Geochemistry of organic-rich river waters in Amazonia: Insights on weathering processes of intertropical cratonic terrain

In this study, eight organic-rich rivers that flow through the Brazilian craton in the southwestern Amazon rainforest are investigated. This investigation is the first of its type in this area and focuses on the effects of lithology, long-term weathering, thick soils, forest cover and hydrological period on the dissolved load compositions in rivers draining cratonic terrain. The major dissolved ion concentrations, alkalinity (TAlk), SiO₂, trace element concentrations, and Sr isotope contents in the water were determined between April 2009 and January 2010. In addition, the isotopic values of oxygen and hydrogen were determined between 2011 and 2013. Overall, the river water is highly dilute and dominated by the major dissolved elements TAlk, SiO₂ and K⁺ and the major dissolved trace elements Al, Fe, Ba, Mn, P, Zn and Sr, which exhibit large temporal and spatial variability and are closely correlated with the silicatic bedrock and hydrology. Additionally, rainwater and recycled water vapor and the size of the basin contribute to the geochemistry of the waters. The total weathering flux estimated from our results is 2–4 t km⁻².yr⁻¹, which is one of the lowest fluxes in the world. The CO₂ consumption rate is approximately 21–61 10³ mol km⁻² yr⁻¹, which is higher than expected given the stability of the felsic to basic igneous and metamorphic to siliciclastic basement rocks and the thick tropical soil cover. Thus, weathering of the cratonic terrain under intertropical humid conditions is still an important consumer of CO₂.     

Isotopic provenancing of Pb in Mitrovica,northern Kosovo: Source identification of chronic Pb enrichment in soils,house dust and scalp hair

Mitrovica, northern Kosovo, is the site of some of the highest Pb concentrations reported in human populations; exemplified by Pb concentrations in scalp hair of up to 130 μg g⁻¹ and widely-publicized of Pb-related ill-health and mortality amongst internally displaced populations. High human Pb burdens are accompanied by elevated concentrations of potentially harmful elements (PHEs) in soils and house dust within the city, which has a long history of mining and metallurgy. In this study enrichment-levels for PHEs in soils are quantified and compared to environmental quality guidelines and a statistically-derived estimation of background concentration. In addition, Pb isotopes (²⁰⁷Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁶Pb) are used to characterise the isotopic signatures of potential point sources of Pb and a mixing model employed to quantify the contribution of sources to Pb present in soils, house dust, and the scalp hair of children and young people. Pb isotopic evidence suggests that Pb in surface soils and house-dust is predominantly sourced from historical deposition of Pb-containing aerosols from metal smelting, with lower contributions from wind-blown dispersal of metalliferous waste. Pb present in scalp hair is interpreted as the result of non-occupational exposure and the ingestion and/or inhalation of Pb-enriched surface soil and house dust. This study represents one of the very few instances where this type of geochemical tracing technique has been successfully applied to definitively identify the source of Pb present within biological samples. The results of this study are of particular relevance to environmental management and highlight the human health risk posed by the legacy of now inactive mining and metallurgy in addition to the challenge posed in mitigating the risk posed by diffuse soil pollution.     

柿竹园钨多金属矽卡岩-云英岩与铅锌银矿脉C、H、O、Pb同位素地球化学研究

柿竹园W_Sn_Mo_Bi_Pb_Zn_Ag矿田是南岭地区典型多金属矿田,其具有显著的蚀变_成矿分带特征:近接触带矽卡岩-云英岩型W_Sn_Mo_Bi矿床(如柿竹园、金船塘、柴山地区)和远接触带脉状Pb_Zn_Ag矿床(如蛇形坪、横山岭、百步窿、枞树板地区)。通过对远—近接触带中主要蚀变岩石和矿石样品的C、H、O、Pb同位素研究,发现在近接触带块状矽卡岩中方解石的δ~(13)C和δ~(18)O值分别在-6.5‰~-3.6‰和4.8‰~8.4‰之间,远接触带Pb_Zn_Ag矿脉中团块状和脉状方解石的δ~(13)C和δ~(18)O值分别在-3.5‰~-1.5‰和8.1‰~15.8‰之间,表明矽卡岩形成于岩浆热液流体的渗滤交代作用,而远接触带碳酸盐脉的形成与热液流体沿灰岩裂隙充填过程中的水岩反应相关。近接触带块状云英岩中石英的δD_(H_2O)和δ_(18)O_(H_2O)值分别为-77‰和5.1‰,矽卡岩中石榴子石的δD_(H_2O)值为-97‰,δ_(18)O_(H_2O)值范围在9.2‰~9.4‰,网脉状云英岩中石英的δD_(H_2O)和δ_(18)O_(H_2O)值分别为-83‰和-8.2‰,退化蚀变矽卡岩中石英的δD_(H_2O)和δ_(18)O_(H_2O)值分别为-65‰和-4.2‰,远接触带石英脉中石英样品的δD_(H_2O)和δ_(18)O_(H_2O)值分别为-83‰和2.8‰,表明近接触带的块状矽卡岩和云英岩与远接触带石英脉成矿流体具有岩浆水的特征,而网脉状云英岩和退化蚀变矽卡岩成矿流体具有岩浆流体与大气水混合的特征。远—近接触带中方铅矿的206Pb/204Pb值范围18.565~18.622,207Pb/204Pb值范围15.694~15.738,208Pb/204Pb值范围38.819~38.986,表明Pb等金属元素来源于上地壳。     

高温高压下元素配分的原位实验与计算模拟研究进展

地球内部元素的配分行为具有重要意义,有助于揭示地球内部物质循环、元素成矿、超临界流体性质等基础地质问题。同步辐射微聚焦X射线荧光光谱(SR-μXRF)结合金刚石压腔(DAC)技术,可以在高温高压条件下实现高准确度和高分辨率的原位(in situ)测试元素在不同物相间的浓度,并获取配分系数。而基于地球化学热力学的理论计算模拟,可以获得元素在不同物相间的赋存形式,有助于揭示元素配分机制。本文综述了SR-μXRF结合DAC技术和地球化学热力学计算模拟原位测定高温高压下元素配分的研究方法,及其在地球内部元素迁移、成矿作用和地球早期形成过程等领域中的应用进展,认为利用该套方法研究高温高压下元素配分行为的体系将变得更加复杂,对温度、压力条件则要求更高。本文旨在更新和丰富高温高压下元素配分系数数据,深化对地球内部物质循环等问题的认知。     

Processes controlling 234U and 238U isotope fractionation and helium in the groundwater of the St. Lawrence Lowlands,Quebec: The potential role of natural rock fracturing

The goal of this study is to explain the origin of ²³⁴U–²³⁸U fractionation in groundwater from sedimentary aquifers of the St. Lawrence Lowlands (Quebec, Canada), and its relationship with ³He/⁴He ratios, to gain insight regarding the evolution of groundwater in the region. (²³⁴U/²³⁸U) activity ratios, or (²³⁴U/²³⁸U)_act, were measured in 23 groundwater samples from shallow Quaternary unconsolidated sediments and from the deeper fractured regional aquifer of the Becancour River watershed. The lowest (²³⁴U/²³⁸U)_act, 1.14 ± 0.01, was measured in Ca–HCO₃-type freshwater from the Quaternary Shallower Aquifer, where bulk dissolution of the carbonate allows U to migrate into water with little ²³⁴U–²³⁸U isotopic fractionation. The (²³⁴U/²³⁸U)_act increases to 6.07 ± 0.14 in Na–HCO₃–Cl-type groundwater. Preferential migration of ²³⁴U into water by α-recoil is the underlying process responsible for this isotopic fractionation. An inverse relationship between (²³⁴U/²³⁸U)_act and ³He/⁴He ratios has been observed. This relationship reflects the mixing of newly recharged water, with (²³⁴U/²³⁸U)_act close to the secular equilibrium and containing atmospheric/tritiogenic helium, and mildly-mineralized older water (¹⁴C ages of 6.6 kyrs), with (²³⁴U/²³⁸U)_act of ≥6.07 and large amounts of radiogenic ⁴He, in excess of the steady-state amount produced in situ. The simultaneous fractionation of (²³⁴U/²³⁸U)_act and the addition of excess ⁴He could be locally controlled by stress-induced rock fracturing. This process increases the surface area of the aquifer matrix exposed to pore water, from which produced ⁴He and ²³⁴U can be released by α-recoil and diffusion. This process would also facilitate the release of radiogenic helium at rates greater than those supported by steady-state U–Th production in the rock. Consequently, sources internal to the aquifers could cause the radiogenic ⁴He excesses measured in groundwater.     

Historical variations in the stable isotope composition of mercury in a sediment core from a riverine lake: Effects of dams,pulp and paper mill wastes,and mercury from a chlor-alkali plant

The Wabigoon River (Ontario, Canada) was affected by dams starting in 1898 and was polluted with pulp and paper mill wastes starting in 1913 and mercury from a chlor-alkali plant from 1962 to 1975. A dated sediment core from a riverine lake was analysed to investigate resultant changes in the biogeochemistry of mercury as revealed by variations in mercury isotope ratios and sediment chemistry. A total mercury maximum formed by the mercury pollution coincided with minimums in the δ-values of the ¹⁹⁸Hg/²⁰²Hg, ¹⁹⁹Hg/²⁰²Hg, ²⁰⁰Hg/²⁰²Hg, and ²⁰¹Hg/²⁰²Hg ratios, and the δ-values decreased in the order δ²⁰¹Hg > δ²⁰⁰Hg > δ¹⁹⁹Hg > δ¹⁹⁸Hg. Thus, mass-dependent fractionation caused depletion in lighter isotopes, implying evaporation of Hg(0) and pollution of the atmosphere as well as the river-lake system. Concurrently, mass-independent fractionation caused ¹⁹⁹Hg enrichment, possibly reflecting an independently documented upsurge in methylmercury production, and ²⁰¹Hg depletion, suggesting removal of methylmercury with anomalously high ²⁰¹Hg/¹⁹⁹Hg ratios by aquatic organisms and accumulation of ²⁰¹Hg-depleted inorganic Hg(II) in sediments. The δ²⁰¹Hg/δ¹⁹⁹Hg ratio rose abruptly when mercury pollution began, reflecting the resultant increase in methylmercury production, and remained high but gradually declined as the pollution abated, paralleling trends shown by methylmercury in aquatic organisms. The δ²⁰¹Hg/δ¹⁹⁹Hg ratio of pre-1962 background mercury increased ca. 1898 and ca. 1913–1929, suggesting accelerated methylmercury production due to stimulation of microbial activities by the damming of the river and the input of pulp and paper mill wastes, respectively. Other variations were linked to economic and technological factors that affected pulp and paper manufacture.     

黔中茶店桥地下河流域不同水体硫酸盐浓度特征及来源识别

茶店桥地下河位于西南岩溶区,流域内"三水"转换迅速,地下水是当地的重要饮用水源。本文对流域内雨水、地表水、地下水中的SO_4~(2-)浓度进行了测试,利用氘(δD_(H_2O))、氧(δ~(18) O_(H_2O))同位素示踪地表水、地下水补给来源,用硫酸盐硫(δ~(34)S_(SO4))、氧(δ~(18) O_(SO4))同位素探讨了地表水、地下水中SO_4~(2-)的来源,并计算了地下河出口河水中不同SO_4~(2-)来源的贡献比例。结果表明:1不同水体中SO_4~(2-)浓度大小顺序为地表水地下水雨水,与邻近区域相比,茶店桥地下河流域雨水、地表水、地下水呈现富集SO_4~(2-)的特征。2地表水、地下水的主要补给来源为大气降水,硫酸不仅和HCO_3~-共同参与了流域内碳酸盐岩的溶解,也参与了雨水中含钙镁颗粒物的溶解。3地表水δ~(34)S_(SO4)、δ~(18) O_(SO4)值分别介于-12.98‰~-10.19‰和-0.54‰~+9.13‰之间,地下水δ~(34)S_(SO4)、δ~(18) O_(SO4)值分别介于-14.32‰~+16.58‰和+2.81‰~+14.35‰之间,SW02的SO_4~(2-)主要来源于大气降水,SW01、SW03、GW02、GW03、GW06主要来源于煤层,GW05主要来源于石膏,GW01、GW04为混合输入源。4地下河出口河水中大气降水带来的SO_4~(2-)贡献比例为13%,煤层硫化物氧化的贡献比例为40%,石膏溶解的贡献比例为47%。     

纳米比亚欢乐谷地区白岗岩型铀矿成矿物质来源分析

本文对纳米比亚欢乐谷地区与铀成矿关系密切的白岗岩进行了系统的主量元素、微量元素及Sr-Nd同位素研究。结果表明,矿化白岗岩具有较高的SiO_2(68.81%~76.02%,平均值73.11%),富钾,A/CNK为0.96~1.07,平均值1.01,为亚碱性系列的准铝质-弱过铝质岩石。岩石富集轻稀土[LREE/HREE=2.53~7.71;(La/Yb)_N=2.14~10.40],Eu亏损中等,高Rb/Sr比值(2.03~5.50,平均值4.36),岩石同时富集Rb、Th、U、K及Pb等大离子亲石元素,亏损Ba、Nb、Ta及Sr等元素。岩石的初始~(87)Sr/~(86)Sr比值为0.73035~0.79345,ε_(Nd)(t)值为-13.5~-17.4,晶质铀矿的ε_(Nd)(t)值为-14.8~-16.5,两阶段Nd模式年龄为2.43~2.56Ga。元素和Sr-Nd同位素地球化学特征表明矿化白岗岩是在碰撞后的伸展构造环境中形成的,主成矿期的成矿物质来源于富铀的前达马拉基底;热液叠加改造期的铀可能来源于原生铀矿物本身。     

Secondary Ion Mass Spectrometry Bias on Isotope Ratios in Dolomite–Ankerite,Part II: δ13C Matrix Effects

This study is Part II of a series that documents the development of a suite of calibration reference materials for in situ SIMS analysis of stable isotope ratios in Ca‐Mg‐Fe carbonates. Part I explored the effects of Fe²⁺ substitution on SIMS δ¹⁸O bias measured from the dolomite–ankerite solid solution series [CaMg(CO₃)₂–CaFe(CO₃)₂], whereas this complementary work explores the compositional dependence of SIMS δ¹³C bias (calibrated range: Fe# = 0.004–0.789, where Fe# = molar Fe/(Mg+Fe)). Under routine operating conditions for carbonate δ¹³C analysis at WiscSIMS (CAMECA IMS 1280), the magnitude of instrumental bias increased exponentially by 2.5–5.5‰ (session‐specific) with increasing Fe‐content in the dolomite structure, but appeared insensitive to minor Mn substitution [< 2.6 mole % Mn/(Ca+Mg+Fe+Mn)]. The compositional dependence of bias (i.e., the matrix effect) was expressed using the Hill equation, yielding calibration residual values ≤ 0.3‰ relative to CRM NBS‐19 for eleven carbonate reference materials (6‐μm‐diameter spot size measurements). Based on the spot‐to‐spot repeatability of a drift monitor material that ‘bracketed’ each set of ten sample‐spot analyses, the analytical precision was ± 0.6–1.2‰ (2s, standard deviations). The analytical uncertainty for individual sample analyses was approximated by combining the precision and calibration residual values (propagated in quadrature), suggesting an uncertainty of ± 1.0–1.5‰ (2s).     

Calcium Isotopic Fractionation during Ion‐Exchange Column Chemistry and Thermal Ionisation Mass Spectrometry (TIMS) Determination

Significant isotopic fractionation can occur during column chemistry and determination by mass spectrometry. Improper correction may produce uncertainties in the isotopic composition of geological samples. We investigated calcium isotopic fractionation during these two processes and set up a model to check data quality. The δ^44/40Ca_915a value of IAPSO seawater in different Ca cuts (e.g., 0–20, 20–40, 40–60, 60–80 and 80–100%) on column chemistry ranged from ~ 4‰ to 0‰. The more Ca was eluted, the lower the δ^44/40Ca_915a value of the elution was found. The isotopic fractionation of calcium on the column appeared to follow the exponential law. However, TIMS instrumental fractionation during Ca runs did not always follow the exponential law due to mixing effects from sample reservoirs on the filament. Our results show that errors could be caused if the instrumental fractionation deviates from the exponential law, especially when the fractionation degree is large. To improve the measurement uncertainty, a model is proposed to check the behaviour and degree of instrumental fractionation, which will provide a quick and reasonable verdict on the data quality of TIMS runs.