Phosphorus fractionation and release characteristics of sediment in the Saemangeum Reservoir for seasonal change

Periodical algal blooms result in deposition and release of phosphorus (P) from the sediment into the water. Therefore, during seasonal changes when algal particles begin to settle to the bottom, understanding the behavior and distribution characteristics of the P in sediment is the most important key to manage the water quality of the Saemangeum Reservoir. In this study, the variation of water quality and sediment composition including chlorophyll-a (Chl-a) and P was investigated to determine the interaction between water and sediment. The study focused primarily on algal particle sedimentation that affects the P release and mineralization of sediment. The Chl-a concentration in water showed a sharp decline in October when the algae began to die in the fall, and afterward the concentration of chemical oxygen demand (COD) and total P (TP) in the sediment increased due to the sedimentation of decaying algal particles in November. During the same period of time, the readily bio-available P (RAP) in the sediment showed a drastic increase in the upper region where the Chl-a concentration of water was high. In sequence, the high RAP zone shifted from the upper region to the lower region in the early winter. The RAP shift was considered to be derived from the physical flow of the overlying water from which the decomposing algae settled on the surface of the sediment. The Saemangeum Reservoir was constructed recently; therefore, all the types of inorganic P fractions except soluble reactive phosphorus (SRP) that exist on the bottom surface of the lake and the marsh's sediment layer were not sufficient to significantly influence the overlying water. On the other hand, the released P from the algae was distinct and sensitive to the seasonal change. In conclusion, the algal particle sedimentation was important to control eutrophication rather than P release from the mineralized inorganic P of the sediment surface layer in the Seamangeum Reservoir.     

Application of Lithium Isotope Geochemistry to the Study of the Continental Geothermal System

The lithium-rich brine in salt lakes is the main raw material of the world’s lithium products, while the continental geothermal fluids with a high salinity often contain a high concentration of lithium. Continental geothermal system is the focus in the study of geothermal formation mechanism. However, less attention is paid to the system due to the complexity of lithology, and the application of lithium isotopes in this field has not been systematically recognized. The newest application and progress of lithium isotope geochemistry in continental geothermal research in recent years were discussed, the problems in this field were put forward, and future research methods and directions were expected. The study of continental geothermal fluids should attach great importance to the application of Li-B-Sr-U multi-isotopic method, and should also be combined with water-rock reaction experiments under different temperature conditions. Moreover, in the future, the research on continental geothermal system should pay more attention to the various sediment/rock lithium isotopic compositions and their spatio-temporal distribution characteristics in the regional or geothermal field’s scales, mineralogy of reservoir rock, and behaviors of lithium isotopes related to the formation of secondary minerals in the process of water-rock interaction, in order to reveal the complex process of fluid evolution in the geothermal system and provide scientific reference for the exploration, exploitation and utilization of lithium resources in the system.     

Total Organic Carbon (TOC) as a Sum Parameter of Water Pollution in Selected Polish Rivers (Vistula,Odra, and Warta)

This paper reports on total organic carbon (TOC) and its fractions dissolved organic carbon (DOC) and particulate organic carbon (POC) studied in different Polish rivers. The samples investigated came from the Vistula, Odra, and Warta rivers, and were compared with similar data on river waters available in the literature. The DOC concentrations ranged from 10.0 to 14.2 mg/L and did not vary during the vegetative season. The POC values considerably increased from May through September and reached a maximum in summer. Results for the years 1991τ1996 evidenced a significant increase in the POC value for the Polish rivers from 10.8 to 24.5 mg/L, in comparison with analogous values for West European rivers and North American ones. The enhanced values of TOC and POC were interpreted as being due to anthropogenic pollution.     

The rare earth element (REE) mineralisation potential of highly fractionated rhyolites: A potential low-grade,bulk tonnage source of critical metals

The rare earth elements (REE) have become crucial for modern industry, technology and medicine, with the increase in demand for these elements over the past few years currently being met by relatively few well-known mineral deposits. This lack of a secure supply of the REE has led to increased research into potential alternative sources of these in demand elements. The primary fractionation processes involved in the petrogenesis of highly fractionated high-silica rhyolites can cause the magmas that form these units to become preferentially enriched in the REE, especially in the more valuable heavy REE (HREE), although this is dependent on the mineral assemblages fractionated by the system in question, a factor that is in turn a function of the source and tectonic setting of a given magmatic event. The mineralogy of the REE is also important, with volatile exsolution and vapour-phase activity within highly evolved rhyolite systems potentially having a key role in concentrating the REE and other elements into concentrations (and more importantly potentially acid leachable and therefore processable minerals) that may be economically viable to extract. This, combined with the fact these rhyolites are often enriched in other critical and/or economically important metals (e.g., Y, Nb, Ta, Be, Li, F, Sn, Rb, Th, and U) means that these volcanic units should be considered as potential sources of these critical metals. In addition, the large volume nature of these rhyolites combined with the fact they frequently crop out at the Earth’s surface makes them ideally suited for more economical bulk open pit extraction. This suggests that these high-silica REE-enriched rhyolites should be considered potential REE analogues of bulk-tonnage, low-grade porphyry Cu deposits, warranting further investigation to determine whether these rhyolites are a viable new source of the REE (especially the HREE) and are potential targets for future mineral exploration.     

Ferromanganese Nodules and their Associated Sediments from the Central Indian Ocean Basin: Rare Earth Element Geochemistry

The rare earth element (REE) distribution in nine deep-sea ferromanganese nodules and their associated siliceous sediments from the Central Indian Ocean Basin (CIOB) have been studied to elucidate the REE relationship among them. Total REE concentration varies from 398-928 ppm in the nodules and 137-235 ppm in the associated sediments, suggesting two- to four-fold enrichment in the nodules compared to associated sediments. REE of nodules and their associated sediments show a positive correlation, suggesting REE are supplied from a common source such as seawater. The positive correlation between REE of nodules and sediments from the CIOB is contrary to the competitive scavenging of REE between nodules and sediment in the equatorial Pacific Ocean. REEs in the nodules are carried by Fe, P, and Ti, whereas in the sediment they are carried by P and Mn phases. A similar REE fractionation pattern with middle REE enrichment over heavy and light REE in both the nodules and their associated sediment suggest fractionation is independent of REE abundance and their carrier phases.     

腾冲地块晚白垩世-古近纪富锡花岗岩成因:岩浆源区及分异演化条件SCIEI北大核心CSCD

腾冲地块锡成矿作用主要与晚白垩世-古近纪岩浆活动相关,但仅矿区花岗岩体具有较高的锡含量(平均25×10^(-6)),区域上同时代的非成矿花岗岩体并未发生锡的富集。本文通过搜集分析现有研究数据,总结了富锡成矿岩体和区域非成矿岩体在岩浆源区、演化条件和结晶分异程度的异同:区域非成矿岩体锆石ε_(Hf)(t)值(-15.1~+3.39)表明,自东北向西南幔源物质加入有升高的趋势,但区域玄武岩中低含量的Sn(1.61×10^(-6))表明幔源物质混入不利于岩浆中锡的富集。晚白垩世部分非成矿岩体与成矿岩体具有相同ε_(Hf)(t)(-9.7)值,表明其皆源于古老地壳物质的部分熔融,但岩体均表现为准铝质-弱过铝质特征,且锆石Hf同位素(t_(DM2)=1724Ma)和全岩Nd同位素(t_(DM2)=1836Ma)二阶段模式年龄基本一致,因此其源区可能并非富锡的高黎贡山群变质沉积岩,而可能是其中未经风化的变质花岗岩。根据腾冲地块地层厚度(28km)和莫霍面深度(47~35km)推断岩浆源区至少位于地下30km(8.4kbar),由于仅靠地温梯度(25℃/km)无法达到初始熔融温度(>1066℃),源区部分熔融过程很可能受地幔热的影响。根据Fe_(2)O_(3)/FeO比值,非成矿岩体(0.59)与成矿岩体(0.48)均具有较低的氧逸度,属钛铁矿系列,但成矿岩体的结晶分异程度明显高于非成矿岩体,且成矿岩体富含挥发分,高含量的挥发分降低了岩浆固结温度(650~550℃),延长了结晶分异时间,促进了锡在晚期岩浆中的富集。因此腾冲地块富锡花岗岩主要是普通岩浆在低氧逸度环境下发生高度结晶分异的结果。     

Preliminary15N studies on atmospheric nitrogenous trace gases

Preliminary nitrogen isotope data for ammonia from animal urine, fuel combustion, fertilizer use and fertilizer factories have been measured or estimated. It turns out that direct nitrogen isotope measurements of atmospheric ammonia at Jülich are in the expected range calculated from the ranges of different sources. For deposition of atmospheric ammonium in Jülich-rain a depletion in¹⁵N with respect to atmospheric ammonia has been found which is explained by isotope fractionations during rainout and washout. In correspondence with this fractionation model are nitrogen isotope data of rain-ammonium from coastal areas, which are enriched in¹⁵N due to the fact that sea water acts as a sink for atmospheric ammonia.For Jülich rain-nitrate a pronounced seasonal trend has been detected with lower¹⁵N data in spring and summer than in autumn and winter. This trend is interpreted by different nitrogen isotope data of anthropogenic and natural nitric oxides which have been measured or estimated from isotope fractionation effects during nitrification and denitrification reactions in soils. It should be possible to get better global estimations for anthropogenic and natural nitric oxides from nitrogen isotope measurements.     

有效全岩成分的计算方法及其在变质相平衡模拟中的应用

变质相平衡模拟是变质岩领域近几十年最重要的进展之一，它已经成为确定变质作用P-T-t轨迹和探索变质演化过程的有力工具。变质岩的矿物组合不但与其形成的温度（T）和压力（P）条件有关，而且受控于岩石的全岩成分（X）。但是变质岩通常是不均匀的并且往往保留两期以上的矿物组合，因此计算不同成分域或不同变质演化期次的有效全岩成分是模拟P-T视剖面图的核心问题之一。在中-低温变质岩中，石榴石变斑晶的生长会不断地将其核部成分"冻结"而不参与后续变质反应，这导致根据实测全岩成分计算的P-T视剖面图无法有效地模拟石榴石幔部或边部生长阶段的变质演化过程。"瑞利分馏法"和"球体积法"利用电子探针实测的石榴石成分环带可以模拟计算石榴石各个生长阶段所对应的有效全岩成分，本文推荐使用这两个方法来处理石榴石变斑晶的分馏效应问题。相比较而言，石榴石在高温变质岩中通常无法保留生长阶段的成分环带特征，这是因为石榴石成分在高温条件下会发生扩散再平衡，并同时与多数基质矿物达到热力学平衡，这时一般不需要考虑石榴石的分馏效应。但是高温变质岩通常会发生部分熔融并伴随熔体的迁移，进而改变岩石的有效全岩成分。因此，通过P-T视剖面图模拟熔体迁移前后的变质演化过程需要使用"相平衡法"计算迁移的熔体成分以及熔体迁移前后岩石的有效全岩成分。此外，后成合晶与反应边是变质岩中最常见的退变质反应结构，但是后成合晶或反应边中的矿物之间并未达到热力学平衡。这种情况需要结合岩相学观察和矿物成分，利用最小二乘法确定后成合晶或反应边中发生的平衡反应方程式，进而获取变质反应发生时的有效全岩成分并通过计算P-T视剖面图来估算退变质的温压条件。除此之外，岩石体系中三价铁（Fe₂O₃）和H₂O含量的估算一直以来都是相平衡模拟研究中的难点，本文推荐使用P/T-X（Fe³⁺/Fe^tot，MH₂O）视剖面图来确定这两个组分的含量，这是因为P/T-X图可以估算各个变质演化阶段或特定矿物组合的Fe₂O₃或H₂O含量。     

Melting of enstatite from 13 to 18 GPa under hydrous conditions

Experiments on MgSiO₃ enstatite were conducted in the pressure range from 13 to 18 GPa under hydrous conditions in order to clarify the effect of water on the melting phase relations of enstatite at pressures corresponding to the Earth’s mantle transition zone. In some previous experiments [Geol. Soc. Am. Bull. 79 (1968) 1685; Phys. Earth Planet. Inter. 85 (1994) 237], incongruent melting behavior to form Mg₂SiO₄ forsterite and SiO₂ enriched liquid up to 5 GPa was observed, and congruent melting behavior at pressures up to 12 GPa was observed. Under hydrous conditions, we found that the melting reaction changes from congruent to incongruent at around 13.5 GPa. Liquid formed above 13.5 GPa is enriched in MgO component relative to MgSiO₃ because it coexists with stishovite (SiO₂). Moreover, the solidus temperature decreases drastically at around 13.5 GPa, in unison with the change in the melting reaction. The solidus temperature is about 1400 °C at 13 GPa, but approximately 900 °C at 15 GPa. Our results show that the liquidus phase changes from clinoenstatite to stishovite with increasing pressure and water content above 13.5 GPa. MgSiO₃ enstatite is one of the major constituent minerals in the Earth’s mantle, and it is expected that MgO-enriched liquid will be generated in the transition zone if water is present.