Iodine budget in surface waters from Atacama: Natural and anthropogenic iodine sources revealed by halogen geochemistry and iodine-129 isotopes     

《Applied Geochemistry》2016

Iodine enrichment in the Atacama Desert of northern Chile is widespread and varies significantly between reservoirs, including nitrate-rich “caliche” soils, supergene Cu deposits and marine sedimentary rocks. Recent studies have suggested that groundwater has played a key role in the remobilization, transport and deposition of iodine in Atacama over scales of millions-of-years. However, and considering that natural waters are also anomalously enriched in iodine in the region, the relative source contributions of iodine in the waters and its extent of mixing remain unconstrained. In this study we provide new halogen data and isotopic ratios of iodine (¹²⁹I/I) in shallow seawater, rivers, salt lakes, cold and thermal spring water, rainwater and groundwater that help to constrain the relative influence of meteoric, marine and crustal sources in the Atacama waters. Iodine concentrations in surface and ground waters range between 0.35 μM and 26 μM in the Tarapacá region and between 0.25 μM and 48 μM in the Antofagasta region, and show strong enrichment when compared with seawater concentrations (I = ∼0.4 μM). In contrast, no bromine enrichment is detected (1.3–45.7 μM for Tarapacá and 1.7–87.4 μM for Antofagasta) relative to seawater (Br = ∼600 μM). These data, coupled to the high I/Cl and low Br/Cl ratios are indicative of an organic-rich sedimentary source (related with an “initial” fluid) that interacted with meteoric water to produce a mixed fluid, and preclude an exclusively seawater origin for iodine in Atacama natural waters. Iodine isotopic ratios (¹²⁹I/I) are consistent with halogen chemistry and confirm that most of the iodine present in natural waters derives from a deep initial fluid source (i.e., groundwater which has interacted with Jurassic marine basement), with variable influence of at least one atmospheric or meteoric source. Samples with the lowest isotopic ratios (¹²⁹I/I from ∼215 to ∼1000 × 10⁻¹⁵) strongly suggest mixing between the groundwater and iodine storage in organic-rich rocks (with variable influence of volcanic fluids) and pre-anthropogenic meteoric water, while samples with higher values (∼2000–93,700 × 10⁻¹⁵) indicate the input of anthropogenic meteoric fluid. Taking into account the geological, hydrologic and climatic features of the Atacama region, we propose that the mean contribution of anthropogenic ¹²⁹I is associated with ¹²⁹I releases during nuclear weapon tests carried out in the central Pacific Ocean until the mid 1990's (¹²⁹I/I = ∼12,000 × 10⁻¹⁵). This source reflects rapid redistribution of this radioisotope on a global scale. Our results support the notion of a long-lived continental iodine cycle in the hyperarid margin of western South America, which is driven by local hydrological and climate conditions, and confirm that groundwater was a key agent for iodine remobilization and formation of the extensive iodine-rich soils of Atacama.  相似文献   

大湖塘矿集区燕山成矿阶段矿床成矿系列研究及找矿问题探讨          下载免费PDF全文

王西荣  潘家永  李绍侠  王佳鑫 《地质找矿论丛》2016,31(2):206-212

大湖塘矿集区位于赣西北九岭成矿带西北部位,区内燕山期岩浆岩侵入活动及成矿作用强烈。大湖塘燕山期岩浆岩形成时间分布在130.3 Ma~151.4 Ma之间,可划分为三次侵入:130.3 Ma~134.3 Ma、140.4 Ma~144.4 Ma、146.4 Ma~151.4 Ma;在144.4 Ma~146.4 Ma之间,岩浆活动处于休宁阶段。区内燕山期岩浆岩与矿床在形成时间上十分接近,空间关系上相互依存,并显示特定的分布格局。根据区内矿床的分布特点、产出位置、成矿时间、燕山期花岗岩与矿床的相关性等特征,可将大湖塘矿集区由北向南依次划分为W、Mo—W、Mo、Cu、Pb、Zn—Cu、Pb、Zn、Au、Ag三个成矿系列,并提出了"北钨南铜"的找矿观点。区内双桥山群与成矿,燕山期岩浆岩的起源,矿床等间距分布,以及重力勘探方面的研究应加强。  相似文献   

新疆白杨河铍铀矿床萤石Sm-Nd和沥青铀矿U-Pb年代学及其地质意义   总被引：3，自引：2，他引：1  

衣龙升  范宏瑞  翟明国  李月湘  马汉峰  田建吉  修晓茜 《岩石学报》2016,32(7):2099-2110

白杨河矿床是我国类型独特的一个特大型铍、铀多金属矿床,铍矿物主要确定为羟硅铍石,铀矿物主要发现沥青铀矿和次生的硅钙铀矿以及少量的铌铀矿,伴生矿物主要是萤石。为恢复铀和铍的成矿过程,划分成矿阶段,本次工作通过系统采集钻孔中的萤石样品,进行了Sm-Nd同位素测年研究,获得了三组等时线年龄,分别为291±16Ma、265±33Ma和207±37Ma,代表了成矿前、成矿期和成矿后萤石的形成;采集中心工地、新西工地和九号工地平巷内的沥青铀矿样品,进行了UPb同位素测年研究,获得了~(206)Pb/~(238)U表观年龄237.8±3.3Ma、224±3.1Ma、197.8±2.8Ma、97.8±1.4Ma和30.0±0.4Ma,利用U-Pb表观年龄将铀矿化划分为四个阶段:中三叠世、晚三叠-早侏罗世、晚白垩世和古近纪中期。因此,白杨河矿床具有铍早铀晚的成矿特点,铀成矿经历了四个阶段。  相似文献   

湘南荷花坪锡多金属矿床成矿年代研究   总被引：1，自引：1，他引：0  

蔡明海  张文兵  彭振安  刘虎  郭腾飞  谭泽模  唐龙飞 《岩石学报》2016,32(7):2111-2123

荷花坪锡多金属矿床是本世纪初在南岭中段湘南地区新发现的一个大型矿床,区内的锡多金属矿化产在王仙岭岩体东南内、外接触带,已发现有Ⅰ、Ⅱ、Ⅲ和Ⅳ号4个主要锡多金属矿体。其中,Ⅰ、Ⅱ和Ⅳ号矿体由早期矽卡岩型和晚期蚀变碎裂岩型矿石组成,Ⅲ号矿体则由独立产出的蚀变碎裂岩型矿石组成,且包含有部分碎裂花岗斑岩。以往研究已对Ⅳ号矿体中的矽卡岩型矿石和Ⅲ号矿体中含矿斑岩脉分别采用辉钼矿Re-Os法和锆石SHRIMP U-Pb法进行了测年,获得的年龄分别为224.0±1.9Ma和142±2Ma。本文补充了晚期蚀变碎裂岩型矿石的~(40)Ar/~(39)Ar测年,结果显示,Ⅱ号矿体中蚀变碎裂岩型矿石白云母样品和石英样品的坪年龄分别为151.88±1.58Ma和155.39±7.04Ma;Ⅳ号矿体中蚀变碎裂岩型矿石石英样品的坪年龄为156.94±1.64Ma。结合前人研究资料综合分析,认为荷花坪矿区存在印支晚期(224Ma)、燕山早期(151~156Ma)和燕山晚期(142Ma)三期成矿作用,分别与区内印支期中粗粒含电气石黑云母花岗岩、燕山早期中粗粒黑云母花岗岩和燕山晚期花岗斑岩脉有关,不同期成岩、成矿作用的构造环境均为岩石圈的拉张伸展。湘南地区印支期(205~224Ma)基性岩浆活动及荷花坪矿床印支期成岩、成矿过程中均有幔源物质的参与,它们共同指示南岭地区中生代构造体制的转换或岩石圈伸展减薄可能始于印支主期(230~244Ma)之后的224Ma左右,即晚三叠世。  相似文献   

新疆“帕米尔式”铁矿床成因与成矿背景分析     

张德贤  曹汇  曾敏  许明珠  李广旭  星显宏 《岩石学报》2016,32(12):3847-3864

帕米尔式"铁矿床是新疆西昆仑地区重要的磁铁矿床类型之一,其矿床地质特征、形成时代明显有别于典型的BIFs类型磁铁矿床。本文以塔什库尔干地区翁吉勒磁铁矿床和孜勒依磁铁矿床作为研究对象,通过研究其赋矿围岩和岩体的岩石地球化学特征、矿石矿相学特征、磁铁矿微量元素地球化学特征和原位Pb-Pb同位素特征,探讨了"帕米尔式"磁铁矿床的矿床成因和成矿背景。岩石地球化学研究表明翁吉勒黑云母二长花岗岩具有高SiO_2、Al_2O_3、K_2O和Na_2O。低MgO、CaO和TiO_2,而Na_2O/K_2O值变化范围很小。铝饱和指数为(1.44~1.51),显示其具有为弱过铝质岩石的特征,稀土总量富集,具有强的负Eu异常。在微量元素蛛网图上显示其富集大离子亲石元素(LILE),如K、Rb、Sr、Ba及轻稀土元素(LREE),亏损Nb、Ta,P、Ti等高场强元素。而黑云母石英片岩稀土含量亦较富集,具有中等强度的负Eu异常。低的Rb/Sr比,明显的Th、Zr、Hf、Nb、Ta,P、Ti负异常,明显的Ba正异常,显示岩石具有古大陆边缘环境的富铝沉积岩特征。翁吉勒黑云母二长花岗岩和布伦阔勒岩群黑云母石英片岩地球化学性质非常相似,表明翁吉勒黑云母二长花岗岩的形成与布伦阔勒岩群黑云母石英片岩的重熔有关。锆石LA ICP-MS定年结果表明翁吉勒黑云母二长花岗岩形成于15.0±0.3Ma和15.4±0.2Ma。磁铁矿LA ICP-MS微量元素地球化学特征表明翁吉勒铁矿床中的磁矿床中主要Si、Mn、Zn、Sn、Hf和Pb相对较高,其中Mn和Ga变化范围较大,而孜勒依铁矿床中的磁铁矿具有相对较高的亲石元素,如Mg、Al、Ti、V、Co、Ni、Ga和Sc等,其Mn和Zn含量较低且变化范围较大,其它元素变化范围均相对较窄。二者相比,翁吉勒铁矿床中的磁铁矿中微量元素变化范围相对较大,而孜勒依铁矿床中的磁铁矿变化范围较小。两个矿床的磁铁矿的原位Pb-Pb同位素存在明显的不同,两类岩石全岩Pb同位素与两个矿床中磁铁矿Pb-Pb同位素研究表明翁吉勒铁矿床中磁铁矿可能与黑云母二长花岗岩有关,为热液成因。综上所述,在塔什库尔干地区不仅存在与沉积作用有关的铁矿床,还可能存在一部分与年轻岩浆岩有关的热液型磁铁矿床。  相似文献   

西藏盐湖地区闪长玢岩锆石LA-ICP-MSU-Pb年龄及岩石成因     

孔旭  密文天  莫雄  张旦  胡隽  周新  万永文 《铀矿地质》2016,(5):279-286

西藏盐湖地区的闪长玢岩体位于班公湖-怒江缝合带西段,其岩石的矿物组合为斜长石(45%~55%)、钾长石(20%~25%)、角闪石(10%~15%)、石英(5%~10%)和黑云母(5%)。锆石LA-ICP-MS U-Pb测年显示,该岩体的形成年龄介于117.6~121.3Ma,即早白垩世。岩石化学研究表明,盐湖地区的闪长玢岩具有I型花岗岩类的地球化学特征,其形成的构造背景为岛弧大陆挤压碰撞造山环境(IAG)。该闪长玢岩体的成因可能与向南俯冲的班公湖-怒江洋壳俯冲板片的断离导致的软流圈物质上涌和地壳重熔有关,即由下地壳基性岩类的部分熔融所形成。  相似文献   

黄铁矿ReOs法测年在胶东金矿中的应用初探          下载免费PDF全文

李洪奎  耿科  禚传源  梁太涛  张玉波 《山东国土资源》2016,32(4):1-6

该次工作为黄铁矿Re-Os法测年在胶东金矿中的首次应用。在大尹格庄金矿中获得了由3件黄铁矿样品组成的(144.8±1.8)Ma等时线年龄,暗示着大尹格庄金矿区可能存在一期晚侏罗世的Au成矿事件。通过对大尹格庄、夏甸、土堆金矿黄铁矿Re-Os同位素年代学的研究,表明黄铁矿的Re-Os同位素特征在胶东金矿中具有一定的复杂性。该文总结了影响黄铁矿Re-Os同位素测年结果的因素,认为在利用该方法进行金矿床定年时,应当将不同期次黄铁矿分别送样,适当拉大采样间距,并尽可能降低实验测试误差,以期获得更精确可靠的年龄。  相似文献   

Direct dating of folding events by 40Ar/39Ar analysis of synkinematic muscovite from flexural-slip planes     

《Journal of Structural Geology》2016

Timing of folding is usually dated indirectly, with limited isotopic dating studies reported in the literature. The present study investigated the timing of intracontinental, multi-stage folding in Upper Proterozoic sandstone, limestone, and marble near Beijing, North China, and adjacent regions. Detailed field investigations with microstructural, backscattered electron (BSE) images and electron microprobe analyses indicate that authigenic muscovite and sericite crystallized parallel to stretching lineations/striations or along thin flexural-slip surfaces, both developed during the complex deformation history of the study area, involving repeated compressional, extensional and strike-slip episodes. Muscovite/sericite separates from interlayer-slip surfaces along the limbs and from dilatant sites in the hinges of folded sandstones yield muscovite ⁴⁰Ar/³⁹Ar plateau ages of ∼158–159 Ma, whereas those from folded marble and limestone samples yield ages of 156 ± 1 Ma. Muscovite from thin flexural-slip planes on fold limbs and hinges yields ages within analytical error of ∼155–165 Ma. Further muscovite samples collected from extensionally folded limestone and strike-slip drag folds yield younger ages of 128–125 Ma with well-defined plateaus. To assess the potential influence of the detrital mica component of the host rock on the age data, two additional muscovite samples were investigated, one from a folded upper Proterozoic–Cambrian sandstone outside the Western Hills of Beijing and one from a folded sandstone sampled 20 cm from folding-related slip planes. Muscovite separates from these samples yield significantly older ages of 575 ± 2 Ma and 587 ± 2 Ma, suggesting that the timing of folding can be directly determined using the ⁴⁰Ar/³⁹Ar method. This approach enables the identification and dating of distinct deformation events that occur during multi-stage regional folding. ⁴⁰Ar/³⁹Ar dating can be used to constrain the timing of muscovite and sericite growth at moderate to low temperatures (<400 °C) during folding, yielding well-defined plateau ages and thereby the age of deformation in the upper crust.  相似文献   

滇东北火德红铅锌矿床地球化学特征与成矿机制分析   总被引：1，自引：0，他引：1  

武昱东  王宗起  罗金海  程家孝  张英利  王师迪 《矿床地质》2016,35(5):1084-1098

文章通过研究滇东北火德红铅锌矿床岩石地球化学和S、Pb同位素地球化学特征,分析其成矿金属和成矿流体来源,进而对其成矿机制进行探讨。围岩主量与微量元素分析结果表明,火德红铅锌矿床为后生热液矿床,铅锌等成矿金属物质随热液进入赋矿围岩,结合围岩蚀变特征判断,其应属中_低温热液成因;闪锌矿与黄铁矿的δ34S主要分布在-17‰~-11.4‰,其S源极可能来自生物成因硫酸盐还原,与川滇黔地区铅锌矿的S同位素来源(总体来自海水硫酸盐热化学还原)有着明显的不同;矿石硫化物的Pb同位素比值变化范围较窄,均为正常Pb;Pb同位素主要来自于上地壳,有少量岩浆物质混入。上述特征表明火德红铅锌矿床为构造和岩性共同控制的后生热液型矿床,其成矿机制与典型MVT型铅锌矿相似。  相似文献   

河南嵩县店房金矿区花岗斑岩锆石U-Pb年龄、Hf同位素及岩石地球化学     

田永飞  叶会寿  李正远  毕珉烽  王鹏  原瑞杰  刘艺博 《地质学报》2016,90(8):1755-1777

华北陆块南缘外方山店房金矿区内出露后沟、水漉塘和店房钾长花岗斑岩体(脉),其与隐爆角砾岩筒及金矿化有密切的空间关系。为查明钾长花岗斑岩体的侵位时代、岩石成因和源区性质,本次开展了锆石U-Pb定年、锆石Hf同位素及岩石地球化学分析等研究。结果表明岩体具有高硅、高钾、富铝、低镁的特征,属钾玄岩系列Ⅰ型花岗岩,轻重稀土元素分馏明显,具有弱的Eu负异常,岩石富集Rb、K、Ba等,亏损Nb、Ta、Sr、P、Ti等元素。锆石具有核—边结构,其中锆石边SHRIMP U-Pb年龄142.6±2.1Ma(MSWD=1.4),_(εHf)(t)=-23.0~-13.8,两阶段模式年龄主要集中于2075~2652 Ma;锆石核LA-ICPMS U-Pb年龄可分为两组,即2169~2336Ma和1732~1881Ma,Hf同位素组成可分为两组,_(εHf)(t)分别集中于-13.1~-4.8和-4.5~3.7,模式年龄主要集中于2376~2805Ma。表明钾长花岗斑岩体形成于142.6±2.1Ma的早白垩世早期,岩浆可能由2169~2336Ma的古老下地壳新太古代太华群部分熔融而成,并有地幔组分参与,岩浆在上升或定位过程中捕获了1732~1881Ma熊耳群火山岩的锆石。结合区域构造背景认为,该岩体是早白垩世古太平洋板块向欧亚大陆俯冲致使华北陆块岩石圈减薄伸展而引起的岩浆活动的产物。  相似文献