Solid Earth Sciences最新文献

The provenance of clastic sediments in stream beds, river terraces, rivers, swamps, lakes and beaches from different geological settings was investigated based on their compositional and geochemical variations. The geochemistry data of 622 sediment samples from 22 sites in the Cameroon were compiled to infer the provenance. The results suggest that, their mineralogy is dominated by quartz, low amount of feldspars, clay minerals, heavy minerals, ferric minerals, and rock fragments. The SiO₂/Al₂O₃ ratio indicate that the sediments of Cameroonian region are mostly rich in quartz and clay-minerals. The enrichment of K₂O/Na₂O ratio implies plagioclase disintegration as K-feldspar during weathering and/or K-reintroduction in the system during diagenesis. The sediments are rich in light rare earth elements (LREE) and classified as shale, Fe-shale, Fe-sand, wacke, arkose, litharenite, sublitharenite, and quartzarenite. The sediments are composed of detritus derived from felsic igneous rocks, which correspond to the geology of the source areas. Weathering indices such as chemical index of alteration (CIA), chemical index of weathering (CIW), plagioclase index of alteration (PIA) and, A–CN–K (A=Al₂O₃, CN=CaO∗ + Na₂O, K=K₂O) plot indicated that the source rocks are subjected to low, moderate and intense weathering.

The Bayan Obo REE-Nb-Fe deposit, which reserves the current largest REE resources globally, also hosts 63.4% of China's Nb resources. Previous studies mainly focus on the isotopes and petrographic mineralogy of carbonatite dyke, ore-host dolomite and rare earth ore in Bayan Obo deposit, niobium mineralogy is comparatively insufficient. In order to promote the utilization of niobium resources in the Bayan Obo deposit, we focus on the petrological and mineralogical study on the biotite-type Fe-REE-Nb ore of West Mine, by scanning electron microscope (SEM), X-ray energy spectrum (EDX) imaging and micro-XRF scan. From the analysis, we observe that 1) this type of ore shows relative enrichment in niobium, and the size of niobium-bearing minerals up to 1 mm; 2) the niobium mineral composition are extremely complex, with main niobium minerals including aeschynite, fergusonite and columbite and minor niobium minerals ilmenorutile and baotite; 3) REEs are mainly distributed in monazite, bastnaesite and aeschynite and the particle size of the first two is relatively fine; 4) aeschynite occurring as large aggregates maybe the hydrothermal in origin and fluid–rock interaction leads to the aggregation of biotite and the precipitation of niobium-bearing minerals. This study on biotite type Fe-REE-Nb ore has important insights for mineral processing and directive significance on niobium prospecting in the Bayan Obo deposit.

The rapid increase in population and infrastructural development has triggered unplanned groundwater development leading to severe stress on groundwater couple with several unsuccessful boreholes or failure of existing in the University of Calabar, Calabar (Nigeria). Hence, an integrated hydrogeological study was undertaken in the university using vertical electrical sounding (VES), to delineate and characterise aquifers and assess the groundwater quality for drinking and irrigation uses, in addition to evolution and human health risk assessment. The results reveal two water bearing units. The first is composed of medium-coarse-gravelly sand with thickness and resistivity in the range 3.6–118.8 m and 540–3500 Ω m, while the second underlying the first aquifer is composed of clayey, fine-medium sand with resistivity and thickness values in the range 44–2200 Ω m and 50 - α. Aquifer parameters from VES and pumping tests showed average hydraulic conductivity (K) and transmissivity (T) of 180 m/day and 25,740 m²/day for the first aquifer and 180 m/day and 21,384 m²/day for the second aquifer. Regionally, the groundwater flow in the university occurs toward the south. Hydrochemical data show that all the physical parameters, major and minor ions, trace and rare earth elements are within the maximum acceptable limits for drinking and agricultural uses. The dominant hydrochemical facies are Na⁺-Ca²⁺-Cl^--SO₄^2-, Mg²⁺-Ca²⁺-HCO₃^--Cl^- and Ca²⁺-Mg²⁺-HCO₃^--Cl^- with silicate weathering, ion exchange and reverse ion exchange as the major processess controlling the groundwater chemistry. Health risk of water through oral (drinking) and dermal (bathing) pathways showed that values of hazard quotients (HQs) and hazard index (HI) of all the trace elements (Al, As, Cd, Co, cr, Cu, Fe, Mn, Ni, Pb, Zn) were less than one. This suggests that these elements does not pose any adverse risks to the local people through drinking and bathing, but children are more sensitive than adults. This study will serve as a guide for future sustainable development and management of groundwater resource in the university and its environs.

The high light rare earth elements contents (up to 412 ppm) in the weathering crust over the REE industrial grade were observed in the Huangmeijian alkaline pluton of the Luzong Volcanic Basin, firstly revealing the mineralization potential of ion-adsorption rare earth elements deposit in central Anhui Province.

Based on results of geological survey and mineral resources research over the past decades, the authors have systematically summarized the metallogenic geologic settings of Laos, Cambodia, Vietnam, Thailand, Myanmar, Malaysia, Indonesia, and the Philippines in Southeast Asia. Mineral geological database has been established, regional geological maps, geotectonic units with division maps, magmatic rock distribution maps and metallogenic regularities of some important metallogenic belts in Southeast Asia have been compiled. The distribution characteristics of major minerals such as copper, gold, aluminum, potassium, nickel, chromium, tungsten and tin, lead and zinc, iron, manganese and antimony, and the genetic types of these minerals are summarized. Meanwhile, twenty metallogenic belts are divided and nine main metallogenic epochs are summarized. We also analyze the influence of the tectonic evolution of the East Tethys, as well as the subduction and collision between the Indian-Australian plate, the Pacific plate, the Philippine sub-plate and the Eurasian plate on the mineralization in Southeast Asia. This study provides a number of valuable data and geological information for understanding the spatial distribution and temporal evolution of minerals, and the prospecting targets in Southeast Asia.

Evolution of the late Ordovician–Silurian Caledonian orogeny (ca. 460–420 Ma) in the South China Block (SCB) remains controversial due to the overprinting Triassic (Indosinian) and Jurassic-Cretaceous (Yanshanian) orogenic tectonics and the absence of enough petrologic records. This work reported a systematic study of whole-rock geochemistry, zircon U–Pb geochronology and Hf isotopes of the first Caledonian A-type granitoids (Dishui) in Jinxiu county, Guangxi (SW China). The Dishui granitoids are tectonically located in the southwestern Qin-Hang suture belt, which is the largest ancient orogenic belt formed by the collision of the Yangtze and Cathaysia blocks in South China. The Dishui granitoids consist primarily of a syenogranite pluton with a small-scale granodiorite porphyry dike. The Dishui syenogranite and granodiorite porphyry have LA-ICP-MS zircon U–Pb ages of 437.9 ± 1.0 Ma (MSWD = 0.77) and 436.6 ± 0.8 Ma (MSWD = 1.7), respectively. The syenogranite has high contents of SiO₂ (73.20–77.35 wt.%), total alkalis (Na₂O + K₂O = 7.42–8.99 wt.%), total REE (198–445 ppm), high field strength elements (HFSEs: Zr + Nb + Ce + Y = 253–520 ppm), and 10,000∗Ga/Al (2.93–3.11) and FeO_t/(FeO_t + MgO) (0.77–0.96) ratios and high F concentration, resembling highly-fractionated A-type granite. The granodiorite porphyry displays similar A-type granite affinities, including high (Zr + Nb + Ce + Y) (410–485 ppm), 10,000∗Ga/Al (2.47–4.59), and zircon saturation temperature (T_Zr = 908–927 °C), medium to high SiO₂ (64.56–64.95 wt.%), Fe₂O₃ (7.70–8.11 wt.%), and MgO (3.69–4.09 wt.%), and low FeO_t/(FeO_t + MgO) (0.61–0.64), resembling magnesian unfractionated A-type granitoid. The Dishui syenogranite and granodiorite porphyry dike have zircon ε_Hf(t) value and two-stage model age (T_DM2) of −3.9 to +1.5 and 1.32–1.66 Ga, and −1.7 to +11.8 and 0.94–1.53 Ga, respectively, both much more depleted than many Caledonian gneissic/massive granites and the Devonian A-type granites (ε_Hf(t) = −14.9 to −3.5) in South China. All these data suggest that the Dishui syenogranite was derived from partial melting of the Proterozoic metamorphic basement with mantle-derived melt input, and the magma subsequently underwent extensive fractionation. Meanwhile, the Dishui granodiorite porphyry was likely derived from the same crustal melt with more mantle-derived input. New ages of the Dishui A-type granitoids (ca. 436–437 Ma) in the Qin-Hang belt indicate a tectonic transition from syn-collisional crustal thickening to post-collisional extension at ∼437 Ma in South China.

Earth and planetary sciences require extensive microanalyses to quantify most common major and minor elements O, Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, Fe and Ni in minerals/rocks. With O usually calculated, this is frequently done with expensive electron probe X-ray microanalyzer using a wavelength dispersive method (WDS), and much less so with expensive ground-based scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). Both instruments are not readily accessible to many scientists though. Here we selected eight natural minerals, containing those elements to various amounts, to test the performance of an economical desktop SEM attached with an EDS consisting of just one 10 mm² silicon drift detector (SDD). The compositions of the minerals were established by extensive electron probe X-ray microanalyses (EPMA)-WDS conducted under routine analytical conditions. They were used to evaluate the performance of the desktop SEM/SDD-EDS system. The examination shows that under modest analytical conditions it can generate accurate results for those elements, with detection limits (∼0.1 wt%) much comparable to routine WDS analyses. Therefore, economical desktop SEM/SDD-EDS system can be an affordable and widely-accessible instrument for extensive and accurate quantification of those most common major and minor elements in minerals/rocks.

This work studies the mineralogical and geochemical features of ooidal ironstone formation of the Upper Cretaceous Ayat Formation located in the Turgay depression (Kazakhstan). The origin of ooidal ironstone deposits has been the subject of many discussions for a long time. These results present diagenetic conditions of the marine ironstone precipitation in the Ayat Formation. Various authigenic minerals, such as siderite, glauconite, goethite, pyrite, hydroxylapatite, wurtzite, and barite indicate fluctuations in the different geochemical conditions during the diagenesis of marine sediments of the Ayat Formation. The precipitation of in situ pyrite and wurtzite was controlled by an oxygen-deficient environment at the interface between water and sediment, which was accompanied by bacterial sulphate reduction under seabed conditions and, in consequence, by the concentration of sulfides. The authigenic assemblage of siderite, wurtzite, and barite indicates an integrated process of their input to site the sedimentation. The stable isotopic composition of siderite supports the microbial carbonate origin by decomposing the organic matter. However, geochemical features (the pattern Co/Zn vs (Co + Ni + Cu)) evidence the hydrogenous precipitation of iron. It involves the interaction of two central in situ processes to form Ayat ooidal ironstones. One of them is the iron precipitation from the bottom water, and the second is the microbial generation of hydrocarbons. Marine Ayat and channel Lisakovsk ironstones have similar features of bulk rock geochemistry. It reflects the exact environments of the ooidal iron ore formation, while the wall rocks have distinctive facies conditions.

Parts of A-type granites are closely related to some critical mineral resources. The study of origin and geochemical properties of those A-type granites are of great significance in revealing the metallogenic potential. The Early Cretaceous Huangmeijian (HMJ) complex is located in the Lower Yangtze River Belt (LYRB), eastern China, which is proposed to be associated with uranium deposits. Here, we present whole-rock major and trace elements, and zircon U–Pb geochronology to reveal the formation of the two-stage, uranium mineralization of A-type granites. The high Zr + Nb + Ce + Y concentrations (598−1181 ppm) and Ga/Al ratios (2.7−4.2) suggest an A-type geochemical affinity. On the ternary discriminant diagrams, they can be further divided into A₁-type. In-situ LA-ICP-MS U–Pb dating on the zircon grains from the HMJ complex yielded weighted mean ages of 129.7 ± 1.6 Ma (quartz alkali feldspar syenite), 131.3 ± 1.0 Ma (quartz alkali feldspar syenite), and 118.7 ± 0.7 Ma (alkali feldspar granite), respectively. The former two age results are consistent within error, and similar to other A-type granites in the LYRB. The latter one is newly identified, and is obviously younger than most A-type granites developed in the LYRB. Geochemical data suggest that these A-type granites are formed under high temperature and low oxygen fugacity conditions in an extensional setting. The presence of huttonite favors for the hydrothermal event and the uranium mineralization. It is important to note that, compared to the ca. 130 Ma quartz alkali feldspar syenites, the ca. 118 Ma alkali feldspar granites have obviously higher U (21.3–79.2 ppm) and Th (81.2–104 ppm) concentrations, which are also higher than those of other A-type granites developed in the LYRB. Moreover, the U concentration is even higher than some uranium mineralized granites of South China. Thus, besides the previously reported ca. 130 Ma A-type granite, the ca. 118 Ma A-type granite is of great probability to be a main source of uranium for the formation of uranium deposits in the LYRB, eastern China.