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The petrology of base metal sulfides and associated accessory minerals in rocks away from economically significant ore zones such as the Merensky Reef of the Bushveld Complex has previously received only scant attention, yet this information is critical in the evaluation of models for the formation of Bushveld-type platinum-group element (PGE) deposits. Trace sulfide minerals, primarily pyrite, pyrrhotite, pentlandite, and chalcopyrite are generally less than 100 microns in size, and occur as disseminated interstitial individual grains, as polyphase assemblages, and less commonly as inclusions in pyroxene, plagioclase, and olivine. Pyrite after pyrrhotite is commonly associated with low temperature greenschist alteration haloes around sulfide grains. Pyrrhotite hosted by Cr- and Ti-poor magnetite (Fe3O4) occurs in several samples from the Marginal to Lower Critical Zones below the platiniferous Merensky Reef. These grains occur with calcite that is in textural equilibrium with the igneous silicate minerals, occur with Cl-rich apatite, and are interpreted as resulting from high temperature sulfur loss during degassing of interstitial liquid. A quantitative model demonstrates how many of the first-order features of the Bushveld ore metal distribution could have developed by vapor refining of the crystal pile by chloride–carbonate-rich fluids during which sulfur and sulfide are continuously recycled, with sulfur moving from the interior of the crystal pile to the top during vapor degassing. 相似文献
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Waruntorn Kanitpanyacharoen Hans‐Rudolf Wenk Frans Kets Christian Lehr Richard Wirth 《Geophysical Prospecting》2011,59(3):536-556
Scanning and transmission electron microscopy, synchrotron X‐ray diffraction, microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried Qusaiba shales from the Rub’al‐Khali basin, Saudi Arabia. Kaolinite, illite‐smectite, illite‐mica and chlorite show strong preferred orientation with (001) pole figure maxima perpendicular to the bedding plane ranging from 2.4–6.8 multiples of a random distribution (m.r.d.). Quartz, feldspars and pyrite crystals have a random orientation distribution. Elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution, assuming a nonporous material. The average calculated bulk P‐wave velocities are 6.2 km/s (maximum) and 5.5 km/s (minimum), resulting in a P‐wave anisotropy of 12%. The calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample. In the ultrasonic experiment, which measures the effects of the shale matrix as well as the effects of porosity, velocities are smaller (P‐wave maximum 5.3 km/s and minimum 4.1 km/s). The difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample, which have not been taken into account in the matrix averaging. 相似文献
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Lowell Miyagi Waruntorn Kanitpanyacharoen Stephen Stackhouse Burkhard Militzer Hans-Rudolf Wenk 《Physics and Chemistry of Minerals》2011,38(9):665-678
The D′′ region that lies just above the core mantle boundary exhibits complex anisotropy that this is likely due to preferred
orientation (texturing) of the constituent minerals. (Mg,Fe)SiO3 post-perovskite is widely thought to be the major mineral phase of the D′′. Texture development has been studied in various
post-perovskite phases (MgSiO3, MgGeO3, and CaIrO3), and different results were obtained. To clarify this controversy, we report on transformation and deformation textures
in MgGeO3 post-perovskite synthesized and deformed at room temperature in the diamond anvil cell. Transformed from the enstatite phase,
MgGeO3 post-perovskite exhibits a transformation texture characterized by (100) planes at high angles to the direction of compression.
Upon subsequent deformation, this texture changes and (001) lattice planes become oriented nearly perpendicular to compression,
consistent with dominant (001)[100] slip. When MgGeO3 post-perovskite is synthesized from the perovskite phase, a different transformation texture is observed. This texture has
(001) planes at high angle to compression and becomes slightly stronger upon compression. We also find that the yield strength
of MgGeO3 post-perovskite is dependent on grain size and texture. Finer-grained samples exhibit higher yield strength and are harder
to induce plastic deformation. Strong textures also affect the yield strength and can result in higher differential stresses.
The inferred dominant (001) slip for pPv is significant for geophysics, because, when applied to geodynamic convection models,
it predicts the observed anisotropies of S-waves as well as an anti-correlation between P- and S-waves. 相似文献
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P. Kaercher S. Speziale L. Miyagi W. Kanitpanyacharoen H.-R. Wenk 《Physics and Chemistry of Minerals》2012,39(8):613-626
Magnesiowüstite, (Mg0.08Fe0.88)O, and wüstite, Fe0.94O, were compressed to ~36?GPa at ambient temperature in the diamond anvil cell (DAC) at the Advanced Light Source. X-ray diffraction patterns were taken in situ in radial geometry in order to study the evolution of crystallographic preferred orientation through the cubic-to-rhombohedral phase transition. Under uniaxial stress in the DAC, {100}c planes aligned perpendicular to the compression direction. The {100}c in cubic became { $\left\{ {10\bar 14} \right\}$ }r in rhombohedral and remained aligned perpendicular to the compression direction. However, the {101}c and {111}c planes in the cubic phase split into { ${10{\bar{1}}4}$ }r and { ${11{\bar{2}}0}$ }r, and (0001)r and { ${10{\bar{1}}1}$ }r, respectively, in the rhombohedral phase. The { ${11{\bar{2}}0}$ }r planes preferentially aligned perpendicular to the compression direction while { ${10{\bar{1}}4}$ }r oriented at a low angle to the compression direction. Similarly, { ${10{\bar{1}}1}$ }r showed a slight preference to align more closely perpendicular to the compression direction than (0001)r. This variant selection may occur because the 〈 ${10{\bar{1}}4}$ 〉r and [0001]r directions are the softer of the two sets of directions. The rhombohedral texture distortion may also be due to subsequent deformation. Indeed, polycrystal plasticity simulations indicate that for preferred { ${10{\bar{1}}4}$ }〈 ${1{\bar{2}}10}$ 〉r and { ${11{\bar{2}}0}$ }〈 ${{\bar{1}}101}$ 〉r slip and slightly less active { ${10{\bar{1}}1}$ }〈 ${{\bar{1}}2{\bar{1}}0}$ 〉r slip, the observed texture pattern can be obtained. 相似文献
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