Solid Earth Sciences最新文献

Most W mineralization in the world is genetically related with highly fractionated granites, but little is known about ore-forming fluid evolution of W mineralization associated with weakly fractionated granites. To reveal the ore-forming fluid evolution of W mineralization related to the weakly fractionated granites, a combined study of field and petrographic observations, mineralogical, morphological, and in-situ geochemical data of different-type quartz from Dongyuan porphyry W deposit in the world-class Jiangnan W belt, China, was carried out. The petrographic observation and cathodoluminescence (CL) imaging revealed the quartz in the Dongyuan W deposit can be divided into hydrothermal quartz (Qz1 with core-edge structure, and Qz2 with oscillating zone) in the mineralized alteration zone, and magmatic quartz (Qz3 with inherited core) in granodiorite porphyry. The LA-ICP-MS results of the Dongyuan quartz samples show that Al may enter the quartz structure with trivalent Al³⁺ instead of Si⁴⁺, monovalent alkali metals and bivalent (Ge²⁺, Sr²⁺) cations is mainly of charge compensators in quartz, while Ti possibly is in the form of microinclusions of titanium-containing minerals in quartz. The integrated interpretation of the trace element compositions (e.g., Al and Ti contents, Al/Na ratios) and CL texture of quartz indicate high temperature (>400 °C) and uniform Al-rich acidic fluid are conducive to W precipitation of the Dongyuan deposit. Furthermore, trace element compositions (e.g., Ge, Al) and micro-textures of quartz have the potential for distinguishing magmatic and hydrothermal quartz in the Dongyuan W deposit.

The study utilized the fuzzy analytical hierarchical process (F-AHP) in the multicriteria decision analysis of seven important hydrogeologic parameters associated with groundwater potentiality/yield. The purpose was to develop groundwater potential map using groundwater potential index values (GWPIV) for Ondo metropolis, Southwestern Nigeria. The hydrogeologic parameters were prioritize and assigned different weights hierarchically according to their level of importance using F-AHP, as aquifer layer thickness (0.05), aquifer layer resistivity (0.04), overburden thickness (0.12), transverse resistance (0.18), transmissivity (0.32), coefficient of anisotropy (0.25), and formation factor (0.03). From regional perspective, based on drainage basin, and river network, the region was categorized to be of low/moderate groundwater yield, with moderate to high flow connectivity. The higher and lower elevations are generally remarkable in the northern and southern areas respectively, hence possibility of movement of water towards the southern part with the northern forming the watershed. Furthermore, the longitudinal unit conductance recorded regional average value of 1.168, while 1.20, 1.16, and 1.10 were recorded for granite, gneiss and migmatite, which suggests moderate vulnerability to contamination. The average values recorded for overburden thickness, hydraulic conductivity, transmissivity, transverse resistance, formation factor, coefficient of anisotropy, fracture contrast, and reflection coefficient are 22.5 m, 0.33 m/d, 5.56 m²/d, 4966 ohm-m², 2.42, 1.17, 15.3, and 0.66 respectively. The water table aquifer and the fractured basement are the major water bearing units in the area; while the geological units showed overlapping hydrogeologic properties. The obtained GWPIV ranged from 1.21 to 3.55 with regional average of 1.86, suggesting a moderate potential. Nevertheless, the southern part showed more propensity/yield than the northern area. The study showed the importance of geospatial mapping technique, involving fuzzy analytical hierarchical process, in groundwater evaluation, as it was able to solve and obtain different hydrogeological parameters, which were integrated to prioritize and define the area's groundwater prolificacy for the purpose of improving, expanding, and management of the existing water scheme in the study area.

Fine and coarse typical sand are among the most vital raw materials in building construction. A lot of drilling has been done without appropriate subsurface information resulting to a waste of resources and time. Geophysical methods give information on subsurface lithologies to locate areas with huge success. Thus, a geophysical investigation of subsurface deposits was carried out in this research to ascertain the quantity of fine/Coarse sand or areas with viable fine/Coarse sand utilizing Schlumberger configuration, Dipole–Dipole (2D) and well logging in parts of Okpe and Ughelli North LGA of Delta State, Nigeria, before extraction (dredging) for the benefit of exploitation and development. This was done by assessing the geo-electric formation of fine/coarse sand in the studied areas concerning their depths and thicknesses. Seven Vertical Electrical Sounding (VES) were obtained with the application of Schlumberger array, seven 2D and three well logging to estimate the viability of sand deposits in the study areas. These techniques have the efficacy of detecting near-bed formation with vital resolution. The data obtained from the field were illustrated by partial curve matching coupled with computer iteration using the WIN RESIST and Dipro Software to obtain sounding curves which revealed four to six layers. The layers consist of topsoil, lateritic clay and clayey sand, fine sand deposit, medium to coarse grain sand and coarse sand. For Agbarho, thicknesses of fine/coarse sand in the VES stations ranges from 18.0 to 55.6 m with resistivity varying from 223.7 to 572.9 Ωm, Osubi Fine/Coarse sand thickness ranges from 13.5 to 59.9 m with resistivity values within 211.9–891.0 Ωm and Oha town locations have fine/coarse sand thickness varied from 46.6 to 83.7 m with resistivity interval computed between 145.9 Ω-m and 466.4 Ω-m. Thus, the best VES stations that are more viable for sand mining are VES 1, 5 and 7 which contain relatively huge viable sand deposits in the study areas to a depth above 80 m.

Serpentines are geologically important minerals, and antigorite (Atg), lizardite (Lz) and chrysotile (Ctl) are the three key varieties. Their quick and accurate identification with micro-Raman spectroscopy requires to consider the effects of different crystallographic orientations and different chemical compositions. By collecting from existing literatures all Raman spectroscopic data and compositional data acquired from the same or identical Atg, Lz and Ctl samples, we critically examined the compositional effects for the first time, and found that some compositional parameters like the Al₂O₃ and Cr₂O₃ contents have significant impacts on the Raman features. Taking into account the effects of both compositional difference and crystallographic orientation difference, we propose two identification schemes for Atg, Lz and Ctl: the first one uses those weak but characteristic Raman peaks at 1200–1000 cm⁻¹, and the second one uses those intense and unanimously-observed Raman peaks at ∼688, 378 and 229 cm⁻¹. As for the first identification scheme, no peak at 1200–1000 cm⁻¹ suggests the presence of Lz; a single peak at ∼1045, at ∼1070, or at ∼1106 cm⁻¹ indicates the presence of Atg, Lz, or Ctl, respectively; two Raman peaks at ∼1040 and 1070 cm⁻¹ implies the presence of Lz; the occasionally observed one single peak at ∼1040 cm⁻¹ may imply the presence of either Atg or Lz, which can be sought out by resorting to the peak position ratio R_∼1045/688 (Atg having R_∼1045/688 > ∼1.521 whereas Lz attaining R_∼1045/688 < ∼1.521). As for the second identification scheme, Atg can be readily separated from Lz and Ctl by using the exact wavenumbers of the Raman peaks at ∼688 and ∼378 cm⁻¹, and Lz and Ctl can be further discriminated by using the exact wavenumbers of the Raman peaks at ∼378 and ∼229 cm⁻¹. Under most circumstances, both identification schemes do not require the information of crystallographic orientation or composition, and can be conveniently applied to identify the serpentines of Atg, Lz and Ctl.

Two 500-m-deep holes are proposed to be drilled at the Kane oceanic core complex (OCC), one aimed at a serpentinized peridotite massif and the other at a gabbroic body. Ocean drilling is vital to validate lithological interpretation derived from seismic structures. Utilizing a long marine streamer, seismic imaging can effectively delineate the dominant lithologies within the OCCs. This study applied a suite of techniques, including downward-continued multi-channel seismic data, full waveform inversion, and reverse time migration, to obtain detailed fine-scale shallow structures beneath the Kane OCC. Through the downward continuation method, refracted seismic data at near offsets were utilized, thus doubling the resolution at shallow depths. Compared to previous findings, our results greatly enhance the understanding of shallow subseafloor structures, revealing a more precise morphology of the gabbroic bodies and well-imaged very shallow low velocities caused by seawater percolation in the shallow fissure due to footwall rotation extension. We present reference drilling hole velocities and link them to the likely composition, considering potential alteration processes such as serpentinization of mantle peridotite. Our investigation suggests that the lower crustal melt fluxes of the Kane OCC represent a transitional phase from low to medium accretion, providing valuable insights for future scientific ocean drilling projects in this region.

In order to ascertain the governing mechanisms, sources, and speciation of ionic species, identify hydrochemical facies, and assess their appropriateness for agricultural use, groundwaters from several portions of the semi-arid basement complex of north–central Nigeria were analyzed based on chemistry. Basement aquifers made of gneiss-migmatites, metasediments, and granitoids store groundwater. Standard analytical techniques were used to analyze the fluids for main cations, anions, and physical characteristics. The results showed that the waters were slightly acidic (with a mean pH of 5.38, below the permissible range of 6.5–8.5), and that the predominant cations and anions were Na⁺ >Ca²⁺ >K⁺ >Mg²⁺ and Cl⁻ > NO₃^- > HCO₃^- > SO₄²⁻, respectively. Analysis of the ions' stoichiometric ratios reveals that alkali elements predominate, making up about 55.3% of the ions and being connected to silicate weathering. Based on ionic ratio calculations, it was determined that ion exchange was a key factor controlling water chemistry. Ionic species cross plots show that silicate weathering (sodic and calcic plagioclase) predominates. Hydrochemical facies, Gibbs plots, and principal component (correlation, cluster and factor) studies all show that ionic elements are geogenic, essentially coming from the weathering of silicates with ion exchanges. Based on predicted saturation indices, hydrochemical modeling by the computer program VISUAL-MINTEQ reveals that the majority of main ions occur in free mobile states with associated mineral species, all at undersaturated levels. Based on measurements of the sodium adsorption ratio (SAR), sodium percentage (% Na), and chloro-alkaline indices (CAI), the waters have been evaluated for their suitability for agricultural use.

Geochemistry was performed on clastic core sediments from the Tiko Mangroves estuary, South western region of Cameroon, to categorise the rock source composition, tectonic setting, past weathering intensity of the source area in relation to past climate and sediment maturity in relation to sedimentary cycle. Plots of La/Co, La/Sc, Cr/Th, discriminant function (DF1&2), TiO₂ vs Al₂O₃ and TiO₂ vs Zr point to an acid (felsic) and mixed (intermediate) rock source composition for the Tiko sediments. The acid composition portrayed by the sediments is also confirmed by their LREE (Light rare earth elements) abundance, and a negative Europium anomaly on chondrite normalisation, while the intermediate (mix) composition reflects the multiple sources of the sediments (Douala Basin and basaltic debris from Mount Cameroon). Binary plots Discriminant function (A-P) M, and Discriminant function (A-P) MT signpost active tectonic domain for the studied sediments, that resulted from the tectonothermal of the Pan African orogenic history and eruptive activity of the mount Cameroon. The weathering indexes denoted as CIX (chemical index of weathering) and PIX (plagioclase index of weathering) for the Tiko sediments advocate an intense source area weathering in a humid hot climate. The PIX advocate a high-level plagioclase lixiviation. The low values of ICV (index compositional variation) less than 1 (<1) couple with correlation plots Zr/Sc vs Th/Sc, and Zr vs (La/Yb)_N confirms that Tiko mangrove sediments are matured recycled sediments with compositional variations. This is the first comprehensive provenance study of mangrove ecosystem sediments in Cameroon.

The thermal springs of the study area are situated in North-eastern Arunachal Himalayas, India along Subansiri and Siang River valleys with surface temperature ranging between 20 and 57 °C. The pH of thermal springs varies from 7.69 to 9.31, indicating near neutral to alkaline nature of thermal and non-thermal waters. The major geochemical processes influencing hydrochemistry are demonstrated using conventional graphical plots, geochemical modelling by PHREEQC and multivariate statistical analysis. The thermal waters of Chetu and Taksing in Subansiri valley are primarily Na–Cl and Na–HCO₃ type, while, thermal water of Yangte in Siang valley is also mixed water-type and others of Ca–Mg–HCO₃ type. The geochemically distinct type of waters is obvious from dendrogram derived from hierarchical cluster analysis. Quartz geothermometer predicts reservoir temperatures of thermal springs of 88 ± 13 °C; while, Na–K Giggenbach geothermometer predicts 182 °C and 176 °C for Chetu and Taksing hot springs. Thermal waters are immature and highly prone to mixing with meteoric waters as evident from enthalpy-chloride modelling. Evaporite dissolution, silicate weathering and ion exchange processes are found to contribute to total ion budget in geothermal waters. The saturation indices studies depict oversaturation of all thermal waters with calcite and dolomite. Considering all geochemical features, a conceptual hydrological model resembling geomorphology and origin of thermal springs of North-Eastern Arunachal Himalaya has been proposed. The thermal waters of Subansiri valley display very high Sr and F⁻ content which prohibit them from drinking and utilization purposes. High concentration of toxic elements is addressed to geogenic causes over anthropogenic contributions due to lesser accessibilities at hot spring spots.