Journal of Geochemical Exploration最新文献

The Huixian karst wetland, situated in southwest China, is the largest karst wetland. Historically, organochlorine pesticides (OCPs) have negatively affected the aquatic environment and the health of surrounding residents. In this study, the pollution status and environmental fate of OCPs in multiple environmental media in the Huixian wetland were investigated. The 15 OCPs' total concentration ranges in lake water, ditch water, groundwater, and lake sediment were 46.8–306 ng·L⁻¹, 77.8–251 ng·L⁻¹, 26.0–233 ng·L⁻¹, and 44.8–345 ng·g⁻¹, respectively. The concentrations and proportions of the different OCPs demonstrated significant seasonality. Historical residues are the main source of OCPs in the region, as evidenced by the typical ratios of DDTs and HCHs. Karst regions are extremely vulnerable to environmental changes, as evidenced by the highly dynamic character of the karst wetland system and the rapid migration of multimodal OCPs in different media without considerable damage. According to the risk assessment, both the possible carcinogenic risk to sediments in the Huixian wetland and the ecological risk to water bodies were acceptable. In contrast, the consumption of lake water may put the local population at health risk, which is a cause of concern.

Heavy metals (HMs) are often abnormally enriched in soils in geologically high background areas, posing a serious threat to the ecosystem and human health. However, the material origin of HMs in overlying soils is unclear. In this paper, we studied the accumulation control and formation process of HMs (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn) in soils overlying bedrock from different geological periods in a typical anticline structure area in southwest of Guizhou province. The results revealed that the content of HMs in the bedrock were ranked as Carboniferous carbonate rocks < Permian carbonate rocks < Triassic clastic rocks, while the opposite trend was observed for the HMs content in the overlying soil. The slopes of the EF-Q values of HMs in the soils overlying the Carboniferous, Permian, and Triassic rocks were 0.003, 0.007, and 0.83, respectively, which suggests that HMs enrichment or leaching was more complicated in the process of carbonate weathering soil-forming, whereas it was mainly in situ weathering during the process of clastic weathering soil-forming. The soils overlying the bedrock of the three geological periods experienced similar weathering processes and had the same source of soil-forming matrices, as it was observed that their Fe₂O₃-Al₂O₃, Hf-Zr, Nb-Ta, Th/Sc-Zr/Sc and Y/Ho-Y contents were significantly correlated (with R² values of 0.80, 0.94, 0.72, 0.60, and 0.76, respectively) with very similar REE assignment patterns. The results corroborated the causes of the high background geological heterogeneity of HMs in the overlying soils in karst areas and supported the theory of the source of weathering soil-forming materials from carbonate rocks in karst areas.

Weathering indices are widely used in soil science and some other environmental disciplines for a variety of purposes (e. g. for soil classification, in soil formation studies, or in wider palaeoclimatic research). Two main categories of weathering indices have been developed: geochemical and mineralogical. In both cases, an approach is developed that takes into account the compositional nature of the geochemical data. To date, however, the most commonly used weathering indices are geochemical indices that do not consider the geochemical data as compositional. Although the compositional approach minimises possible statistical errors, the weathering indices developed in both approaches, i.e., compositional and classical, axiomatically assume two things that are inaccurate in some cases. First, that soil composition is invariant with respect to the preferential translocation of clay-sized particles, i.e. lessivage, and second, that the selective sorting of minerals during transport does not affect the values of weathering indices. As a result, in some cases bulk analyses of mineralogical and geochemical content are an unreliable tool for determining weathering rates of soil. To overcome these difficulties, this study proposes a new weathering index (W_p-min) based on the orthonormal log ratio (olr) transformation of quantitative mineral data derived from silt- to sand-sized allochthonous mineral assemblages. The size fraction used ensures that only the parent mineral assemblages, which are not prone to translocation, are analysed. In this paper, olr transformation is done using the concept of balances. This enabled the construction of variables, which essentially are various mineral log ratios, with the desired properties, i.e. transport invariance and sensitivity to selective dissolution. In this way, undesirable effects, i.e. selective sorting and lessivage, which ultimately affect bulk analyses, are avoided, allowing a more accurate estimation of weathering in the soil profiles studied. The new index was validated by comparison with the geochemical W index, which was modified by consulting the standardized variation matrix prior to element selection. Ultimately, compared to the geochemical index, the new index was better able to characterise weathering in soils where intense lessivage was detected. The study was conducted on terra rossa soils, which have common source, mostly of aeolian origin.

This study examines the influence of lithospheric architecture on regional metallogenesis, using geological and geochemical data from the East Kunlun Orogen (EKO). We explore how specific lithospheric components and structures affect the formation of orogenic gold and various polymetallic mineral deposits. The study reveals that metallogenic processes in the EKO initially targeted sources within the metasomatized-enriched subcontinental lithospheric mantle (SCLM) and reactivated lower crust during the Paleozoic era.

Lithospheric architecture, shaped by crust-mantle interactions occurred in the Early Mesozoic led to variations in the sizes of orogenic gold deposits between the eastern and western EKO. In the west, smaller gold deposits are linked to moderate mantle underplating and slightly enriched SCLM. Gold-bearing fluids released by mantle devolatilization mixed with metamorphism fluid in collision stage, contributing to the formation of these deposits. In contrast, the eastern EKO hosts larger gold deposits, resulting from significantly enriched SCLM. Extensive lithospheric thinning process in post-collision stage lead to the mixing of gold-bearing mantle-derived and magmatic-hydrothermal fluids. Fertilized magma differentiation potentially increases gold concentrations in this region.

Additionally, Triassic-era melting of the lower crust led to diverse mineralization types in porphyry-skarn-epithermal deposit systems. Key findings include the role of juvenile fertile lower crustal materials in forming copper polymetallic deposits, the importance of metamorphic basement reworking for molybdenum and tungsten deposits, and the influence of lead and zinc leaching from old sedimentary rocks on the formation of silver‑lead‑zinc deposits. This study broadens our understanding of the geological factors influencing metallogenesis and provides a framework for future exploration and research in regions with similar lithospheric architectures.

The Jurassic coalfield in the mining area of western China exhibits a multi-layered groundwater system. However, it is subject to an arid and semi-arid climate with limited water resources. Consequently, the ecological environment is highly vulnerable, and the chemistry and quality of groundwater may be influenced by multiple factors. This study systematically the coal mining-motivated effect on the hydrochemistry and water quality of the groundwater system, using the Caojiatan Coal Mine as a case study. The analysis incorporates a combination of the self-organizing maps (SOM), entropy-weighted water quality index (EWQI), and traditional hydrochemical analysis methods. After coal mining, there was an increase in the proportion of HCO₃-Ca and HCO₃-Mg in the groundwater samples of J₂z, J₂y⁴, and J₂y⁵. The groundwater is controlled by cation exchange as a whole. The J₂y⁴ and above groundwater is influenced by both the dissolution of carbonate and silicate rocks before coal mining. After coal mining, the Quaternary and J₂a groundwater in the western wing is primarily influenced by the dissolution of carbonate rocks; the J₂z, J₂y⁴ and J₂y⁵ groundwater is primarily governed by the dissolution of silicate rocks and the oxidation of FeS₂; the J₂y³ and below groundwater is primarily controlled by the dissolution of evaporate rocks. The resulting dilution effect after coal mining and the implementation of measures for the discharge of treated mine water make the groundwater quality of the J₂y⁴ and higher aquifers tend to be better. The research findings serve as a valuable reference for promoting the sustainable development and protection of groundwater resources not only in the study area but also in other coal mines.

Jiaodong stands out among three global provinces boasting gold reserves surpassing 5000 tons. As geological exploration in the region continues to rise, the significance of deep and covered areas in Jiaodong for ore prospecting becomes increasingly evident. In this study, a Fine-grained soil prospecting method was employed in the Qujia hidden gold deposit and its surrounding region, situated in Yantai City, Shandong Province, and concealed by alluvial soil. The gold (Au) content exhibited a high enrichment level, and the range of Au and silver (Ag) geochemical anomalies demonstrated a robust correlation with known hidden orebodies. Furthermore, transmission electron microscopy and nano-CT were utilized to identify nano-micron metal particles and micro-fractures in the wall rock. A hereditary relationship between the nano-micron metal particles of ore-forming elements present in surface media and the deep orebody was observed. A migration model detailing the movement of deep ore-forming materials in the form of nano-micron metal particles, governed by a multi-agent relay dominated by ascending geogas flow, was established in the Qujia gold deposit in Jiaodong. These findings contribute theoretical support for the fine-grained soil prospecting method in geochemical exploration within alluvial soil covered areas.

Well-exposed mineral deposits are scarce at a global level and presently potential mineral-rich sites are underlying vegetation cover and topsoil, which are suboptimal for direct remote sensing based exploration techniques. This study aims to implement an indirect approach to arsenic (As) distribution mapping using the surface manifestations of the subsurface geology and link it to the known gold mineralisation in the study area. Rise and Shine Shear Zone (RSSZ) in New Zealand is broadly a part of the Otago schist hosting lower to upper green-schist facies rocks manifesting mesothermal gold mineralisation. The area has several surficial geological imprints separating mineralised and non-mineralised zones, but these are dominated by topographic ruggedness, soil moisture and vegetation (mainly grass/tussock) spectra in the hyperspectral data. Initially, a band selection using Recursive Feature Elimination (RFE) was executed. The bands generated were tallied with the field and geological understanding of the area. The resultant 85 bands were then further put through Orthogonal Total Variation Component Analysis (OTVCA) to concise the information in 10 bands. OTVCA output was then classified using Random Forest classifier to map three levels of As concentration (<20 ppm, between 20 and 100 ppm and >100 ppm). The potentially high As concentration zones are likely to be related to the gold mineralisation. The geology of the area correlates with soil exposure which is captured by the classification in some parts, this increases the accuracy but also makes the classification analysis challenging.

The Jiajika hardrock-type rare metal deposit in western Sichuan, China, is considered the largest spodumene deposit in Asia. The quaternary overburden of this area leads to ineffectiveness for ore prospecting using geochemical soil and geochemical stream sediment surveys. Although geogas prospecting has been proven to be effective in exploring buried orebodies, it is seldom deployed to explore concealed lithium deposits. In this work, the geogas samples were collected using the dynamic collection technique along the traverses over three concealed lithium deposits, namely, V-804, V-X03 (Line 7 and Line 35 were selected for sampling, denoted as V-X03–7 and V-X03–35, respectively), and V-STG. The samples were also collected from a Li-poor pegmatite (V-CLZ). The concentrations of Li, Be, Rb, Cs, Nb, Ta, Sn, B, Sr, Ba, and W in the nitric acid collector were measured by performing inductively coupled plasma-mass spectrometry (ICP-MS) measurements. The nanoparticles in geogas were analysed by using a transmission electron microscope coupled with performing energy dispersive spectroscopy (TEM-EDS) measurements. Apparent anomalies of Li, Be, Rb, Cs, B, and Sr were observed on all the traverses. These elements are regarded as pathfinders for the detection of concealed lithium deposits. Clear anomalies of Li, Be, Rb, Sn, B, and Sr were also found over V-CLZ. The concentrations of these elements in the nitric acid solutions were close to those over V-X03–35 and V-STG. The pathfinders are thus not effective in accurately recognizing the false anomalies over Li-poor pegmatite. The TEM-EDS measurements are not suitable for the characterization of nanoparticles in the Jiajika area because the particles from Li-rich and Li-poor pegmatites exhibited similarities in their morphologies. In addition, Li and Be cannot be detected by studying the EDS spectra, and the disturbance from the high background was non-negligible. To effectively address these issues, factor analysis (FA) was conducted on the concentrations of Li, Be, Rb, Cs, Nb, Ta, and Sn in geogas. The synthesis score (SSC) was computed based on three factors extracted by FA. At some sampling sites over V-804, V-X03, and V-STG, the SSC values were larger than 0.25, whereas the maximum SSC over V-CLZ was 0.15. Therefore, FA of geogas data is arising as a feasible method to detect concealed lithium deposits and identify false anomalies in the Jiajika area. The elemental concentrations in the samples from V-X03–7 were much higher than those from the other veins. This effect was attributed to the migration of the elements from buried orebodies to the ground surface, which was possibly promoted by the tourmalinized hornfels.

Beryllium is a strategically critical metal, and its accurate in situ analysis in beryllium minerals is challenging in the field of earth science. High spatial resolution is also a difficult point in the analysis. A new analysis approach for the accurate and precise determination of beryllium contents in beryl using an ablation spot size of 13 μm by LA–ICP–MS was first achieved in this study. The control variables were used to optimise the instrument conditions and determine the laser ablation parameters suitable for determining beryl under an ablation spot size of 13 μm. The energy density was set at 5.5 J/cm² with a repetition rate of 4 Hz, and the ablation time was 50 s. A new concept, the Relative Fractionation Index (RFI), was proposed to measure fractionation and matrix effects. Two potential beryl reference substances (B4–2 and Brl-3) were also assessed by determining their homogeneity to further improve the measurement accuracy. Other common beryllium minerals, including phenakite, chrysoberyl, and herderite, were identified in this study. By comparing the RFI values of different minerals and reference materials, appropriate reference materials and determination conditions were selected, and ideal analysis results were obtained. Therefore, the accurate and precise determination of beryllium contents in common beryllium minerals was achieved using an ablation spot size of 13 μm by LA–ICP–MS.

Phosphate is an indispensable component in the fertilizer industry. It has recently become a critical part of the green energy transition because of the demand for lithium ferro phosphate in rechargeable batteries. A significant amount of phosphate ore (∼90 %) is globally produced from sedimentary rocks. High-quality phosphate ore containing low amounts of toxic elements, however, is mostly produced from igneous carbonatite.

The Lac à l'Orignal deposit (∼1069–993 Ma), Canada, in the central Grenville Province, contains a large amount of fluorapatite (≤ 20 %) hosted in oxide-bearing norite-gabbronorite-anorthosite layered intrusions. The deposit is hosted in the Vanel Anorthosite (1080 ± 2 Ma) near the northern border of the Mattawa Anorthosite (1016 ± 2 Ma). The major host rock oxide-apatite-gabbronorite (OAGN) is primarily composed of plagioclase, orthopyroxene, clinopyroxene, fluorapatite, ilmenite, and magnetite. The Al contents of the OAGN orthopyroxene indicate that the magmatic deposit was emplaced at mid-low crustal levels (∼2.0–3.6 kbar) and reverse zoning in the OAGN plagioclase suggests <2.5 kbar of pressure change during their crystallization. An overall increase of REE + Y concentrations in the OAGN fluorapatite with decreasing their fluorapatite contents indicates that the magma went through fractional crystallization. This study suggests that high abundances (ca. > 8 %) of fluorapatite in some OAGN were produced from crystal avalanching after initial crystal settling. Antithetic correlation between the Cl content of fluorapatite and the Mg# [Mg/(Mg + Fe²⁺)] of coexisting orthopyroxene suggests that phosphate ores with low Cl contents are expected for OAGN that formed at the initial stages of magma crystallization. Therefore, the Mg# of the OAGN orthopyroxene provides an exploration tool for targeting phosphate ore with low Cl content, which is preferred in the production of phosphoric acid, a major intermediate feedstock for the fertilizer and green energy industries. Apatite contents in carbonatite and average P₂O₅ content in carbonatite melt are generally similar to those of the Lac à l'Orignal OAGN. The average concentrations of REE, and toxic metals, such as Pb, Th, and U, in the OAGN fluorapatite are, however, lower than those in apatite from carbonatite worldwide. Therefore, the apatite of the OAGN appears to be of high quality and more environmentally-friendly as a source of phosphate ore.