The U-Th-REE-Nb (Ta)-polymetallic mineralization is generally related to either the silica-undersaturated syenites, the silica-oversaturated alkaline/peralkaline granites or igneous carbonatites. In this study, the authors report a new mineralization type, which is related to the magmatic-hydrothermal albitite (with mineral assemblage predominated by albite with volume content > 90%), as exemplified by the Chachaxiangka deposit in Qinghai Province of China. The Chachaxiangka deposit is the first albitite-related U-Th-REE-Nb deposit recognized in China and the mineralization can be divided into 3 types: the vein-type, the disseminated veinlet type and breccia type, of which the former 2 are predominant. Three mineralization stages can be identified according to the detailed mineralogical analyses, including the magmatic stage, main hydrothermal mineralization stage and post-ore stage. By comprehensive analyses of the mineralogical, major and trace element compositions, the authors suggest that the albitite vein is magmatic-hydrothermal in origin and both the magmatic evolution and overprint of the hydrothermal fluids play important roles in the formation of the albitite and related polymetallic mineralization. Phase separation between the silicate melt and carbonate/phosphate melt might take place in the magmatic stage, yet the immiscibility between the silicate melt and chloride-dominated fluids is the most important mechanism for the REE mineralization and also causes the Nb-Th re-mobilization and enrichment. The red color of the albitite aplite vein is an eye-catching prospecting mark in the field and more mineralization can be expected at depth and in the surrounding areas. The discovery of the new albitite type U-Th-REE-Nb mineralization give rise to new ideas during future U-Th-REE-Nb exploration, not only in the Qaidam-Altun belt, but also other areas across China.
A change detection approach based on independence component analysis (ICA) was proposed in this letter. Traditional multivariate change detection schemes such as principal component analysis (PCA) were based on 2nd‐order statistics to remove the correlation among multi‐temporal images. However, for the regions where data did not fit a normal distribution, PCA might not be effective. In this letter, ICA was used to separate change information in independent components by reducing the 2nd‐order and higher order dependences in multi‐temporal images. Firstly, the number of images was expanded to the number of land classes by nonlinear band generation. Then, independent component images were obtained based on ICA. The obtained independent component images corresponded to some kind of land or land variation. At last, different kinds of land variation are located by applying maximum likelihood classification (MLC). The experimental results in synthetic and real multi‐temporal images show the effectiveness of the proposed approach.
Lithology identification is an essential fact for delineating uranium-bearing sandstone bodies. A new method is provided to delineate sandstone bodies by a lithological automatic classification model using machine learning techniques, which could also improve the efficiency of borehole core logging. In this contribution, the BP neural network model for automatic lithology identification was established using an optimized gradient descent algorithm based on the neural network training of 4578 sets of well logging data (including lithology, density, resistivity, natural gamma, well-diameter, natural potential, etc.) from 8 boreholes of the Tarangaole uranium deposit in Inner Mongolia. The softmax activation function and the cross-entropy loss function are used for lithology classification and weight adjustment. The lithology identification prediction was carried out for 599 samples, with a prediction accuracy of 88.31%. The prediction results suggest that the model is efficient and effective, and that it could be directly applied for automatic lithology identification in sandstone bodies for uranium exploration.
Abstract Free-space coupling, essential for various communication applications, often faces significant signal loss and interference from ambient light. Traditional methods rely on integrating complex optical and electronic systems, leading to bulkier and costlier communication equipment. Here, we show an asymmetric 2D–3D–2D perovskite structure device to achieve a frequency-selective photoresponse in a single device. By combining two electromotive forces of equal magnitude in the opposite directions, the device output is attenuated to zero under constant light illumination. Because these reverse photodiodes have different response speeds, the device only responds near a certain frequency, which can be tuned by manipulating the 2D perovskite components. The target device achieves an ultrafast response of 19.7/18.3 ns in the frequency-selective photoresponse range 0.8–9.7 MHz. This anti-interference photodetector can accurately transmit character and video data under strong light interference with a source intensity of up to 454 mW cm −2 .
ABSTRACT A new mineral species of the pyrochlore supergroup, hydroxyplumbopyrochlore (IMA2018-145), (Pb 1.5 ,□ 0.5 )Nb 2 O 6 (OH), has been discovered in the Jabal Sayid peralkaline granitic complex of the Arabian Shield, Saudi Arabia. It is associated with quartz, microcline, ‘biotite’, rutile, zircon, calcite, rhodochrosite, columbite-(Fe), goethite, thorite, bastnäsite-(Ce), xenotime-(Y), samarskite-(Y), euxenite-(Y), hydropyrochlore and fluornatropyrochlore. Hydroxyplumbopyrochlore usually shows euhedral octahedra, slightly rhombic dodecahedra and cubes or their combination (0.01–0.06 mm). The mineral is pale yellow to pale brown, transparent with white streak, and has adamantine to transparent lustre. It is brittle with conchoidal fracture. No cleavage or parting are observed. It is isotropic and non-fluorescent. The average microhardness is 463.4 kg mm –2 . The calculated density is 6.474 g cm –3 . Hydroxyplumbopyrochlore belongs to the cubic crystal system and exhibits the space group Fd $\bar{3}$ m with unit-cell parameters a = 10.5456(6) Å, V = 1172.8(2) Å 3 and Z = 8. Electron microprobe analysis gave (6-point average composition, wt.%): CaO 0.32, SrO 0.16, FeO 0.17, Ce 2 O 3 0.07, Pr 2 O 3 0.02, PbO 51.69, Nb 2 O 5 40.06, SiO 2 0.05, TiO 2 1.68, Ta 2 O 5 4.74, H 2 O calc 0.95, total 99.90, yielding the empirical formula (Pb 1.34 Ca 0.03 Fe 0.01 Sr 0.01 □ 0.61 ) Σ2 (Nb 1.75 Ti 0.12 Ta 0.12 Si 0.01 ) Σ2 O 6 (OH 0.53 O 0.08 □ 0.39 ) Σ1 , where □ = vacancy . The Raman spectrum of hydroxyplumbopyrochlore contains the characteristic bands of O–H vibrations and no bands for H 2 O vibrations.
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