (2008) reported the presence of FeSi 2 in mantle-derived kimberlites in Russia. Griffin et al (2016) described Fe 3 Si from mantlederived materials in Late Cretaceous ash deposits on Mount Carmel in Israel, although a recent paper argues that these and other mantle-derived super-reduced phases including the silicides may be caused by contamination during sample preparation (Litasov et al, 2019). Mavlyanovite (Mn 5 Si 3 ), the manganese analogue of xifengite, has also been reported from a lamproite in Uzbekistan (Yusupov et al, 2009).…”

Section: Background To Iron Silicides and Si-bearing Metalsmentioning

confidence: 99%

The origin of iron silicides in ureilite meteorites

et al. 2019

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Ureilite meteorites contain iron silicide minerals including suessite (Fe,Ni) 3 Si, hapkeite (Fe 2 Si) and xifengite (Fe 5 Si 3 ). Despite occurring mostly in brecciated varieties presumed to be derived from the regolith of the ureilite parent asteroid, suessite has also been confirmed in one lithology of a dimict ureilite (NWA 1241). In contrast, Si-bearing Fe-metals occur in both brecciated and unbrecciated ureilites, implying that they were formed throughout the ureilite parent asteroid. We examined major, minor and trace element data of Fe-metals in seven brecciated ureilites (DaG 319, DaG 999, DaG 1000, DaG 1023, DaG 1047, EET 83309, and EET 87720) in addition to the dimict ureilite NWA 1241.In this study we show that the silicides and Si-bearing metals in ureilites have similar siderophile trace element patterns; therefore, the precursors to the silicides were indigenous to the ureilite parent body. Sifree kamacite grains in brecciated ureilites show flatter, more chondritic siderophile element patterns. They may also be derived from the interior of the ureilite parent body, but some may be of exogenous origin (impactor debris), as are rare taenite grains.On Earth, iron silicides are often formed under high-temperature and strongly reducing conditions (e.g. blast furnaces, lightning strikes). On the Moon, hapkeite (Fe 2 Si) and other silicides have been found in the regolith where they were formed by impact-induced space weathering. In the Stardust aerogel, iron silicides derived from comet Wild2 were also formed by an impact-related reduction process. Silicides in ureilite regolith breccias may have formed by similar processes but ureilites additionally contain abundant elemental carbon which probably acted as a reducing agent, thus larger and more abundant silicide grains were formed than in the lunar regolith or cometary material. The origin of suessite in NWA 1241 may be analogous to that of reduced lithologies in the terrestrial mantle, although a regolith origin may also be possible since this sample is shown here to be a dimict breccia.

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Section: Background To Iron Silicides and Si-bearing Metalsmentioning

confidence: 99%

The origin of iron silicides in ureilite meteorites

et al. 2019

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“…Citing similarity in mineralogy and textures to those in fused alumina abrasive, as described in the literature, most comprehensively by Filonenko and Lavrov (1958), Polubelova et al (1968), and in their own paper, Litasov and his colleagues allege that the corundum grains from Cr-11 are none other than brown fused alumina abrasive that was inadvertently introduced into the separate despite the great care taken in processing. A similar rationale led Litasov (2019a) to conclude that a significant proportion of the corundum at Mount Carmel, Israel, could also be fused alumina abrasive, which is a conclusion rebutted by Griffin et al (2019b) and subsequently defended by Litasov et al (2019b).…”

Section: Mineral Formulamentioning

confidence: 92%

Two new minerals, badengzhuite, TiP, and zhiqinite, TiSi<sub>2</sub>, from the Cr-11 chromitite orebody, Luobusa ophiolite, Tibet, China: is this evidence for super-reduced mantle-derived fluids?

Xiong

Mugnaioli

et al. 2020

Eur. J. Mineral.

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Abstract. Titanium minerals enclosed in corundum separated from the Cr-11 orebody include native Ti, zamboite (FeTiSi2), osbornite (TiN)-khamrabaevite (TiC) solid solutions, and jingsuiite (TiB2), as well as the new minerals badengzhuite (TiP) and zhiqinite (TiSi2) and two potentially new minerals, Ti11(Si,P)10 and Ti10(Si,P,□)7, where □ indicates a vacancy. These minerals together constitute a spheroid 20 µm across inferred to have crystallized from a droplet of Ti–Si–P intermetallic melt. Energy-dispersive spectroscopy and three-dimensional electron diffraction were applied to characterize the two new minerals. Badengzhuite has a primitive hexagonal cell with a=3.49(7) Å, c=11.70(23) Å, V=124(4) Å3, and crystallizes in space group P63∕mmc (Z=4). It is isostructural with synthetic TiP. Two EDX (energy dispersive X-ray spectroscopy) analyses of badengzhuite gave 60.56 wt %Ti and 39.44 wt % P and 62.74 wt % Ti and 37.26 wt % P from which an empirical formula of Ti1.020P0.980 was calculated on the basis of two atoms (ideally TiP). Zhiqinite has a primitive orthorhombic cell with a=8.18(16) Å, b=4.85(10) Å, c=8.42(17) Å, V=334(12) Å3, and crystallizes in space group Fddd (Z=8). It is isostructural with synthetic TiSi2 (C54 type). Four EDX analyses of zhiqinite gave 39.58–44.79 wt % Ti and 55.21–60.42 wt % Si, from which an empirical formula of Ti0.905Si2.095 was calculated on the basis of three atoms (ideally TiSi2). We suggest that interaction of mantle-derived CH4 + H2 fluids with basaltic magmas in the shallow lithosphere (depths of ∼ 30–100 km) under conditions more reducing than 6 log units below the oxygen fugacities corresponding to the iron–wüstite buffer resulted in precipitation of corundum that entrapped intermetallic melts, some of which crystallized to ultra-reduced Ti–P–Si phases. Experimental work on the Ti–Si and Ti–P systems indicates that the minerals enclosed in corundum could have crystallized from the alloy melt at the lowest temperature accessible on the liquidus. It has been alleged that these ultra-reduced phases are anthropogenic contaminants inadvertently introduced with fused alumina abrasive during preparation of mineral separates. Nonetheless, we conclude that the differences between the ultra-reduced minerals in the separates and the ultra-reduced phases in fused alumina are more convincing evidence for these minerals having a natural origin than the similarities between them are evidence for an anthropogenic origin.

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“…Assertions that the highly reduced assemblages from Mt Carmel area are of anthropogenic origin (Litasov et al, 2019a;Litasov et al, 2019b) are untenable on the basis of detailed geological evidence (Griffin et al, 2020c;Griffin et al, 2019b). In brief: (1) all of the mineral assemblages described in this and previous papers are found in situ in the it unlikely that the super-reduced phases have formed by lightning strikes (Griffin et al, 2018a (IW-9 to -10) is required by the precipitation of a coarse-grained hibonite-grossitevanadium assemblage (Griffin et al, 2019a;Griffin et al, 2020b), also found in the volcanic debris.…”

Section: Geological Settingmentioning

confidence: 99%

Immiscible metallic melts in the upper mantle beneath Mount Carmel, Israel: Silicides, phosphides, and carbides

Griffin

Gain

Saunders

et al. 2022

American Mineralogist

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Xenolithic corundum aggregates in Cretaceous mafic pyroclastics from Mount Carmel contain pockets of silicate melts with mineral assemblages (SiC (moissanite), TiC, Ti 2 O 3 (tistarite), Fe-Ti-Zr silicides/phosphides) indicative of magmatic temperatures and oxygen fugacity (fO 2 ) at least 6 log units below the Iron-Wüstite buffer (IW≤-6). Microstructural evidence indicates that immiscible, carbon-rich metallic (Fe-Ti-Zr-Si-P) melts separated during the crystallization of the silicate melts. The further evolution of these metallic melts was driven by the crystallization of two main ternary phases (FeTiSi and FeTiSi 2 ) and several near-binary phases, as well as the separation of more evolved immiscible melts.Reconstructed melt compositions fall close to cotectic curves in the Fe-Ti-Si system, consistent with trapping as metallic liquids. Temperatures estimated from comparisons with experimental work range from ≥1500 °C to ca 1150 °C; these probably are maximum values, due to the solution of C, H, P and Zr. With decreasing temperature (T), the Si, Fe and P contents of the Fe-Ti-Si melts increased, while contents of Ti and C decreased. The increase in Si with declining T implies a corresponding decrease in fO 2 , probably to ca IW-9. The solubility of P in the metallic melts declined with T and fO 2 , leading to immiscibility between Fe-Ti-Si melts and (Ti,Zr)-(P,Si) melts. Decreasing T and fO 2 also reduced the solubility of C in the liquid metal, driving the continuous crystallization of TiC and SiC during cooling. The lower-T metallic melts are richer in Cr, and to some extent V, as predicted by experimental studies showing that Cr and V become more siderophile with decreasing fO 2 .These observations emphasise the importance of melt-melt immiscibility for the evolution of magmas under reducing conditions. The low fO 2 and the abundance of carbon This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Enigmatic super-reduced phases in corundum from natural rocks: Possible contamination from artificial abrasive materials or metallurgical slags

Cited by 35 publications

References 61 publications

The origin of iron silicides in ureilite meteorites

The origin of iron silicides in ureilite meteorites

Two new minerals, badengzhuite, TiP, and zhiqinite, TiSi<sub>2</sub>, from the Cr-11 chromitite orebody, Luobusa ophiolite, Tibet, China: is this evidence for super-reduced mantle-derived fluids?

Immiscible metallic melts in the upper mantle beneath Mount Carmel, Israel: Silicides, phosphides, and carbides

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Enigmatic super-reduced phases in corundum from natural rocks: Possible contamination from artificial abrasive materials or metallurgical slags

Cited by 35 publications

References 61 publications

The origin of iron silicides in ureilite meteorites

The origin of iron silicides in ureilite meteorites

Two new minerals, badengzhuite, TiP, and zhiqinite, TiSi&lt;sub&gt;2&lt;/sub&gt;, from the Cr-11 chromitite orebody, Luobusa ophiolite, Tibet, China: is this evidence for super-reduced mantle-derived fluids?

Immiscible metallic melts in the upper mantle beneath Mount Carmel, Israel: Silicides, phosphides, and carbides

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Two new minerals, badengzhuite, TiP, and zhiqinite, TiSi<sub>2</sub>, from the Cr-11 chromitite orebody, Luobusa ophiolite, Tibet, China: is this evidence for super-reduced mantle-derived fluids?