Liu Congqiang

Geochemistry of carbonatites in Maoniuping REE deposit, Sichuan Province, China

Carbonatites in the Maoniuping REE deposit, Sichuan Province, which are spatially and temporally associated with rare earth mineralization, were emplaced at the time of Himalayan. The rocks are carbonatite-syenite complexes, with the mineral assemblages of calcite-aegirine-acmite-arfvedsonite-mica-orthoclase. The rocks are characterized by the enrichment in incompatible elements, such as Sr, Ba and REE, with C and O isotopic compositions of the “primary igneous carbonatites”, relatively high initial 87Sr/86Sr ratios and low ɛnd values. All of these suggest that the rocks were derived from the metasomatic enriched mantle. It is demonstrated by geological and geochemical evidence that the mixing of the Himalayan subducting crustal materials with mantle source EM1 is probably the main factor responsible for the formation of carbonatites. The carbonatite-syenite complexes were generated from liquid immiscibility of CO2-rich alkalic silicate magma, which was derived from partial melting of the metasomatic mantle.

Complex trace-element effects of mixing-fractional crystallization composite processes: applications to the Alaer granite pluton, Altay Mountains, Xinjiang, northwestern China

Abstract Complex patterns of intersection of linear with power-function curvilinear data point arrays are observed on ratio-ratio correlation plots of trace elements in the Alaer Palaeozoic granite pluton, Altay Mts., Xinjiang, northwestern China. Data points in the linear array are relatively lower in SiO 2 content and differentiation index (D.I.), and they become progressively decreased rightwards along the array in abundances of Zr and Hf, which could be better explained by mixing between zircon-rich restite and the granite melt. Data points in curvilinear arrays are higher in SiO 2 content and D.I. value and, therefore, have presumably suffered more extensive fractional crystallization. The complex patterns cannot be resolved with the classical models. Two models for the complex trace-element effects of mixing-fractional crystallization are developed in the paper, with which the patterns can be resolved. In all models, we begin with a linear data-array formed by simple two-component mixing, and then superpose fractional crystallization trends to generate a family of curves. Model (1) ( D 1 ≤ D 3 , D 2 ≤ D 3 or D 1 ≥ D 3 , D 2 ≥ D 3 ): in the general situation, fractional crystallization curves assume a cluster of concave-up or convex-up power-function curves which intersect the initial mixing line sloping positively. Special cases 1–3 ( D 1 = D 2 ≠ D 3 or D 1 ≠ D 2 = D 3 or D 2 ≠ D 1 = D 3 ): the fractional crystallization curve is transformed into a straight line. Special case 4 ( D 1 = D 2 = D 3 ): the fractional crystallization line coincides with the initial mixing line. Model (2) ( D 1 > D 3 > D 2 or D 1 D 3 D 2 ): fractional crystallization curves assume the form of hyperbolic curves which intersect the initial mixing line sloping negatively. In all of the two models the iso-fraction lines are uniformly steeper ( D 1 D 2 ) or more gentle ( D 1 > D 2 ) than the initial mixing line. Iso-fraction lines increase ( D 1 D 2 ) or decrease ( D 1 > D 2 ) progressively in slope with the decrease of residual liquid mass fraction F . Through modelling of the data point arrays on ratio-ratio correlation plots of trace elements, one can discern and distinguish between simple mixing, pure fractional crystallization and mixing-fractional crystallization composite processes. Initial compositions of the magma and the mixing modes can also be constrained. Through modelling the functional form, concavity or convexity, and the power index of the fractional crystallization curves, the relative incompatibility of trace elements can be estimated semi-quantitatively and the incompatibility sequence can be established. It is demonstrated through modelling that the Alaer granite pluton experienced mixing-fractional crystallization composite processes. The mixing mode is probably described by the restite model. The incompatibility sequence of the 7 concerned trace elements is D Th D La D Y ≈ D Nb ≈ D Ta D Hf D Zr . This incompatibility sequence may be applicable to the anatectic granites.

Effects of heavy metal contamination on microbial biomass and community structure in soils

Zinc smelting near Magu Town, Hezhang County, Guizhou Province, resulted in vegetation destruction and the accumulation of heavy metals, to varying extent, in adjacent soils, where up to 162.2–877.9 mg·kg−1 Zn, 37.24–305.6 mg·kg−1 Pb, and 0.50–16.43 mg·kg−1 Cd, were detected. These values greatly exceed the background levels of these elements in soils. The concentrations of heavy metals (particularly Pb, Zn) were positively correlated with the contents of Fe2O3 and Al2O3 in the soils, showing that Fe and Al oxides play an important role in retaining heavy metals. Chemical fractionation indicates that Pb and Zn were associated mainly with Fe and Mn oxides and minerals, whereas Cd was dominated by exchangeable form. Microbial biomass in the soils was relatively low, in the range of 57.00–388.0μg C·g−1, and was negatively correlated with heavy metal concentrations in the soils. The correlation coefficient of microbial biomass C to Zn concentrations in the soils was as high as −0.778 (p<0.01), indicating that the heavy metal contamination has toxic effects on microorganisms in soil. The results of Biolog measurements demonstrated that there were no significant changes in microbial community structure in the heavy metal contaminated soils. Gene fragments were similar to one another after the DNA was extracted from soil microbes and experienced PCR (polymerase chain reaction) and DGGE (denaturing gradient gel electrophoresis) reactions. These results indicated that light heavy-metal pollution may not result in any change in soil microbial community structure.

Study on the Flocculability of Metal Ions by Bacillus Mucilaginosus GY03 Strain

This study deals with the flocculability of two types of metal ions byBacillus mucilaginosus GY03 Strain, with an emphasis on the influence of pH conditions, volume and time of flocculants produced by GY03 Strain on the adsorption of metal irons such as Pb2+ and Mn2+ and the capabilities of flocculants to adsorb metal ions of different concentrations. The results showed that microbial flocculants produced byBacillus mucilaginosus GY03 Strain are highly capable of flocculating metal ions, but show different effectiveness with respect to the adsorption of Pb2+ and Mn2+. In accordance with the experimental data and actual waste-water treatment conditions, the relevant regression equation of flocculation has been deduced, which has found some application in practice. The experimental results of this study demonstrated that microbial flocculants produced byBacillus mucilaginosus can be used to treat metallic ion-containing waste water. In practical application the volume of microbial flocculants required and flocculation conditions should be taken into comprehensive consideration in accordance with the properties of metal ions, the composition of anions and the solubility of other metals, in combination with the cost and effectiveness of flocculants to be used. Flocculant used in this experiment has the advantages of being applied over a wide range of pH values, small flocculant volume, and rapid speed of flocculation. So this kind of flocculant is within excellent prospect of application.

Controls of interactions between iron hydroxide colloid and water on REE fractionations in surface waters: Experimental study on pH-controlling mechanism

The influence of pH on the partitioning behavior of REE at the water/particulate interface has been studied experimentally. At the beginning of colloid formation the adsorption of REE on iron hydroxide colloids is dominant, followed by REE desorption. Finally adsorption and desorption tend to reach equilibration. The capability of iron hydroxide colloids to adsorb the HREE is greater than that to adsorb the LREE. With increasing pH, LREE/HREE fractionations will take place between iron hydroxide colloids and water, leading to the reduction of their partition coefficient ratio (DLREE/DHREE). The DREE distribution patterns show Y anomalies (DY/DHo ;1), with obvious REE tetrad effects appearing under low pH conditions. Experimental results have shown that there do exist REE tetrad effects in nature. In addition to pH, the chemical type of surface water and ion intensity are also the important factors controlling REE tetrad effects and leading to fractionations between particulate-adsorbed REE and dissolved REE.

Noble gas abundances and isotopic compositions in mantle-derived xenoliths, NE China

Following the researches of helium isotopic compositions in mantle-derived xenoliths in eastern China, this study reported noble gas abundances and isotopic compositions of mantle-derived xenoliths from Kuandian of Liaoning Province, Huinan of Jilin Province and Hannuoba of Hebei Province. Compared with the middle ocean ridge basalt (MORB) and other continental areas, mantle-derived xenoliths in NE China are characterized by slightly low noble gas abundances, 3He/4He equivalent to or lower than that of MORB, 40Ar/36Ar lower than that of MORB, 38Ar/36Ar and Ne-Kr-Xe isotopic ratios equivalent to those of atmosphere. These results indicate the heterogeneity of subcontinental lithospheric mantle beneath northeastern China, that is, a MORB reservoir-like mantle beneath Kuandian and an enriched/metasomatized mantle beneath Huinan. Low 40Ar/ 36Ar ratios in the three studied areas may imply that a subducted atmospheric component has been preserved in the subcontinental lithospheric mantle.

Enzymatic and microbial degradation of organic matter in Lake Hongfeng, Guizhou Province, China

In this work, enzymatic and microbial degradation of organic matter in Lake Hongfeng, Guizhou Province, is described in terms of variations in DNA, α-glucosidase and sulfatereduction bacteria (SRB). Organic matter is degraded by microbes and extracellular enzymes excreted by the former, to a relatively low content below the 11-cm sediment depth. The distribution of DNA indicated that microbes are very active at the 9-cm sediment depth, where organic matter is degraded by microbes intensively. The contents of α-glucosidase are highest in suspend layer (0.75 μmol · min−1· g−1 dry sediments), showing that starch and hepatin in organic matter have been degraded intensively. α-glucosidase activity weakens with sediment depth. At the 11-cm depth where the degradation of organic matter started to slow down, α-glucosidase activity has been reduced to 0.17 μmol · min−1 · g−1 (dry sediment). Molecular biological research indicated that sulfate reduction bacteria (SRB) are distributed mainly at the upper 7-cm sediments in Lake Hongfeng. Combined with the results of research on the variations of organic matter and SO42−, it is indicated that SO42− is unlikely to become an important electron acceptor and sulfate reduction is not limited by the supply of organic matter in Lake Hongfeng.

A preliminary study on the distribution characteristics of nutrients (N, P, Si, C) in the Wujiang River Basin*

The distribution of nutrients (N, P, Si, C) in the Wujiang River surface water was studied during the high-flow and low-flow periods in 2002. The results showed that nitrate nitrogen (NO3-N) is the main form of dissolved inorganic nitrogen (DIN) in the Wujiang River Basin. It accounts for about 90% of DIN. The average NO3-N concentrations in the mainstream are 147.5 µM in the high-flow period and 158.0 µM in the low-flow period, respectively. The average concentrations of total phosphorus (TP) are 6.43 µM in the high-flow period and 4.18 µM in the low-flow period, respectively. Of the various forms of phosphorus, particulate phosphorus (PP) has the highest percentage (62.9%) of TP in the high-flow period. In the low-flow period, however, phosphate is the main form of phosphorus, which accounts for 49% of TP. With the Wujiangdu Reservoir as the boundary, the concentrations of DIN and phosphorus in the upper reaches are different from those in the lower reaches of the Wujiang River. As a whole, the concentrations of DIN and phosphorus are both higher in the low-flow period than in the high-flow period. The spatial and temporal variations of DIN and phosphorus concentrations suggested that DIN and phosphorus come from agricultural and domestic wastewaters and groundwaters and that the Wujiangdu Reservoir has an important impact on the concentrations and distribution of DIN and phosphorus in the Wujiang River. The distribution patterns of dissolved silica (DSi) and dissolved organic carbon (DOC) are similar. Both of them maintain no change in the whole course of the river and their concentrations (with the exception of the reservoir itself) are higher in the high-flow period than in the low-flow period. The average DSi and DOC concentrations in the mainstream are 85.4, 84.6 µM in the high-flow period and 60.8, 53.9 µM in the low-flow period, respectively. The concentrations of nutrients in most of the major tributaries are lower than in the mainstream. This suggested that the contributions of most tributaries are relatively small but importance should be attached to the influence of some individual tributaries such as the Qingshuijiang River and the Weng’ an River on the mainstream.

REE geochemistry of altered tectonites in the Huize base-metal district, Yunnan, China

Hydrothermally altered tectonites (e.g. mylonites, cataclasites) occur in ore-controlling fault zones in the Huize base-metal district. Non-altered wallrocks and altered but non-mineralized tectonites have similar REE characteristics indicating seawater origin of the host carbonate rocks but with significant terrigenous input. Calcite gangues in mineralized (argillaceous/barite-bearing) tectonites and tectonite ores contain the highest REE values and exhibit convex-upward and roughly roof-shaped REE patterns with positive Eu anomalies, which are typical of hydrothermal crustal fluids. Negative Ce and negative La anomalies in calcite gangues imply hydrothermal fluids that previously interacted with marine and terrigenous rocks underlying the carbonate host rocks. Similarities in the REE characteristics of mineralized tectonites with those of the non-altered wallrocks and non-mineralized tectonites support earlier propositions that hydrothermal fluids were derived from the Kunyang Group basement rocks. REE characteristics of mineralized (argillaceous/barite-bearing) tectonites indicate fluid-wallrock interactions during migration of hydrothermal fluids along faults. Convex-upward REE patterns of tectonite ores were likely due to remobilization of early-formed base-metal sulphides whereas convex-upward REE patterns of strongly mineralized tectonites (i.e. with disseminated–massive base-metal sulphides) were likely due to recrystallization of early formed calcite gangues. REE characteristics of altered tectonites due to fluid-rock interactions during fluid migration and metal/mineral remobilization/recrystallization are depicted in Y/Ho–La/Ho, Tb/Ca–Tb/La, and Yb/Ca–Yb/La plots of the data. Migration of hydrothermal fluids along ore-controlling faults was likely induced by seismic pumping associated with tectonic deformation, whereas the remobilization/recrystallization process likely occurred in ‘pressure shadows’ along ore-controlling faults.

Geochemical study of boron isotopes in the process of loess weathering

In this paper the boron contents and boron isotopic composition of acid-soluble phases in loess and paleosol samples are determined for the first time. The boron contents of acid-soluble phases in the Luochuan loess section (S0–S2) vary within the range of (0.8–2.7)×10−6 and their δ11 B values vary from −1.8‱ to +18.6‱, mostly within the range of 0−+10‱. The boron contents and δ11 B values of paleosol layers are higher than those of loess layers, especially in the loess layer S1. Varying chemical weathering intensity and loess adsorption capability are the main factors leading to the variations of boron contents and δ11B values of acid-soluble phases in the loess section. The variation of chemical weathering intensity in response to the variation of climatic conditions seems to be the main factor leading to the variations of boron contents and δ11B values of acid-soluble phases in the loess section.