恩施渔塘坝富硒碳质岩中硒的赋存状态

在渔塘坝富硒碳质岩中发现了自然硒及其系列硒矿物的组合.这些硒矿物有自然硒、方硒铜矿、硒铜蓝、水硒铁石、硒银矿、含硒黄铁矿、含硒黄铜矿和难以确定名称的Fe-Se矿物.其中自然硒、方硒铜矿和硒铜蓝的矿物组合主要分布在断层面附近的碳质硅质岩中,自然硒与方硒铜矿的矿物组合主要分布在高碳质泥岩中,水硒铁石及未确定的Fe-Se矿物主要赋存于露头处的富硒碳质岩中.硒矿物中除自然硒较普遍地存在外,其他矿物并不是均匀地分布于富硒碳质岩中,而是局部性地出现.Cu-Se矿物的大量发育表明铜可能在硒的表生迁移转化中起着某种重要的作用.     

渔塘坝硒矿床硒赋存形式的高分辨透射电镜研究

高分辨电镜研究发现渔塘坝硒矿石中硒主要以独立硒矿物和类质同象两种形式存在.独立硒矿物主要以自然硒大量出现,以有机吸附所占比重较大,而较少出现硒铁矿、硒银矿、蓝硒铜矿、硒铜蓝、方硒铜矿等独立硒矿物.以类质同象形式存在的硒,在Fe-S-Se系列中,以不同量替代S,形成的含硒黄铁矿和硒黄铁矿,颗粒很细,大多为纳米级(＜100nm).     

湖北恩施渔塘坝地区发现的系列硒矿物

湖北恩施渔塘坝发现了自然硒和硒的系列矿物.硒矿物有自然硒、方硒铜矿、硒铜蓝、水硒铁石、硒银矿和难以定名的Fe-Se矿物,含硒矿物有含硒黄铁矿和含硒黄铜矿.自然硒分布广泛,成因上可分为原生型、次生型和"石煤"燃烧型.自然硒与方硒铜矿的矿物组合在高炭质泥岩中比较发育,而与硒铜蓝和方硒铜矿的矿物组合主要分布在紧邻断层面的炭质硅质岩中,水硒铁石及未确定的Fe-Se矿物主要见于富硒炭质页岩露头、废弃"石煤"堆和石窑的废渣堆.自然硒、水硒铁石和铜硒矿物的大量发育,表明不同氧化还原条件对硒的表生迁移和转化起着重要作用.     

恩施硒中毒区土壤高硒的成因:自然硒的证据

在湖北恩施渔塘坝土壤硒分布的调查过程中,发现不同地段田地土壤中存在异常高硒样品。其硒含量变化范围是346~2018 mg/kg,平均(899±548)mg/kg(n=11),相对于坝内成土基岩和耕作土硒含量0.5 mg/kg与3.5 mg/kg的水平而言,表明这些土壤硒受到了外来源硒的严重污染。扫描电子显微镜的观察表明,这些土壤样品中均有大量晶体状自然硒的出现,其特征类似燃煤型成因的自然硒,证实了上世纪50年代后期恩施当地居民石煤火熏土作肥的耕作方式,并直接导致了田地土壤硒的骤然增加。渔塘坝当地居民在1963年间的硒中毒爆发性流行,乃至恩施地区人畜硒中毒的普遍流行,极可能是人为因素引起。     

地衣芽孢杆菌对亚硒酸盐的还原

利用高硒碳质泥岩中筛选出的地衣芽孢杆菌(Bacillus licheniformi),研究了该菌对亚硒酸盐硒的耐受与还原行为。结果表明,液体培养基(YEG)中,它能耐受320 mM亚硒酸盐硒的浓度,耐受硒酸盐硒的浓度可高达1000 mM。然而,高浓度的亚硒酸盐硒对它的生长有明显的抑制作用。在有氧和厌氧的环境中,地衣芽孢杆菌均能还原亚硒酸盐中的硒:将四价硒还原为纳米球状的元素硒颗粒,使其分布在菌体的周边和细胞内。在含5 mM亚硒酸钠的液体培养基中,还原亚硒酸钠硒成为元素硒的平均效率约为42%。地衣芽孢杆菌在生存环境无严格要求的条件下,其还原亚硒酸盐硒形成纳米元素硒颗粒的现象,是研究生物合成低毒的纳米活性元素硒和生物修复硒污染技术的基础,也为硒的微生物矿化过程提供了契机。     

多形态自然硒的首次发现及其成因初探

在湖北省恩施市渔塘坝的富硒碳质硅质岩、碳质页岩及其废弃岩中堆中,作者首次发现了多种形态的自然硒。本文根据自然硒的产出环境和成因将其分为三种,一种产于近地表废弃“石煤”堆中;一种与构造作用有关;另一种与表生风化作用有关。近地表废弃“石煤”堆中的自然硒是与岩层（或自燃）有关,见有晶形完好、颗粒粗大的晶体;与构造作用有关的自然硒多为毛发状、针状;与表生风化作用有关的自然硒颗粒细小,针状晶体少见。     

硒矿物综述

本文对分散元素硒的矿物种类进行了初步总结,列出了自然界发现的已被ＩＭＡＣＮＭＭＮ承认的９０种硒矿物,并对硒矿物的元素组成、产出条件以及中国的硒矿物学研究进行了综述,指出了硒矿物学研究中存在的问题。     

渔塘坝富硒碳质岩石中硒淋滤实验的初步研究

渔塘坝是中国较为典型的高硒地区之一。从该区选取了4个典型的富硒碳质岩样品,并在常温条件下进行了淋滤实验研究(pH=2.0,4.0和6.5)。初步结果表明:随着液固比的增大和淋滤时间的延长,淋滤液中硒含量变化的总体呈降低趋势。不同岩类间硒的淋失量有所差别,但岩石总量硒并不是影响硒淋失的主要因素。淋滤原液的不同pH值对岩石硒的淋失有显著影响,其淋失量的排列顺序是pH=2.0>pH=6.5>pH=4.0。岩石中碳酸盐与黄铁矿含量之比同淋滤液pH的变化有关,并且极可能是影响岩石风化初始阶段硒淋失的重要因素之一。     

拉尔玛硒-金矿床中硒矿物形成的地质地球化学环境

文章介绍了拉尔玛硒 -金矿床中出现的大量的硒矿物的主要特征和矿物组合。根据成矿流体的物理化学性质 ,构造了硒矿物形成时的逸度 -逸度图解、逸度 -温度图解、逸度 - p H图解 ,推导了硒矿物形成时的物理化学条件 ,认为高的 f Se2 、f Se2 / f S2 值、高 f O2 、中酸性条件以及低温有利于硒矿物的形成。同时根据大量统计数据 ,认为 S<0 .5%、Corg<1.5%、Se>10× 10 -6时出现硒矿物的几率最高 ,可作为宏观上的判别标志。     

鄂西南恩施高硒土壤中硒的结合态与自然硒

自然界中硒能够以多种氧化态形式存在,如Se0、SeO32-,HSeO3-,H2SeO3、SeO42-和H2SeO4等.不同形态的硒具有显著差异的地球化学特性,影响着地质环境中硒的迁移、循环、生物可利用性和毒性.     

Accumulation and speciation of selenium in evaporation basins in California,USA

The accumulation of selenium in evaporation basins (or ponds) in the San Joaquin Valley, California is of a great concern due to its potential hazards to environments. In this study, the accumulation, speciation and concentrations of Se were examined in waters as well as sediments in a system of the evaporation ponds. A significant decrease in the total dissolved Se concentration in Cell 1 in which drainage water with higher Se concentration was pumped from Inlet Channels indicated that the immobilization of Se was active in the Cell 1 and resulted in the higher Se concentration in sediments compared to the terminal cell such as Cell 9. The percentage of reduced Se species such as selenite [Se(IV)] and org-Se of total Se in drainage waters was also found increased in Cell 1 compared to Inlet Channels. The total dissolved Se concentrations in water along flow paths from Cell 1 were relatively constant except for terminal cells such as Cells 9 and 10, which showed higher total dissolved Se concentrations due to evapoconcentration. The percentage of reduced Se forms of total Se was inversely proportional to the percentage of Se(VI) depending on the redox condition of evaporation ponds along the flow paths. Sequential extractions of Se species in sediments indicated that organic associated Se and elemental Se were prevalent forms in sediments in the ponds system. The higher concentrations of elemental Se and organic associated Se in sediments in Cell 1 indicated that the immobilization of Se was active in the sediments compared to Cell 9, while the percentage of both fractions of total Se in sediments in Cells 1 and 9 was relatively constant. The organic materials from algae might provide carbon sources for Se reduction and Se sink in sediments in its elemental and organic associated forms.     

Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores: VI. Solubility of synthetic analogs of ahlfeldite and cobaltomenite at 25°C

The understanding of the mechanisms of the selenium behavior under near-surface conditions is an urgent problem of modern mineralogy and geochemistry, and is very important for solving environmental problems. The objective of this study is to synthesize analogs of ahlfeldite and cobaltomenite and to estimate their solubility in water. These analogs have been synthesized by mixing aqueous solutions of cobalt and nickel nitrates, respectively, and sodium selenite acidified with a solution of nitric acid. The obtained samples have been identified by X-ray diffraction and IR spectroscopy. The solubility has been determined by the isothermal saturation method in ampoules at 25°C, while the solubility products have been calculated using the Geochemist’s Workbench (GMB 7.0) software package. The solubility products of ahlfeldite and cobaltomenite are 10^?9.20 and 10^?9.44, respectively. The Eh-pH diagrams were calculated and plotted with the GMB 7.0 software package. The Eh-pH diagrams of the Ni-Se-H₂O and Co-Se-H₂O systems have been calculated for the average contents of these elements in underground water and their contents in acidic water of the oxidation zone of sulfide deposits. The formation of ahlfeldite and cobaltomenite under near-surface conditions is discussed.     

Geochemical Characteristics of the Sandstone—type Uranium Deposits in Northern Sichuan Province

Described in detail in this paper are the geochemical characteristics of the sandstone-type uranium deposits in northern Sichuan Province .Favorable and unfavor-able conditions for the enrichment of uranium are explored on the basis of the elemental abundances and ratios of U,Th and K determined by gamma-ray spectroscopy. Gamma-ray spectroscopic(U, Th and K) and XRF analyses(As, Ba) are helpful to distinguish U-bearing light-colored sandstones from U-barren light-colored ones and red sandstones (red claystone) from light-colored sandstones. Therefore, the favorable target area for prospecting the sandstone-type uranium deposits can be difined in northern Sichuan Province.     

江西龙南地区富硒土壤资源开发可行性研究

多目标区域地球化学调查结果显示,江西龙南地区表层土壤Se 平均含量为0.34 mg/kg,总体足硒,局部富硒,且土壤中重金属元素含量处于安全水平?异常查证结果表明,富含硒的基岩是富硒土壤分布的控制因素?在研究区发现天然富硒水稻?富硒大豆优质农产品,其中大豆的富硒率达100%?土壤中有效Se 与总Se 呈极显著的正相关,总Se 含量增大可增加有效Se 量;有效Se 与阳离子交换量(CEC)?N?P呈较显著的正相关,土壤中粘土矿物及有机质对Se 有较强的吸附?络合作用,且土壤中有效Se 主要以亚硒酸盐形式存在?水稻?大豆中Se 的生物富集系数均与土壤Se?N呈显著负相关,与土壤K2O呈显著正相关?     

中亚成矿域斑岩铜矿床基本特征

中亚成矿域发育许多大型和超大型斑岩铜矿床,是世界上重要的斑岩铜矿成矿域。我们对9个大型和超大型斑岩铜矿床进行了研究,包括地质特征、含矿岩体地球化学、SIMS锆石U-Pb定年和成矿流体成分等,结合前人成果,我们认为中亚成矿域斑岩铜矿床具有如下特点:(1)成矿时代为古生代和中生代,成矿高峰期为泥盆纪和石炭纪;(2)含矿岩浆为钙碱性中酸性岩浆和少量的碱性岩浆,含矿岩体为花岗闪长岩、闪长岩、英云闪长岩和少量的二长岩;(3)含矿岩浆大多数源于新生的洋壳,少量有古老的基底物质和围岩物质参与;(4)成矿构造背景主要为岛弧,少量为陆缘弧和岛弧向陆缘弧过渡的环境;(5)矿床可分为三类,包括斑岩型Cu-Au、Cu(Au,Mo)和Cu-Mo矿床;(6)成矿流体可分为两类,包括氧化性H2O-Na Cl-CO2-SO2体系和少量的还原性H2O-Na Cl-CH4-CO2体系;(7)成矿系统可分为三类,包括简单的斑岩系统和少量的斑岩-矽卡岩成矿系统和斑岩-浅成低温热液成矿系统。     

Aeolian origin of the red earth in southeast China

A clay‐like deposit known as ‘red earth’ is widely distributed over the terraces and high lands of the Yangtze River valley in southeast China. Its typical pedo‐stratigraphical features have attracted the interest of pedologists and geologists for many years, although its origin is still debated. Here we report an analyses of the grain‐size distributions, rare‐earth element (REE) patterns and upper continental crust (UCC)‐normalised major elemental composition of the red earth and compare them with those of the loess and other aeolian deposits in northern China. The results show that the red earth in southeast China has two or three end‐member grain‐size distributions, similar to the sedimentary characteristics and geochemical composition of aeolian deposits found in northern China. Together with other evidence from field observations, these results suggest that the red earth is probably of aeolian origin. On the basis of these data, we suggest that thick aeolian dusts were also deposited in the wet subtropics and that the effect of the winter monsoonal winds upon the dust transport in eastern China was more important than previously believed. Copyright © 2002 John Wiley & Sons, Ltd.     

氧化性富金斑岩-矽卡岩矿床中碲、硒、铊富集机制的研究进展

富金斑岩-矽卡岩矿床目前提供了全球几乎所有的硒、碲及部分铊产量,其中氧化性富金斑岩-矽卡岩矿床可共伴生碲、硒、铊等稀散金属。文章从元素地球化学行为、矿床类型、岩浆作用、赋存状态、稀散金属与铜金关系等方面,总结了氧化性富金斑岩-矽卡岩矿床中有关碲、硒、铊富集机制的研究进展。碲、硒具有亲铁和亲硫的特征,而铊具有亲硫和亲石的双重特征,三者具有不同程度的挥发性。岩浆热液型矿床伴生有碲、硒、铊矿化。基性岩浆的注入和岩浆硫化物熔离可能是氧化性富金斑岩-矽卡岩矿床碲、硒、铊富集的主要岩浆作用。氧化性富金斑岩-矽卡岩矿床中铜和金含量通常呈正相关性,发育有丰富的含碲/硒/铊矿物,但碲、硒、铊与铜、金的关系还不清楚。长江中下游成矿带发育多个氧化性矽卡岩金矿、矽卡岩铜金矿,伴生大规模的碲、硒、铊矿化,且已被综合回收利用,该带是探讨氧化性富金矽卡岩矿床中碲、硒、铊富集机制的理想对象。     

Geochemistry of selenium: formation of ferroselite and selenium behavior in the vicinity of oxidizing sulfide and uranium deposits

The geochemistry of Se is largely controlled by that of iron, with which Se is closely affiliated in both oxidizing and reducing environments. In aerated waters the Se(IV) oxyanions, HSeO^?₃ and SeO^2?₃, are strongly adsorbed by hydrated surfaces of ferric oxides over the pH range 2–8; above pH8 adsorption decreases to complete desorption at pH 11. This adsorption immobilizes Se(IV) in neutral-to-acid waters and increases the range of oxidation potential over which Se(IV) is stable. During experimental aeration of aqueous Fe-S-Se systems, the stability field of Se(IV) is attained and elemental Se is slowly oxidized to this higher valence; oxidation potentials of the Se(VI) stability field were never reached, however, even by continued aeration of an alkaline system. Under reducing conditions, elemental Se either is incorporated within pyrite or forms the mineral ferroselite (FeSe₂.Selenium geochemistry is summarized on an Eh-pH diagram, synthesized from equilibrium calculations, experimental work and reported geologic occurrences. A stability field for ferroselite, constructed for a Gibbs free-energy value of ?23.2 kcal/mole, is in accord both with its geologic occurrence and behavior and with conditions under which ferroselite has been synthesized. Traces on this diagram of Eh-pH variation show the behavior of selenium during oxidation of associated iron-sulfide minerals. Such considerations also demonstrate the manner in which selenium migrates, is deposited and is increasingly concentrated in roll-type sandstone uranium deposits, as well as the relative positions of the several forms of selenium within the deposit.     

中国硒矿成矿规律概要

文章在全国矿产资源潜力动态评价项目开展过程中，对中国硒矿资源特征、硒矿类型、时空分布、成矿谱系进行分析与归纳，初步总结了中国硒矿成矿规律。文章对中国硒矿的资源特征及存在的问题进行了介绍；将中国硒矿划分为斑岩型、岩浆型、热液型、矽卡岩型、沉积型5大硒矿预测类型，初步总结了各类型硒矿的时空分布特征；将中国硒矿成矿时代总结为元古代、早古生代、晚古生代、中生代、新生代5个成矿期，划分了24个硒成矿带；厘定出39个与硒矿有关的成矿系列，建立了中国硒矿成矿谱系；最终选取了重点矿床类型和潜力评价工作区域。