Trace Element Characteristics Research Articles

Application of Machine Learning to Research on Trace Elemental Characteristics of Metal Sulfides in Se-Te Bearing Deposits

This study focuses on exploring the indication and importance of selenium (Se) and tellurium (Te) in distinguishing different genetic types of ore deposits. Traditional views suggest that dispersed elements are unable to form independent deposits, but are hosted within deposits of other elements as associated elements. Based on this, the study collected trace elemental data of pyrite, sphalerite, and chalcopyrite in various types of Se-Te bearing deposits. The optimal end-elements for distinguishing different genetic type deposits were recognized by principal component analysis (PCA) and the silhouette coefficient method, and discriminant diagrams were drawn. However, support vector machine (SVM) calculation of the decision boundary shows low accuracy, revealing the limitations in binary discriminant visualization for ore deposit type discrimination. Consequently, two machine learning algorithms, random forest (RF) and SVM, were used to construct ore genetic type classification models on the basis of trace elemental data for the three types of metal sulfides. The results indicate that the RF classification model for pyrite exhibits the best performance, achieving an accuracy of 94.5% and avoiding overfitting errors. In detail, according to the feature importance analysis, Se exhibits higher Shapley Additive Explanations (SHAP) values in volcanogenic massive sulfide (VMS) and epithermal deposits, especially the latter, where Se is the most crucial distinguishing element. By comparison, Te shows a significant contribution to distinguishing Carlin-type deposits. Conversely, in porphyry- and skarn-type deposits, the contributions of Se and Te were relatively lower. In conclusion, the application of machine learning methods provides a novel approach for ore genetic type classification and discrimination research, enabling more accurate identification of ore genetic types and contributing to the exploration and development of mineral resources.

Ultrahigh-temperature crustal anatexis and final cratonization in Eastern Hebei, North China Craton: Insights from ca. 2.46 Ga Taipingzhai enderbites

Charnockitic rocks are a suite of granulite-facies plutonic rocks that include dominantly granitic−tonalitic and partly dioritic rocks. The Na-rich endmembers of the charnockite series, including dioritic to tonalitic rocks, are also termed enderbites. Charnockitic rocks are the main component of the cratonic-type lower continental crust in Precambrian cratons worldwide. These rocks are generally considered to be products of the anatexis of the lower crust under high- to ultrahigh-temperature conditions and play a key role in stratification between upper and lower crustal layers as well as the cratonic stabilization (cratonization) of Precambrian continents, although further study is required to gather detailed information about these rocks. In this study, a group of igneous enderbites (dioritic−tonalitic charnockites) from Eastern Hebei, North China Craton, is investigated. Zircon U-Pb dating reveals that the enderbites formed at ca. 2.46 Ga, which is coeval with the regional granulite-facies metamorphic overprinting. The enderbites are primarily composed of clinopyroxene, orthopyroxene, plagioclase, and quartz, with minor amphibole, biotite, K-feldspar, and Fe-Ti oxides. The rocks are characterized by high Fe2O3T + MgO (9.80−15.9 wt%), Cr (71.0−292 ppm), and Ni (41.2−107 ppm) contents, as well as low Al2O3 (13.9−16.6 wt%) and K2O (1.07−2.43 wt%) contents, with high Na2O/K2O ratios (1.51−4.43) and low Sr/Y (24.5−49.5) ratios. Moreover, these rocks are enriched in light rare earth elements (LREEs), (La/Yb)N = 8.06−17.8, and yield weak Eu anomalies, (Eu/Eu* = 0.80−1.18), with negative Th, U, Ta, Nb, and Ti anomalies. Various mineral thermobarometers, oxybarometers, and hydrometers are used to constrain the crystallized P-T-ƒO2-H2O conditions of the enderbites. These rocks crystallized at high temperature (860−1000 °C), crystallization pressure (8.0 ± 1.0 kbar), and H2O-poor (1.5−2.4 wt%) conditions, with oxygen fugacities (ΔQFM) of 0.0−3.0, which suggests “hot” (high-temperature) and “dry” (water-poor) crystallization conditions. The enderbites also have heterogeneous in situ zircon Hf-O isotopic compositions: εHf(t) = 2.4−7.5; δ18O = 5.78‰−7.74‰. These new data, combined with trace element characteristics, suggest that the enderbites were derived from the partial melting of metabasites, and that assimilation and fractional crystallization controlled the compositional variation in the enderbites. Further thermodynamic and geochemical modeling suggests that the anatexis of Mg-Fe−rich metabasite under ultrahigh-temperature (>1000 °C) and H2O-poor (1.0−1.5 wt%) conditions at a low crustal depth (∼9.0 kbar) could yield a melt composition comparable to that of the observed enderbites. Postcollisional lithospheric extension and mafic magma underplating prompted the partial melting of lower crustal metabasite at ultrahigh temperatures and normal lower crustal depths, resulting in the formation of enderbites. This study demonstrates that the enderbites could be formed by ultrahigh-temperature anatexis of metabasite with amphibole dehydration melting (Pl + Amp → Opx + Cpx + melt) and offers robust evidence of the genetic links between the ultrahigh-temperature anatexis of basic rocks and the generation of enderbites. In addition, the occurrence of ca. 2.46 Ga enderbites may mark the final cratonization of the North China Craton, and the ca. 2.50−2.45 Ga tectono-thermal event was an ultrahigh-temperature metamorphic-anatexis process rather than simple regional granulite metamorphic overprinting. Therefore, the generation and emplacement of enderbites involved not only a magmatic process but also an element redistribution process in the lower crust, which has important implications for stabilization of the North China Craton at ca. 2.5 Ga.

Geochemistry of magnetite from Fe-skarn deposits along the central Loei Fold Belt, Thailand

Abstract Fe-deposits in Thailand are mostly located along the Loei Fold Belt in Central Thailand. The study areas, Khao Lek (KL) and Khao Thab Kwai (KTK), have Fe-deposits hosted in contact metamorphized Permian limestone and Permo-Triassic volcanic rocks. Magnetite forms over a wide range of geological conditions and incorporates various trace elements into its cubic spinel structure. The KL and KTK Fe-skarn deposits are mainly composed of massive magnetite. The main discriminator elements for magnetite are characterized by the distribution of Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, and Cu. Thus, this study focused on the chemical characteristics of magnetite to identify the origins of the iron ore deposits. This study investigated the trace element chemistry of the magnetite using laser ablation inductively coupled plasma mass spectrometry. The high Ca + Al + Mn and low Ti + V and Ni/Cr + Mn contents of hydrothermal magnetite in the KL and KTK deposits support a typical skarn origin, and the textural and trace element features of the KL and KTK magnetite are analogous to those of typical calcic-Fe skarn deposits worldwide.

Shallow groundwater quality and health risk assessment of fluoride and arsenic in Northwestern Jiangsu Province, China

Assessing groundwater quality is critical to regional water resource conservation and human health safety, especially in areas with co-existence of toxic constituents fluoride (F−) and arsenic (As). In this study, fourteen groundwater samples were collected in Feng County, Northwestern Jiangsu Province to identify dominant contaminants and their spatial distribution and health risk. The composition and variation characteristics of major ions (K+, Na+, Ca2+, Mg2+, Cl−, SO42−, HCO3−, and NO3−) and trace elements (F−, As, and Mn) were analyzed. The hydrochemical results revealed that high F− groundwater was mainly distributed in the northern areas whereas As-riched groundwater was primarily distributed in southern areas. Notably, over 85.7% and 21.4% of the shallow groundwater samples exceeded the drinking water quality standard of 1.5 mg/L for F− and 10 µg/L for As, respectively. Based on the water quality index (WQI) appraisal result, 71.4% of the groundwater in the study area is classified as “poor”, and thus unsuitable for drinking directly. We assessed the human non-carcinogenic health risk of F− (HQFluoride) and As (HQArsenic) and the carcinogenic health risk of As (CRArsenic). The calculated hazard quotient (HQ) for F− indicated nearly all groundwater samples have an unacceptable risk (HQ > 1) for each age group. However, HQArsenic values revealed that 28.6%, 21.4%, 21.4%, and 21.4% of groundwater samples posed potential non-carcinogenic health risks for infants, children, females, and males, respectively. The calculated results of CRArsenic showed that 0%, 21.4%, 28.6%, and 28.6% of groundwater samples posed unacceptable health risks (CR > 1.0 × 10−4) to infants, children, females, and males, respectively. The groundwater irrigation suitability assessment results showed that 21.4% of samples were doubtful to unsuitable for irrigation, and 85.7% owed magnesium hazards. The findings of this study will assist policymakers in formulating proper remedial policies and mitigation strategies to ensure the safety of drinking and irrigation water.

Genesis of the Devonian Habaqin ultramafic arc complex and associated low-grade Fe–Ti oxide mineralization in the northern North China Craton

In the northern North China Craton (NCC), abundant non-layered ultramafic complexes and associated low-grade Fe–Ti oxide ores (over 1000 million tons) were uncovered. However, their petrogenesis and metallogeny have remained unclear. The Habaqin complex is one of the larger intrusions of the region and hosts the largest low-grade magnetite occurrence. Here we present petrography, zircon U–Pb geochronology, mineral and whole-rock major and trace element compositions, and whole-rock Sr–Nd and zircon Lu–Hf isotopes of the complex to constrain its genesis. The complex includes early pyroxenite (∼75% clinopyroxene, ∼15% amphibole, ∼10% magnetite) and late hornblendite (∼80% amphibole, 15–20% magnetite, 0–5% apatite). Zircon grains from the hornblendite yielded a weighted mean 206Pb/238U age of 395 ± 2 Ma. The increasing whole-rock FeOtot and TiO2 contents from pyroxenite (FeOtot = 18.9 wt%, TiO2 = 1.31 wt%) to hornblendite (FeOtot = 19.1–30.4 wt%, TiO2 = 2.63–3.12 wt%) correlate with higher modal proportions of amphibole and magnetite. The pyroxenite and hornblendite display similar arc-like trace element characteristics of enrichment in LILEs and LREEs, and depletion in HFSEs. The complex formed by fractional crystallization of clinopyroxene, amphibole, magnetite, and apatite from a hydrous parent magma. Early removal of clinopyroxene caused H2O enrichment in evolved residual magmas and crystallization of magnetite and amphibole, forming low-grade mineralization with Ti-V-poor magnetite in hornblendite. The complex displays high initial 87Sr/86Sr ratios of 0.706413–0.707341, negative εNd(t) values of −16.0 to −14.2 and negative εHf(t) value of −30.6 to −12.0, suggesting a parent magma derived from an enriched lithospheric mantle, with possible existence of amphibole-bearing pyroxenite veins within the source. During the Early Devonian, the retreat of the subducted Paleo-Asian oceanic slab as well as arc-continental collision along the northern NCC induced partial melting of the veins and eventually formation of the complex.

Identification of variable contributions to arc rocks by Li[sbnd]Mo and Sr–Nd–Hf–O isotope compositions: A study of the Mafan mafic rocks in the Hong'an orogen, Central China

The geochemistry of arc rocks provides a window to probe compositional variability in mantle wedge and slab-derived inputs. However, quantitative estimation of their contribution is a great challenge. Here we report an integrated study for determination of variable contributions to early Paleozoic arc plutons (the Mafan diorites and gabbros), from the northern Hong'an orogen, central China. Zircon grains from the diorites yielded crystallization age of 445 ± 3 Ma, whereas the gabbros have zircon UPb age of 432 ± 3 Ma. Although both the two mafic rocks suites exhibit typical arc-like trace element distribution patterns, they show a series of differences in stable Li–Mo–O and radiogenic Sr–Nd–Hf isotope compositions, as well as major and trace element features. Geochemically, the diorites are medium-K calc-alkaline series with high and positive whole-rock εNd(t) (+3.8 to +4.5) and zircon εHf(t) values (+12.4 to +14.3), and normal mantle-like zircon δ18O values (5.1 ± 0.2 ‰). Contrarily, the gabbros are tholeiitic and have relatively low whole-rock εNd(t) (+ 2.3 to +3.1) and zircon εHf(t) (+5.0 to +8.5) values with normal mantle-like zircon δ18O values (5.4 ± 0.3 ‰). The diorites have δ98Mo values of −0.15 to −0.03 ‰, while the gabbros have δ98Mo values of −0.28 to −0.12 ‰. These values are slightly higher than those of the mid-ocean ridge basalts (MORB) (−0.20 ± 0.01 ‰). Whereas, δ7Li values of the studied diorites (2.15–4.49 ‰) and gabbros (2.89–5.33 ‰) are mostly consistent within the range of MORB. In combination with the above results, the primary magma of diorites was inferred to be derived from 1 to 5% partial melting of depleted lithospheric mantle metasomatized by slab-derived fluid with minor sediment-derived melts. While the gabbros were suggested to be generated by 5–10% partial melting of more depleted lithospheric mantle that had undergone perhaps extra 0.3% melt extraction, which had further been metasomatized by more subducted materials. In summary, both the slab-derived components and nature of the mantle wedge sources are quantitatively constrained for the mafic rocks in the Mafan plutons. Our new data suggest that the Mafan plutons exhibited the Mariana arc-affinity and represented products of an intra-oceanic subduction system in the northern Hong'an orogen. Combined with previously published data for the early Paleozoic mafic magmatic rocks along the Qinling-Tongbai-Hong'an orogenic belt, there exists an oceanic arc in the east (Hong'an orogen) and an Andean-type continental arc in the west (Qinling-Tongbai orogen).

Improving the characterization of red coloring matter from prehistoric cave art by means of laboratory confocal XRF depth profiling combined with synchrotron XRF imaging

Chemical in situ study of red coloring matter in cave art is challenging because characteristic trace elements can be present both in the matter and in the wall support, and the latter has a quite heterogeneous composition.In this study, a stalactite presenting red iron oxide coloring matter from La Garma cave, Northern Spain, has been analyzed with complementary techniques. The aims are, on the one hand, confirming for the first time the feasibility of confocal XRF (CXRF) depth-resolved scans to successfully separate the complex stratigraphy of red prehistoric coloring matter on a calcitic support. On the other hand, finding differentiation criteria and improving the characterization of this red iron-based coloring matter would help understand and virtually separate it from its support, as well as improve future in situ analyses in cave sites.CXRF depth-resolved scans were performed using the LouX3D device available in our laboratory. With this technique, we can precisely determine the chemical depth composition of an object, layer by layer, with a spatial resolution in the micrometer scale. These measurements were combined with a synchrotron induced micro-X-ray fluorescence (SR-µXRF) chemical mapping performed at the PUMA beamline, SOLEIL synchrotron. These highly sensitive measurements not available with any other non-destructive lab-based technique allow seeing a greater number of trace and minor elements associated with Fe. Complementing them with the direct depth-resolved information given by CXRF, it was possible to find differentiation criteria distinguishing the wall support and the coloring matter, finely characterize this red iron-based matter, and confirm the feasibility as well as the advantages of applying CXRF for the non-invasive technical study of prehistoric cave figures.

Geochemical Evidence of Plume Sources for High-MgO Lavas in the Western Kunlun Orogenic Belt

Abstract Plume-derived high-MgO lavas provide important information on the lithological, thermal and chemical variations of Earth’s deep mantle. Here we present results from detailed field, mineralogical and geochemical studies of Late Permian–Late Triassic high-MgO lavas near the Chalukou area in the Western Kunlun (WK) orogenic belt, NW China. The major element compositions of the lavas show extremely high MgO contents (26.6–33.8 wt %) in accordance with olivine accumulation. The parental magma is inferred to be picritic in composition with MgO of 17.2 ± 0.9 wt %. Olivine Zn/Fe and Mn/Zn ratios suggest a peridotite-dominated source with a minor fraction of pyroxenite. The temperature and oxygen fugacity estimates based on multi-methods including olivine-melt Mg–Fe equilibria, Al-in-olivine and olivine–spinel thermometry and oxybarometer yield a mantle potential temperature of 1522–1556 °C and high oxygen fugacity of FMQ (fayalite-magnetite-quartz) + 0.93. The H2O contents in the picrite flows are estimated as 3.67 ± 1.0 wt %, indicating the volatile-rich nature of parental magma and its mantle source. The immobile trace element features show that the WK picrites are OIB (oceanic island basalt)-like, with the enrichment in light rare earth elements and positive Nb, Ta, Zr and Hf anomalies. Furthermore, the Nd–O–Os isotopes display typical mantle values without involvement of recycled materials. Our results suggest the high-MgO volcanism in the WK orogenic belt originated from a volatile-rich plume source.

Trace Element and Sulfur Isotope Signatures of Volcanogenic Massive Sulfide (VMS) Mineralization: A Case Study from the Sunnhordland Area in SW Norway

The Sunnhordland area in SW Norway hosts more than 100 known mineral occurrences, mostly of volcanogenic massive sulfide (VMS) and orogeny Au types. The VMS mineralization is hosted by plutonic, volcanic and sedimentary lithologies of the Lower Ordovician ophiolitic complexes. This study presents new trace element and δ34S data from VMS deposits hosted by gabbro and basalt of the Lykling Ophiolite Complex and organic-rich sediments of the Langevåg Group. The Alsvågen gabbro-hosted VMS mineralization exhibits a significant Cu content (1.2 to >10 wt.%), with chalcopyrite and cubanite being the main Cu-bearing minerals. The enrichment of pyrite in Co, Se, and Te and the high Se/As and Se/Tl ratios indicate elevated formation temperatures, while the high Se/S ratio indicates a contribution of magmatic volatiles. The δ34S values of the sulfide phases also support a substantial influx of magmatic sulfur. Chalcopyrite from the Alsvågen VMS mineralization shows significant enrichment in Se, Ag, Zn, Cd and In, while pyrrhotite concentrates Ni and Co. The Lindøya basalt-hosted VMS mineralization consists mainly of pyrite and pyrrhotite. Pyrite is enriched in As, Mn, Pb, Sb, V, and Tl. The δ34S values of sulfides and the Se/S ratio in pyrite suggest that sulfur was predominantly sourced from the host basalt. The Litlabø sediment-hosted VMS mineralization is also dominated by pyrite and pyrrhotite. Pyrite is enriched in As, Mn, Pb, Sb, V and Tl. The δ34S values, which range from −19.7 to −15.7 ‰ VCDT, point to the bacterial reduction of marine sulfate as the main source of sulfur. Trace element characteristics of pyrite, especially the Tl, Sb, Se, As, Co and Ni concentrations, together with their mutual ratios, provide a solid basis for distinguishing gabbro-hosted VMS mineralization from basalt- and sediment-hosted types of VMS mineralization in the study area. The distinctive trace element features of pyrite, in conjunction with its sulfur isotope signature, have been identified as a robust tool for the discrimination of gabbro-, basalt- and sediment-hosted VMS mineralization.

Petrogenesis of the eudialyte-bearing syenite and indication for Nb-Zr-REE mineralization in Bashisuogong, Northwest China

The Bashisuogong alkaline igneous intrusion is located between the South Tianshan Orogenic Belt and the Kepingtage foreland thrust belt at the northern margin of the Tarim Craton and hosts economically significant Nb–Ta–Zr–rare earth element mineralization. Eudialyte has recently been discovered in the syenite unit of this intrusion, which is the primary host mineral for high-field-strength and rare earth elements. Based on detailed petrographic investigations, this study investigated the behavior of trace elements during magma evolution and the enrichment of ore-forming elements using whole-rock geochemical analyses of eudialyte-bearing syenite and compositional analyses of aegirine–augite and different types of eudialyte. We also undertook in situ titanite U-Pb dating. The Bashisuogong syenite comprises aegirine–augite and aegirine–augite–eudialyte syenite, the latter of which have higher total rare earth element contents. Both types of syenite exhibit slight enrichments in light rare earth elements, significant enrichments in high-field-strength elements (Nb, Ta, Zr, Hf, and Th), depletions in large-ion lithophile elements (Ba and Sr), and large negative Eu anomalies. There are two types (I and II) of eudialyte. Eudialyte I has higher Mn/Fe, Zr/Hf, and Nb/Ta ratios but lower Th/U ratios compared with eudialyte II but similar Y/Ho ratios. Eudialyte II crystallized earlier than eudialyte I, and aegirine–augite, titanite, and apatite crystallized earlier than eudialyte I. Both aegirine–augite and eudialyte have similar trace element characteristics to the host rocks, exhibiting enrichments in highly incompatible high-field-strength and rare earth elements, as well as marked negative Eu anomalies and depletions in Sr. These characteristics suggest that the Bashisuogong alkaline rocks formed by low-degree partial melting of geochemically enriched, metasomatized lithospheric mantle, which formed an alkaline basaltic parental melt that then underwent protracted magma evolution and fractionation in the shallow crust. The eudialyte syenite yield a titanite U-Pb age of 277.3 ± 1.2 Ma, which is consistent with the ages of different types of alkaline igneous rocks in the study area, indicating they were the products of the same magmatic event. Temporally and spatially, the Bashisuogong ore-bearing alkaline rocks were associated with the Tarim mantle plume, and the mantle plume provided the heat for their formation.

Syn- and post-collisional mafic igneous rocks from the East Kunlun Orogenic Belt: Implications for recycling of subducting continental crust during the Silurian-Devonian

Syn- to post-collisional mafic igneous rocks are widely distributed along continental collision orogenic belts and can be used to constrain the nature of the orogenic mantle and relevant chemical geodynamic processes during orogenesis. However, there is uncertainty about the mechanisms of recycling of continental crustal materials in continental subduction channels. We report chronological and geochemical data for syn- and post-collisional mafic dikes from the East Kunlun Orogenic Belt (EKOB), western China, which provide insights into the processes of geochemical transfer and geodynamic evolution of this fossil orogen. Zircon UPb dating of the mafic dikes yields ages of 433 Ma and 409–407 Ma, corresponding to syn- and post-collisional magmatism, respectively. The rocks exhibit typical arc-like trace-element characteristics and weakly enriched Sr–Nd–Hf isotopic compositions, as well as variable zircon O isotopic compositions. These geochemical characteristics are comparable to those of Neoproterozoic paragneiss influenced by Early Paleozoic metamorphism associated with high–ultrahigh-pressure eclogitization in the EKOB and indicate that paragneiss-derived hydrous melts were likely involved in the mantle source of the studied mafic igneous rocks during continental collision. This qualitative interpretation is supported by quantitative modeling of the geochemical transfer in the continental subduction zone. We propose that the syn-collisional mafic igneous rocks were formed during the continental collision between Central Kunlun and South Kunlun Belts, whereas the post-collisional mafic igneous rocks formed in an extensional regime associated with orogenic lithosphere thinning and asthenospheric upwelling.

Study on the distribution, enrichment and migration characteristics of trace elements in particulate matter during solid waste combustion

Trace element emissions caused by the entrainment of particulate matter (PM) has led to serious environmental pollution. This research focuses on the distribution, enrichment and migration characteristics of trace elements in different sizes of PM during the typical solid waste combustion. The results indicate that the mass concentration of trace elements in different PM is closely related to their volatility. Volatile trace elements such as Cu, In, Ag, Pb, and Cd tend to distribute in PM1. Higher temperatures facilitate the volatilization of trace elements, promoting their migration and enrichment in finer PM. The removal effect of Si–Al-based additives on trace elements in PM1 decreases with the increase of Si/Al ratio. Among them, the removal efficiency of 5% kaolin is the best. After the addition of Si–Al-additives, Zn and In mainly migrate to PM1-10, while Cu, V, Mo, As, Se, Cr, Ba, Mn, Co, Sr, and Ti mainly migrate to PM10+. Ag, Pb, and Cd migrate to both PM1-10 and PM10+ simultaneously.

Geochemical Characteristics of Trace Elements and Mineralization Model of the Ediacaran-Early Cambrian Phosphorites, South China.

As a nonrenewable resource, phosphate rock is an important support for the development and survival of the national economy. The regional distribution and output of phosphate rock in China are extremely uneven, and the amount of high-quality ore resources is relatively poor, which seriously restricts the development and utilization of phosphate rock resources in China. This paper briefly summarizes the distribution characteristics of phosphate rock resources and summarizes the characteristics and research progress of Ediacaran-early Cambrian phosphorus mineralization types, geological characteristics, and deposit genesis of the Yangtze platform in South China. The Ediacaran-early Cambrian sedimentary phosphorite deposits in China are mainly distributed in Yunnan, Guizhou, Hubei, Sichuan and Hunan provinces of the Yangtze platform, in which the early Cambrian phosphate deposits are also rich in rare earth elements, associated with uranium, nickel, molybdenum, vanadium, and other beneficial metal elements. The increase of atmospheric oxygen content at the Ediacaran-Cambrian boundary may have promoted the extensive oxygenation of the late Neoproterozoic oceans, so the Ediacaran-early Cambrian oceans generally showed a reductive environment, and there may be dynamic chemical stratification of the oxidation zone-sulfide zone-iron zone. Up to the early Cambrian, the redox stratified structure of Precambrian seawater may still be inherited, showing that the surface water is an oxidizing environment, changing to a reduction environment, and even wedge-shaped sulfide water is developed at the bottom of the deep basin. The main phosphorus sources are deep phosphorus-rich seawater, continental weathering, and deep hydrothermal activity of Ediacaran-early Cambrian marine sedimentary phosphorite deposits in South China. The genetic mechanisms of phosphorite deposits in the Yangtze platform in South China are mainly biogenic, upwelling phosphorus-forming theory, mechanical mineralization, and syn-sedimentary hot water mixed genesis. In the future, it is still necessary to further explore the internal relationship between phosphorus deposits and major geological events, the in situ analysis of microstructure of phosphate rock ores, and the genetic mechanism of phosphate deposits and the reconstruction of paleo-marine environment.

In-situ analysis of sphalerite trace elements and sulfur isotope of the Zhaxikang Pb-Zn-Sb-Ag deposit in southern Tibet: Implications for source and mineralization process

The metallogenesis of collisional orogen has been a significant research topic for comprehending the linkage between magmatism, metamorphism, hydrothermalism and ore deposition. In Southern Tibet, the Zhaxikang deposit is a super-large Pb-Zn-Sb-Ag polymetallic deposit with metal reserves of 2.367 Mt Zn + Pb (average grade of 6.43 %), 0.2552 Mt Sb (average grade of 1.14 %), and 2960.6 t Ag (average grade of 101.64 g/t), constituting the largest deposit within North Himalayan Metallogenic Belt. However, the metal sources of the ore-forming material and mineralization process in this deposit remain a subject of controversy due to previous studies primarily relying on a bulk analysis of sulfides, which record the mixed results of multistage mineralization and intergrown minerals of different stages. The objective of this study is to constrain the sources and mineralization process of the Zhaxikang deposit through in-situ analyses of trace elements and sulfur isotopes in sphalerite. Based on ore textures and mineral paragenesis, four mineralization stages and three generations of sphalerite deposited respectively in stage 1 (Sp1), stage 2 (Sp2), and stage 4 (Sp3), were identified. The Pb and Zn mineralization mainly occurred in stage 2, while Sb and Ag were dominantly in stage 4. The trace elements characteristics (Cd, Fe, In, Ga, Ag, Cu, Co, and Mn) observed in sphalerite indicate that the Zhaxikang deposit could be a hydrothermal vein-type deposit associated with magmatism. The δ34S values of sulfides (7.7–18.4 ‰) in the deposit generally exhibit a slight elevation compared to those (4.1–12.9 ‰) of the Jurassic Ridang Formation slate, indicating that the sulfur of the deposit primarily originated from seawater sulfate in the slate through thermochemical sulfate reduction, although a small amount of contribution from mafic rocks also existed in stage 4. The Pb isotopes in stage 2 range from 19.662 to 19.705, 15.852 to 15.865, and 40.214 to 40.283 for the ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb, respectively, indicating that the metals primarily from the Greater Himalayan Crystalline complex (GHC) with a minor contribution from host rocks. While, the Pb isotopes in stage 4 range from 19.687 to 19.849 for 206Pb/204Pb, from 15.86022 to 15.885 for 207Pb/204Pb, and from 40.261 to 40.414 for 208Pb/204Pb, respectively, indicating that the metals originated from sulfides in the earlier stage as well as the more radiogenic GHC.

Geochemical Characteristics of Trace Elements of Hot Springs in the Xianshuihe–Xiaojiang Fault Zone

Trace elements in hot-spring waters are indicators for tracing hydrochemical processes, such as the deep circulation of geothermal water, the degree of water–rock interaction, redox reactions, the contamination of shallow water by thermal water, etc. In this study, 74 hot springs in the Xianshuihe–Xiaojiang Fault Zone (XSHF-XJF) were chosen for an investigation of the geochemical characteristics of trace elements using classic geochemical tools and multivariate statistical analysis. The results indicated (1) the hot-spring waters were mainly derived from atmospheric precipitation as indicated by δD and δ18O values that generally increased with decreasing elevations; (2) the high concentrations of B, As, Fe, and Mn in the waters, as well as the values of the Water Quality Index (WQI), indicated that the water quality was spatially heterogeneous and the hot-spring waters are not entirely suitable for drinking; and (3) B/Cl ratios showed that hot springs have different reservoir sources in the XSHF and XJF, respectively. The leaching of surrounding rock during water circulation contributed predominantly to the trace elements of the study’s waters. Diversity of lithology was the main factor affecting their concentrations. In addition, deep circulation controlled by the fault could influence trace-element enrichment. Our results offer a guide for the exploration and use of geothermal resources.

The Geochemical Characteristics of Trace Elements in the Magnetite and Fe Isotope Geochemistry of the Makeng Iron Deposit in Southwest Fujian and Their Significance in Ore Genesis

The Makeng iron deposit in southwest Fujian is a significant iron polymetallic deposit containing various types of iron ore, including garnet magnetite, diopside magnetite, and quartz magnetite. The metallogenetic type of the deposit has been a subject of debate, particularly in relation to the genesis of magnetite and the source of iron. In situ microanalysis of trace elements in magnetite from different ores shows relatively low levels of V, Ti, Cu, and Zn, with higher concentrations of Ca and Si, indicating the characteristics of a skarn type deposit. The δ57Fe values of the magnetite range from −0.091‰ to 0.317‰. Combining these data, whole-rock iron isotope analyses, including Juzhou and Dayang granites, diabase, and the Lower Carboniferous Lindi Formation sandstone, suggest that Fe in the magnetite primarily originates from granitic pluton, with potential contributions from diabase and the Lower Carboniferous Lindi Formation sandstone. Combined with field work, these results indicate that Makeng iron deposit is a skarn-type magnetite deposit associated with Yanshanian granitic intrusions. Therefore, the initial ore-forming fluid is postulated to be a high-temperature magmatic hydrothermal fluid with high oxygen fugacity. This fluid infiltrates spaces such as interlayer fracture zones between the Upper Carboniferous Jingshe Formation–Middle Permian Qixia Formation carbonate rocks and the Lower Carboniferous Lindi Formation sandstone, resulting in diverse magnetite ores due to metasomatism. The mineralization process of the Makeng iron deposit is basically the same, as it is composed of typical skarn deposits. Magnetite was mainly formed during calcic skarn formation stage, and this process persisted until the initial phase of the retrograde alteration of skarns. In contrast, sulfide minerals, including molybdenite, sphalerite, and galena, precipitated during the quartz–sulfide stage.

Contribution of carbonatite and recycled oceanic crust to petit-spot lavas on the western Pacific Plate

Abstract. Petit-spot volcanoes, occurring due to plate flexure, have been reported globally. As the petit-spot melts ascend from the asthenosphere, they provide crucial information of the lithosphere–asthenosphere boundary. Herein, we examined the lava outcrops of six monogenetic volcanoes formed by petit-spot volcanism in the western Pacific. We then analyzed the 40Ar/39Ar ages, major and trace element compositions, and Sr, Nd, and Pb isotopic ratios of the petit-spot basalts. The 40Ar/39Ar ages of two monogenetic volcanoes were ca. 2.6 Ma (million years ago) and ca. 0 Ma. The isotopic compositions of the western Pacific petit-spot basalts suggest geochemically similar melting sources. They were likely derived from a mixture of high-μ (HIMU) mantle-like and enriched mantle (EM)-1-like components related to carbonatitic/carbonated materials and recycled crustal components. The characteristic trace element composition (i.e., Zr, Hf, and Ti depletions) of the western Pacific petit-spot magmas could be explained by the partial melting of ∼ 5 % crust bearing garnet lherzolite, with 10 % carbonatite flux to a given mass of the source, as implied by a mass-balance-based melting model. This result confirms the involvement of carbonatite melt and recycled crust in the source of petit-spot melts. It provides insights into the genesis of tectonic-induced volcanoes, including the Hawaiian North Arch and Samoan petit-spot-like rejuvenated volcanoes that have a similar trace element composition to petit-spot basalts.

Transformation and environmental chemical characteristics of hazardous trace elements in an 800 t/d waste incineration thermal power plant

The hazardous trace elements (HTEs) emitted during the municipal solid waste incineration (MSWI) process have been widely concerned. In this work, the bottom ash (BA), heat recovery boiler ash (HA), and ash after desulfurization (SA) were collected to explore the occurrence forms of HTEs in the three types of ash and their relationship with minerals and leaching characteristics. The results show that the volatility of the seven studied HTEs follows the order of Cd, As > Ni, Zn > Pb > Cr, Cu. In the process of BA → HA → SA, the content of Cd, As, Zn, and Pb shows an increasing trend. The seven HTEs are mainly in the forms of chlorides and oxides. There is an obvious relationship between the occurrence forms and simulated existence form of HTEs. SiO2 and CaCO3 are the major mineral components in the three ashes, while SA also contains chlorine-containing compounds which are easily leached out. The risk assessment code and soluble ratio show that HTEs in SA are more leachable than BA and HA, where Cd, Pb and Ni need to be addressed to reduce their impact on soil or water during subsequent landfill treatment of SA.

Trace element geochemistry of sediments in the Pearl River Estuary and its implication for provenance

The Pearl River system is China’s third longest river and the Pearl River Estuary is a major estuary in China. In the paper, a sediment core collected from the coastal zone in the Pearl River Estuary was analyzed for trace element concentrations and grain size to identify provenance during the past decades. In addition, the tectonic framework of the study area has also been studied using reliable geochemical tracers, including rare earth elements (REEs) and trace elements. The results reveal a significant contribution of reworked sediment from multiple sources. Discrimination diagrams suggest that the sediments display felsic characteristics with recycled components, and therefore, the source rock types of the sediments are presumed to be granitic rocks. The REE patterns observed in the samples primarily reflect the influence of an ancient continental crust that contains felsic materials on the sediments with an LREE/HREE ratio of 7.94–9.56 (mean 8.46) and a δ Eu value of 0.61–0.70 (mean 0.65). The sediments are plotted into a zone of continental island arcs, which was formed during the late Mesozoic subduction of the ancient Pacific. The study on the source of sediment cores shows that the main source of sediments in this area excludes the possibility of the upper middle river from the Pearl River Watered, which reflects the importance of the lower Pearl River Basin, especially the Dongjiang River, for material transport in the study area. Our results demonstrate that the geochemical characteristics of trace elements in sediment could provide an efficient approach to identify sediment provenance in estuaries worldwide.

Late Palaeozoic tectonic transformation of the North Qinling Orogenic Belt: Insight from the geochronology, geochemistry and Sr‐Nd‐Hf isotopes of Carboniferous magmatic rocks

The North Qinling Orogenic Belt (NQB) records the pivotal geological information for understanding the Palaeozoic evolution of the Qinling Orogenic Belt (QOB). Previous studies mainly focused on the subduction–collision process along the Shangdan suture zone before the Early Devonian. However, as the significant interim period between the Early Palaeozoic and Mesozoic orogeny, the Late Palaeozoic tectonic evolution of the NQB remains poorly understood. Fortunately, the Carboniferous magmatic rocks discovered this time provide substantial geological evidence for revealing the Late Palaeozoic tectonic history of the Qinling Orogenic Belt. This paper will provide a detailed analysis of zircon U–Pb ages, geochemical characteristics and Sr‐Nd‐Hf isotopic compositions of Carboniferous rocks. The Carboniferous magmatic rocks are categorized as highly differentiated S‐type granite and monzodiorite, formed at 350 ± 2.4 Ma and 353 ± 5.2 Ma, respectively. The granite shows weak peraluminous (A/CNK = 1.02–1.11) and shoshonite nature. Based on the isotopic composition and trace element characteristics, we propose that the Qinling Group paragneiss is the primary source of the Carboniferous granite. Monzodiorite is characterized by enriched LREEs and LILEs (Ba, K and Pb), depleted HFSEs (Th, Nb, Ta and Ti) and enriched Sr‐Nd isotopic composition. Monzodiorite magma source region consists of continental crustal material and lithospheric metasomatized mantle. Carboniferous magmatic rocks are the product of an extensional tectonic setting, which indicates the NQB tectonic regimes transition from compression to extension during the Carboniferous.