Trace Element Variations Research Articles

Trace elements mineral chemistry of sulfides from the Woxi Au‐Sb‐W deposit, southern China

AbstractThe Woxi Au‐Sb‐W deposit is one of the largest polymetallic ore deposits in the Xuefengshan Range, southern China, hosted in low‐grade metamorphosed Neoproterozoic volcaniclastic rocks. The orebodies of the deposit are predominantly composed of banded quartz veins, which are strictly controlled by bedding and faults. Petrographic observations and geochemical results are reported on the occurrence of Au and properties of the ore‐forming processes for different stages in the deposit. The veins extend vertically up to 2 km without obvious vertical metal zoning. The ore‐forming process can be subdivided into four mineralization stages: Pre‐ore stage; Early stage (scheelite‐quartz stage); Middle stage (pyrite‐stibnite‐quartz stage); and Late stage (stibnite‐quartz sage). Four types of pyrite (Py0, Py1, Py2, and Py3) were identified in the ores and host‐rock: Py0 occurs as euhedral grains with voids in the core, ranging in size from 50 to 100 μm and formed mainly in the Pre‐ore stage and Early stage; Py1 occurs as subhedral grains. Small grains (around 10 μm) of Py1 form irregularly shaped clusters of variable size ranging from tens to hundreds of μm and mainly formed in the Middle stage; Euhedral‐subhedral fine‐grained Py2 formed in the Late stage; Minor subhedral fine‐grained Py3 was deposited in the Late‐stage. Stibnite is widely distributed in the Middle and Late stage ore veins. No systemic difference was recognized in mineralogical features among stibnite formed in different stages. In addition to native gold, the lattice bound Au+1 widely exists in Py1 and Py2 in the deposit, and widespread Py1 is considered as the main Au‐bearing mineral with the highest Au contents. Most elements (such as Co, Ni, Cu, As, Sb, Ba, and Pb) are considered to occur as solid solution within the crystal lattice and/or invisible nanoparticles in sulfides minerals. The Co/Ni ratio of most pyrite is lower than 1, suggesting that the metals in the ore‐forming fluid are sourced from sedimentary rocks. The coupled behavior between Au and As; Au and Sb suggests that the substitution of As and Sb in pyrite can enhance the incorporation of Au. Variation of trace elements in pyrites of different stages suggests some information on the mineralization processes: Large ion lithophile elements (such as Ba and Pb) are enriched in Py0 indicating that water‐rock reaction occurred in the Early stage; Fine‐grained Py1 with a heterogeneous distribution of elements suggests fast crystallization of pyrite in the Middle stage.

Geochemical evolution of the Paradise Mountain Caldera complex, Davis Mountains: Implications for the tectonic and magmatic evolution of Trans-Pecos Texas and adjacent Mexico

The Paradise Mountain Caldera (~20 × 14 km), located west of Fort Davis, Texas, produced two major ignimbrite/lava complexes at ~36.2 and 35.9 Ma. The older unit (Fort Davis Tuff) is composed of rheomorphic tuff and overlying chemically similar lava. The younger unit (Wild Cherry Tuff) forms thick intracaldera deposits and an outflow sheet that spread over an estimated 2000 km2. Near the caldera, the two ignimbrites are separated by trachytic lava of the Mount Locke Formation. The 5-km diameter Point of Rocks intrusion, which crops out within the eastern margin of the caldera, may have fed the Mount Locke flows. Wild Cherry Tuff is overlain by silicic lava (Casket Mountain Formation, ~35.8 Ma), with which is shares chemical similarities. Intracaldera Wild Cherry Tuff was intruded by silicic intrusions and locally intensively silicified and kaolinized. In a revision of stratigraphic nomenclature, we assign all of the above volcanic units to a Barrel Springs Group.Collectively, the above units form a series ranging from trachyte to alkali rhyolite. Glomeroporphyritic trachyte of Mount Locke lavas represents silicic melt incompletely segregated from more mafic material within a source magma chamber. Variation between Mount Locke Formation trachyte and Fort Davis Tuff rhyolite can be modelled by fractionation of a mineral assemblage of plagioclase, clinopyroxene, FeTi oxides, and apatite; variation within the two major tuff units can be modelled almost exclusively by alkali feldspar. Central eruption within the caldera produced intracaldera tuff more evolved than most of its outflow. Alkali rhyolite of the Wild Cherry Tuff and Casket Mountain lavas, although similar in major element chemistry and mineralogy, show wide variation in incompatible trace elements, suggesting that evolution of silicic magmas in terms of major element chemistry had reached an impasse due to fractionation of a mineral assemblage whose bulk composition was similar to that of parental rhyolite.Paradise Mountain units represent a transition from alkalic magmatism in northeastern Trans-Pecos Texas to metaluminous to peraluminous magmatism in southwestern Trans-Pecos Texas and adjacent Mexico. Over a span of 10 Ma, silicic magmatism terminated southwestward over this region at a rate of about 24 km/Ma. This termination may reflect continued foundering of a sinking Farallon slab and associated asthenospheric mantle upwelling. Mafic magma derived by melting of lithospheric mantle formed plutons that, through filter pressing of silicic magma from crystalline mush, generated silicic melts. The transition across the Trans Pecos region from alkalic to metaluminous magmatism may have resulted through preferential modification of lithospheric mantle along the easternmost extent of Laramide subduction.

Quartz chemistry of granitic pegmatites: Implications for classification, genesis and exploration

Quartz from 254 pegmatites representing eight pegmatite fields and provinces worldwide was investigated by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) to determine concentrations of trace elements Al, Ti, Li, Ge, B, Be, Rb, Na, K, Ca, P, Ga, Sb, Zn and U. A total of 271 new analyses combined with 535 published LA-ICP-MS quartz chemistry data were evaluated with binary and ternary trace element discrimination plots and principal component analysis (PCA). The classifications applied for discrimination of pegmatite types include the widely applied NYF(Nb-Y-F) - LCT(Li-Cs-Ta) classification and the new RMG (pegmatites derived from residual melts of granite magmatism) - DPA (pegmatites as direct products of anatexis) grouping. Pegmatites of both classifications can be well distinguished via Al-Ti, Al-Li and Al/Ti-Ge/Ti binary trace element plots and the Ti - Al/10 - 10*Ge ternary diagram. PCA applied to Al, Li, Ti, Be, B, Ge and Rb contents in quartz allowed to further distinguish between anatectic DPA-1 (Li-enriched DPA) and granite-pluton-derived RMG-1 (Li-enriched RMG) pegmatites. Some pegmatite fields and provinces (Hagendorf-Pleystein, Oxford County) are distinguishable by region-specific Li, Ge and Al contents. The results imply that the chemistry of pegmatite quartz is mainly controlled by the origin (source rock chemistry) of pegmatite melts and, to a much lesser extent, by the geodynamic setting of the pegmatite fields and provinces. Chemically primitive NYF and DPA-2 type pegmatites contain quartz with the lowest total trace-element contents and lowest internal-pegmatite trace-element variation, making it potentially suitable for high-tech application. Pegmatite quartz containing >30 μgg-1 Li and >100 μgg-1 Al is strongly indicative of economic spodumene/montebrasite mineralization and, thus, serves as a strong Li-mineralization pathfinder mineral. Quartz with >5 μgg-1 B may be a potential indicator for gem-quality tourmaline mineralization.

Sn-Ta-Nb mineralization potential of pegmatitic bodies in Bunu area, part of Kabba-Lokoja-Igarra Schist Belt, SW Nigeria

The Bunu area in Southwestern Nigeria lies within the Basement Complex that forms part of the Pan-African platform of the crystalline rocks. The complex lies within the vast Trans-Saharan Pan African mobile of Neoproterozoic. The belt is characterized by voluminous post-collision granitoid plutons that are well exposed around the study area. The Bunu area consist of two major lithologic suites namely: (i) the gneiss-schist suite which comprised of Migmatized-gniess/ Migmatized Schist and quartz/mica schist with interbedded amphibolites (ii) intrusive suite that include fine-medium grained granite, medium-coarsed grained granodiorite and porphyritic granite and the minor intrusions like pegmatite, aplite, dolerite and quartz veins. Pegmatite outcrops in the Bunu area of the Kabba-Lokoja-Igarra Schist belt belong to the rare-element type and are mined for columbite-tantalite and gem tourmaline. Pegmatitic textures are well developed, these include large K-feldspar (comb textures), layering and graphic intergrowth of K-feldspar + albite + quartz + schorl and linearly arranged garnet crystals that may be developed at deeper levels of the dyke. Ductile and brittle structural features mapped in the area from remotely sensed and field data are generally consistent with the N-S and NE-SW regional orientation associated with Pan-African event and with minor axes of NNW-SSE and E-W planar structures. Trace elements geochemistry of the pegmatite (bulk rock and mineral extracts of K-feldspars and Mica) revealed that Rb, Sr, Ba, Li and Cs are enhanced in the Otafun and Okutose pegmatites indicating higher fractionation levels. Also, the rare-metals Nb, Ta and Sn were also enriched in the most evolved Otafun and Okutose pegmatites. Trace-element variations in mica from the pegmatites indicate that they are per-aluminous LCT (lithium, cesium, and tantalum) family and bery-columbite subtype. The origin of the gradual composition variation trend observed from the host granite bodies to the pegmatites reflects the increasingly fractionated melt composition and systematic enrichment of the incompatible trace elements Li, Rb, Cs, Be, Na, Ta and Sn. The Zr-SiO2 and Sr-Rb plots of the pegmatite bulk rock samples suggest that they are genetically magmatic and poorly differentiated with little or no post-magmatic metasomatism. Ta vs Cs and Ta vs Ga plots for the chemistry of K-feldspar and muscovite mineral extracts from the pegmatites in Bunu area show potential for tantalum and niobium (>75 ppm) mineralization, thus implying that the mineralization in these pegmatites is probable, therefore investors should use caution.

Lithium distribution and isotopic composition in zircon megacrysts as constraints for their mantle origin and volcanic transfer timescales

Lithium in zircon has attracted considerable attention for identifying magma sources and as a diffusion chronometer, despite the exact diffusion mechanisms remaining controversial. Zircon megacrysts sourced from Quaternary intraplate basaltic volcanoes in the Ratanakiri Volcanic Province of northeastern Cambodia were analyzed here for Li isotopic and elemental concentration profiles to constrain diffusion behavior of Li in zircon megacrysts entrained in high temperature melts. This is complemented by high-spatial resolution U-Pb geochronology, O-Hf isotope compositions and trace element abundances to refine the long-term pre-eruptive history of these zircon megacrysts. Ratanakiri zircon megacrysts yield a Tera–Wasserburg regression U-Pb age of 0.98 ± 0.02 Ma (n = 615 spot analyses) that is indistinguishable from eruption ages reported for the host basalts, although zircon was unstable in the enclosing magma as evidenced by marginal corrosion and abundant tubular channels within the crystals. Extreme Li-isotopic variations (within −30 to +96‰ on the δ7LiLSVEC scale) of the zircon megacrysts require kinetic Li fractionation due to diffusive mobilization, which is further supported by offsets in intracrystalline domain boundaries with different Li and Y abundances detected in scanning ion images. Complex abundance and isotopic ratio patterns for Li in zircon megacrysts point to multi-mode Li diffusion that is influenced by variable trace element inventories within individual crystals, which correlate with minor differences in the O-Hf isotopic compositions. The overall tendency of decreasing Li abundances along with increasing δ7Li values toward crystal rims indicates diffusion-driven equilibration between zircon and Li-depleted basaltic melt. Diffusion modeling of Li and δ7Li on domain-boundaries within crystals show pre-eruptive heating timescales of about 18 days, which is consistent with the magma transfer duration estimated from zircon megacryst settling rate calculations, implying the zircon megacrysts should be transported from their source region to the surface by ascending alkali basaltic magma within few weeks. Nearly one to two orders of magnitude longer Li diffusion model timescales were computed for crystal rim domains. This apparent faster diffusion of Li is attributed to H+ loss into a volatile phase during eruption, providing an additional driving force for Li+ diffusion, which might become more pronounced at the crystal boundary where zircon is exposed to strong chemical gradients in volatile elements due to decompression and concomitant degassing. Lithium isotope compositions for the innermost domains of zircon megacrysts are relatively heavy with δ7Li values of +12 to +22‰. These values are considered to be less influenced by Li-loss after entrainment by the host basalts than rim compositions. These values in combination with O (δ18O = +3.5 to +5.3‰) and Hf (εHf(0.98 Ma) = +6.5 to +7.9) isotopic compositions as well as inclusions and internal structures suggest that zircon megacrysts were originally derived from partial melting of a metasomatized lithospheric mantle source altered by fluid released from dissolved carbonates during subduction. Lithium isotopes in Ratanakiri zircon megacrysts provide novel insights into using Li isotopes as a tool to constrain the durations of magma transfer from the mantle to the surface, although Li diffusion mechanisms in zircon need to be further scrutinized.

Major and Trace Element Compositions of Basaltic Lavas From Western Margin of Central Main Ethiopian Rift: Enriched Asthenosphere vs. Mantle Plume Contribution

Major and trace element data are presented for basaltic lavas from western rift margin of central main Ethiopian rift located at Kella area to investigate the processes involved in the petrogenesis of the erupted magmas and the nature of mantle source compositions. Kella area is composed of Quaternary (<1.6 Ma), Miocene (10.6-8.3 Ma) and Oligocene basalts (30-29 Ma) ranging from alkaline to tholeiitic in composition. The geochemical variations of basaltic samples from Kella area exhibit two compositionally distinct basaltic groups. The Oligocene tholeiitic basalts display low MgO (5.29-6.11 wt.%), TiO2 (2.15-2.47 wt.%), P2O5 (0.28-0.34 wt.%), and high ratio of CaO/Al2O3 (0.68-0.72) and La/Nb (0.89-1.10). Whereas Quaternary and Miocene alkaline basalts display high MgO (7.40-8.86 wt.%), TiO2 (2.4-2.53 wt.%), P2O5 (0.44-0.52 wt.%) and low ratio of CaO/Al2O (0.62-0.66) and La/Nb (0.71-0.76). The contrasting incompatible element ratios (e.g., K/Nb, La/Nb, Rb/Zr and Zr/Nb) between tholeiite and alkaline basalts reflect differences in their mantle sources. Major and trace element variations, therefore, reflect the involvement of two geochemically distinct mantle sources in the petrogenesis of Kella basaltic lavas: i) the Oligocene tholeiite basaltic melts derived from enriched asthenosphere mantle source (E-MORB) and ii) the Miocene and Quaternary alkali basaltic melts show close similarity with ocean island basalts (OIBs) geochemistry, and this end member ascribed to the arrival of Afar plume head. The geochemical modeling reveals that the Oligocene tholeiite basaltic melts produced by equilibrium melting with 3-5 % degree of partial melting in spinel lherzolite mantle source, whereas the alkali basalts are produced with ~2% degree of partial melting within spinel-garnet lherzolite transition zone mantle sources.

Quartz‐Hosted Melt Inclusions as Windows Into Magma Assembly and Storage Processes in the Youngest Toba Tuff

AbstractQuartz‐hosted melt inclusions are windows into the assembly and storage of compositionally zoned magmas systems like the giant magma body responsible for the 2,800 km3 Youngest Toba Tuff (YTT), Indonesia. Feldspar‐sensitive element concentrations and interelement ratios in YTT quartz‐hosted melt inclusions are found to cluster into three discrete melt inclusion populations. Each population represents a small fraction of the overall range in YTT melt compositions and no more than ∼12% to ∼21% fractional crystallization at mostly eutectoid conditions accounts for the trace elements variations within them. Kinships between host matrix glasses and co‐hosted phases are interpreted as evidence of spatially discrete chemical domains of magma within a more broadly zoned magma system. Quartz growth in the dominant portion of the system apparently occurred after extraction of melt from mush, whereas chemically distinct crystal cores in the more crystal‐rich, low‐silica magmas may have been derived from mush during extraction or remobilized by mush rejuvenation. Collectively, the chemical zoning of the YTT appears to have developed prior to most quartz growth, likely “bottom‐up” due to mush‐derived melt heterogeneity.

Paleoproterozoic ca. 2.2 Ga high-Cl metagabbro in the Belomorian province, Eastern Fennoscandian Shield: Origin and tectonic implications

Tectonic and fluid reworking of deep-seated mafic intrusions in the orogenic belts often erase primary magmatic characteristics, and crystallization parameters of mafic melts enriched in volatiles remain an issue. This study presents new U-Pb geochronological data for zircons, mineral composition, whole-rock geochemistry and Sr-Nd isotopic data for Pechnoy ca. 2.2 Ga mafic layered sill in the central Belomorian province, Eastern Fennoscandian Shield. The Pechnoy intrusion comprises low-alumina, silica-undersaturated, Cl enriched mafic rocks depleted in HREE and HFSE with εNd values of -0.1–+1.5 and (87Sr/86Sr)2200 = 0.7024–0.7039. Field and petrological studies indicate that studied rocks preserved relicts of primary magmatic characteristics because it was encapsulated in host gabbronorite intrusion and avoided intensive fluid reworking during 1.8-2.0 Ga Lapland-Kola orogeny. Variations of mineral composition, major, and trace elements within intrusion originated via in situ fractional crystallization with dominated settling of clinopyroxene and plagioclase. Chlorine distribution within intrusion and in the host rocks inferred a magmatic origin Cl enrichment. High-Na scapolite is the main concentrator of the Cl in the rocks. The inclusions of scapolite in the relict magmatic plagioclase and higher Ca content relative to adjacent Na-rich plagioclase likely indicate early crystallization of high-Na scapolite. Trace element and isotopic characteristics of rocks indicate OIB and subduction modified SCLM signatures of their primary melts. A comparison of the available data for Pechnoy sill and coeval mafic sills in the Karelian Craton reveals a common mantle source for ca. 2.2. Ga igneous rocks in the Fennoscandian Shield although intrusions in the Belomorian province represent deeper levels of 2.2 Ga large igneous province plumbing system.

A reactive transport approach to modeling cave seepage water chemistry II: Elemental signatures

Karst systems are useful for examining spatial and temporal variability in Critical Zone processes because they provide a window into the subsurface where waters have interacted with vegetation, soils, regolith, and bedrock across a range of length and timescales. These hydrologic pathways frequently include the precipitation of speleothems, which provide long-term archives of climate and environmental change. Trace element ratios in speleothems (Mg/Ca, Sr/Ca, Ba/Ca) have the potential to provide information about past changes in rainfall and infiltration, but controls on them can be complex and their interpretation must be based on an understanding of the modern cave system. Here we integrate observations of surface conditions, bedrock, soil, and drip water chemistry of Blue Spring Cave in Tennessee, USA with the reactive transport model CrunchTope, which we have calibrated for karst systems to investigate the primary controls on trace element variations in cave seepage waters. We find that measured drip water Mg/Ca and Sr/Ca are captured within the model through variable amounts of limestone dissolution followed by precipitation of secondary calcite that happens within the cave rather than the host limestone. However, strong spatial controls on drip water Mg/Ca and Sr/Ca likely reflect seepage water interactions with variable amounts of diagenetic phases in the host rock. In contrast, Ba/Ca values are consistent across the cave and vary with effective rainfall, suggesting that this parameter may be the most consistent metric for limestone dissolution and prior calcite precipitation and can act as a proxy for rainfall and infiltration in this cave system. Our findings emphasize the importance of evaluating spatial heterogeneity in cave drip waters and outline a novel modeling approach for determining the dominant controls on drip water chemistry in support of the interpretations of paleoclimate records.

Investigations into the Trace element variations in Wheat grains by Hand held X-ray Fluorescence

Wheat of different genotypes was analyzed for their micro and macronutrient contents using HHXRF. It was found that K and Ca was present in significant quantities and besides other trace elements Fe and Zn were present showing a positive trend for crop improvement programme.

A Biogeochemical Imprint of the Panama Basin in the North Andean Arc

AbstractOceans and continents mingle at convergent margins. However, the effects of this interaction in the construction and evolution of the continental crust remain poorly understood. Here we use geochemical data from the Panama Basin and the Northern Volcanic Province of Colombia to reveal that the oceanological and biogeochemical processes of a subducted ocean basin are imprinted in the compositions of continental arc volcanoes. The Panama Basin is a biologically highly productive area of the Eastern Equatorial Pacific in which the strongly biogenic sedimentation is reclassified and preserved differently depending on tectonically controlled depositional environments. Due to a shallow lysocline, sediments deposited on newly formed spreading centers are carbonate‐rich, whereas those accumulated on older subsiding seafloor become gradually richer in terrigenous components, organic carbon and authigenic U. Volcanoes of the North Volcanic Province of Colombia erupt high‐Mg# andesites that are common in some arcs, but display unusually high U contents and a symmetrical or “parabolic‐shaped” along‐arc trace element and isotopic variations that appear unrelated to differentiation or the pre‐existent crustal architecture. Instead, the parabolic‐shaped elemental trends mirror the reconstructed compositional variations of sediments deposited across axis on the currently subducted Sandra and Buenaventura ocean ridges. We interpret that subduction of these ocean ridges delivered a compositionally variable sediment influx that influenced the compositions of arc magmas. These findings demonstrate a strong connectivity between oceans and continents, and further imply that arc volcanoes can be reliable records of the oceanological and biogeochemical conditions of long subducted ocean basins.

Geochemical Characteristics of Late Ordovician Shales in the Upper Yangtze Platform, South China: Implications for Redox Environmental Evolution

Changes to the redox environment of seawater in the Late Ordovician affect the process of organic matter enrichment and biological evolution. However, the evolution of redox and its underlying causes remain unclear. This paper analyzed the vertical variability of main, trace elements and δ34Spy from a drill core section (well ZY5) in the Upper Yangtze Platform, and described the redox conditions, paleoproductivity and paleoclimate variability recorded in shale deposits of the P. pacificus zone and M. extraordinarius zone that accumulated during Wufeng Formation. The results showed that shale from well ZY5 in Late Ordovician was deposited under oxidized water environment, and there are more strongly reducing bottom water conditions of the M. extraordinarius zone compared with the P. pacificus zone. Excess silica (SiO2(exc)) and substitution index of paleoproductivity (Y) indicated that the P. pacificus zone had higher paleoproductivity whereas the M. extraordinarius zone was lower. The high productivity level controlled O2 release in the shallow water area as well as the oxidation degree of the P. pacificus zone. The decrease of productivity and the relatively stagnant water mass of the inner Yangtze Sea controlled the formation of relatively reduced water conditions in the M. extraordinarius zone. The chemical index of alteration (CIA) results suggested that palaeoclimatic conditions changed from warm and humid to cold and dry climate from the P. pacificus to the M. extraordinarius zones in the study area. A comparative analysis of the published Fe-S-C data for the Xiushan Datianba section showed that in the P. pacificus zone of the inner Yangtze Sea, warm and humid climate conditions drove high productivity, sulphate flux and low reactive iron flux, which promoted the expansion of oxic ocean-surface waters and mid-depth euxinic waters. In the M. extraordinarius zone, the cold and dry climate with significant uplift of the Xiang’e Submarine High led to the relative sea level decline, resulting in low productivity, sulfate flux and high reactive iron flux, which promoted the expansion of the mid-depth ferruginous waters and the shrinkage of oxic ocean-surface waters. The results offered new insights into the co-evolution of continents and oceans, and explained the role of continental weathering and uplift of the Xiang’e Submarine High in the exchange of sulfate flux and nutrients in the redox environment change of inner Yangtze Sea during the Late Ordovician.

Petrochronology of hydrothermal rutile in mineralized porphyry Cu systems

Hydrothermally formed rutile is a common mineral in porphyry Cu (-Au-Mo) deposits and has the potential to provide versatile information about the physical-chemical conditions and timing of mineralization. In this study, we investigated the trace element composition and U-Pb dates of hydrothermal rutile by LA-ICP-MS together with its petrographic context, in four well-studied porphyry systems: Batu Hijau (Indonesia), Bingham Canyon (USA), El Salvador (Chile) and Northparkes (Australia). A similar sequence of rutile generations occupying comparable textural positions was found to be common to all investigated deposits. We particularly focused on the most common rutile generation that is formed by the breakdown of biotite and temporally closely associated with mineralization as demonstrated by intergrowth relationships between individual, blocky rutile grains and Cu-Fe sulfides as well as cathodoluminescence imaging of mineralized quartz veins. Compositionally, rutile shows large trace element variations within and among the porphyry deposits, indicating that the compositions of both the local host rock and the fluid phase influence that of hydrothermal rutile. In comparison with non-hydrothermal rutile of various petrogenetic origins, rutile from porphyry Cu deposits show characteristic differences regarding their Sn, W, Si and Fe concentrations, indicating that rutile might be used to fingerprint porphyry-style mineralization. Due to its temporal link to Cu mineralization, texturally controlled in-situ U-Pb dating of blocky rutile grains by LA-ICP-MS provides the possibility to directly determine the absolute timing of Cu mineralization. Despite variable incorporation of initial Pb in the investigated hydrothermal rutile, we obtained robust lower intercept U-Pb dates that overlap within uncertainty with previously obtained mineralization ages for all four deposits, including those based on high-precision (ID-TIMS) zircon dating of bracketing porphyry intrusions. This demonstrates that rutile can be used to accurately predict the age of porphyry Cu deposit formation and with a precision better than 1.5% relative for deposits older than ca. 10 million years.

Trace element contamination of soil and dust by a New Caledonian ferronickel smelter: Dispersal, enrichment, and human health risk

Metallurgical industries remain a considerable source of trace element contamination and potential human health risk. Determination of sources is a key challenge. With respect to the South Pacific's largest and longest operating metallurgic smelter in Nouméa, New Caledonia, determining the environmental impact and subsequent human health risk associated with local ferronickel smelting is complicated by natural geological enrichment of Ni and Cr. This study applies a multi-method and multi-matrix approach to disentangle smelter emissions from geogenic sources and model the consequent health risk from industrial activity. Dust wipes (n = 108), roadside soil (n = 91), garden soil (n = 15) and household vacuum dust (n = 39) were assessed to explore geospatial trace element (As, Cr, Cu, Fe, Mn, Ni, Pb, S, V and Zn) variations across outdoor and indoor environments. Enrichment factors (EF) identified elevated levels of smelter-related trace elements: S (EF = 7), Ni (EF = 6) and Cr (EF = 4), as well as Zn (EF = 4). Smelter-related elements in soil and dust deposits were negatively correlated with distance from the facility. Similarity of Pb isotopic compositions between dust wipes, surface soil and vacuum dust indicated that potentially toxic trace elements are being tracked into homes. Non-carcinogenic health risk modelling (Hazard Index, HI) based on 15 spatial nodes across Nouméa revealed widespread exceedance of tolerable risk for children (0–2 years) for Ni (HI 1.3–15.8) and Mn (HI 0.6–1.8). Risk was greatest near the smelter and to the north-west, in the direction of prevailing wind. Given the elevated cancer risk documented in New Caledonia, disentanglement of environmental from industrial sources warrants further attention to ensure community health protection. Our analysis illustrates how the confounding effects from complex environmental factors can be distilled to improve the accuracy of point source apportionment to direct future mitigation strategies.

Trace elements in the shoreline and seabed sediments of the southern Caspian Sea: investigation of contamination level, distribution, ecological and human health risks, and elemental partition coefficient.

This study assesses the occurrence of trace elements (TEs) in sediments of the southern Caspian Sea. A total of 16 shoreline sediment samples and 15 seabed sediment samples along five coastal transects were studied. The mean concentration of TEs follows the order of Zn > V > Cr > Ni > Cu > Pb > Co > As > Sb > Mo > Cd. The TEs had an uneven, heterogeneous distribution within the shoreline and seabed sampling sites. This is due to that the study area comprises a large number of different pollution sources, also different sediment physicochemical characteristics. Levels of individual TEs within the seabed sediment transects were higher where their shoreline sites had higher concentrations, reflecting that the coastal sites play an important role in diffusing the contaminants towards the sea. The main anthropogenic source of TEs in this highly populated region, especially in the western part, is likely a large number of discharge points of greywater entering the sea. In addition, dominant fishing industry, tourism, intense agriculture, and textile and paper industry, as well as several other commercial activities, contribute significantly to the overall loading of TEs. Based on the statistical analyses, the organic matter and mud fraction had a strong explanatory value for the spatial variation of Cu, while oxyhydroxides of Fe and Mn had good explanatory factors to govern the spatial variation of other TEs. Pb and Zn had a relatively high partition coefficient (Kd), reflecting the affinity of these elements to be sorbed to the sediment phase. Cd and Sb had lower Kd, tending to remain in the aqueous phase. Geochemical indices indicated high enrichment of Cd, Sb, Zn, and Pb at a number of sampling sites, reflecting potential local sources of contamination. The Sisangan recreational area was identified as the most contaminated site. From a public health perspective, the non-carcinogenic risk of TEs was significant only at this site. The carcinogenic risks of Pb(II) and As(III) in adults, and Pb(II), Cd(II), and As(III) in children, were tolerable.

Combined fluorescence imaging and LA-ICP-MS trace element mapping of stalagmites: Microfabric identification and interpretation

Here, we map a series of stalagmites from Asturias, Spain, by laser ablation inductively-coupled-plasma mass spectrometry and confocal laser scanning (fluorescence) microscopy and discuss the origins of trace element and fluorescence variations. Seasonal banding is evident with both methods and may be attributed to lignins/humic acids based on fluorescence absorption and emission characteristics. Some lateral variations in fluorescence present as saw-tooth fluorescent “spires” and demonstrate disruptions of seasonal banding, corroborated by trace element variations (most prominently Mg and Na). Such features likely reflect the differential partitioning of trace elements by sectoral zoning as a result of low supersaturation and/or high organic matter load, combined with the effects of dissolved organic matter on the calcite growth surface and the association of each element with colloidal organic matter. The lateral variability of trace elements demonstrates the pitfalls of obtaining trace element information from one-dimensional transects without prior reconnaissance mapping. It is, however, possible that traditional drilling with ~1 mm holes homogenizes these features and provides reliable trace element estimates.

Evidence for Mesoarchean subduction in Southern Bundelkhand Craton, India: Geochemical fingerprints from metavolcanics of Kurrat - Girar - Badwar Greenstone Belt

The metavolcanic suites from southern Bundelkhand Craton, India provides a comprehensive record of the little-explored evolutionary history of Southern Bundelkhand Craton. The present work is a detailed petrological and geochemical account of the metavolcanics to (i) constrain the mantle processes and tectonic realm involved in its genesis and (ii) evaluate the Archean geodynamics of Bundelkhand Craton. The metavolcanics of Kurrat, Badwar and Girar are compositionally slightly evolved tholeiitic basalts. Chondrite normalized REE distribution pattern reflects a slightly super-chondritic LREE distribution pattern (Kurrat metavolcanics, KMV: (La/Yb)N = 1.9–2.9, Badwar-Girar metavolcanics, BGMV: (La/Yb)N = 0.89–2.86) and negative Nb and Ti anomaly on a primitive mantle normalized trace element variation diagram. ƐNd(t) of the samples vary from −1.0 to 6.3 and ƐNd(t) versus 87Sr/86Sr diagram imply the absence of crustal contamination. These attributes are consistent with the formation of the metavolcanics from a slightly enriched heterogeneous mantle source at shallower depths where the original depleted MORB underwent later episode(s) of enrichment via fluid addition. The metavolcanics originated in an intra-oceanic subduction setting, essentially exhibiting back-arc basin basalts (BABB) characteristics. TDM age (3.07 Ga) calculated for the KMV is coherent with the 2.98 Ga age of the BGMV from the adjacent Badwar-Girar volcano-sedimentary sequence. Collectively, all the features implicate the formation of metavolcanics in a modern style Mesoarchean extension-subduction geodynamic regime.

Spatial variation, water quality, and health risk assessment of trace elements in groundwater in Beijing and Shijiazhuang, North China Plain.

Metal(loid)s pollution of groundwater in northern China is of great concern due to the increasing shortage of fresh water resources. In the present study, total 159 of groundwater samples were collected from the Miyun-Huairou-Shunyi (MHS) districts in Beijing city and the Hutuo River Plain (HRP) in Shijiazhuang city. Nineteen trace elements dissolved in groundwater were measured. Results showed that Al (12.3 %), Mn (5.3%), Zn (1.8%), As (1.8%), and Pb (1.8%) in the MHS samples, and Mn (2.2%) in the HRP samples exceeded their standard threshold of WHO and China. Exceedance of trace elements was attributed to both geochemical background and local human activities. Human health risk assessment showed that local consumers were exposed at a low level of health risk, except in specific area with a high level of arsenic. Elements of arsenic and chromium were important risk contributors in the two regions. The risk of oral exposure was greater than that of skin uptake. Children were more susceptible to non-carcinogenic risk and less to carcinogenic risk than adults. A Nemerow index and CRITIC-weighted WQI were applied to classify groundwater quality. The results from the two methods were comparable to a large extend. More population living in plain rather than mountain resulted in a gradual deterioration trend of groundwater quality from mountain to plain. The samples with poor water quality were almost collected in the area with heavy industrial and agricultural activities. The CRITIC-weighted WQI was recommended for groundwater quality assessment. A simple classification criterion was reformulated based on the MHS hazard index analysis. The groundwaters in the two research fields were not seriously polluted, but potential risks should not be ignored.

Textures and trace element geochemistry of magnetite in the Beiya gold deposit, SW China

The Beiya gold deposit (323t of gold @ 2.47 g/t) is located in the centre of the Jinshajiang‐Ailaoshan potassium alkaline porphyry Cu‐Au metallogenic belt in SW China, which is the largest skarn gold deposit in China. As the dominant ore mineral at Beiya, magnetite has been selected as a petrogenetic indicator to understand the ore‐forming process. In this study, magnetites have been divided into the euhedral–subhedral (ME), anhedral (MA), lamellar (ML), and replaced (MR) types based on their textures, which have been further determined by in situ laser ablation inductively coupled plasma mass spectrometry analyses. In detail, plots in discriminant diagrams constrain the Beiya magnetite a hydrothermal origin. Trace elements in magnetite vary with respect to different textures. Titanium concentrations are similar in all magnetite types, suggesting that all magnetites were precipitated in a relatively narrow temperature range. The decreasing V content combined with haematite after magnetite (martitization) suggests that the oxygen fugacity increased from ME and MA and then decreased to ML and MR. All magnetite types show similar content variations and similar (Mg + Mn)/Al ratios, indicating a decreasing degree of fluid–rock interactions. The rim–core texture indicates that the MR type magnetite has experienced the dissolution–reprecipitation process. Mushketovite marks the later ore‐forming environment and the iron‐rich hydrothermal fluids transformed from high temperature and oxidized to low temperature and reduced features. Magnetite textures, combined with its trace element variations, could be used as a potential tool for inferring the ore‐forming fluid evolution.

Melt addition to mid-ocean ridge peridotites increases spinel Cr# with no significant effect on recorded oxygen fugacity

Mid-ocean ridge peridotites record significantly greater variability in major and trace elements, isotopic compositions, and thermodynamic properties such as oxygen fugacity (fO2) than do their basaltic counterparts. This variability may derive from modern ridge processes related to melting and melt-rock interaction or from long-lived source heterogeneity related to recycled material or ancient melting events. In this study, we investigate variations in spinel geochemistry as well as silicate major and trace element chemistry and oxygen fugacity of a suite of peridotites from a single segment of the Southwest Indian Ridge (SWIR). We present new petrographic analysis and trace element data for samples with previously-published fO2 results and combine this with new data for a suite of SWIR gabbro-veined peridotites. We find that SWIR residual lherzolites record low spinel Cr# (Cr# = 100*Cr/(Cr+Al) < 30) and represent low to moderate degrees of melting (∼5-8%) beneath the ridge axis, with no change in oxygen fugacity during melting. In contrast, a subset of SWIR peridotites with high spinel Cr# (Cr#>30) record both melt extraction as well as melt-rock interaction. In these samples, spinel Cr# has been substantially elevated by reaction of spinel to form plagioclase during melt addition, complicating the use of spinel Cr# in mid-ocean ridge peridotites as a proxy for degree of melt extraction alone. While spinel Cr# remains a robust proxy for melt extraction within residual, non-melt-influenced samples, mid-ocean ridge peridotites must first be evaluated to ensure that modification by melt-rock reaction has not occurred. Although addition of MORB melt to a peridotite residue modifies spinel Cr#, this melt addition does not result in significant changes to the fO2 recorded by the peridotite. Residual SWIR lherzolites record fO2 of 0.66±0.39 relative to the quartz-fayalite-magnetite buffer (QFM), statistically indistinguishable from melt-influenced and veined SWIR samples (QFM+1.13±0.61). In contrast to other tectonic settings, such as subduction zones, ocean islands, and continental cratons—locations where peridotite is oxidized by petrogenetically unrelated, presumably high-fO2 melts/fluids—ridge peridotites interact with MORB, which has little to no oxidizing power over its own mantle residues. Thus, modern processes beneath the ridge modify peridotite major and trace elements, but do not generate variability in oxygen fugacity.