Search

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, 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 D 3:49.7/ Å, c D 11:70.23/ Å, V D 124.4/Å3, and crystallizes in space group P63=mmc (Z D 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 D 8:18.16/ Å, b D 4:85.10/ Å, c D 8:42.17/ Å, V D 334.12/Å3, and crystallizes in space group Fddd (Z D 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 CH2 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. [ABSTRACT FROM AUTHOR]

Various combinations of diamond, moissanite, zircon, quartz, corundum, rutile, titanite, almandine garnet, kyanite, and andalusite have been recovered from the Dangqiong peridotites. More than 80 grains of diamond have been recovered, most of which are pale yellow to reddish-orange to colorless. The grains are all 100-200 µm in size and mostly anhedral, but with a range of morphologies including elongated, octahedral and subhedral varieties. Their identification was confirmed by a characteristic shift in the Raman spectra between 1325 cm−1 and 1333 cm−1, mostly at 1331.51 cm−1 or 1326.96 cm−1. Integration of the mineralogical, petrological and geochemical data for the Dongqiong peridotites suggests a multi-stage formation for this body and similar ophiolites in the Yarlung-Zangbo suture zone. Chromian spinel grains and perhaps small bodies of chromitite crystallized at various depths in the upper mantle, and encapsulated the UHP, highly reduced and crustal minerals. Some oceanic crustal slabs containing the chromian spinel and their inclusion were later trapped in suprasubduction zones (SSZ), where they were modified by island arc tholeiitic and boninitic magmas, thus changing the chromian spinel compositions and depositing chromitite ores in melt channels. [ABSTRACT FROM AUTHOR]

The article presents a study which examined the composition and textual characterization of platinum-group mineral (PGM) in chromites from the Zedang ophiolite in Tibet, China as of December 2015. The aim includes the identification of petrogenetic nature of parental melt of chromitites. Also cited are the voluminous PGM inclusions like erlichmanite, laurite, and irarsite, as well as the main factors that control platinum-group elements (PGE), namely, sulfur fugacity and temperature.