花岗岩铀成矿作用的模拟实验

根据花岗岩铀成矿作用的"铀预富集系"和沉淀等理论进行一系列实验模拟。对华南产铀花岗岩及其母岩进行"部分熔融实验",可知其寒武系等下古生界是形成产铀花岗岩重要母岩之一。实验表明,岩浆温度下产铀花岗岩流体(f)与共存相熔体(m)铀分配系数Kf/m测定值明显<1,这说明铀强烈趋向熔体,不断重熔会使花岗岩更富铀。岩浆结晶过程中流体(f)与结晶熔体(c)铀分配系数Kf/c随结晶作用加强而增长,说明对形成热液铀矿床有利。岩浆结晶过程中晶体与晶体共存相间铀的分配系数中,以含铁物质与铀矿物共存相间铀的分配系数为最大。此结果与产铀花岗岩含晶质铀矿,黄铁矿含铀较高,黑云母结晶捕获一定量铀的地质事实相一致。成矿前的"前提蚀变"阶段的铀活化实验得出,黑云母在白云母化时铀释出约达3%～30%;花岗岩白云母化过程中,全岩将有30%～60%的铀释出。在花岗岩白云母化时锆石迁出铀可达1.4%～21%。晶质铀矿在花岗岩白云母化时发生崩解和部分溶蚀,实验得出转入溶液的w(U)为(1.04～1.30)×10-6。大量水-岩反应的热液实验表明,在封闭体系统的溶液中,随压力(pH2O)降低,产铀花岗岩中的铀溶解增加(最高可增达2～3个数量级),从而打破了"压力降低铀沉淀"的一般传统说法。对热液铀矿成矿机理进行多次实验取得如下新认识:(1)适度脱碳酸(或脱CO2)对铀沉淀有利;也可使铀-硅-碳酸盐体系中的"铀-硅分离"沉淀;(2)成矿溶液"pH显著降低(落差)"是铀沉淀几大因素中的关键。这些实验结果证实和发展了"地层、岩石等预富集系"理论,并有重要找矿意义。     

胶东地区地质体的含金性与金成矿关系

本文以新近的测试分析资料为基础,较系统地论述了胶东金矿集中区地质体的含金性。大量的测试资料表明：变质岩和地层中金的丰度并非很高（ω（Ａｕ）１．９×１０＾－９￣４．５×１０＾－９,而与金矿有关的花岗岩金的量更低（ω（Ａｕ）０．２７×１０＾－９￣１．８３×１０＾－９。地质体的成因、演化与金矿化的相互关系,表现随岩石成分向酸性变化和碱交代程度增加过程,金及相关成矿元素的含量降低;花岗岩形成过程和碱交代作     

Hydrothermal Mobilization and Enrichment of Iron in the Iron Deposits of the Middle—Lower Yangtze Valley District

There are two main types of iron deposits in the Middle-Lower Yangtze Valley district.Both of them underwent post-magmatic hydrothermal processes during ore formation.Iron in the hydrothermal ore bodies was derived largely through mobilization from substantially consolidated diroitic intrusives.Wall-roch alteration zonation indicates that iron-mobilizing hydrothermal fluids evolved in a trend of decreasing alkalinity,which is suggested by regularly distributed wall-rock alterations formed by iron-mobilizing hydrothermal fluids and is in contradiction with the current chloride,chloride complex and bicarbonate models for iron mobilization.The close association of carbonatization with iron ores and the high concentrations of reduced gases such as CO,CH4 and H2 in fluid inclusions suggest that iron is most probably transported in the form of iron carbonyls during post-magmatic hydrothermal processes. In the light of the iron carbonyl mobilization model,explanations are made of the constraints on ores of some geologic factors such as melanocratic alteration,carbonatization,carbonate strata,structural fractures,cyptoexplosive pipes and embryo ores.     

Lithogenic concentrations of trace metals in soils and saprolites over crystalline basement rocks: A case study from SW Nigeria

In this study, an assessment of the lithogenic concentrations of trace metals in soils and saprolite over basement rock units in Ibadan, SW-Nigeria is presented in respect of bedrock types and geochemical controls on the weathering-associated release of trace metals. Consequently, soil, weathered and fresh rock samples from the Precambrian Basement of SW Nigeria were collected from three different bedrock units within Ibadan metropolis and subjected to mineralogical and geochemical analyses. The analytical results revealed major proportions of oxides in the range of 18–20% Al₂O₃, 2–6% Na₂O and 1–6% K₂O for weathered profiles over granite-gneiss and pegmatite units, compared to 2–3% Al₂O₃, <0.5% Na₂O and <1.0% K₂O over schist-quartzite. For the trace elements, weathered profiles on granite-gneiss and schist-quartzite settings exhibit similar enrichment trends (enrichment factor, EF l) for most of the trace elements, unlike the pegmatite bedrock. However, enrichments are relatively greater in the top soil unit compared to the intermediate saprolite unit, especially for Pb, Ni, Zn, Cr, Co, Rb, Sr and Ba, a situation attributed to leaching and redistribution within the weathered profiles through pedogenetic process and percolating groundwater.Furthermore, the estimated weathering indices using Ruxton Ratio (RR = {SiO₂/Al₂O₃}) and Chemical Index of Alteration (CIA = 100{Al₂O₃/[Al₂O₃ + CaO + Na₂O + K₂O]}) revealed RR of 2.9–3.7 and CIA of 54–73% for granite-gneiss and pegmatite units, implying medium levels of weathering, compared to RR of 30.8–35.5 and CIA of >60% for schist-quartzite units, which suggest weak chemical weathering. Also, the estimated high percentage loss, especially for Pb, Rb, Sr, Ba relative to the bedrocks, shows that the trace elements can be mobilized within the weathering profiles even at a low degree of chemical weathering. Such weathering-induced release of trace metals is of environmental significance as natural lithogenic input sources and as background reference for future monitoring of possible human/anthropogenic impacts.     

金在碱性富硅热液中溶解和迁移的实验研究

实验测定了金在碱性富硅溶液中的溶解度，并标定了Ａｕ与ＳｉＯ２之间的配合关系Ａｕ＾＋Ｈ２ＳｉＯ＾－４＝ＡｕＨ３ＳｉＯ＾０４在８０￣２５０℃的温度范围内，其平衡常数为ｌｇＫ＝－１．９８８９＋１００８５。１８／Ｔ（Ｔ为绝对温度）各温度下的平衡常数值与Ａｕ－ＨＣｌ－ＳｉＯ２－Ｈ２Ｏ体系中得到的结果一致。它表明溶液在酸性和碱性条件下，ＳｉＯ２均作为配位体，与Ａｕ形成ＡｕＨ３ＳｉＯ＾０４在热液中溶解、迁移。Ａ     

Underestimation of roughness in rough rock joints

Numerous studies have been made to improve Barton's shear strength model for the quantification of rock joints. However, in these previous studies, the roughness and shear strength of the rock joint have been underestimated especially for relatively high undulated profiles (joint roughness coefficient (JRC) >14). The main factors of roughness underestimation in rough rock joints are investigated for the proper quantification of rock joint roughness. The aliasing effect and the roughness characteristics are analyzed by using artificial joint profiles and natural rock joint profiles. A 3D camera scanner is adopted to verify the main source of underestimation when using conventional measurement methods. Shear strength tests are carried out by using two types of shear apparatus to study the roughness mobilization characteristics, which may also affect the roughness underestimation. The results of joint roughness assessment, such as aliasing and undulation of waviness, show that the roughness can be underestimated in relatively rough joint profiles (JRC>14). At least two components of roughness parameters are needed to properly represent the joint roughness, for example, the amplitude and the inclination angle of joint asperity. Roughness mobilization is affected by both the normal stress and the asperity scale. Copyright © 2008 John Wiley & Sons, Ltd.     

Accumulation of total CO2 during stagnation in the Baltic Sea deep water and its relationship to nutrient and oxygen concentrations

Accumulation of total CO₂ (C_T) was investigated in the sub-halocline deep water of the Gotland Sea (Baltic Sea) during a period of stagnation from 1995 to 1999. Depth profiles for C_T, nitrate, phosphate, and oxygen were measured during seven cruises in a grid consisting of 26 stations. The mean C_T increased by more than 60 μmol/kg from October 1995 to July 1999 corresponding to a mean accumulation rate of 1.1 mol/m² year. Taking into account vertical mixing, the vertical distribution of the C_T accumulation was used to determine mineralization rates at different depths. High rates immediately below the halocline indicated the existence of a fraction of organic matter, which is rapidly mineralized during sinking through the water column. A second fraction is more refractive and accumulates at the sediment surface in the deep center of the basin where it is slowly mineralized and partly buried. Phosphate release rates in anoxic waters and especially at the redoxcline were substantially higher than those estimated on the basis of the carbon mineralization and the Redfield C/P ratio. This is attributed to non-Redfield mineralization ratios and the dissolution of iron oxide/phosphate associates. The formation of nitrate by mineralization under oxic conditions was almost completely compensated by denitrification. Using the carbon mineralization rates and a C/N ratio of 8.4, a denitrification rate of 280 mmol/m² year was obtained, which approximately balances the input of nitrate/ammonia into the surface water. Relating the apparent oxygen utilization (AOU) to the C_T fraction that was generated by mineralization yielded a carbon mineralization/O₂ consumption ratio of 0.83.     

Soil erosion processes in subtropical plantations (Diospyros kaki) managed under flood irrigation in Eastern Spain

Persimmons (Diospyros kaki) are trees cultivated under subtropical environmental conditions but are also found in other regions such as the Mediterranean. However, no research has been conducted to investigate soil erosion processes under Mediterranean soil management systems characterized by flood irrigation and/or tillage. The Improved Stock Unearthing Method (ISUM) for assessing long-term soil mobilization was applied to two fields, one under tillage and the other under no-till with herbicide within a 25-year old Mediterranean persimmon plantation. Replicating methods used in vineyard studies, graft unións on persimmon plants were used as passive bio-indicators of soil surface changes in this study. The tilled field showed a total soil mobilization volume of 48.4 m³ on a 408.5 m² plot, representing a total soil loss of 52.6 Mg ha^-1 yr^-1. For the plot (468 m²) managed with no-till and herbicide, the results indicated total soil mobilization of 33.6 m³ which translates to 31.9 Mg ha^-1 yr^-1. It is concluded that flood irrigation is able to modify the runoff pathways and landforms in Mediterranean persimmon plantations, and the flood impact is more extensive when combined with tillage. For the first time, ISUM has been successfully applied to estimate soil erosion in a plantation under flood irrigation.     

Hydrogeochemical contrast between two study areas of Bengal delta,India: A comparative insight to understand arsenic mobilization process in shallow aquifers

A comparative hydrogeochemical study evaluated arsenic release mechanism and differences in contamination levels in the shallow groundwater of two areas within the deltaic environment of West Bengal (i.e. Karimpur and Tehatta blocks of Nadia district) in India. Groundwaters from both the areas are Ca-Na(K)-Cl-HCO₃ type with highly reducing character (−110.16 ± 16.85 to −60.77 ± 16.93 mV). Low correlations among As, Fe, and Mn and the higher association between As and DOC are indicative of microbial decomposition of organic matter enhancing the weathering of shallow aquifer materials. Arsenic contamination in groundwater is higher in Karimpur (95 ± 81.17 μg/L) than that in Tehatta (43.05 ± 41.06 μg/L). The release mechanism of arsenic into groundwater is very complex. Low Fe (0.27–4.78 mg/L and 0.81–4.13 mg/L), Mn (0.08–0.2 mg/L and 0.03–0.22 mg/L), and SO₄²⁻ (3.82 ± 0.31 and 2.78 ± 0.40 mg/L) suggest that the mechanism of arsenic release is not a single mechanistic pathway. Clustering of redox-active parameters in the principal component planes indicate that the reductive dissolution, and/or weathering/co-precipitation of Fe/Mn-bearing minerals in the shallow aquifer sediments control the dominant mechanistic pathway of arsenic release.     

黑云母与氯化物热水溶液相互作用的实验研究

本文在500℃和1×108Pa条件下，利用冷封口高温高压水热系统和焊封金管技术实验研究了黑云母和Na－Ca－氯化物溶液的相互作用，着重考察反应不同时间的黑云母表面和溶液化学的变化。黑云母中的K、Fe和Si不同程度地进入溶液相，而溶液中原有的Na和Ca含量降低；SEM／EDAX和EMAX研究表明，反应后的黑云母边缘部分明显失去K和Fe，应得到相当数量的H2O和一些Ca。黑云母中Fe活化的控制反应可能是H+交代作用。