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1.
东昆仑祁漫塔格东段晚二叠世-早侏罗世侵入岩岩石组合时空分布、构造环境的讨论 总被引：4，自引：2，他引：2
祁漫塔格地区是青藏高原北部最重要的多金属矿集区,晚二叠世-早侏罗世岩浆作用与成矿作用关系密切,以祁漫塔格东段为研究区分析讨论了祁漫塔格及临区晚二叠世-早侏罗世花岗岩特点,从晚二叠世-早侏罗世可以识别出4个阶段5个花岗岩组合.(1)晚二叠世弱过铝质高钾钙碱性系列二长花岗岩+正长花岗岩组合与偏铝质-弱过铝质钙碱性系列英云闪长岩+花岗闪长岩组合,LA-ICP-MS U-Pb年龄在252.0~258.5Ma,普遍含暗色铁镁质微粒包体;(2)中三叠世闪长岩+英云闪长岩+花岗闪长岩+(二长花岗岩)组合,LA-ICP-MS U-Pb年龄在226.9~238.6Ma,富含暗色铁镁质微粒包体,为偏铝质-弱过铝质钙碱性-高钾钙碱性系列岩石,Sr含量一般在400×10-6~537×10-6,δEu在0.67~0.95;(3)晚三叠世石英闪长岩+英云闪长岩+花岗闪长岩+二长花岗岩组合,LA-ICP-MS U-Pb年龄在211.7~214.1Ma,为偏铝质高钾钙碱性系列岩石,Sr含量一般在341×10-6~515×10-6,δEu在0.69~0.95之间;(4)晚三叠世-早侏罗世正长花岗岩组合,LA-ICP-MS U-Pb年龄在199.5~204.4Ma,为偏铝质高钾钙碱性系列岩石,Sr含量在54×10-6~195×10-6.晚二叠世花岗岩组合为大陆边缘弧火成岩构造组合,与古特提斯洋俯冲相关;中三叠世花岗岩组合出露面积巨大,构成了印支期北昆仑岩浆弧的主体,形成于俯冲-碰撞转换阶段,与俯冲岩石圈板片的断离相关,这一事件在东昆仑具有普遍意义,是东昆仑造山带最具规模的地幔物质注入与壳幔岩浆混合事件,晚三叠世花岗岩组合形成于后碰撞阶段,是加厚陆壳底部幔源玄武质岩浆底侵作用的结果. 相似文献
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东昆仑香日德地区晚三叠世花岗岩LA-ICP-MS锆石U-Pb定年、岩石成因和构造意义 总被引：10，自引：6，他引：4
东昆仑地区广泛分布了大量花岗岩.已有的研究工作表明,东昆仑地区的花岗岩主要形成于晚二叠世-中三叠世和晚三叠世两个时期.本文提供了香日德地区二长花岗岩和花岗闪长岩的锆石U-Pb定年数据和全岩化学,稀土微量元素及Sr、Nd同位素地球化学研究资料,结合前人对该区不同时期花岗岩的研究成果,对香日德晚三叠世花岗岩的成因及其形成的动力学背景进行了讨论.研究表明东昆仑东段香日德地区的二长花岗岩和花岗闪长岩分别形成于223.2±1.7Ma和220.6±1.5Ma,属晚三叠世花岗岩浆作用的产物.根据该花岗岩的主量元素(特别是A/CNK比值),岩石富集大离子亲石元素(LILE:Rb、Th和K)和轻稀土(LREE),明显亏损高场强元素(HFSE:Nb、Ta、Ti和P),以及岩石具有相对高的Isr值(0.70820~0.71148)和相对低的εNd(t)值为-6.4~-3.6和较古老的模式年龄t2DM(1.5~1.7Ga)等地球化学特征,论证了该花岗岩的成因,指出香日德花岗闪长岩-二长花岗岩的起源和成因与碰撞后的背景下岩石圈的拆沉诱发的古老地壳物质的部分熔融作用有关,晚三叠世花岗岩岩浆作用是对自晚海西期以来幔源玄武质岩浆长期的底侵作用及地壳不断加厚的一种响应.它进一步证明在东昆仑地区,阿尼玛卿古特提斯洋的俯冲作用一直持续到早三叠纪,至晚三叠世才全面转入陆内碰撞造山阶段.晚三叠世花岗岩与晚二叠世-中三叠世花岗岩在暗色包体含量、岩浆混合作用的特征等方面的差异,可以用幔源物质贡献量的差异以及花岗质岩浆作用所经历的MASH过程的不同来解释. 相似文献
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浙江绍兴地区广山花岗杂岩体的锆石U-Pb年代学、锆石Hf同位素、岩石地球化学特征及其地质意义 总被引：4，自引：2，他引：2
广山花岗杂岩体主体部分由中粒碱长花岗岩和侵入其内部的细粒碱长花岗岩组成,LA-MC-ICP-MS锆石U-Pb定年显示其形成年龄分别为162.4±0.9Ma和156.3±0.7Ma,表明岩体为燕山期多期次岩浆活动产物。两期岩体为高钾钙碱性系列,A/CNK值为0.95~1.05,属准铝质-弱过铝质花岗岩类;稀土含量中等,强Eu亏损,呈略右倾的海鸥型稀土配分模式,均为A2型花岗岩。锆石Hf同位素研究表明,εHf（t）变化范围主要集中在-4.35~0之间,均为负值,二阶段模式年龄tHf2（Ma）变化范围主要集中于1219~1478Ma,反映其源区物质来源于中元古代地壳物质。结合前人研究成果,本文认为华南燕山早期晚阶段A型花岗岩形成于由碰撞造山向板内（非造山）环境转换的后造山拉张阶段。 相似文献
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华南板块南缘二叠纪与三叠纪之交的构造属性仍存在较大争议。对新兴岩体详细的野外调查和研究发现,新兴岩体的侵位时间为晚三叠世（240~224 Ma）而非侏罗纪,其主要岩性为细中粒-细粒斑状黑云母二长花岗岩。地球化学分析显示,新兴花岗岩具有高钾钙碱性、过铝质-强过铝质花岗岩特征,具轻稀土元素富集、重稀土元素相对亏损的右倾稀土配分模式,富集大离子亲石元素（Rb、U）而亏损高场强元素（Nb、Ta、Zr、Hf、Ti）。Sr-Nd、Lu-Hf同位素分析显示,新兴花岗岩εNd（t）值介于-11.5~-10.5,εHf（t）值介于-2.9~-10.3,具有壳源源区特征。本次研究表明,粤西地区印支期构造-岩浆活动可能开始于~250 Ma,华南板块南缘海西-印支期岩浆作用自晚二叠世（大容山岩体）一直延续到晚三叠世（新兴岩体）,且晚三叠世仍存在强烈的岩浆活动。新的证据支持古特提斯洋东段分支的关闭时间在~250 Ma,而印支板块和华南板块的陆陆碰撞拼贴一直延续到240~224 Ma。 相似文献
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浙江临海猫狸岭岩体的成因：年代学、地球化学与Sr-Nd-Hf同位素制约 总被引：2，自引：0，他引：2
猫狸岭岩体位于浙江省临海县仙人桥-猫狸岭一带,其主体岩性为石英二长闪长岩、石英二长岩和细粒花岗岩。LA-ICP-MS 锆石U-Pb定年表明石英二长闪长岩和细粒花岗岩的年龄分别为105.6±1.0Ma和104.8±0.9Ma。主量元素组成上,石英二长闪长岩具准铝质、钙碱性和富钾的特征,MgO、Fe2O3T、CaO等含量较高,Mg#值变化于47.6~50.6;细粒花岗岩同样具富钾和准铝质特征,但偏酸性,MgO、Fe2O3T、CaO等含量相对偏低,Mg#值变化于41.6~47.0。微量和稀土元素组成上,石英二长闪长岩富集Rb、Th、U、Pb,贫Nb、Ta、P、Ti,且Zr、Hf、Sr含量相对较高,铕负异常不显著（Eu/Eu*=0.77~0.95）。细粒花岗岩具有相似的微量元素特征,但P、Ti亏损程度更明显,且明显贫Sr,并具一定程度的铕负异常（Eu/Eu*=0.55~0.78）。石英二长闪长岩和细粒花岗岩具有相似的Sr-Nd同位素组成,ISr分别为0.7088和0.7079~0.7088,εNd（t）值分别为-7.57~-7.56和-8.06~-7.95。同时,二者具有大致相似的锆石Hf同位素组成,εHf（t）值分别为-12.2~-6.6和-9.6~-4.4。综合分析表明,猫狸岭石英二长闪长岩和细粒花岗岩最可能是在区域伸展拉张的构造背景下,由底侵或内侵的幔源岩浆与其诱发的壳源岩浆经混合后,并经过不同程度的分异演化,最后在浅成环境侵位的产物。 相似文献
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【研究目的】查明松潘—甘孜地块东南部花岗岩地球化学及构造演化特征,对在该区寻找稀有金属矿产具有重要意义。【研究方法】在野外地质调查基础上,采集了地块东南部前人研究未涉及的苏地岩体二长花岗岩样品开展了镜下鉴定、岩石地球化学及锆石LA-(MC)-ICP-MS U-Pb和Lu-Hf同位素测试工作。【研究结果】结果表明,苏地岩体二长花岗岩SiO2含量为63.72%~66.48%,中—高钾、富钠、贫钙,AR值为1.44~1.83,A/CNK值为0.98~1.16,为中—高钾钙碱性系列;岩石相对富集K、Rb、Cs等大离子亲石元素（LILE）,亏损Nb、Ta、Ti等高场强元素（HFSE）;岩石稀土总量为157.16×10-6~187.88×10-6,LREE/HREE为6.26~9.46,δEu为0.62~0.74,具有弱—中等的负铕异常;锆石U-Pb定年结果为（221.1±1.5）Ma（MSWD=0.30,n=22）和（214.5±1.5）Ma（MSWD=0.22,n=22）,表明苏地岩体原始岩浆初始结晶时代为晚三叠世中期;锆石Lu-Hf同位素εHf(t)和TDM2分别为-6.56~-4.12和1.67~1.51 Ga。【结论】综合分析认为苏地二长花岗岩为较为典型的I型花岗岩,其可能为源于下地壳的初始岩浆于晚三叠世中期在造山碰撞闭合转入伸展体制下上升侵位过程中形成。松潘—甘孜地块东南部在晚三叠世中期处于后碰撞造山环境。 相似文献
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提要：分布于湖南衡山的南岳岩体,侵位于新元古代冷家溪群中,为复式岩体。通过锆石U-Pb年龄测定,其锆石LA-ICP-MS U-Pb年龄为（215.5±1.5）Ma,主体形成于晚三叠世;其中部分小岩体形成于早白垩世,锆石LA-ICP-MS U-Pb年龄为（140.6±0.8）Ma。晚三叠世花岗岩由三个岩石单元组成,第一期细中粒斑状角闪石黑云母二长花岗岩、第二期中细粒黑云母二长花岗岩、第三期二云母二长花岗岩;早白垩世花岗岩为二云母二长花岗岩。晚三叠世花岗岩属过铝质高钾钙碱性系列;早白垩世花岗岩属强过铝质高钾钙碱性系列。岩石明显富集大离子亲石元素,亏损高场强元素;∑REE中等（92.88×10-6~296.56×10-6）,Eu均为弱负异常(δEu=0.28~0.87),其中早白垩世花岗岩Eu亏损更大;ISr值较大（0.7093~0.7189）;低εNd（-8.04~-11.38）, 高T2DM（1.63 ~1.90 Ga）。综合研究表明,南岳花岗岩石为壳源含白云母过铝花岗岩类（MPG）,为华南前寒武系基底重熔而成,晚三叠世花岗岩有少量下地壳或地幔物质加入;其形成的构造背景应为碰撞造山作用晚期或结束时期,是陆内碰撞造山作用增温减压体制下的产物。 相似文献
8.
松林口岩体位于松潘—甘孜造山带中东部,为确定岩体的侵位时代和地球化学特征,通过镜下薄片观察、主微量元素分析以及锆石U-Pb测年,对松林口岩体进行了研究。结果表明,松林口岩体由二长花岗岩体和花岗闪长岩体组成,花岗闪长岩锆石206Pb/238U年龄加权平均值为（212.4±0.9） Ma （MSWD=0.66）,二长花岗岩锆石206Pb/238U年龄加权平均值为（222.4±1.1） Ma （MSWD=0.39）,形成于晚三叠世,由两期次岩浆作用形成;岩石的SiO2含量56.56%~61.97%;铝饱和指数A/CNK=0.93~1.05,全碱含量3.78~5.38,K2O/Na2O=1.02~1.68,里特曼指数σ=1.194~1.612,样品属于准铝质中—高钾钙碱性岩系列。岩石轻重稀土比值LREE/HREE=5.22~7.13,LaN/YbN比值为6.93~8.96,轻、重稀土分异较明显,具较强的负Eu异常。岩石Mg#值较高（50.97~61.27）,w（Rb）/w（Sr）为0.12~0.25,Rb-（Y+Nb）图解显示为后碰撞环境。因此,松林口二长花岗岩—花岗闪长岩属后碰撞准铝质中—高钾钙碱性I型花岗岩类。 相似文献
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新疆准噶尔北东缘乌图布拉克岩体形成时代、地球化学特征及地质意义 总被引：9，自引：5，他引：4
乌图布拉克岩体位于准噶尔北东缘,额尔齐斯-玛因鄂博构造带南侧。岩体主要由花岗闪长岩和二长花岗岩组成,有少量石英闪长岩和钾长花岗岩。岩体的锆石SHRIMP U-Pb年龄为360.1±3.6Ma。岩石的K2O+Na2O=7.05%~9.48%,A/NKC=0.91~1.04,属准铝-过铝质“I”型花岗岩。岩石稀土总量低,∑REE为72×10-6~184×10-6,轻稀土富集,(La/Yb)N=5~13。石英闪长岩、花岗闪长岩、二长花岗岩具弱的铕负异常或无明显异常（δEu=0.72~0.98）;钾长花岗岩铕负异常明显（δEu=0.15~0.21）。在微量元素配分模式中,具有Sr、Ba、P、Ti的亏损,而Nb、Ta亏损不明显。岩石有低的Sr初始值（0.70165~0.70462）和高的εNd(t)u（+4.7~+6.9）。2个样品的Nd模式年龄分别为758Ma和551Ma。上述特征表明,岩浆可能具有较复杂的来源,推测该岩体岩浆可能来源于年轻的玄武质地壳,并有幔源物质的加入。综合本文资料及区域地质特征分析,阿尔泰造山带后碰撞时限可能为360~290Ma,即泥盆纪末-石炭纪末。 相似文献
10.
河北高寺台含铬超基性岩杂岩体成岩成矿时代及岩石成因 总被引：4，自引：1，他引：3
河北高寺台含铬超基性岩杂岩体产于华北克拉通北缘,具有环状分带的特征,核部为纯橄岩,向外依次为辉橄岩、辉石岩、角闪石岩,各岩相之间为过渡接触关系,在纯橄岩相中赋存有铬铁矿床。本文对该杂岩体的锆石年龄、Hf同位素和主量、微量元素进行了测试和研究。结果表明,随着基性程度的降低,各岩相岩石在主量元素特征上呈现连续的变化特征,Al2O3、TiO2和K2O逐渐升高,MgO含量逐渐降低;微量元素特征上配分曲线形态相似,具有富集Ba、K等LILEs,亏损Nb、Zr等HFSEs,稀土元素具一定程度的分异,无明显Eu异常的特征,说明各岩相为同源岩浆结晶分异作用的产物。通过对3件铬铁矿石和1件辉石岩的LA-ICP-MS锆石U-Pb定年,确定高寺台含铬超基性岩杂岩体的成岩成矿时代为213±1Ma,为晚三叠世,形成于华北板块和西伯利亚板块碰撞后的伸展阶段;年龄值介于214~211Ma之间的锆石的176Hf/177Hf比值介于0.282589~0.282693之间,εHf(t)介于-2.0~+1.6之间,说明高寺台含铬超基性岩杂岩体的岩浆源区组成为亏损地幔物质和富集地幔物质的混合,在岩浆上升过程中有大陆地壳物质的混染,其侵位时代晚三叠世可能代表了华北克拉通北缘岩石圈减薄的开始。高寺台杂岩体年龄测试样品中广泛存在继承锆石,其年龄值介于2800~244Ma之间,分布范围宽,但相对集中于2.6~2.5Ga、400~360Ma、300~280Ma、244Ma共4个年龄段,很可能是岩浆上升过程中的捕获锆石,记录了区域内在新太古代、中泥盆世、早二叠世、晚二叠世-中三叠世存在的岩浆活动。 相似文献
11.
S. Viswanathan K. Surya Prakash Rao B. Mahabaleswar 《Journal of the Geological Society of India》2013,82(6):621-627
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. 相似文献
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奥地利安东帕有限公司 《岩矿测试》2009,28(3):306-306
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 相似文献
14.
E. M. Prasolov S. A. Sergeev B. V. Belyatsky E. S. Bogomolov K. A. Gruzdov I. N. Kapitonov R. Sh. Krymsky V. O. Khalenev 《Geochemistry International》2018,56(1):46-64
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. 相似文献
15.
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. 相似文献
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岩石密度和超高压岩石折返速率 总被引：1，自引：3，他引：1
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。 相似文献
18.
Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA 总被引：1，自引：0，他引：1
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. 相似文献
19.
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. 相似文献
20.
Alexander E. C. Broberg J. S. Kehren A. R. Graziani M. M. Turri W. L. 《Environmental Geology》1993,22(4):353-361
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. 相似文献