Journal of Geochemical Exploration最新文献

Cassiterite is a weathering-resistant mineral, which can incorporate a variety of trace elements. Trace elements in cassiterite samples collected from twelve deposits in the Herberton Mineral Field, Australia, were measured with the use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results were combined with published data from other tin fields, including the Andean Sn belt in South America; the Karagwe Ankole belt in Rwanda; and, from China, the Kangxiwa-Dahongliutan pegmatite field, the Youjiang basin, the Nanling belt and the Da Hinggan Range belt. Tin deposits in the dataset can be subdivided into four deposit types: 1) greisen and veins; 2) skarns; 3) Li-Cs-Ta pegmatites; and 4) polymetallic veins. The cassiterite dataset was analyzed using basic descriptive statistics, principal component analysis (PCA), and cluster analysis. Cassiterite grains from greisen and vein deposits are characterized by high concentrations of Ti (avg. 1751 ppm) and moderate concentrations of Al (avg. 97 ppm), whereas cassiterite grains from skarn deposits generally contain lower concentrations of Ti and Al. Chemical compositional boundaries in cassiterite from different deposits were recognized with cluster analysis. The relative enrichment of Al and Ti in cassiterite grains from greisen and vein deposits is likely due to greisenization reactions. The Ti vs. Al diagram can be used to differentiate between cassiterite grains derived from greisen and vein deposits, as compared to cassiterite grains derived from skarn deposits, whereas Sb vs. V diagram can be used to differentiate between cassiterite grains from polymetallic vein deposits. Zirconium and Nb concentrations are useful in identifying cassiterite grains sourced from LCT pegmatite deposits. The discrimination diagrams developed in this study through cluster analysis indicate that cassiterite grains sourced from different deposit types can be differentiated based on their trace element geochemistry and this can be a useful tool in critical mineral exploration. Therefore, these diagrams can be used effectively to understand metal association and deposit types in a region with detrital cassiterite from stream sediments, till and heavy mineral placer deposits.

The change of hydrostatic pressure caused by the fluctuation of groundwater table in the aquifer will lead to the partial dissolution of excess ⁴He gas, resulting in the isotope imbalance of ³He/⁴He-⁴He. The dissolved Ne in groundwater is mainly derived from the atmosphere, and its isotopic composition can correct the isotopic imbalance of ³He/⁴He-⁴He. We collected thirty-eight groundwater samples from the second aquifer of the Jianghan Plain, and the isotopic concentrations and ratios of He and Ne were measured. ²¹Ne/²²Ne-²⁰Ne/²²Ne illustration is proposed to estimate the shares of atmospheric and mantle components. The ²¹Ne content and isotopic ratios of atmospheric and mantle components are used to estimate a calculated Ne content. The difference between the calculated Ne content and the measured Ne content (∆Ne) is used to evaluate the percentage of error estimated“excess air”. The accumulation of crustal ⁴He is corrected with the measured ⁴He content and the percentage of error estimated “excess air”. We found the maximum percentage of error estimated “excess air” was 7.57 % occurring in the groundwater samples from the second aquifer of Jianghan Plain, and the disequilibrium of ³He/⁴He-⁴He led to overestimation of the share of mantle He. The percentage of mantle He in total dissolved components is reassessed and range from 0.03 % to 0.74 %, indicating the mantle component is minor. The reassessed ⁴He ages (1.79 ka to 21.90 ka) were uniformly older than those estimated by traditional method which only use the measured ³He/⁴He ratio to distinguish the crust ⁴He (1.28 ka to 18.74 ka). ⁴He age is significantly underestimated up to 47.05 %.

The Iberian Pyritic Belt (IPB) is one of the most important metallogenic provinces, which hosts massive sulfides and extends over 230 km from Canal Caveira-Lousal in Portugal to Gerena (near Seville) in Spain. It has 88 active and inactive mines only in the Spanish part and near 30 in Portugal that generate Acid Mine Drainage (AMD) pollution to the main river basins, Corona, Roxo (Portugal), Odiel, Tinto, Guadiamar (Spain) and Chanza-Guadiana (Portugal/Spain) and consequenty to the 35 acidic sampling sites, 14 in Portugal and 21 in Spain, selected for this unique study. The physico-chemical parameters of waters (EC, Eh, pH, Al, As, Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn, SO₄²⁻), acidic diatoms (%Pinacid) and diatom diversity (N°sps) were determined in the laboratory. Then, the results were integrated in a database with 16 variables and 35 sampling points to be statistically analyzed by factor and cluster analysis. In the first, for the 35 sampling sites, it showed a clear inexistence of ecological barriers, exposing how could distantly sampling points be paired together. The last, allowed the pollution–biota interaction models formulation governed by 2 factors: 1-Unrestored Mining Surfaces and 2-WFD (Water Framework Directive) exceeding limits. Dispersion diagram showed that although the unrestored mining surface increases, starting from a certain concentration of contaminants, salts begin to precipitate: the AMD process increases but the WFD does not. There are numerous works in the scientific literature aimed to define diatom-hydro-geo-chemistry interrelationships, but none that covers an entire metallogenetic province where ecological barriers could exist, conditioning the diatom species and groups evolution and distribution in an acidic (pH: 1.90–4.43) environment.

Geochemical characteristics of uranium minerals is an important content for uranium deposits, and is conducive to understand the formation mechanism, environment and genesis of sandstone-type uranium deposits. In the Diantou-Shuanglong uranium deposit from southern Ordos basin, carbonaceous debris (CD), dispersed organic matter, is widely distributed in sandstones from uranium-bearing strata, and is the dominant enrichment agent for uranium precipitation. The geochemical compositions of uranium-rich CD were investigated by using inductively coupled plasma mass spectrometry (i.e., ICP-MS) and scanning electron microscope-energy dispersive X-ray spectroscopy (i.e., SEM-EDS). The results show that element U bears a close relationship with elements W, Ta, Mo, Pb, Th, Bi, Mn, V, Ti, Co, Be, especially Mo, and Pb, indicating that these elements are rich in uranium-bearing minerals. The contents of rare-earth element (i.e., REE) and light rare-earth element (i.e., LREE) increase with the increasing uranium abundance, implying that REE primarily enrich in uranium minerals, especial for LREE. Moreover, LTEE (e.g., Nd) and Y are detected in uranium-bearing minerals. Besides, uranium-bearing CD exhibits similar REE geochemical characteristics and distribution patterns with the surrounding sandstones, indicating that they are homologous in sedimentary source, sedimentary environment, and tectonic background, and the CD is deposited during synsedimentary period. Given the distribution characteristics of trace element and REE, it is comprehensively inferred that the formation of uranium mineralization is not related to deep hydrothermal fluid below the lower crust, but is altered by the low-temperature hydrothermal fluid. Synsedimentary CD at the stage of low to medium thermal maturity is of certain adsorption and reduction, and is favorable for the precipitation and enrichment of uranium-bearing phase and the other trace element (e.g., Mo, V) similar in geophysical-chemical properties with U element, and the sedimentary environment is beneficial for preservation of uranium. It will be contributed to clarify the genesis of sandstone-type uranium deposit and to provide some guidance for the exploration of the uranium deposit in the studied area.

The Paleogene-Neogene Thrace Basin in northwestern Türkiye has long been known to host economic gas and oil resources and has recently been reported to potentially host sandstone-type uranium deposits in the Oligocene Süloğlu Formation. The latter discovery raises questions about the source and deposition mechanism of uranium mineralization in the basin. This contribution reports on the results of a detailed electron paramagnetic resonance (EPR) spectroscopic study of detrital quartz from four sandstone and one mudstone samples in the Süloğlu Formation and documents the distribution and speciation of uranium using combined microbeam synchrotron X-ray fluorescence maps (μsXRF) and microbeam X-ray near edge structure spectroscopy (μsXANES). The EPR spectra of quartz separates are characterized by the presence of diagnostic radiation-induced defects (i.e., silicon-vacancy hole centers H′₃, H′₄, and H′₇ with g_max = 2.049, 2.034, and 2.018, respectively, and the oxygen-vacancy electron center E′₁), formed by the bombardment of alpha particles emitted from uranium, thorium, and their unstable progenies. Moreover, notable decreases in the intensity of silicon-vacancy hole centers in the EPR spectra of quartz separates after partial dissolution with hydrofluoric acid, provide compelling evidence for the circulation of uranium-bearing fluids in the Thrace Basin. The μsXRF and μsXANES data reveal the occurrences of mixed U⁶⁺ and U⁴⁺ species in hematite partially replacing pyrite aggregates but dominantly U⁴⁺ in disseminated pyrite and illite in sandstones of the Süloğlu Formation. These results provide new insights into uranium transport, reduction, and deposition mechanisms, with important implications for better understanding sandstone-type uranium deposits in general and further exploration in the Thrace Basin.

The oxidation of pyrite involves a series of chemical reactions that, depending on climatic conditions, can give rise to different mineral phases and morphologies. When oxidation takes place in semi-arid climate, the development of efflorescent salts on the surface of mine tailings is characteristic. These salts are mainly composed of Fe, Al and Mg sulfates and may accumulate valuable metals liberated through the dissolution of tailing minerals.

This research aims to describe the evolution of salt precipitation from the economic and environmental perspective. For this purpose, we sampled efflorescent salts formed during the summer season on the surface of a tailing impoundment located in the north of Chile. The materials underwent comprehensive characterization utilizing X-ray techniques and scanning electron microscopy.

The findings reveal a fractional precipitation in the crystallized salts. In an advanced oxidation system, characterized by multiple seasons of crystallization, dissolution and oxidation, the dry season begins with the precipitation of sulfates from a highly acidic solution dominated by Fe³⁺. This solution results from the dissolution and oxidation of the previous season sulfates. This initial stage is characterized by the presence of jarosite and gypsum, which are subsequently replaced by ferricopiapite. Towards the progress of the dry season, copiapite becomes more magnesian and precipitates alongside coquimbite and alunogen. Finally, halotrichite and pickeringite begin to crystallize. Base metal cations such as Co, Cu, Mn, Ni and Zn are preferentially incorporated into halotrichite-pickeringite sulfates during the most advanced evaporation phase.

Accurately determining the presence of subterranean deposits is challenging due to the intricate geological processes that give rise to these deposits. The use of stream sediment geochemical data to identify and map geochemical anomalies is a widely employed technique in mineral exploration and offers a robust indicator of the possible presence of mineral deposits. This research presents a comparison between the weighted drainage catchment basin (WDCB) technique and its improved version, the dynamic enhanced weighted drainage catchment basin (DE-WDCB) approach, in the context of mineral exploration. We constructed a model of the catchment basin for the study area, clarified the upstream and downstream relationships between the basins, determined the background value in each basin via the trend surface method, and carried out geochemical anomaly mapping based on the DE-WDCB method. Then we conducted two comparative experiments using the WDCB method, employing both dynamic and nondynamic classification methods for anomaly classification. Finally, we compared the mineralization of the three methods and find that the DE-WDCB method exhibited superior performance in identifying sedimentary manganese ore anomalies, followed by the dynamic grading WDCB method and the nondynamic grading WDCB method. These results indicated that the DE-WDCB method revealed excellent performance when applied to stream sediment geochemistry in prospecting, hence enhancing its utility in mineral resource exploration.

Geochemical anomalies are gaining importance due to the Europe's renewed prospecting activities for technologically critical metals, such as nickel (Ni) and cobalt (Co). In this context, soils developed on Ni laterites near old open pit mining and exploration works near Křemže in southern Czech Republic were investigated using multi-method approach to assess the distribution, solid speciation, and (bio)availability of the trace metals, with a particular focus on Ni, chromium (Cr), and Co. The total concentrations of metals in the studied soils (Ni: 170–4950 mg/kg, Cr: 56–1190 mg/kg, Co: 14–424 mg/kg) exceeded the median world regulatory guideline values (Ni: 112 mg/kg; Cr: 250 mg/kg; Co: 50 mg/kg) as well as the Czech concentration limits for agricultural soils for most of the samples. The concentration of metals in the soil profiles generally increased as a function of depth with surface horizons in agricultural plots homogenized by ploughing. The effect of a former open pit mine (already closed for ca 80 years) on the vertical distribution of metallic elements has not been demonstrated. The extractable metals were relatively low (extraction efficiency order: water < DTPA < EDTA). The mean EDTA-extractable values corresponded to 4.2 % Ni_tot, 8.6 % Co_tot, and only 0.14 % Cr_tot. This contrasting metal availability is strictly related to the metal speciation in the solid phase. The primary minerals (olivine, clinopyroxene) are highly weathered to secondary phyllosilicates (lizardite, talc) and Fe oxyhydroxides and Mn oxides, all representing important carriers for Ni. Cobalt was exclusively hosted by Mn oxides, and the less mobile Cr was mainly bound in insoluble phases, likely spinel-family oxides. Despite the relatively low metal availability, elevated concentrations of Ni in the crop biomass (86 mg/kg) collected in the agricultural area suggest a metal uptake from the soil, which should be further investigated in detail.

The focus of this study was to comprehend the spatial distribution, source apportionment, evaluation of natural background level (NBL), and mobilization mechanisms of arsenic (As) and manganese (Mn) in the Ghaghara river basin, located in the middle Gangetic plain (MGP) of India. A combination of analytical tools was employed, including multivariate statistical analysis (MSA), correlation analysis, and receptor models such as positive matrix factorization (PMF) and principal component analysis-multi linear regression (PCA-MLR). Taking into consideration the compositional constraints of the geochemical data, compositional data analysis (CoDA) methods were applied on the raw data prior to the correlation analysis and MSA. The results of MSA, correlation analysis and receptor models showed that major ion chemistry and As, Mn enrichment in groundwater were largely controlled by carbonate weathering, Fe and Mn oxyhydroxides dissolution. Anthropogenic activities, such as the infiltration of dissolved organic matter-rich water from local surface water bodies used as dumping sites and the infiltration of fertilizer-rich water from agricultural lands, were found to notably impact the groundwater geochemistry and release of As in the research area. The lower NBL of As (5.92 μg/L) compared to its mean concentrations (17.9 μg/L) in the study area also indicated that the rate of As release in groundwater through natural processes was comparatively low but various anthropogenic activities operating in the study region possibly acted as a trigger for the mobility of As from the mineral phases of the subsurface sediments. This study also highlighted the significance of applying CoDA techniques on geochemical data prior to statistical analysis, and the importance of receptor models, to better understand the nature and contribution of various natural and anthropogenic processes governing the hydrochemistry of groundwater in the alluvial aquifers.

The Mbarga itabirite deposit in the Mbalam iron district on the northwest edge of the Congo Craton (CC) hosts two main types of iron ore enrichments: supergene and specularite ores. This study presents mineralogical, geochemical, and isotopic datasets on these ores to determine their genesis.

Ore microscopic studies indicate that the itabirites are of the oxide facies type, with magnetite showing partial to extensive alteration to hematite-martite. The supergene ores consist of hematite + martite + goethite ± gibbsite ± magnetite ± quartz, while the specularite ores are mainly composed of hematite + martite ± quartz. Magnetite microchemistry suggests formation under low-T hydrothermal conditions (~200–300 °C) with high fO₂. Geochemical analyses show that the supergene and specularite ores have higher Fe₂O₃ (88.27 to ~100 wt%) and lower SiO₂ (<0.01 to 0.18 wt%) contents than the itabirites (31.95 wt% Fe₂O₃, 67.16 wt% SiO₂). The enrichment of Fe in the supergene ores is attributed to the depletion of major oxides and trace elements due to weathering and supergene enrichment, while the high Fe content in the specularite ores stems from the precipitation of iron-rich, but trace- and rare earth elements (REE)-deficient hydrothermal fluids. The slightly higher Al₂O₃ content and positive Ce anomalies in the supergene ores suggest the retention of Al-bearing minerals (gibbsite) and reveal highly oxidative conditions during martitization. Stable isotope analyses reveal that the supergene and specularite ores have δ¹⁸O values of −2.5 to −0.3 ‰ and − 2.0 to −3.4 ‰, and δ²H values of −75 to −123 ‰ and − 70 to −119 ‰, respectively, suggesting the involvement of isotopically light-evolved meteoric water in their formation. In contrast, the itabirites exhibit heavier δ¹⁸O (8.5 to 10.2 ‰) and δ²H (−85 to −91 ‰) values, suggesting formation from mixed magmatic and metamorphic fluid sources. A “polygenic-supergene-hydrothermal” model is suggested for the formation of the Mbarga itabirite-hosted iron ores.