东秦岭钼矿Re-Os同位素年龄及其成矿动力学背景

东秦岭钼矿带位于华北克拉通南缘 ,集中分布于陕西省的金堆城地区、河南省栾川县南泥湖 -三道庄 -上房沟、嵩县雷门沟地区。钼矿床类型主要为斑岩型、斑岩 -矽卡岩型 ,少量热液碳酸盐岩脉型。采用电感耦合等离子体质谱仪法对南泥湖钼矿田、雷门沟钼矿床等 4个矿床 8件辉钼矿进行了 Re-Os同位素年龄测定 ,获得南泥湖矿床的辉钼矿 Re- Os模式年龄为 14 1.8± 2 .1Ma;三道庄矿床的辉钼矿 Re- Os模式年龄为 14 4 .5± 2 .2～ 14 5 .0± 2 .2 Ma,平均为 14 5 .0± 2 .2 Ma;上房沟矿床的辉钼矿 Re- Os模式年龄为 14 3.8± 2 .1～ 14 5 .8± 2 .1Ma,平均为 14 4 .8± 2 .1Ma;6件样品的等时线年龄为 14 1.5±7.8Ma(2σ) ;雷门沟钼矿床的 2件辉钼矿样品的 Re- Os模式年龄为 131.6± 2 .0～ 133.1± 1.9Ma,平均为 132 .4± 2 .0 Ma。结合前人资料 ,认为东秦岭钼矿的形成时代局限于 2 2 1.5± 0 .3～ 132 .4± 2 .0 Ma之间 ,主要出现在 2 2 1.5± 0 .3Ma左右和 14 4 .8± 2 .1～ 132 .4± 2 .0 Ma时限之间 ,其对应的地球动力学背景分别为华北克拉通与扬子克拉通的碰撞造山后陆内造山和伸展过程、中国东部构造体制大转换时期     

大别山北麓斑岩型钼矿床地质特征、成矿时代及其成矿构造背景

在野外调查和测试分析的基础上,结合前人的研究成果,综合论述了大别山北麓斑岩型钼矿床的地质特征、形成时代和构造背景。大别山北麓斑岩型钼矿床总体沿区域构造线呈北西向狭长带状展布,具有近东西向成带、南北向成群的空间展布特征,其形成与燕山期中酸性浅成-超浅成小型花岗斑岩体有关,钼矿床直接产于岩体内外接触带及其附近的围岩中,矿床类型主要为斑岩型、斑岩-矽卡岩型及少量热液石英脉型。结合Re-Os同位素年龄数据,探讨了大别山北麓斑岩型钼矿床的成矿物质来源、成矿流体、成矿时代、主要成矿作用的时限以及成矿地球动力学背景。结果表明:大别山北麓地区钼矿床的主要成矿作用时限为142~137 Ma和127~110 Ma,对应的地球动力学背景为中国东部地球动力学体制大转换晚期的岩石圈拆沉及伸展减薄的构造背景。     

东秦岭东沟超大型斑岩钼矿SHRIMP锆石U-Pb和辉钼矿Re-Os年龄及其地质意义

东沟钼矿是在东秦岭钼矿带中于近年新发现的超大型斑岩钼矿床。对其含矿斑岩和矿石进行了成岩成矿年龄精测。采用SHRIMP锆石U-Pb测年技术,对东沟含矿铝质A型花岗斑岩体进行了年代学研究,获得成岩年龄为112±1Ma;采用ICP-MS法测定东沟钼矿中辉钼矿Re-Os同位素年龄,获得模式年龄为116.5±1.7~115.5±1.7Ma;两种方法获得的年龄相近,表明成岩与成矿大致同时形成。东沟斑岩钼矿与东秦岭金堆城、南泥湖、上房沟、雷门沟等斑岩钼矿具有20Ma以上的时差,反映它们形成于不同的地球动力学背景。     

河南汝阳地区竹园沟钼矿地质特征、成矿时代及地质意义

位于东秦岭钼成矿带内的河南汝阳钼铅锌多金属矿田是国内近几年发现的大型矿床集中区,区内发育东沟超大型斑岩钼矿床、竹园沟大型钼矿床和老代仗沟、西灶沟、王坪西沟等大型铅锌矿床。介绍了竹园沟大型钼矿床的地质特征,并利用Re-Os同位素定年方法对竹园沟钼矿体中的辉钼矿进行了成矿年代的测定,获得辉钼矿同位素的模式年龄为(122.2±2.3~119.6±2.2)Ma,平均为120.9 Ma±2.3Ma。该成矿年龄显示竹园沟钼矿的成矿时代与汝阳南部其他钼铅锌等多金属矿床的形成时代相近,表明汝阳南部钼铅锌多金属成矿带成岩成矿年龄(120~110Ma)的一致性,均形成于统一的地球动力学背景,即中生代晚期中国东部岩石圈大规模伸展时期的板内拉张环境。     

东秦岭钼矿带成矿特征及其与美国克莱马克斯-亨德森钼矿带的对比

东秦岭钼矿带是中国最主要的钼矿带,钼矿呈近东西向展布。钼矿以斑岩型为主,从南到北,钼矿带钼矿大体有斑岩Cu-Mo矿、斑岩Mo矿、斑岩Au-Mo矿分带的趋势,与从俯冲带到克拉通边缘斑岩Cu矿、斑岩Cu-Mo矿、斑岩Mo矿依次发育的分带现象相似,表明钼矿的形成与扬子地块向华北地块俯冲有关。根据钼矿Re-Os年龄资料统计钼矿分为～220Ma、～140Ma和～110Ma三期,其成矿动力学背景分别为碰撞造山、碰撞造山后伸展和中国东部岩石圈减薄。钼矿流体包裹体均一温度介于83℃～424℃;平衡盐度介于0.61%～42.5%。流体包裹体水的δD介于-100‰～-40‰,δ18OH2O介于-4.3‰～8.7‰;且从成矿早期到晚期流体包裹体水的δD和δ18OH2O分别变小,表明钼矿的成矿流体主要来源于岩浆,后期有大气水的加入。东秦岭钼矿的铅同位素为206Pb/204Pb=17.12～17.89、207Pb/204Pb=15.23～15.70、208Pb/204Pb=37.57～39.10,与区域下地壳铅同位素一致;小斑岩体的Sri=0.705～0.714,δ18O=7.2‰～12.1‰,与I型花岗岩的锶、氧同位素相一致,表明钼矿的成矿物质主要来源于下地壳。东秦岭钼矿带的钼资源总量占中国钼资源的51%以上,美国克莱马克斯-亨德森钼矿带(Climax and Hender-son)的钼资源总量占美国钼矿资源的42%以上,美国和中国的钼资源在世界上的排名分别为第一和第二位,两钼矿带是世界钼资源高度集中的两个区域。克莱马克斯-亨德森钼矿带位于美国中西部、美洲克拉通西缘;钼矿主要形成于33～18Ma,稍晚于拉腊米(Laramide,75～54Ma)陆内造山运动;钼矿形成于碰撞造山后伸展环境。东秦岭与克莱马克斯两钼矿带相比:1)两钼矿带都位于克拉通边缘;2)两钼矿带的钼矿化都形成于陆内碰撞造山之后的伸展环境,与成矿有关的岩体都为花岗斑岩小岩体;3)两钼矿带钼矿的辉钼矿平均丰度分别为0.073%～0.140%和0.171%～0.264%,东秦岭钼矿的丰度明显较低;4)两钼矿带钼矿的辉钼矿成矿温度分别为300～400℃和460～600℃,东秦岭钼矿明显较低,反映与其成矿有关的岩浆的侵位深度较浅。通过两钼矿带间的综合对比得出:克拉通边缘经历陆内碰撞造山作用后在伸展环境下有利于斑岩钼矿的形成;与钼矿有关的小斑岩体岩浆的侵位深度影响钼矿中辉钼矿的丰度,岩浆的侵出深度越深其钼矿的辉钼矿品位越高。     

中国东部钼矿成矿背景与成岩-成矿时差讨论

中国东部中生代钼矿带属滨太平洋成矿域,钼矿床多沿不同构造单元的交界部位及区域性深大断裂呈带状分布,集中分布在东秦岭、燕辽、长江中下游、南岭和大兴安岭等钼矿成矿带。结合前人成果,以典型矿床为例,初步讨论了中国东部各个钼矿成矿带的成矿背景,成矿很可能与碰撞造山后的伸展背景和(或)太平洋板块俯冲有关。文章根据收集到的中国东部典型钼矿床的成矿年龄及相关岩体的同位素测年数据,详细讨论并定量厘定了钼矿床的成岩与成矿时差。结果表明,钼矿成矿同步或略滞后于同源岩浆活动,两个成矿高峰的时差分别为0～10.0 Ma和0～15.0 Ma;对于单个矿床,成岩_成矿时差集中在0～14.0 Ma,均值为4.1 Ma;从斑岩型→斑岩-矽卡岩型→矽卡岩型→石英脉型钼矿床,成岩-成矿时差呈递增趋势,这恰与岩浆热液成矿过程的客观地质事实相吻合。     

陕西华县八里坡钼矿床锆石U-Pb和辉钼矿Re-Os年龄及其地质意义

八里坡钼矿是在金堆城钼矿床外围找矿中新发现的斑岩型钼矿床,对其含矿斑岩和矿石进行了成岩成矿年龄精测。采用LA-ICP-MS方法对八里坡斑岩体进行单颗粒锆石U-Pb测年,获得成岩年为155.9±2.3 Ma;采用ICP-MS法测定八里坡钼矿中辉钼矿Re-Os同位素年龄,获得模式年龄为156.3±2.2 Ma;两种方法获得的年龄一致,表明成岩与成矿同时形成。八里坡斑岩体与东秦岭南泥湖、上房沟等斑岩体成岩年龄一致,早于金堆城钼矿床成矿年龄,表明八里坡斑岩体可能是新一期成岩成矿作用,形成于燕山运动的A幕,产出于东亚构造体制转变初期的地球动力学背景,具有重要成岩成矿意义。     

华北克拉通南北缘三叠纪钼矿化类型、特征及地球动力学背景

华北克拉通南北缘是中国最重要的钼成矿带,特别是近年来在南北缘陆续发现了大量的钼矿床,显示了巨大的钼资源前景。其中三叠纪钼矿床的不断发现引人注目。在华北克拉通北缘及邻区三叠纪钼矿床在空间上总体呈EW向展布,矿床产出受区域东西向断裂控制,钼矿床的形成与三叠纪酸性侵入体关系密切,多产于花岗岩体中、斑岩体内外接触带或附近,矿床类型包括斑岩型和石英脉型。在华北克拉通南缘及邻区,三叠纪钼矿床总体上呈NW向展布,受区域NW向断裂控制,钼矿床的形成与晚三叠世酸性侵入体及碳酸盐脉有关,矿床产于斑岩体内及附近,矿床类型包括斑岩型、石英脉型及碳酸盐脉型。成矿年代学研究表明,华北克拉通北缘及邻区三叠纪钼矿主要形成于248~220Ma,而南缘及邻区三叠纪钼矿床主要形成于226~210Ma。其对应的成矿动力学背景为印支期华北板块与西伯利亚板块同碰撞造山过程和扬子板块与华北板块同碰撞造山过程。     

西藏冈底斯东段斑岩铜钼铅锌成矿系统的发育时限：帮浦铜多金属矿床辉钼矿Re-Os年龄证据

通过对西藏冈底斯成矿带东段的帮浦矿床中的辉钼矿进行Re_Os精确测年 ,首次获得北矿带的铜多金属矿化时间。其Re_Os模式年龄为 (14 .30± 0 .2 5 )Ma～ (14 .75± 0 .2 8)Ma ,5件样品得到的187Re_187Os等时线年龄为 (15 .32± 0 .79)Ma。年龄数据与冈底斯成矿带东段南侧斑岩铜矿化带的矿化时间 (14Ma左右 )具有一致性 ,表明北矿带的成矿作用与斑岩有关。斑岩成矿是冈底斯成矿带内的一次主导成矿事件 ,冈底斯南矿带以斑岩型铜钼矿床为主 ,其北矿带以斑岩型铜铅锌多金属矿床为主。冈底斯南、北矿带的成矿作用具有统一的成矿动力学背景 ,发生在碰撞造山带侧向伸展时期 ,均为陆_陆碰撞造山带演化过程中同构造岩浆活动期的产物     

东秦岭钼矿的主要类型、成矿特征和成矿时代

东秦岭钼矿带是中国著名的钼多金属成矿带,也是中国最大的钼矿基地与重要的矿集区之一。本文根据矿床成因、控矿构造、矿石成分及结构构造等,把东秦岭钼矿床分为两组八大类：斑岩．接触带型矿床、矽卡岩型矿床、斑岩-矽卡岩型矿床、斑岩一爆破角砾岩型矿床;破碎带型矿床、石英脉型矿床、韧性剪切带型钼矿床和碳酸盐脉型矿床,丰富了河南省内钼矿的类型。并选取有代表性的矿床进行了成矿地质特征和成矿时代研究,认为东秦岭钼矿的成矿年龄从1884±210Ma～106．89±2．14Ma,把成矿时代空间从中生代扩展到了早元古代。     

Wavelength-dispersive X-ray fluorescence spectrometric determination of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites

Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours.     

硅酸盐类样品中硅、铁、铝、钛、锰、钙、镁、钾、钠和磷的x射线荧光光谱测定

本文拟定了一种以熔融法制备样片,用X射线荧光光谱测定硅酸盐类样品中Si、Fe、Al、Tj、Mn、Ca、Mg、K、Na、P等元素的分析方法。在对不同靶材X光管和分光晶体实验对比的基础上,选择了最佳的测量条件。该法具有快速、准确,测量范围广,检测限低,价格便宜等优点。经过近百个各种类型标样或管理样品的分析对比表明,本法不仅适用于硅酸盐类岩石样品的分析,还适用于铁矿、铝土矿、碳酸盐类岩矿样品以及水泥、耐火材料等样品的分析。     

高压微波消解法测定醋酸纤维过滤器采集的微尘粒子中的砷镉钴铬铜铁锰镍铅钒锌

最新的流行病学研究表明,空气中较高浓度的悬浮细颗粒可能对人类的健康有不利的影响。根据该项研究显示,由于心脏病、慢性呼吸问题和肺功能指标恶化而导致死亡率的升高与细尘粒子有关。这些研究结果已经促使欧盟于1999年4月出台了限制空气中二氧化硫、二氧化氮、氧化氮、铅和颗粒物含量的法案(1999/30/EC),对各项指标包括对可吸入PM10颗粒的浓度提出了新的限制性指标。PM10颗粒是指可以通过预分级器分离采集的气体动力学直径小于10μm的细颗粒。目前研究的兴趣重点逐步偏向PM2.5这些更细微颗粒物,PM2.5这种颗粒物对健康有明显的不利影响。在欧盟指令2008/50/EC中,对PM10和PM2.5都提     

Isotopic systematics of He,Ar, S,Cu, Ni,Re, Os,Pb, U,Sm, Nd,Rb, Sr,Lu, and Hf in the rocks and ores of the Norilsk deposits

This paper reports the first results of a study of 11 isotope systems (³He/⁴He, ⁴⁰Ar/³⁶Ar, ³⁴S/³²S, ⁶⁵Cu/⁶³Cu, ⁶²Ni/⁶⁰Ni, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206–208Pb/²⁰⁴Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.     

硅酸盐中铁、锰、钛、钙、钾、磷、硅、铝、镁、钠、锶、铷、钡的X-射线荧光光谱定量测定

本文介绍样品经四硼酸锂熔融制成玻璃小饼。采用Lachance模式和理论a系数来校正元素间的效应,由3080E型X-射线荧光谱仪和DF-350B数据处理系统完成硅酸盐中十三个项目的测定。     

Viscous, cohesive, non-Newtonian, depositing, radial slurry flow

Mining induced subsidence can significantly affect mining costs where major surface facilities and natural environment need to be protected. Overburden grout injection is a technology used to control coal mine subsidence by injecting the mine waste material extracted from the coal back into the inter-burden rock during longwall mining. The flowing slurry is here categorised as a nonlinear viscous cohesive (Bingham plastic) fluid. During longwall mining the grout slurry is pumped into the separated beds of the rock mass through a central vertical borehole, which is drilled deep into the inter-burden rock strata above the coal seam. However, a blockage can occur in the injection system when the slurry velocity falls below a certain critical threshold velocity, indicating a material phase change from cohesive-viscous to cohesive-frictional. In situ field injection tests through boreholes have been simulated at a smaller scale at the CSIRO laboratory in Brisbane by pumping the slurry through a radial disk (gap = 4 mm) from its centre. Laboratory experiments indicate a general, nonlinear, cohesive, viscous, frictional model for shear behaviour of the slurry, in which the material shear parameters are functions of the disk radial distance. Complete dimensional and dimensionless analytical solutions have been developed based on an approach related to Bingham–Herschel–Bulkley fluid mechanics. The derived formulae include relations for minimum pump pressure, local pressure and pressure gradient, wall shear stress, volume rate, velocity and velocity gradient. The theoretical results match the experimental measurements. The experiments covered slurries with maximum particle sizes of 0.5 to 2 mm with about 50% being larger than 100 µm. The viscosities at the various solids concentrations were measured with a standard torsion viscometer. This study differs from the previous research in several distinct aspects, namely, consideration of the variable shear parameters rather than fixed values, inclusion of total nonlinear behaviour, and implementation of a friction function to mimic behaviour of the deposited and consolidating stiff slurry, which can cause a significant pressure rise as a result of the increased shear resistance.     

岩石密度和超高压岩石折返速率

在常温常压条件下对中国大陆科学钻CCSD主孔100-3000米岩心样品进行了密度测量,建立了密度连续剖面,并界定了不同超高压岩石的密度值。通过对比高温高压物性实验资料,岩石密度随着退变程度增强而降低,榴辉岩密度变化序列为3.52g/cm3→3.49g/cm3→3.07g/cm3→2.93g/cm3。超高压长英质岩石密度变化序列为3.00g/cm→2.80g/cm3→2.65g/cm3。上述实验资料是讨论不同折返阶段岩石所受浮力的基础,为研究折返速率大小提供了基本参数。本文通过折返板块运动平衡时,上浮力与粘滞力平衡这一关系式,定量研究了大陆俯冲板块的折返速率,认为密度差产生上浮力从而引起折返,温度对板块折返速率的影响最为显著;密度差大小、折返角度、折返板块大小对折返速率也有直接的影响。定量模拟分析表明,在温度高于850℃时,板块的折返速率可以超过100mm/a;当温度降至700℃时,折返速率则低于1.5mm/a。作者认为在折返早期,温度较高,板块快速折返至60-70km榴辉岩相深度;随着传导散热,温度降低,板块以较慢的速率折返至中下地壳。折返速率的估算表明,浮力是板块折返第一阶段(从>100km深部折返至<40km的中下地壳)的主要驱动力。     

Bellechester,Minnesota, USA,lagoon collapses

Bellechester, Minnesota, is a small community of approximately 155 residents located on the county line between Goodhue and Wabasha counties in southeast Minnesota's karst region. Bellechester is served by a 21-year-old wastewater treatment facility (WWTF) consisting of three waste-stabilization ponds. On 28 April 1992 six sinkholes were discovered to have drained cell 2 of the WWTF resulting in the loss of approximately 8.7×10⁶ 1 of partially treated effluent and about 600 m³ of soil into previously undetected subsurface voids of unknown dimensions. In the week following the collapse, approximately 200 water wells located within a 5-km radius of the WWTF were sampled in an after-the-fact, emergency sampling program. Twelve samples with elevated fecal coliform levels, 18 samples with nitrate-nitrogen greater than the 10 mg/1 standard, and no samples with elevated chlorides were found. However, the elevated levels could not be unambiguously attributed to the WWTF collapse. This is the third WWTF to fail by sinkhole collapse in southeast Minnesota since 1974. All three collapsed lagoons have been located in similar geomorphic and stratigraphic settings. However, at least two lagoons have collapsed in the adjacent area in northeast Iowa, and these lagoons are located at different stratigraphic positions. Twenty-two WWTFs constructed in southeast Minnesota's karst region in the last 25 years have been identified as subject to potential sinkhole collapse. An unknown but significant number of manure storage lagoons, flood control structures, etc., have also been constructed in the karst region and are at risk. Public agencies are beginning to develop plans to deal with the risk associated with existing and future waste lagoons in this environment. The critical hydrogeologic parameters that can be used to prioritize the risk of collapse at existing facilities include: (1) the lithology of the first bedrock beneath each lagoon, (2) the thickness of surficial materials between the lagoon and the bedrock surface, (3) the presence and construction of liners (seepage rate), and (4) the proximity to existing sinkholes.     

滇东南花岗岩与锡、银、铜、铅、锌多金属矿床的成因关系

滇东南锡、银、铅、锌多金属矿床主要分布在个旧、白牛厂、都龙3个矿区,而滇东南较大的3个花岗岩体又分别出露在3个矿区或附近.花岗岩体均形成于燕山晚期,岩石化学、矿物成分相似,富含锡、银、铅、锌、钨、铜等成矿元素.矿床主金属元素组合与岩体之间的距离由远而近出现由锡、钨、(铍、铌、钽)→锡、钨、(铁)、铜、铟→锡、铅、锌、银、铟、(锑)有规律的变化.花岗岩浆是成矿物质来源和成矿热源.岩浆侵入初期使上覆地层隆起产生背斜(凹陷部位成向斜);同时使地层产生一系列裂隙、压性断层或层间断裂;岩浆侵入晚期,这些断层再次活动,表现为张性,岩浆产生的含矿热液沿由其活动所造成的断裂迁移、充填、交代、沉淀而形成矿床.     

Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA

The Kuskokwim River at Bethel, Alaska, drains a major mercury-antimony metallogenic province in its upper reaches and tributaries. Bethel (population 4000) is situated on the Kuskokwim floodplain and also draws its water supply from wells located in river-deposited sediment. A boring through overbank and floodplain sediment has provided material to establish a baseline datum for sediment-hosted heavy metals. Mercury (total), arsenic, antimony, and selenium contents were determined; aluminum was also determined and used as normalizing factor. The contents of the heavy metals were relatively constant with depth and do not reflect any potential enrichment from upstream contaminant sources.