Tracing groundwater flow and sources of organic carbon in sandstone aquifers using fluorescence properties of dissolved organic matter (DOM)

The fluorescence properties of groundwaters from sites in two UK aquifers, the Penrith Sandstone of Cumbria and the Sherwood Sandstone of South Yorkshire, were investigated using excitation–emission matrix (EEM) fluorescence spectroscopy. Both aquifers are regionally important sources of public supply water and are locally impacted by pollution. The Penrith Sandstone site is in a rural setting while the Sherwood Sandstone site is in suburban Doncaster. Fluorescence analysis of samples from discrete sample depths in the Penrith Sandstone shows decreasing fulvic-like intensities with depth and also shows a good correlation with CFC-12, an anthropogenic groundwater tracer. Tryptophan-like fluorescence centres in the depth profile may also provide evidence of rapid routing of relatively recent applications of organic slurry along fractures. Fluorescence analysis of groundwater sampled from multi-level piezometers installed within the Sherwood Sandstone aquifer also shows regions of tryptophan-like and relatively higher fulvic-like signatures. The fluorescence intensity profile in the piezometers shows tryptophan-like peaks at depths in excess of 50 m and mirrors the pattern exhibited by microbial species and CFCs highlighting the deep and rapid penetration of modern recharge due to rapid fracture flow. Fluorescence analysis has allowed the rapid assessment of different types and relative abundances of dissolved organic matter (DOM), and the fingerprinting of different sources of organic C within the groundwater system. The tryptophan:fulvic ratios found in the Penrith Sandstone were found to be between 0.5 and 3.0 and are characteristic of ratios from sheep waste sources. The Sherwood Sandstone has the lowest ratios (0.2–0.4) indicating a different source of DOM, most likely a mixture of terrestrial and microbial sources, although there is little evidence of pollution from leaking urban sewage systems. Results from these two studies suggest that intrinsic fluorescence may be used as a proxy for, or complementary tool to, other groundwater investigation methods in helping provide a conceptual model of groundwater flow and identifying different sources of DOM within the groundwater system.     

山东济南下寒武统朱砂洞组软沉积变形中燧石的Sm-Nd年龄测定及其意义

在济南南部下寒武统朱砂洞组丁家庄段硅质白云岩中,发育地震引起的硅质触变脉、硅质触变沉陷构造和触变楔等软沉积变形构造。从同一地震触变沉陷构造中,采得一组灰黑色燧石样品。使用英国VG354同位素质谱仪和同位素质谱分析方法,测得每个样品的 ¹⁴⁷Sm/¹⁴⁴Nd 和 ¹⁴³Nd/¹⁴⁴Nd 同位素值。采用Sm-Nd 等时线法,对燧石进行了测年。获得燧石的成岩年龄为530.8±6.1 Ma,由于软燧石(硅胶体)成岩至少经历了0.1 Ma的时间,所以,地震沉积事件发生在530.7±6.1 Ma,属早寒武世早期。由于测年结果与沧浪铺阶的下界年龄接近,山东朱砂洞组丁家庄段无化石且河南省标准地层剖面中的整个朱砂洞组属沧浪铺阶,这暗示济南地区朱砂洞组丁家庄段属沧浪铺阶。本次测年得到了鲁西地区第1个下寒武统的同位素年龄值,这对确定该地区早寒武世地震沉积事件发生的时间具有参考价值和意义,也为深入研究鲁西地区寒武纪地层提供了新资料。     

Metamorphic evolution of oceanic gabbros: recrystallization from subsolidus to hydrothermal conditions in the MARK area (ODP Leg 153)

The 117.38 m of gabbroic core drilled during the Ocean Drilling Program (ODP) Leg 153 at Sites 921 to 924 in the Mid-Atlantic Ridge (MAR) between 23 °N and the Kane Fracture Zone, exhibits a remarkable primary compositional heterogeneity, such as magmatic layering, intrusive contacts and late magmatic veining, which express a succession of magmatic events. Textural indicators suggest that the cooling of the crystal mush occurred in a dynamic environment, with infiltration of progressively evolved liquids. Magmatic features include random shape fabric and magmatic lamination; the subsequent deformational overprint occurred in subsolidus conditions. The ductile deformation, generally concentrated in discrete domains of the gabbro, is associated with continuous re-equilibration of the metamorphic assemblages of (1) olivine + clinopyroxene + orthopyroxene + plagioclase + ilmenite + Ti-magnetite, (2) olivine + clinopyroxene + plagioclase + ilmenite + Ti-magnetite + red hornblende. At lower temperatures brittle deformation prevails and subsequent fractures control the development of metamorphic assemblages: (3) clinopyroxene + plagioclase + red brown hornblende + Ti-magnetite + magnetite (?) + ilmenite, (4) plagioclase + brown hornblende + Ti-magnetite + magnetite + hematite + titanite ± Ti-oxide, (5) plagioclase + green hornblende + magnetite + titanite, (6) plagioclase + actinolite + chlorite + titanite + magnetite, (7) albite + actinolite + chlorite + prehnite ± epidote ± titanite and (8) albite + prehnite + chlorite ± smectite. Assemblages 1 to 8 express increasing water/rock ratios and decreasing degrees of recrystallization.

During the ductile phase, red hornblende is stable and its abundance increases with deformation intensity, possibly as an effect of the introduction of hydrous fluids. During the brittle phase, water diffusion controls the development of the fracture-filling mineral assemblages and re-equilibration of the adjacent rock; temperatures decrease further, as demonstrated by mineral zoning and incompletely re-equilibrated assemblages. The lowest temperatures correspond to the development of hydrothermal assemblages.

Compared with oceanic gabbros from fast-spreading transform environments, high-temperature ductile phases (granulite and amphibolite) are well developed, whereas brittle phases are widespread, as microcracks, prevalent on fracturing associated with discrete veins.     

Constraints of stable isotopes on the origin of alunite from advanced argillic alteration systems in Bulgaria

Voluminous areas of advanced argillic alteration (AAA) constitute major exploration targets for surficial Cu–Au epithermal and potentially underlying porphyry-type deposits. In Bulgaria, more than 30 alunite occurrences are recognised, few of them being associated with a mineralised system. A mineralogical study combined with a stable isotopic (O, H, S) study has been carried out on nine alunite occurrences of advanced argillic zones hosted by volcanic rocks of Late Cretaceous age in the Srednogorie belt and of Oligocene age in the Rhodopes belt. This work was realised in order to constrain the origin of alunite and to define criteria to discriminate alunite from ore deposits and alunite from large barren alteration systems.Mineralogy of the nine occurrences consists of alunite + quartz + minor alumino-phospho-sulphates, associated with more or less kaolinite, dickite, pyrophyllite, diaspore and zunyite, depending on formation temperature. Alunite generally occurs as tabular crystals but is also present as fine-crystalline pseudocubic phases at Boukovo and Sarnitsa, in Eastern Rhodopes. In the advanced argillic alterations associated with economic ore, the presence of zunyite in the deeper parts indicates acid–fluorine–sulphate hydrothermal systems, whereas it is absent in uneconomic and barren advanced argillic alteration. All occurrences are formed at temperatures between 200 and 300 °C.(H, O, S) isotopic signatures of alunite combined with mineralogical features from all the studied occurrences, whatever their type, show characteristics of magmatic-hydrothermal systems. Sulphur data indicate essentially a magmatic origin for sulphur. Oxygen and hydrogen data suggest that hydrothermal fluids result from a mixing between magmatic fluids and an external component, which is identified as seawater-derived fluids or meteoric water in the vicinity of a sea. In most of the alunite occurrences, magmatic fluids are dominant and H₂S/SO₄ ratios are estimated to be higher than 2. Two exceptions exist in the Rhodopes. At Boukovo and Sarnitsa, where the estimated formation temperatures of alunite are the lowest, the external fluids are dominant and H₂S/SO₄ratios are estimated to be lower than or close to 1.At this stage of the work, the mineralogical and isotopic criteria do not enable a clear distinction between economic and uneconomic systems. However, some features are common in the economic ore deposits: the presence of zunyite in the deeper part of the system, the relatively high temperatures suggested by the zunyite + pyrophyllite + alunite + diaspore assemblages, the (O, H, S) signature of alunite, which is characteristic of dominant magmatic–hydrothermal acid–sulphate–fluorine systems.     

The mechanisms of reduction of hexavalent chromium by green rust sodium sulphate: Formation of Cr-goethite

The molecular-level processes that control green rust sodium sulphate (GR_Na,SO4) reaction with chromate were studied using high-resolution techniques. Changes in solid morphology, structure and composition were observed with atomic force microscopy, transmission electron microscopy and X-ray diffraction. The results suggest the following mechanisms: Chromate replaces sulphate in the GR interlayer and is reduced by Fe(II). Formation of sparingly soluble Cr(III)-solid blocks further chromate entry, but Cr(VI) reduction continues at the GR solid/solution interface. Electron transfer from the centre of the GR crystals to the surface facilitates rapid reaction. Less stable zones of the reacted GR_Na,SO4 dissolve and amorphous Cr(III),Fe(III)-solid forms. During equilibration, Cr-substituted goethite evolves in association with remaining GR_Na,SO4, fed by material from the amorphous phase and dissolving oxidised GR. In contrast, previous Cr(VI) experiments with the carbonate form of GR, GR_CO3, have suggested only reaction and deposition at the surface. From the perspective of environmental protection, these results have important implications. Goethite is sparingly soluble and the inclusion of Cr(III) as a solid-solution makes it even less soluble. Compared to Cr adsorbed at the surface of an Fe(III)-phase, Cr(III) incorporated in goethite is much less likely to be released back to groundwater.     

Geochronology of zircon megacrysts from nepheline-bearing gneisses as constraints on tectonic setting: implications for resetting of the U-Pb and Lu-Hf isotopic systems

Nepheline-bearing gneisses from the 75 km² Tambani body in the Mozambique Belt of southern Malawi, are miaskitic biotite-nepheline monzodiorites, reflecting an absence of K-feldspar, alkali amphiboles or pyroxenes, and contain euhedral zircon megacrysts up to 5 cm across. The zircons contain U = 1–1,860 ppm, Th = 0–2,170 ppm and Y = 400–1,100 ppm, and very low concentrations of all other measured trace elements except Hf (HfO₂ = 0.53–0.92 wt. %). Cathodoluminescence images reveal oscillatory sector growth zoning and no evidence for xenocrystic cores, indicating that the zircons represent primary magmatic crystallization products that have survived amphibolite grade metamorphism. U-Pb isotopic analyses (by TIMS) yield an upper intercept age of 730 ± 4 Ma (MSWD = 1.7), which we interpret as the time of magmatic crystallization of the zircons. This is coincident with 11 SHRIMP spot analyses, which yield a mean age of 729 ± 7 Ma (MSWD = 0.37). Metamorphism, at 522 ± 17 Ma as suggested by monazite, caused partial Pb-loss during local recrystallization of zircon. Lu-Hf isotopic data for three whole-rock samples of nepheline-bearing gneiss are collinear with those for zircon megacrysts, and correspond to an age of 584 ± 17 Ma (MSWD = 0.37. We interpret the Lu-Hf array to represent a mixing line defined by the Hf isotopic signature of primary zircon and that of the rock-forming minerals reset during metamorphic (re-)crystallization; hence the 584 Ma age is likely geologically meaningless. Given the well-defined association of nepheline syenites (and phonolitic volcanic equivalents) with continental rifting, we suggest that the Tambani body represents a magmatic product formed at 730 Ma during the break-up of the Rodinia supercontinent. The 522 Ma age is akin to other Pan-African metamorphic ages that record collisional suturing events during the final assembly of Gondwana. Zircon-bearing nepheline gneisses thus preserve a record of intra-continental rifting and of continental collision in southern Malawi.     

Petrology,geochemistry and geochronology of the Chilka Lake igneous complex,Orissa state,India

The Chilka Lake igneous complex of Orissa, the largest known anortosite massif of the Indian Shield, occurs in a catazonal environment of high-grade metamorphics of the Eastern Ghats Precambrian Orogenic Province. The syntectonic massif consists of the anorthositic Balugaon dome, leuconoritic Rambha lobe and quartz-mangeritic Kallikota cover. A completely gradational suite comprising anorthosite-leuconorite-norite-minor jotunite (the anorthositic suite) constitutes most of the complex. The subordinate of suite of acid rocks spatially associated with this is of a broad quartz-mangeritic lithology with minor granitic rocks (the acidic suite). Geochemical evolution of the complex in the sequence anorthosite-leuconorite-norite-jotunite-acidic rocks shows moderate iron enrichment in the noritic-jotunitic stage and is marked by an overall decrease in Al₂O₃, CaO, MgO, Ni/Co, Sr/Ba, K/Rb and increase in SiO₂, K₂O, V/Ni, K/Ba and Rb/Sr. Such progressive variation in geochemical parameters appears (i) essentially gradual and frequently overlapping in rock members of the intergradational anorthositic suite and (ii) rather abrupt across transition zones between the anorthositic suite and the acidic suite due to near absence of intervening intermediate lithologies. RbSr whole rock isochron studies indicate that the complex was emplaced ca. 1400 Ma ago. The initial ⁸⁷Sr/⁶⁸Sr (0.70661) implies limited hybridisation of the parent magma prior to emplacement. A critical appraisal of all the available evidence suggests that (i) the anorthositic suite of rocks form a perfectly consanguinous and comagmatic assemblage and (ii) the spatially associated acidic suite emerged through a convergence of magmatic and metasomatic processes (the latter brought about by contact anatexis of the host rocks). The complex as well as the host metamorphics are intruded by an atectonic suite of noritic dykes emplaced ca 850 Ma ago.     

辽宁海城大房身稀有金属伟晶岩包裹体研究及找矿意义

大房身3号伟晶岩脉是含铀、铌、钽等稀有金属伟晶岩矿床,分异较好,可分为4个岩相带。经对各带石英中包裹体的研究,表明含矿带含挥发份H₂O和CO₂较高,流体包裹体丰度较大,富含纯CO₂包裹体及含液相CO₂包裹体。该伟晶岩与围岩接触界线清楚,其边缘相含有围岩的捕掳体。伟晶岩结晶分异好,矿物成分简单,以长石、石英为主,其核心带产有巨晶状黑云母和微斜长石。包裹体气相成分中不含游离氧（O₂）。这些特点说明该伟晶岩是由硅酸盐熔浆在埋深大、较封闭的环境下,缓慢结晶分异而成。     

Silicate globules in kyanite from grospydites of the Zagadochnaya kimberlite pipe,Yakutia: The problem of the origin

The results of complex study of silicate globules and α-quartz paramorphs after coesite in kyanite from grospydites from the Zagadochnaya kimberlite pipe, Yakutia, using optical and scanning electron spectroscopy, electron and ion microprobes, LA ICP MS and Raman spectroscopy, are presented. The existence of radial fractures diverging from silicate globules into the matrix (kyanite) attests to the fact that the content of the globules is extremely condensed. A zonal structure is usually typical for globules: a coat and a core, which can be explicitly distinguished under the electron microscope, can be differentiated in them. Compositionally, the coat of the globule corresponds to potassium feldspar (wt %: 66.4 SiO₂; 16.9 Al₂O₃; 0.4 FeO; 0.1 CaO; 0.2 Na₂O; 14.7 K₂O). The globules were also detected in which along with K, a high content of Na and Ca was also ascertained in the silicate coat. The globule coat is considerably enriched with Ba, La, Ce, Nb, and a number of other noncompatible elements as compared with xenolith minerals. The water content in globules is ∼0.6 wt %. As compared with the host mineral (kyanite), the core part of the globules is also enriched with Co, Ni, Zn, and Cu; their content in kyanite is negligibly low. The entire data collection attests to the fact that the formation of silicate globules could have been caused by interaction of the conservated fluid and/or water-silicate melt with the host mineral and crystalline inclusions of clinopyroxene and garnet with decreasing pressure during the transportation of grospydite xenoliths by the kimberlite melt to the Earth’s surface.     

A modeling of the structure and favorable H-docking sites and defects for the high-pressure silica polymorph stishovite

Employing first-principles methods, the docking sites for H were determined and H, Al, and vacancy defects were modeled with an infinite periodic array of super unit cells each consisting of 27 contiguous symmetry nonequivalent unit cells of the crystal structure of stishovite. A geometry optimization of the super-cell structure reproduces the observed bulk structure within the experimental error when P1 translational symmetry was assumed and an array of infinite extent was generated. A mapping of the valence electrons for the structure displays mushroom-shaped isosurfaces on the O atom, one on each side of the plane of the OSi₃ triangle in the nonbonded region. An H atom, placed in a cell near the center of the super cell, was found to dock upon geometry optimization at a distance of 1.69 Å from the O atom with the OH vector oriented nearly perpendicular to the plane of the triangle such that the OH vector makes a angle of 91° with respect to [001]. However, an optimization of a super cell with an Al atom replacing Si and an H atom placed nearby in a centrally located cell resulted in an OH distance of 1.02 Å with the OH vector oriented perpendicular to [001] as observed in infrared studies. The geometry-optimized position of the H atom was found to be in close agreement with that (0.44, 0.12, 0.0) determined in an earlier study of the theoretical electron density distribution. The docking of the H atom at this site was found to be 330 kJ mol^–1 more stable than a docking of the atom just off the shared OO edge of the octahedra as determined for rutile. A geometry optimization of a super cell with a missing Si generated a vacant octahedra that is 20% larger than that of the SiO₆ octahedra. The valence electron density distribution displayed by the two-coordinate O atoms that coordinate the vacant octahedral site is very similar to those displayed by the bent SiOSi angles in coesite. The internal distortions induced by the defect were found to diminish rather rapidly with distance, with the structure annealing to that observed in the bulk crystal to within about three coordination spheres.