The Effects of High-Grade Metamorphism on Cr-Spinel from the Archean Sittampundi Complex, South India

We investigated the crystal and structural behavior of Cr-bearing spinels from the Archean chromitites of Sittampundi (India), which had been subjected to very high-grade metamorphism. The structural data show that their oxygen positional parameters are among the highest ever recorded for Cr-bearing spinels with similar Cr# and Mg# and very similar to those found for other Archean occurrences. The general agreement between electron microprobe and Mössbauer data indicates that the analyzed spinels are stoichiometric. It is therefore most likely that the PH2O and Ptotal values as well as both the oxygen fugacity and the temperature reached during high-grade metamorphism inhibited the possibility of the non-stoichiometry of chromites, contrary to what can happen in ophiolites, where non-stoichiometry has recently been documented.

New Dates for Megalithic Stele Monuments of Gedeo, South Ethiopia

This paper reports the results of an archaeological survey and test excavation conducted in one of the ancient megalithic stele sites in south Ethiopia, Sakaro Sodo. The Sakaro Sodo stele site is situated in Gedeo zone, which is known to have the largest number and highest concentration of megalithic stele monuments in Africa, with an estimate of more than 10,000 stelae in sixty or more sites. Prior to our work, only one absolute date was available (850 ± 40 BP) (Joussaume 2012) from a stele site in the Gedeo zone, suggesting stele sites began to be constructed in the region approximately a millennium ago. We report here new AMS dates suggesting that stelae were being emplaced about 2000 BP, pushing the creation of these monuments back at least a millennium. Additionally, we report preliminary findings from characterizing the geochemical properties of obsidian artifacts recovered from stele sites, and stone used to make stelae. While compositional analysis of obsidian suggests long-distance movement of material from sources located in northern Kenya, petrographic microscopy and electron microprobe analyses show a strong connection of stelae to local geological tuff exposures/sources.

Supplemental Material: Water in omphacite fingerprints the thermal history of eclogites

Fourier transform infrared and Raman spectra, electron microprobe data, and resolved band absorbance ratios of samples.<br>

The Reactivity of New Zealand Ilmenites

<p>The dissolution of West Coast, South Island, New Zealand ilmenite in acid solutions was studied under a variety of conditions, including concentrations approaching those used industrially. The major dissolution medium considered was hydrochloric acid (1-->10 M), at temperatures of 50-->80 degrees C. The series of experiments undertaken souqht to establish the factors affecting the reactivity of the ilmenite samples. Concentrations of dissolved components of the ilmenite were followed by Atomic Absorption spectrometry and the structure and composition of the residual ilmenite was examined by X-ray powder diffraction, X-ray fluorescence, electron microprobe and scanning electron microscopy. Evidence for the rapid dissolution of an iron-rich surface phase was observed, but the dominant feature of early reaction is selective attack along zones parallel to the basal plane of the ilmenite structure. After the initial phase of rapid dissolution, reaction rate declines and all extended period of concentration/time linearity follows. This decline in rate appears to relate to polymerisation and. transport of dissolved titanium within the porous solid. The addition of phosphate and fluoride to the system, has been shown to seriously affect the properties and transport of dissolved titanium. The effects of other interfering reagents such as additional titanium and iron were also considered. The observed behaviour of these ilmenites in dissolution, was related to the pattern of natural weathering identified in other ilmenite concentrates The structure and composition of a range of these materials was examined by X-ray diffraction, Electron microprobe and Mossbauer spectroscopy.</p>

Supplemental Material: Water in omphacite fingerprints the thermal history of eclogites

Fourier transform infrared and Raman spectra, electron microprobe data, and resolved band absorbance ratios of samples.<br>

The Reactivity of New Zealand Ilmenites

<p>The dissolution of West Coast, South Island, New Zealand ilmenite in acid solutions was studied under a variety of conditions, including concentrations approaching those used industrially. The major dissolution medium considered was hydrochloric acid (1-->10 M), at temperatures of 50-->80 degrees C. The series of experiments undertaken souqht to establish the factors affecting the reactivity of the ilmenite samples. Concentrations of dissolved components of the ilmenite were followed by Atomic Absorption spectrometry and the structure and composition of the residual ilmenite was examined by X-ray powder diffraction, X-ray fluorescence, electron microprobe and scanning electron microscopy. Evidence for the rapid dissolution of an iron-rich surface phase was observed, but the dominant feature of early reaction is selective attack along zones parallel to the basal plane of the ilmenite structure. After the initial phase of rapid dissolution, reaction rate declines and all extended period of concentration/time linearity follows. This decline in rate appears to relate to polymerisation and. transport of dissolved titanium within the porous solid. The addition of phosphate and fluoride to the system, has been shown to seriously affect the properties and transport of dissolved titanium. The effects of other interfering reagents such as additional titanium and iron were also considered. The observed behaviour of these ilmenites in dissolution, was related to the pattern of natural weathering identified in other ilmenite concentrates The structure and composition of a range of these materials was examined by X-ray diffraction, Electron microprobe and Mossbauer spectroscopy.</p>

Supplemental Material: Magmatism and related metamorphism as a response to mountain-root collapse of the Dabie orogen: Constraints from geochronology and petrogeochemistry of metadiorites

Table S1: Electron microprobe analyses (wt%) of representative minerals in the NDZ metadiorites; Table S2: Major and trace elements concentrations of the NDZ metadiorites; Table S3: Zircon SHRIMP U-Pb isotopic compositions of the NDZ metadiorites; Table S4: Zircon REE concentrations of sample 1310YZH5 from the NDZ; Table S5: Zircon Lu-Hf isotopic compositions of the NDZ metadiorites; Table S6: Whole-rock Rb-Sr, Sm-Nd, and Pb isotopic data of the NDZ metadiorites; Table S7: P-T estimates of the NDZ metadiorites.

Unique Association of Sulphosalts from the Kľačianka Occurrence, Nízke Tatry Mts., Slovak Republic

Unique association of sulphosalts was discovered at the Kľačianka occurrence, Nízke Tatry Mts., Slovak Republic. It is bound to thin hydrothermal veins with Sb mineralization hosted by the Variscan muscovite-biotite granodiorite and granite of Prašivá type. Ore mineralogy and crystal chemistry of ore minerals are studied here by ore microscopy, X-ray powder diffraction, electron microprobe analyses, and Raman spectroscopy. The early ore mineralization composed of pyrite and arsenopyrite is hosted in quartz gangue and is followed by abundant association of sulfosalts. Stibnite, zinkenite, robinsonite (including Cu-bearing variety), jamesonite, scainiite, dadsonite, disulfodadsonite, rouxelite, chovanite, semseyite, boulangerite, geocronite, tintinaite (with low Bi contents), tetrahedrite-(Fe), tetrahedrite-(Zn), bournonite, chalcostibite, bismuthinite, and gladite in association with sphalerite and rare galena and gold are identified here. The chlorine-rich character of the described sulphosalt association is its characteristic phenomenon. It is represented not only by the occurrence of Cl-sulphosalt and dadsonite, but increased Cl contents were detected in boulangerite, chovanite, disulfodadsonite, robinsonite, rouxelite, scainiite, or tintinaite. The presence of oxygen-containing sulphosalts, such as rouxelite, scainiite and chovanite, is also interesting. The crystallization of these rare chloro-, oxy- and oxy-chloro-sulphosalts at the Kľačianka occurrence required very specific conditions (elevated O2/S2 fugacity) and high chlorine activity in ore-forming fluids.

Hydroxykenopyrochlore, (□,Ce,Ba)2(Nb,Ti)2O6(OH,F), a New Member of the Pyrochlore Group from Araxá, Minas Gerais, Brazil

ABSTRACT Hydroxykenopyrochlore, (□,Ce,Ba)2(Nb,Ti)2O6(OH,F), occurs in a weathered Nb-ore from alkaline-carbonatite complexes and pegmatites of the Brazilian shield mined by Compania Brasileira de Metalurgia e Mineração (CBMM), Araxá, Minas Gerais, Brazil. The mineral is a product of alkali metasomatism. It occurs as parts of granular grains up to 0.1 mm in size in association with Ba-bearing hydrokenopyrochlore. Hydroxykenopyrochlore is lemon yellow to yellow in color, non-fluorescent, and brittle. The hardness is 4½ on the Mohs scale. The calculated density is 4.36 g/cm3. It is cubic, Fd–3m, with cell parameters a 10.590(5) Å, V = 1187.6(10) Å3, and Z = 2. The strongest seven lines in the powder XRD pattern [d in Å (I/I0) hkl] are 6.06 (49) 111, 3.18 (27) 311, 3.05 (100) 222, 2.64 (29) 400, 1.870 (56) 440, 1.594 (50) 622, 1.213 (15) 662, and 1.182 (13) 840. The empirical formula derived from electron-microprobe analyses is [□1.117Ce0.532Nd0.035La0.021Pr0.010Sm0.003Y0.002Ba0.101Ca0.030Pb0.004Th0.061U0.007K0.040Na0.036]Σ2(Nb1.368Ti0.325P0.095Fe0.091Al0.082Zr0.039)Σ2[O4.719(OH)1.281]Σ6[(OH)0.846F0.154]. Hydroxykenopyrochlore is a member of the pyrochlore supergroup (class 4.DH.15 of Strunz & Nickel; class 8.2.1. of Dana). It is the vacancy-dominant analogue of hydroxycalciopyrochlore, (Ca,Na,U,□)2(Nb,Ti)2O6(OH), and the Nb-dominant analogue of hydroxykenomicrolite, (□,Na,Sb3+)2Ta2O6(OH), and of hydroxykenoelsmoreite, (□,Pb)2(W,Fe3+,Al)2(O,OH)6(OH).

Periodic Multilayer for X-ray Spectroscopy in the Li K Range

X-ray spectroscopy of lithium is very difficult, even impossible, with wavelength dispersive spectrometers commonly deployed on scanning electron microscopes or electron microprobe analyzers. This is due to the absence of crystals and lack of efficient periodic multilayer for this spectral range, around 50 eV. To address this issue, we propose using a Be/Si/Al multilayer having a period of about 29 nm. The multilayer was deposited by magnetron sputtering and its reflectivity measured as a function of the glancing angle in the spectral range of the Li K emission and as a function of the incident energy up to ~200 eV. This characterization demonstrates that the designed multilayer is suitable to efficiently perform spectroscopy in the range of the Li K emission in terms of reflectance (0.32 at 51.5 eV), bandwidth (around 3.5 eV) and rejection of high order diffracted radiation.