Importance of organic Fe complexing ligands in the Mississippi River plume

As part of a larger program focused on understanding the biogeochemistry of large river plumes, we participated in two expeditions during 2000 to sample the Mississippi River plume. Surface water samples were collected using a trace metal clean towed fish and analyzed for total dissolved Fe, organic Fe complexing ligands and their associated conditional stability constants. The ligands in the river plume have conditional stability constants (log K′_FeL between 10.5 and 12.3 with an average of 11.2 and standard deviation of 0.6) very similar to ligands found in the open ocean. Comparison of high flow and low flow regimes indicates that variability in flow may be the main cause of the variability in Fe concentrations in the plume. The organic Fe complexing ligands are in greatest excess during a time of higher flow. These ligands are responsible for maintaining very high (5 nM) Fe concentrations throughout the plume. Due to complexation with these organic ligands, the concentration of Fe remains above the Fe-hydroxide solubility level until a salinity above 35 is reached where there appears to be a sink for Fe in the less productive waters. Therefore, Fe is transported a great distance from the river source and is available for biological utilization in the coastal zone.     

中国内蒙古白云鄂博Fe-Nb-REE矿床地质特征与陨石撞击成因

中国内蒙古白云鄂博Ｆｅ－Ｎｂ－ＲＥＥ矿床由于其独特的矿床地质与矿物地球化学特征而明显有别于世界上其它绝大多数的Ｆｅ、Ｎｂ、ＲＥＥ矿床。本文提出该矿床是约１５００Ｍａ前一块富含ＲＥＥ、Ｎｂ的铁陨石撞击在华北地台北缘碳酸盐沉积陆架上形成的。现在矿床矿体中心的块状铁矿石更多地代表了陨石的成分,矿体外侧富含ＲＥＥ、Ｎｂ的环状白云岩是陨石撞击浅海碳酸盐沉积陆架释放的巨大能量使海水（含Ｍｇ）迅速受热溶解陨石中的ＲＥＥ、Ｎｂ等形成的含金属热液蚀变沉积成因方解石质碳酸盐沉积物的结果。块状铁矿石和环状白云岩之间矿物成分异常复杂、结晶颗粒十分细小的条带状、侵染状Ｆｅ－Ｎｂ－ＲＥＥ矿石组成的矿体则是撞击瞬间导致的由陨石（Ｆｅ、Ｎｂ、ＲＥＥ）、海水（Ｍｇ、Ｎａ、Ｋ等）和碳酸盐（含少量硅质夹层）（Ｃａ、Ｓｉ、Ａｌ等）组成的超高温、多组分、富水体系在快速冷却条件下反应生成的产物。撞击释放的巨大热能,在撞击体（陨石）下部相对不易释放,导致部分碳酸盐沉积物在富含ＲＥＥ、Ｎｂ、Ｍｇ等的热液参与下融熔,然后侵入到周围岩石裂隙形成矿区内众多的富含ＲＥＥ、Ｎｂ的白云岩脉。撞击的瞬间导致大量岩石、矿物碎屑、海水、蒸汽弥漫天空,同时引发巨大的海啸,然     

Ecological Differences in the Distribution of two Tethya (Porifera, Demospongiae) Species Coexisting in a Mediterranean Coastal Lagoon

Abstract. In the Sicilian lagoon Stagnone di Marsala, Tethya aurantium and T. citrina show different ecological distributions, although some overlapping occurs. The first species reaches its highest density where linear currents are maximal, and in this habitat it is particularly frequent on Posidonia oceanica rhizomes. The second species is more abundant in still water locations and is equally common on Posidonia rhizomes and on calcareous concretions. Such distributions can be related to water movement, Posidonia shoot density, and associated factors such as sedimentation and food availability. These observations are consistent with an adaptive interpretation of the morphofunctional features distinguishing the two species.     

Eocene migmatite formation and diachronous burial revealed by petrochronology in NW Himalaya,Zanskar

In this contribution, we highlight the importance of in-situ monazite geochronology linked to P−T modelling for identification of timescales of metamorphic processes. Barrovian-type micaschists, migmatites and augengneiss from the Gumburanjun dome in the southeastern extremity of the Gianbul dome, NW Himalaya, have been studied in order to correlate the early stages of Himalayan metamorphism at different crustal levels and infer the timing of anatexis. P−T−t paths are constrained through combined pseudosection modelling and in-situ and in-mount monazite and xenotime laser ablation–split-stream inductively coupled plasma-mass spectrometry. Petrography and garnet zoning combined with pseudosection modelling show that garnet-staurolite schists record burial from ~530 to 560°C and 5.5 kbar to ~630 to 660°C and 7 kbar; staurolite-kyanite schists from ~530 to 560°C and 5 kbar to ~670 to 680°C and 7−9 kbar; and garnet-kyanite migmatites from 540−570°C and 5 kbar to ~680 to 750°C and 7−10 kbar, probably also to >750°C and >9 kbar above the muscovite stability field. The decompression paths of garnet-staurolite schists indicate cooling on decompression, while garnet rim chemistry and local sillimanite growth point to a stage of re-equilibration at ~600 to 670°C and 4−6 kbar in some of the staurolite-kyanite schists, and at ~670 to 700°C and 6 kbar in garnet-kyanite migmatites. Some of the staurolite-kyanite schists and garnet-kyanite migmatites also contain andalusite or andalusite-cordierite. Monazite and xenotime were analysed in thin sections in garnet, staurolite and kyanite, and in the matrix; and in mounts. BSE images and compositional maps of monazite (xenotime was too small) show variable internal structures from homogeneous through patchy zoning with embayed to sharp boundaries. Two groups of samples can be identified on the basis of the presence or absence of c. 44 − 37 Ma ages. The first group of samples—two garnet-staurolite schists—recorded only c. 31 − 27 Ma ages in porphyroblasts and no c. 40 Ma ages. The second group (samples of staurolite-kyanite schist, garnet-kyanite migmatites, augengneiss) have both the older, c. 44 − 37 Ma monazite ages in porphyroblasts and younger ages down to c. 22 Ma. These significantly different ranges of ages from porphyroblasts of 44−37 Ma, and 31−27 Ma, are interpreted as the duration of prograde P−T paths in Eocene and Oligocene, and indicate diachronous two-stage burial of rocks. Early migmatization occurred at 38 Ma. The c. 29 Ma is interpreted as the time when rocks from the lower and middle crustal levels were partially exhumed and came in to contact with rocks that were downgoing at this time. Localized monazite recrystallization is as young as 26−24 Ma. The youngest ages of 23−22 Ma are related to leucogranite emplacement.     

闽北羊角尾萤石矿成因:来自稀土、微量元素地球化学的证据

闽北浦城羊角尾萤石矿产于侏罗系梨山组火山碎屑岩中的断裂破碎带内, 对其地质矿产特征和矿石、围岩及矿区内黑云母正长花岗岩的岩石地球化学特征进行了研究。羊角尾萤石矿矿石∑REE为65.17×10–6～125.87×10–6, 重稀土相对富集, δEu和δCe无明显异常; Ni、Cd、Pb和As等中低温微量元素相对地壳富集。围岩梨山组火山碎屑岩轻重稀土分馏不明显, Eu负异常明显, Sm/Nd值与萤石接近, 微量元素相对地壳的含量曲线趋势与萤石基本一致。黑云母正长花岗岩则显示轻稀土富集、重稀土亏损, Eu正异常和Ce负异常的特征, Sm/Nd值远小于萤石矿。结合稀土微量元素特征及矿床成因判别图解, 认为羊角尾萤石矿的主要成矿物质来源为梨山组火山碎屑岩。成矿流体在形成后经历了长期的演化, 在此过程中与围岩发生了充分的水岩反映, 使Ca、F、REE等重新活化, 最终在构造破碎带就位沉淀形成矿体, 矿床成因类型为中-低温热液充填型。羊角尾萤石矿的矿床成因研究表明晚侏罗世火山-沉积岩系是区域萤石矿成矿的重要物源基础, 在区域找矿工作中应重点关注。     

川滇黔相邻区古陆相沉积型稀土的发现及意义

文章报道了一种在川滇黔相邻区新发现的古陆相沉积型稀土矿床。稀土矿体赋存在二叠系峨眉山玄武岩之上,上二叠统宣威组底部,含矿建造为一套以高岭石及伊利石为主的黏土岩建造,分布广泛,连续性好,稀土氧化物TREO平均品位0.39%,最高可达1.60%。岩相古地理条件及地球化学特征显示,稀土元素源自西侧剥蚀区,经搬运-沉积-改造后富集;赋存状态方面,古陆相沉积型稀土除独立矿物态（<1%）,类质同象态（<1%）和离子吸附态（0.02%~24%）外,75%以上的稀土元素以纳米矿物颗粒的形态被“束缚”在黏土矿物层状结构中;稀土元素配分曲线图显示其高价值关键稀土元素镨、钕、铽、镝占比累计达23.34%;通过短流程的选冶一体化工艺技术,全元素稀土浸出率达到90%以上,综合回收率达80%以上。这一新类型稀土资源具有极大的开发利用前景,有望成为中国新的关键稀土元素来源。     

内蒙古哈素海区域高砷地下水化学特征及其成因

哈素海区域高砷地下水对当地居民饮用水安全造成严重威胁, 揭示其形成演化机制对科学合理的开发利用水资源、保障居民身体健康具有重要意义。本文在水文地质调查的基础上, 应用Piper三线图、PHREEQC的砷形态计算及相关性分析等方法, 研究高砷地下水化学特征、构建砷形态模型(SM)和砷吸附模型(HSM), 以揭示高砷地下水的成因机制。结果表明, 研究区砷浓度为0.2~231.5 μg/L, 高砷区主要分布在大青山以南的冲湖积平原区; 地下水砷的类型以As(Ⅲ)为主, SM分析显示优势形态为H3AsO3, HSM分析显示存在Hfo_wH2AsO3和H3AsO3两种主要形态。地下水中的砷化物可能来源于山区富砷岩石的风化溶解以及第四系富砷河湖相沉积物; 研究区河湖相沉积环境是高砷水形成的前提, 有机质分解主导的还原环境是导致砷从含水介质释放到地下水中的主要因素, 弱碱性环境和HCO– 3的竞争吸附也会引起砷的释放。     

Quantification of Water Content and Speciation in Synthetic Rhyolitic Glasses: Optimising the Analytical Method of Confocal Raman Spectrometry

Quantification of water content in silicate glasses is of vital significance in understanding magma evolution and metamorphic anataxis. Here we provide a method for the determination of total dissolved water content and water speciation in silicate melts by confocal laser Raman spectrometry based on a set of hydrous rhyolitic glasses. A series of alumino-silicate glasses with water contents from 0.33 to 9.05% m/m were synthesised in a piston cylinder apparatus. Synchrotron-FTIR mapping shows that these glasses have relatively homogeneous distributions of dissolved water. Total water contents of the glasses were precisely measured by TC/EA-MS and FTIR. Both external and internal calibration were established for the quantitative analysis of water content and water speciation in the silicate glasses based on excellent linear correlation between total dissolved water content and integrated area of the water Raman band. Furthermore, by decomposing the total water Raman bands into four Gaussians components, the relative concentration of water speciation (OH groups and molecules H₂O_m) dissolved in the glasses was determined with a similar trend to water speciation data derived from FTIR. We suggest that the relative concentration of water speciation can be estimated in rhyolitic glasses with 4–8% m/m H₂O. Our work provides an accurate method to determine total water content and a potential tool to limit the relative concentration of water speciation dissolved in silicic glasses.     

Geochemical speciation and spatial distributions of phosphorus in surface sediments from the basin of the Marcus-Wake seamounts in the western Pacific Ocean

The concentrations of five forms of phosphorus(P) including exchangeable or loosely adsorbed P(Ex-P), Febound P(Fe-P), authigenic P(Auth-P), detrital P(Det-P), and organic P(Org-P) from the basin among the Marcus-Wake seamounts(19.4°–24°N, 156.5°–161.5°E) in the western Pacific Ocean were quantified using a sequential extraction method(SEDEX) to investigate the distribution and sources of different P species.Concentrations of total P(TP) varied from 14.0 μmol/g to 44.1 μmol/g, with an average of...     

黔西北赫章天桥铅锌矿床成矿物质来源:S、Pb同位素和REE制约

赫章县天桥铅锌矿床位于扬子准地台西南缘的黔西北铅锌成矿区中部,是本区已发现的96处中、小型矿(床)点的典型代表。天桥铅锌矿床由三个矿体群组成,其金属资源量(Pb+Zn)超过0.2Mt。本文报道了该矿床矿石硫化物的硫和铅同位素组成及其稀土元素组成特征。矿石硫化物δ34SV-CDT值主要集中在8.4‰～14.4‰之间,总体具有δ34Spyδ34Sspδ34Sga特征,表明成矿流体中硫已达到平衡。该矿床成矿流体中δ34S∑S值与不同时代地层中海相硫酸盐δ34S值(15‰)相近,表明成矿流体中硫来源于不同时代地层,为不同时代地层海相硫酸盐热化学还原(TSR)的产物。铅同位素组成相当均一,n(208Pb)/n(204Pb)值为38.875～39.057(平均38.945),n(207Pb)/n(204Pb)值为15.708～15.763(平均15.728),n(206Pb)/n(204Pb)值范围为18.481～18.544(平均18.516),与碳酸盐地层相近,在n(208Pb)/n(204Pb)—n(206Pb)/n(204Pb)和n(207Pb)/n(204Pb)—n(206Pb)/n(204Pb)图,落入碳酸盐地层范围内,表明铅来源于与矿物铅同位素组成相近的各时代碳酸盐地层。硫化物样品具有低ΣREE(3×10-6)和负的Eu异常(0.13～0.88)特征。在稀土元素球粒陨石标准化配分模式图上,全部样品具有相似特征,且与地层中的黄铁矿(下石炭统大塘组C1d)、地层白云岩及蚀变围岩相比,具有一致的稀土配分模式和Eu负异常特征,表明成矿流体来源围岩及下伏碳酸盐地层。综合S、Pb同位素和REE地球化学特征认为该矿床成矿物质和成矿流体具有多来源特征,各时代地层均不同程度地为成矿提供物质和流体。