Assessment of the collapse mechanisms of tufa deposits

This research assesses the collapse mechanisms of tufa deposits. The city of Antalya, located on the Mediterranean coast of Turkey, has been settled on tufa deposits. By the end of 1980s, the area behind the tufa cliffs became the site of high-rise residential buildings. Some of these buildings have suffered from foundation instabilities, which have given rise to cracking and fissuring of the walls, and overall tilting. The collapsible behaviour upon loading and/or wetting of some tufa deposits has caused foundation settlement.

Voids, bonding of grains and grain properties of the collapsible tufa were investigated using optical and scanning electron microscopes. Our studies indicate that the collapse behaviour of tufa is affected mainly by depositional environment and microfabric. Laboratory tests have been performed in order to determine the index properties and the collapse potential of tufa samples. Young tufa deposits near the surface are weakly bonded with thin films of carbonate cement, giving rise to high void ratios. Analysis of geotechnical parameters has shown that the collapse potential of tufa is closely related to the natural void ratio and the amount of cement binding the grains.     

造山型金矿构造控矿作用

造山型金矿具有重要经济价值, 其成矿理论研究对全球金矿勘查和开采具有重要意义。为了更好的理解挤压和伸展背景下深成-中成-浅成造山型金矿成矿过程中控矿断裂形成过程、构造控制流体流动、流体就位机制以及矿化样式之间的关系, 本文系统综述了岩石破裂原理、挤压和伸展体制断裂网络结构, 全面梳理全球不同构造体制和成矿深度造山型金矿的构造控矿样式、矿脉几何学和蚀变矿化网络结构, 取得以下认识: (1)在挤压背景下, 深成金矿通常受韧-脆性逆冲剪切带控制, 发育窄蚀变带、大脉状和层压状矿石以及黑云母-角闪石-磁黄铁矿等蚀变矿化组合; 中成金矿受脆-韧性逆冲剪切带、褶皱转折端的滑脱空间和里德尔剪切派生裂隙控制, 发育窄-中等宽度蚀变带、层压状和网脉状矿石以及绿泥石-方解石-绢云母-黄铁矿化蚀变矿化组合; 浅成金矿受脆性剪切带和次级毛细裂隙控制, 发育宽蚀变带、角砾状和浸染状矿石以及绢云母-碳酸盐-硫化物(黄铁矿、毒砂)等蚀变矿化组合。研究表明上述不同成矿深度金矿构造-蚀变-矿化差异由构造、流体压力、水岩反应强度和岩石抗张强度等共同控制, 流体就位和矿质沉淀机制由深部的强构造流体互馈、弱水岩反应强度向浅部的弱构造流体互馈、强水岩反应强度转换。(2)在伸展背景下, 深成金矿通常受韧-脆性张剪断裂带控制, 发育窄蚀变带、大脉状矿石以及黑云母-角闪石-斜长石-磁黄铁矿等蚀变矿化组合; 中成金矿受脆-韧性张剪断裂带控制, 发育窄-中等宽度蚀变带、断层充填脉和网脉状矿石以及绢云母化-硅化-绿泥石化蚀变矿化组合; 浅成金矿受脆性断层角砾破碎带控制, 发育宽蚀变带、角砾状和浸染状矿石以及绢云母-碳酸盐-硫化物(黄铁矿、毒砂)等蚀变矿化组合。伸展体制控矿构造多为先存断裂改造和再活化, 当先存断裂优选定向时断裂发生再活化, 成矿流体以充填断裂成矿为主, 当先存断裂差异定向时流体压力驱动水力破裂形成新的断裂并改造先存构造。造山型金矿构造控矿研究已由传统的二维空间定性精细刻画逐渐向三维空间定量可视化拓展。

     

Geochemical controls on a calcite precipitating spring

A small spring fed stream was found to precipitate calcite by mainly inorganic processes and in a nonuniform manner. The spring water originated by rainwater falling in a 0.8 km² basin, infiltrating, and dissolving calcite and dolomite followed by dissolution of gypsum or anhydrite. The Ca²⁺/Mg²⁺ indicates that calcite is probably precipitated in the subsurface from a supersaturated solution. This water emerges from the spring still about 5 times supersaturated with respect to calcite and continues calcite precipitation. When 10 times supersaturation is reached, due to CO₂ degassing the precipitation is more rapid. The calcite accumulation from the stream with a flow of 5 l/s is calculated to be 12600 kg/yr with the highest rates in areas where CO₂ degassing is the greatest. The non-equilibrium, as shown by the high calcite supersaturation, is also reflected in a variable partitioning pattern for Sr²⁺ between the water and calcite.     

Geochemical controls on lead concentrations in stream water and sediments

The equilibrium distribution of lead in solution and adsorbed on cation exchange sites in sediment theoretically may be calculated from equations representing selectivities of substrate for lead over H⁺, Ca²⁺ and Na⁺, and the stabilities of lead solute species. Such calculations include consideration of total concentrations of major ions, cation exchange capacity (CEC) of substrate, and pH, at values expected in various natural systems. Measurements of CEC and selectivity coefficients were made for synthetic halloysite, a finely divided amorphous 1:1 clay prepared by precipitation from a mixture of solutions of aluminum and silica. Where suspended sediment having the same properties is present in concentrations of 10-1,000 mg/1 at pH 6–8, more than 90% of the lead present can be adsorbed on sediment surfaces. The cation exchange behavior of lead and other minor cationic species in natural systems could be predicted by this type of model if enough other supporting information were available. Information of the type needed describing natural stream sediments, however, is presently inadequate for accurate predictions.     

A review of the Tagus river tufa deposits (central Spain): age and palaeoenvironmental record

Here we determined the aminostratigraphy and aminochronology of tufa deposits located in central Spain associated with the Tagus river and some of its tributaries (the Henares, Dulce, Cifuentes, Ruguilla, Trabaque, Escabas and Guadiela rivers). We used aspartic acid and glutamic acid racemization ratios obtained from the ostracod Herpetocypris reptans. Tufa accumulations were found to be of different origins; those in the Henares, Cifuentes and Ruguilla rivers are of paludal origin, while those in the Dulce and Tagus rivers are of fluvial origin. A generally good correspondence was found between the age of the deposits and the position of the terraces above the current thalweg. However, the geomorphological evolution of the Henares, Cifuentes and Ruguilla rivers (infilling of pre-existing valleys) has produced deposits of distinct ages at the same elevation above the current river thalweg, and sometimes, older tufas are located below younger ones.We distinguished eight main tufa-deposition episodes. These occurred predominantly during even Marine Isotopic Stages (MIS), at 406 ± 90 (MIS 11), 264 ± 68 (MIS 7e), 189 ± 40 (MIS 7a), 130 ± 27 (MIS 6-5e), 101 ± 25 (MIS 5c), 32 ± 10 (MIS 3), 14 ± 4 (MIS 1), and 6 ± 2 (MIS 1) ka. These results are in agreement with the dating of similar deposits from nearby areas and other zones of Spain and Europe. The tufa stable-isotope compositions were similar to other examples in central and southern Spain and their plot falls in the same field as other lowland European stream tufas. Oxygen stable isotopes were influenced mainly by temperature and rainfall. The δ¹³C values indicated a major effect of soil-derived carbon rather than carbon from the catchment area, but moderated in each tributary by evaporation, flow regime and biological effects (photosynthesis).     

Geochemical evidence of aeolian deposits in European soils

Hafnium (Hf) and zirconium (Zr) concentrations measured in over 4100 agricultural soil samples from Europe were assessed with the focus on their relationship to the distribution of aeolian deposits, such as loess and coversands. Comparison of extractable (aqua regia; ICP‐MS) and total (XRFS) concentrations shows that only 1.0 to 1.7% of the total Hf and Zr is chemically extractable because of the resistant nature of their host minerals. Resistate minerals, such as zircon, are commonly found in the predominantly silty fraction of loess deposits. In this study a statistical analysis of total Hf and Zr soil data from areas with and without loess was carried out to derive threshold values of 10 mg kg^?1 (Hf) and 318 mg kg^?1 (Zr). These values were subsequently applied across the project area in an attempt to indicate the presence of aeolian deposits. The spatial distribution of above‐threshold concentrations suggests a more extensive and coherent loess belt across central and eastern Europe, providing additional evidence of loess across Brittany, Aquitaine and near the Vosges mountains in France as well as in the basins of central and northern Spain. Above‐threshold concentrations were also detected in loess regardless of its thickness, emphasising the importance of the abundance of zircon in the upper part of the soil profile rather than the actual thickness of the deposit. Soil data however, failed to indicate various loess facies within most of the Pannonian Basin, suggesting that this approach only works where deposits contain a sufficient amount of zircon. This may also explain why the extensive coversands across northern Germany and Poland were largely undetected. This study demonstrates that continental‐scale soil geochemical data can help identify and map the distribution of zircon‐rich loess and coversand, and subsequently enhance and improve current knowledge of the extent of these deposits.     

胶东型金矿床控矿构造及成矿模式

胶东型金矿床受断裂构造控制，断裂控矿规律一直是地质勘查和研究的重点问题。为深入研究断裂对金成矿的控制作用，本文基于大量矿床勘查和地质调查资料，通过对典型断裂剖面和断裂与矿体空间关系的构造解析，判断了成矿期断裂的性质和应力状态，讨论了断裂产状变化的控矿机理，提出了胶东型金矿新的构造成矿模式。将胶东主要控矿断裂分为Ⅰ级缓倾角断裂、Ⅱ级陡倾角断裂和Ⅲ级陡倾角张裂脉，三者分别控制了破碎带蚀变岩型、复合类型和石英脉型金矿床。金矿体主要赋存于断裂产状转折部位，蚀变岩型矿体赋存于断裂的倾角变缓部位，石英脉型矿体赋存于断裂倾角变陡部位。缓倾角断裂控制的矿体具有总体侧伏角小、富矿柱侧伏角大的“双向”侧伏特征。矿体产状与断裂产状的关系指示，三山岛、焦家和招平三条控矿断裂成矿期均属右行正滑或右行张扭性，金牛山断裂具有左行正滑特征。根据金矿体产状分析的胶西北金成矿小区区域构造应力场σ1为294°∠82°和269°∠78°，焦家断裂的σ1为300°∠67°、311°∠78°和321°∠81°，招平断裂北段σ1为130°∠65°和138°∠69°，反映了胶西北玲珑花岗岩体分布区域总体以垂向主压应力为主，其东、西两侧的边界断裂处的主压应力方位分别沿SE向和NW向指向岩体，成矿期断裂处于NW—SE向拉张状态。胶东东部邓格庄金矿田的σ1为287°∠0°，以水平主压应力为主。综合分析认为，产状变化的具张扭性质的断裂是金的有利赋矿构造，断裂的产状变化对金矿体具有明显的控制作用，断裂结构和流体性状的变化是金矿阶梯成矿的关键因素，断裂沿走向和倾向的产状转折联合控制了金矿体的侧伏。胶东地区早白垩世深部大量岩浆岩快速侵位，导致地壳强烈隆升产生伸展构造，来自不同深度和层次岩浆房及不同源区的岩浆梯次上侵，为深部含金流体活化、迁移提供了热动力条件和流动通道，含金流体到达地壳浅部在断裂产状变化的减压扩容空间卸载成矿。     

Geochemical controls on leaching of lignite-fired combustion by-products from Greece

The mobility of inorganic pollutants is of key concern for a range of industrial and engineering applications of fly ash produced during the combustion of lignite in power generation. This paper investigates the role that the geochemical features of lignite, the ash composition and the partitioning of elements during combustion play in determining leaching properties of lignite fired by-products. The work is based on surveys on three lignite-fired power plants in Greece. Calcium-rich ashes show a high abatement potential for SO₂ and other gaseous pollutants. For most elements, the concentrations in the parent lignite and the ashes follow the same trend. Relative enrichments in Cd, Co, Cr, Cu, Mo, Ni, Pb, U, V, W, Zn fingerprint the regional and local geological settings of the lignite basins. The total and leachable concentrations of highly volatile elements are strongly influenced by the interaction with ubiquitous free lime. A broad array of elements is highly insoluble in alkaline ash, while a few oxyanionic-forming elements display substantial mobility. Their mode of occurrence in the parent lignite plays a primary role in the leaching of combustion ashes. The outcomes of this study may assist in addressing the impact of co-firing high ash or high Ca alternative fuels on the leaching properties of combustion by-products.     

Geochemical mechanism of alkali metasomatism and formation of iron deposits

Discussed in this paper are the processes of albitization and iron activation during the formation of iron deposits, the transport and hydrolysis of iron, chemical reaction characteristic of wall-rock alteration responsible for the localization of iron deposits, the dynamic factors affecting these reactions and systematic variations in pH of ore-forming solutions. A metasomatic series of Na→ Ca→ Fe is noticed when diorite and dark minerals + anorthite + quartz react with 1–3m NaCl solutions at 400°–500°C. Hydrolysis of FeCl₂ has been experimentally studied as a function of temperature and pressure. It is suggested that the pH of ore-forming solutions varies in the direction of alkalic→intermediate→acid→intermediate←kalic from early to late stages.     

Geodynamic controls on diamond deposits: Implications for Australian occurrences

Conventional diamond exploration guidelines predict that economic diamond occurrences will be restricted to Archaean cratons, where the lithosphere is thick and cool, and diamond is the stable form of carbon in the lower portions of the lithosphere. However, Australia's current economic diamond deposits are not well predicted by these conventional exploration guidelines. Tomographic images show that Australia's economic diamond deposits lie at step changes in lithospheric thickness within dominantly cratonized Proterozoic provinces with thick (≥ 200 km) lithosphere. The thickest portions of the seismic lithosphere in Australia occur not under the major Archaean cratons, rather the central Proterozoic regions of the continent. We use a numerical code to show that such features are stable, and that the longevity of the diamond stability field is dependent on distance to the continent–ocean boundary, local depth of the chemical boundary layer (CBL), and proximity to changes in CBL depth. We also show that abrupt changes in lithospheric thickness focus lithospheric stress gradients, affecting melt migration paths, and that continental melt production is enhanced in regions adjacent to major cratons. Diamond pipes occur where conditions conducive to diamond stability and deep-seated alkaline volcanism (kimberlite or lamproite) occur simultaneously, and the common confluence of these factors at abrupt changes in lithospheric thickness marks them as potential exploration targets.     

若干以沉积岩为容矿围岩的热液矿床硫同位素地球化学研究

文章对与沉积岩容矿有关的热液广西高龙微细浸染型金矿、新疆霍什布拉克铅锌矿、广西盘龙铅锌矿和下雷锰矿等矿床硫化物进行硫同位素测定,硫同位素组成分别为-15.3‰~+15.6‰,-18.8‰~+24.2‰,-21.0‰~+26.4‰,-32.6‰~+32.2‰。硫同位素可以达到平衡(高龙、霍什布拉克、下雷),也可以没达到平衡(盘龙)。δ34SΣS值在+13‰~+28‰之间,表明与沉积岩容矿热液矿床中硫来源于海水硫酸盐还原硫,但不排除有岩浆硫的加入。     

Sedimentology of coexisting travertine and tufa deposits in a mounded geothermal spring carbonate system,Obruktepe, Turkey

The recent discoveries of deeply buried Cretaceous reservoir bodies in the Atlantic Ocean revealed that relationships between the distribution of spring carbonate deposits and faults are poorly understood. The well‐exposed Quaternary deposits at Obruktepe (Denizli Basin, Turkey) provide an opportunity to reconstruct the three‐dimensional sedimentary architecture of such a system. Integration of sedimentological, lithofacies and geochemical analyses reveals complexity in the lateral relationships between sedimentary environments, faults and geothermal spring carbonates. Five environmental systems are distinguished based on the lithofacies analysis: (i) vent; (ii) smooth slope; (iii) travertine‐terrace; (iv) tufa‐barrage; and (v) flood systems. Encrusting, baffling and settling sedimentary processes are reflected in data acquired at several scales, from lithofacies observations to the morphology and arrangement of geobodies, together with microfabrics and stable carbon and oxygen isotope data. Mean values of +4·9‰ δ¹³C and −8·74‰ δ¹⁸O Vienna PeeDee Belemnite reflect geothermal circulation of springwaters. The environmental distribution and lithofacies indicate a lateral continuum between travertine and tufa deposits within this hot spring system. This finding supports two depositional models in which water flow variation is the main control on both CaCO₃ precipitation and the resulting formation of travertine and tufa. The proposed models address the factors responsible for the development of these complex mound‐shaped carbonate spring deposits, and how they are related to fluid circulation at depth and in association with faults.     

Geochemical specialization of terrigenous deposits of the Bashkirian meganticlinorium

The materials on the geology and geochemical specialization of Riphean terrigenous rocks of the Bashkirian meganticlinorium, including carbonaceous shale and conglomerate, are reported. Conglomerate is characterized by a high concentration of Au and PGEs mostly related to intensely dislocated zones. It is concluded that potentially ore-bearing zones in terrigenous deposits of the Bashkirian meganticlinorium were formed as a result of multistage polygene processes controlled by the Riphean–Vendian geodynamic evolution of the region.     

甘肃天水夏家坪金矿地质特征

夏家坪金矿位于西秦岭反＂S＂弧形构造东段Au-Ag-Cu-Fe-Pb-Zn成矿带中,矿体产出受下古生界李子园群沉积-火山岩系控制。矿体多呈带状、透镜状产出,具收缩膨大、尖灭再现及分支复合特征。容矿岩石主要为变砂（泥）岩、破碎石英脉、硅化角砾岩等。矿石类型以构造蚀变岩型为主,局部为石英脉型。围岩蚀变具分带性,矿化可分为早期的金和晚期的银铅锌两个主要成矿阶段。     

Tectonic controls on gold deposits and their environmental impact, New Zealand

New Zealand is an active orogenic belt which varies along its length from continental collision to continent–ocean subduction tectonics. Mesothermal gold deposits, with rare mercury, have formed in collisional settings from late Mesozoic to Pleistocene, with youngest deposits along the axis of the actively rising Southern Alps mountain chain. Epithermal gold and mercury deposits have formed, and are still forming associated with calcalkaline volcanism above the subduction zone, and with basaltic volcanism associated with extensional faulting. The environmental impact of mineral deposits is related to tectonic setting, mineralogy, and climate, all of which are governed by the geometry of the orogen. Mesothermal mineralisation added carbonates to calcite-bearing host rocks in what is now cool semiarid or extreme Alpine settings, and oxidation of sulphides does not result in significant acidification of the environment. Arsenic is the principal metal of environmental significance, and is readily mobilised from these deposits at neutral to alkaline pH. Mercury may be leached from cinnabar and/or gold on geological time scales. In contrast, epithermal mineral deposits have hydrothermal clay alteration, locally further clay-altered by deep temperate to subtropical weathering, and calcite is generally subordinate to sulphides. Acidification accompanies oxidation of these deposits, and copper, cadmium, lead and zinc are readily mobilised into the environment. Mercury can be mobilised by these acid solutions as well, where mercury occurs in minerals other than cinnabar.     

Some geochemical controls on Ni and Co concentrations in marine ferromanganese deposits

The uptake of Ni and Co in the hydrous Mn oxide or the amorphous Fe-oxide phases of ferromanganese deposits in the oceans was studied by electron-microprobe analyses of 17 natural manganese nodules and by experiments on desorption-dissolution of these metals from synthetic Fe oxide or Mn oxides and natural nodule material. Ni was found to occur nearly always in the Mn-oxide phases of natural nodules, while Co occurs both in the Mn-oxide and Fe-oxide phases, with a slight preference for the latter. The solubility of Ni and Co (from coprecipitates of these metals with Fe hydroxides after aging) in seawater was found to depend strongly on the crystallinity of the host phase. The adsorption of Co by the synthetic Mn oxides from seawater was higher than that of Ni. The experimentally determined solubility of Ni and Co in seawater from natural nodule material is extremely low and matches the concentration range of these metals in ocean water.     

Geochemical controls on sediment reactivity and buffering processes in a heterogeneous aquifer

The injection and recovery of oxic water into deep anoxic aquifers may help to alleviate short- and long-term imbalance between freshwater supply and demand. The extent and structure of physical and geochemical heterogeneity of the aquifer will impact the water quality evolution during injection, storage and recovery. Water–sediment interactions within the most permeable parts of the aquifer, where the bulk of the injectant will penetrate, may dominate, however, water quality may also be impacted by interactions within the finer-grained, less permeable but potentially highly reactive media. In this study, the heterogeneity of the reductive capacity of an aquifer selected for water reuse projects was characterised, the amount, type and reactivity of the sedimentary reductants present determined, and the relationship between reductive capacity and sedimentary lithologies quantified. The average potential reductive capacities (PRC_TOT), based on total organic C and pyrite concentrations of the sediment, were quantified for sands (382 μmol O₂ g⁻¹), clays (1522 μmol O₂ g⁻¹), and silts (1957 μmol O₂ g⁻¹). Twenty-seven samples, spanning the three different lithologies, were then incubated for 50 days and the measured reductive capacities (MRC) determined for the sands (29.2 μmol O₂ g⁻¹), silts (136 μmol O₂ g⁻¹), and clays (143 μmol O₂ g⁻¹). On average, the MRC were 10% of the PRC_TOT. The main consumers of O₂ were pyrite (20–100%), sedimentary organic matter (SOM; 3–56%), siderite (3–28%) and Fe(II)-aluminosilicates (8–55%). The incubation data plus hydrogeochemical modelling, indicated that pH-buffering was controlled firstly by dissolution of trace level carbonates, followed by dissolution of feldspars. Zinc, Co, Ni, Cd and Pb were readily mobilized during incubation.     

湖南省沉积型锰矿床地球化学特征

湖南省锰矿资源丰富,类型多样,沉积型锰矿是最重要的类型,主要沉积成锰期集中在早南华世大塘坡期、中奥陶世烟溪期及晚二叠世孤峰期.通过对三个主要成锰期代表性锰矿石电子探针分析显示,三个主要成锰期所成锰矿床,矿石组分类似,组成矿石的锰矿物主要为锰的碳酸盐,包括菱锰矿、钙菱锰矿、镁菱锰矿、锰白云石、锰方解石等.三个主要成锰期代表性锰矿石及地层稀土元素地球化学标准化参数与配分模式显示,各成矿期含锰地层与锰矿石之间无显著差异,暗示了它们是相似的沉积环境下形成的产物,为正常沉积与热水沉积的复合.一方面,各成矿期岩、矿石稀土元素总量中等偏高,表现为正常沉积物的稀土元素特征.另一方面,在北美页岩标准化配分曲线上,呈现出水平或重稀土相对富集的左倾配分曲线,Ce的负异常,又是典型热水沉积成因呈现出的稀土元素地球化学特征.δCe异常特征,指示了成锰作用处于波动的缺氧还原/氧化沉积环境.     

Geochemical and palaeohydrological controls on the composition of shallow groundwater in the Netherlands

With the exception of the south of the country, the Netherlands has a strong bipartite hydrogeology: the Holocene part with a coastal dune belt and confining top layer of clay and peat further inland, and the Pleistocene, where thick phreatic aquifers dominate. This research aimed to ascertain the geochemical and palaeohydrological controls on the composition of shallow groundwater in 27 regions. Close to 6000 groundwater analyses were grouped and interpreted in terms of 1. salinity, 2. redox status, 3. acid/base and carbonate status and 4. natural nutrients NH₄ and PO₄. The a priori classification into geographical regions and geological formations revealed many statistically significant differences in medians, even for geologically or geographically related data groups. The compound-specific interpretation indicates that there are geogenically controlled, systematic differences in groundwater composition at the regional scale. The imprint of the geological sediments on the groundwater composition decreases in the order marine/estuarine via limnological, fluvial to aeolian. The imprints with respect to pH and carbonate status, natural nutrients and redox status are not necessarily interrelated. The vertical stratification in groundwater composition turns out to be often limited at the regional scale due to mutual occurrence of infiltrating and exfiltrating groundwater in regions and either the presence of a highly reactive Holocene, confining top layer or temporal changes in contamination. In the Holocene part, the salinity is controlled by the palaeoenvironmental conditions during the Holocene and by the recharge origin: the average Cl concentration decreases from estuarine via lagoonal to the former Zuider Sea (which was a bay). The most reduced states and also the highest nutrient concentrations and highest CO₂ pressure are related to the presence of Holocene marine sediments in the confining top layer. Degradation of marine-derived organic matter as a nutrient source, is likely more intense in the Holocene deposits than that of peat and sedimentary remnants of terrestrial plants. A broad range in pH, carbonate status and redox status is encountered in the Pleistocene part. Here, the palaeohydrological evolution in terms of carbonate leaching together with the geological controls on the calcareous nature of the shallow sedimentary deposits cause regional differences in pH, calcite saturation and silicate weathering. One region with Late Pleistocene limnological deposits has deviating groundwater characteristics and appears more similar to the Holocene part of the Netherlands. Furthermore, reactive Fe is not abundant in all Pleistocene fluvial sediments nor is it maximally mobilised, as not all anoxic groundwater in these sediments is siderite-saturated. This leads to considerable intra- and inter-region variability.     

Geochemical types of vein wolframite deposits in Nanling Region

In accordance with the characteristics of associated minerals, trace elements in the altered rocks around the veins and the compositions of wolframite and mica, the vein wolframite deposits in the Nanling Region can be divided into two geochemical types: the wolframite-berylmolybdenite-bismutite (native bismuth) type and the wolframite-cassiterite-sulfide (copper, zinc, lead) type. Vein wolframite deposits of these two geochemical types were formed under different geological conditions. The wolframite-beryl-molybdenite-bismutite (native bismuth) type may be connected with high pH-Eh conditions, whereas the wolframite-cassiterite-sulfide (copper, zinc, lead) type with low pH-Eh conditions. It is concluded that the two geochemical types of vein wolframite deposit are genetically related to two different geochemical types of granite in the Nanling Region.