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The chemical and isotopic characteristics of the water and suspended particulate materials (SFM) in the Yangtze River were investigated on the samples collected from 25 hydrological monitoring stations in the mainsteam and 13 hydrological monitoring stations in the major tributaries during 2003 to 2007. The water samples show a large variation in both δD (-30‰ to -112‰) and δ18O (-3.8%. to -15.4‰) values. Both δD and δ18O values show a decrease from the river head to the Jinsha Jiang section and then increase downstream to the river mouth. It is found that the oxygen and hydrogen isotopic compositions of the Yangtze water are controlled by meteoric precipitation, evaporation, ice (and snow) melting and dam building. The Yangtze SPM concentrations show a large variation and are well corresponded to the spatial and temporal changes of flow speed, runoff and SPM supply, which are affected by the slope of the river bed, local precipitation rate, weathering intensity, erosion condition and anthropogenic activity. The Yangtze SPM consists of clay minerals, clastic silicate and carbonate minerals, heavy minerals, iron hydroxide and organic compounds. From the upper to lower reaches, the clay and clastic silicate components in SPM increase gradually, but the carbonate components decrease gradually, which may reflect changes of climate and weathering intensity in the drainage area. Compared to those of the upper crust rocks, the Yangtze SPM has lower contents of SiO2, CaO, K2O and Na2O and higher contents of TFe2O3 and trace metals of Co, Ni, Cu, Zn, Pb and Cd. The LREE in the Yangtze SPM is also slightly higher than that of the upper crust From the upper to lower reaches, the CaO and MgO contents in SPM decrease gradually, but the SiOz content increases gradually, corresponding to the increase of clay minerals and decrease of the carbonates. The δ30SiSPM values (-1.1‰ to 0.3‰) of the Yangtze SPM are similar to those of the average shale, but lower than those of the granite rocks (-0.3‰ to 0.3‰), reflecting the effect of silicon isotope fractionation in silicate weathering process. The δ30Sispm values of the Yangtze SPM show a decreasing trend from the upper to the middle and lower reaches, responding to the variation of the clay content. The major anions of the river water are HCO3–, SO42–, Cl–, NO3–, SiO44–and F– and the major cations include Ca2+, Na+, Mg2+, K+ and Sr2+. The good correlation between HCO3– content and the content of Ca2+ may suggest that carbonate dissolution is the dominate contributor to the total dissolved solid (TDS) of the Yangtze River. Very good correlations are also found among contents of Cl–, SO42–, Na+, Mg2+, K+ and Sr2+, indicating the important contribution of evaporite dissolution to the TDS of the Yangtze River. High TDS contents are generally found in the head water, reflecting a strong effect of evaporation in the Qinghai-Tibet Plateau. A small increase of the TDS is generally observed in the river mouth, indicating the influence of tidal intrusion. The F– and NO3– contents show a clear increase trend from the upstream to downstream, reflecting the contribution of pesticides and fertilizers in the Chuan Jiang section and the middle and lower reaches. The Dsi shows a decrease trend from the upstream to downstream, reflecting the effect of rice and grass growth along the Chuan Jiang section and the middle and lower reaches. The dissolved Cu, Zn and Cd in the Yangtze water are all higher than those in world large rivers, reflecting the effect of intensive mining activity along the Yangtze drainage area. The Yangtze water generally shows similar REE distribution pattern to the global shale. The δ30SiDiss values of the dissolved silicon vary from 0.5‰ to 3.7‰, which is the highest among those of the rivers studied. The δ30SiDiss values of the water in the Yangtze mainsteam show an increase trend from the upper stream to downstream. Its DSi and δ30SiDiss are influenced by multiple processes, such as weathering process, phytolith growth in plants, evaporation, phytolith dissolution, growth of fresh water diatom, adsorption and desorption of aqueous monosilicic acid on iron oxide, precipitation of silcretes and formation of clays coatings in aquifers, and human activity. The (δ34SSO4 values of the Yangtze water range from -1.7‰ to 9.0‰. The SO4 in the Yangtze water are mainly from the SO4 in meteoric water, the dissolved sulfate from evaporite, and oxidation of sulfide in rocks, coal and ore deposits. The sulfate reduction and precipitation process can also affect the sulfur isotope composition of the Yangtze water. The 87Sr/86Sr ratios of the Yangtze water range from 0.70823 to 0.71590, with an average value of 0.71084. The 87Sr/86Sr ratio and Sr concentration are primary controlled by mixing of various sources with different 87Sr/86Sr ratios and Sr contents, including the limestone, evaporite and the silicate rocks. The atmospheric precipitation and anthropogenic inputs can also contribute some Sr to the river. The δ11B values of the dissolved B in the Yangtze water range from 2.0‰ to 18.3‰, which is affected by multifactors, such as silicate weathering, carbonate weathering, evaporite dissolution, atmospheric deposition, and anthropogenic inputs.

The Maoniuping REE deposit, located about 22 km to the southwest of Mianning, Sichuan Province, is the second largest light REE deposit in China, subsequent to the Bayan Obo Fe-Nb-REE deposit in the Inner Mongolia Autonomous Region. Technically, it is located in the transitional zone between the Panxi rift and the Longmenshan-Jinpingshan orogenic zone. It is a carbonatite vein-type deposit hosted in alkaline complex rocks. The bastnaesite-barite, bastnaesite-calcite, and bastnaesite-microcline lodes are the main three types of REE ore lodes. Among these, the first lode is distributed most extensively and its REE mineralization is the strongest. The δ34SV-CDT values of the barites in the ore of the deposit vary in a narrow range of +5.0 to +5.1‰ in the bastnaesite-calcite lode and +3.3 to +5.9‰ in the bastnaesite-barite lode, showing the isotopic characteristics of magma-derived sulfur. The δ13CV-PDB values and the δ18OV-SMOW values in the bastnaesite-calcite lode range from −3.9 to −6.9‰ and from +7.3 to +9.7‰, respectively, which fall into the range of “primary carbonatites”, showing that carbon and oxygen in the ores of the Maoniuping deposit were derived mainly from a deep source. The δ13CV-PDB values of fluid inclusions vary from −3.0 to −5.6‰, with −3.0 to −4.0‰ in the bastnaesitecalcite lode and −3.0 to −5.6‰ in the bastnaesite-barite lode, which show characteristics of mantle-derived carbon. The δDV-SMOW values of fluid inclusions range from −57 to −88‰, with −63 to −86‰ in the bastnaesite-calcite lode and −57 to −88‰ in the bastnaesite-barite lode, which show characteristics of mantle-derived hydrogen. The δ18OH2OV-SMOW values vary from +7.4 to +8.6‰ in the bastnaesitecalcite lode, and +6.7 to +7.8‰ in the bastnaesite-barite lode, almost overlapping the range of +5.5 to +9.5‰ for magmatic water. The 4He content, R/Ra ratios are (13.95 to 119.58)×10−6 (cm3/g)STP and 0.02 to 0.11, respectively, and 40Ar/36Ar is 313 ± 1 to 437 δ 2. Considering the 4He increase caused by high contents of radioactive elements, a mantle-derived fluid probably exists in the inclusions in the fluorite, calcite and bastnaesite samples. The Maoniuping deposit and its associated carbonatite-alkaline complex were formed in 40.3 to 12.2 Ma according to K-Ar and U-Pb data. All these data suggest that large quantities of mantle fluids were involved in the metallogenic process of the Maoniuping REE deposit through a fault system.

Experiments for oxygen isotope exchange between ferberite and water were carried out and the following equation on oxygen isotope fractionation between ferberite and water against temperature was obtained: 10001nα FeWO4 −H2O = 1.04 × 106T −2 − 2.5 Combining this equation with the equation of Clayton et al. (1972) on oxygen isotope fractionation between quartz and water, an equation on oxygen isotope fractionation between quartz and ferberite was obtained: 10001nαSiO2 − FeWO4 = 2.34 × 106T−2 − 0.4 The Bigeleison-Mayer function method was used to calculate the oxygen isotope fractionation between quartz and ferberite. The theoretical curve obtained agrees with the experimental calibration results quite well in the temperature range of study. The above calibrated equation has been used in 5 world famous tungsten deposits to determine their temperatures of formation. The results show that the temperature range for an idividual deposit determined by this geothermometer agrees with those obtained from fluid inclusion determination and other isotope geothermometers.

A new experimental calibration was undertaken in this study to get a more reliable sphalerite-galena sulfur isotope geothermometer. The experimental conditions selected in study were very similar to those of natural hydrothermal solution. The high-precision SF6 method was used in sulfur isotope analyses. The obtained calibration curve for sulfur isotope fractionation between sphalerite and galena can be expressed with the equation 10001nαSp-Gn = 0.74times106T−2+0.08.

Silicon shows no variation in its chemical valence in nature and exists mainly in the form of silicon-oxygen tetrahedra, so very small silicon isotope thermodynamic fractionation occurs and the resultant silicon isotope variation is limited. Dynamic fractionation of Si isotopes during precipitation of SiO2 from a solution is a main factor leading to substantial variations in silicon isotopes in nature. In this experimental study, we determined the dynamic fractionation factorα for silicon isotopes during precipitation of SiO2 from the solution. And in combination of α, a theoretical explanation is presented of the considerably low δ30Si values of black smokers on modern seafloor, Archean banded magnetite-quartzite and clay minerals of weathering origin, and of clearly high δ30Si values of siliceous rocks in shallow-sea carbonate platforms.

Publisher Summary This chapter discusses the proposed analytical methods for Silicon isotope determinations. A remarkable progress is reported in the field of silicon isotope analysis. There are four isotopes of silicon that exist in the natural environment namely 28 Si, 29 Si, 30 Si and 32 Si. The first 3 isotopes are stable isotopes and the last one is radiogenic. There are two methods presently available for silicon isotope analyses such as gas source isotope ratio mass-spectrometry (IRMS) and secondary ion microprobe mass-spectrometry (SIMS). The IRMS is a routine method and suitable for all kinds of samples. It provides excellent precision, but needs relatively large samples. SIMS is able to determine Si isotopes on a small spatial scale but its precision is low, so that it is only applicable to the study of meteorites at present. The SiF4 method is the conventional extraction method with high precision. The laser fluorination method is successfully used in the sample preparation for silicon isotope analyses of micro sample. The secondary ion probe mass spectrometry also became a powerful tool for in situ micro-field analyses of silicon isotopes, although the precision of measurement is relatively low. These methods will be improved in the future, providing better and better technique base for silicon isotopic study.