Chemical, Isotopic, and Fluid Inclusion Evidence for the Hydrothermal Alteration of the Footwall Rocks of the BIF-Hosted Iron Ore Deposits in the Hamersley District, Western Australia     

Makoto Haruna    Takahiro Hanamuro    Kaoru Uyeda    Hirokazu Fujimaki  Hiroshi Ohmoto 《Resource Geology》2003,53(2):75-88

Abstract. The petrography, chemical, fluid inclusion and isotope analyses (O, Rb-Sr) were conducted for the shale samples of the Mount McRae Shale collected from the Tom Price, Newman, and Paraburdoo mines in the Hamersley Basin, Western Australia. The Mount McRae Shale at these mines occurs as a footwall unit of the secondary, hematite-rich iron ores derived from the Brockman Iron Formation, one of the largest banded iron formations (BIFs) in the world. Unusually low contents of Na, Ca, and Sr in the shales suggest that these elements were leached away from the shale after deposition. The δ¹⁸O (SMOW) values fall in the range of + 15.0 to +17.9 per mil and show the positive correlation with calculated quartz/sericite ratios of the shale samples. This suggests that the oxygen isotopic compositions of shale samples were homogenized and equilibrated by postdepositional event. The pyrite nodules hosted by shales are often rimmed by thin layers of silica of varying crystallinity. Fluid inclusions in quartz crystals rimming a pyrite nodule show homogenization temperatures ranging from 100 to 240C for 47 inclusions and salinities ranging from 0.4 to 12.3 wt% NaCl equivalent for 18 inclusions. These fluid inclusion data give direct evidence for the hydrothermal activity and are comparable to those of the vein quartz collected from the BIF-derived secondary iron ores (Taylor et al, 2001). The Rb-Sr age for the Mount McRae Shale is 1,952 ± 289 Ma and at least 200 million years younger than the depositional age of the Brockman Iron Formation of ∼ 2.5 Ga in age. All the data obtained in this study are consistent with the suggestion that high temperature hydrothermal fluids were responsible for both the secondary iron ore formation and the alteration of the Mount McRae Shale.  相似文献   

Implications of Analcime Hydrothermally Formed from Na-alumino-borosilicate Glasses Containing Cs and Sr for the Stability of High-level Radioactive Waste Form     

Wook Sohn    Tetsuya Shoji  Hiroaki Kaneda  Teruaki Ishii 《Resource Geology》2003,53(1):51-59

Abstract. In order to know the behaviors of radioactive elements such as cesium and strontium during a hydrothermal alteration of borosilicate glass of radioactive waste, some alumino-borosilicate glasses belonging to the systems Na₂O-Al₂O₃-B₂O₃-SiO₂-SrO, Na₂O-Al₂O₃-B₂O₃-SiO₂-Cs₂O and Na₂O-Al₂-O₃-B₂O₃-SiO₂-SrO-Cs₂O have been treated hydrothermally at 200C under a vapor pressure of 1.54 MPa. The result shows that all glasses are changed into crystalline phases with running time up to 60 days, and that analcime-type zeolite is formed as a major product. The formed zeolite is shown to contain cesium and/or strontium. Considering the fact that natural zeolite occurs in wide physicochemical conditions including hydrothermal one, the analcime-type zeolite is expected to fix stably the radioactive elements in the disposal site. Since aluminum is necessary for the formation of the analcime-type zeolite, the waste glass should have aluminum as one of major components.  相似文献   

Old inherited origin for the present near-bimodal topography of Africa     

C. Moctar Doucour  Maarten J. de Wit 《Journal of African Earth Sciences》2003,36(4):371-388

Africa’s landscape is dominated by a manifold of second-order epeirogenic structures superimposed on a first-order bimodal topography. Bivariate regression analysis of Africa’s surface topography shows that this is a complexly folded surface with regionally elevated areas in southern and eastern Africa, and a topographically low northern and western Africa. The apparent spatial relationships between these features are analysed using anomaly correlation between surface topography and free-air gravity anomalies. Occurrences of positively correlated features between gravity and topography in Africa are found to be limited to second-order epeirogenic features. Geophysical modelling and geologic evidence indicate that Africa’s bimodal topography is genetically distinct from these second-order features, and linked to sources as deep as the sublithospheric mantle. The age, measured and modelled elevation of the bimodal topography require that topographic uplift of south-central Africa be episodic. We infer from our findings together with relative sea-level changes, that the near-bimodality of Africa’s topography is an ancient feature inherited at least from upper Paleozoic times. Our reconstructed paleotopography suggests that Africa was largely a low-lying continent dominated by its cratons, and that basement distribution disregards the present-day uplift patterns of Africa.  相似文献   

HUBEX强化观测期雷达测雨在水文过程模拟中的应用(英)   总被引：3，自引：0，他引：3  

REN Liliang  LI Chunhong  WANG Meirong 《大气科学进展》2003,20(2):205-211

选择全球能量与水循环亚洲季风试验区的淮河黄泥庄水文站控制的史河流域(805 km2)为研究区域,基于数字高程模型,生成栅格水流流向,构建数字流域及空间拓扑关系;然后,将阜阳雷达观测数据经过订正校准后作为研究区内每一栅格单元上的雨量输入,并在每一栅格上应用新安江模型构建产流模型;再根据每一栅格至流域出口断面-黄泥庄水文站的距离,运用Muskingum方法进行汇流演算,从而获得黄泥庄站的流量过程。计算结果显示,从1998年5月31日-8月3日的强化观测期内模型确定性系数为92.41％,其间4场洪水的确定性系数分别为85.64％、86.62％、92.57％和83.91％,高于应用地面雨量计观测的数据计算的结果。这说明雷达测雨数据具有较高的时空分辨率,当它应用于水文过程模拟时优于地面雨量计资料,基于栅格的水文模型为充分利用雷达数据提供了良好平台。  相似文献   

数字滤波方法在月尺度数值预报中的应用：II.保留不同低频过程的效果比较          下载免费PDF全文

杨燕  纪立人 《大气科学》1997,21(5):533-534

用数字滤波方法对观测资料序列进行处理，得到初始场用于Ｔ４２Ｌ９全球谱模式的月预报，以去除误差增长较快的高频扰动对低频过程的影响，并且利用多时刻的观测资料提取低频过程的信息。对冬季和夏季两个不同个例进行了实例，并比较了取不同长度的观测序列，截取不同周期的过程作为初值对预报效果的影响。结果说明，经过滤波后对低频分量和平均场的预报都有显著的改进。而且对于较长时效的预报，应保留更低频的过程（比如１０ｄ以上  相似文献   

龙门山地区泥盆纪碳酸盐与硅质碎屑的混积相与混积机理   总被引：7，自引：0，他引：7       下载免费PDF全文

李祥辉  刘文均  郑荣才 《沉积与特提斯地质》1997,17(3):1-10

碳酸盐与陆源碎屑的混合沉积研究至今尚未引起足够重视。文献屈指可数。扬子西经缘龙门山地区盆纪发育了了这类良好的混合沉积。作者根据实际材料，首次从这一思路出发，识别该区泥盆纪Ｅｍｓｉａｎ期到Ｇｉｖｅｔｉａｎ早期的混积相四种，混积亚相约１４种，阐明了其优势混积作用；根据混积作用特征、沉积背景关系，划分出两大混积类型，即泥质背景下的混积１型和砂灰质背景下的混积Ⅱ型；对混积作用机理进行了探讨；并指出不同级次  相似文献   

金伯利岩中新发现的两种Zr-Ti、REE-Ti氧化物矿物──上地幔含大阳离子Cr、Ti、Fe氧化物矿物研究之四     

陆琦  周湖云  刘惠芳  雷新荣 《矿物学报》1997,(3)

在研究沂蒙矿、蒙山矿等地幔矿物时，新发现了两种Zr－Ti、REE－Ti氧化物矿物。Zr－Ti氧化物新相6个样品点的探针成分分析（wt％）：TIO227.756～46.811，ZrO231.724～58.092，TFeo2.75～5．82，CrO31．728～4．765，Nb2O51．353～4．357，Ta2O50．155～2.814，SiO20．894～13．749，主次元素的成分变化幅度均较大，但以氧为4计算的阳离子总数均为2，因此分子式可简写为（Ti，Zr，Si，Fe）2O4或（Ti，Zr）2O4，与人工化合物ZrTiO4相似。REE－Ti氧化物矿物新相的成分也较复杂，主要元素为REE（Ce，Nd，La，Sm，Pr…）及Ti，次要元素有Nb，根据五个样点的探针分析结果，简化的分子式（Ce…）2（Ti…）3O9，与人工化合物Ce2Ti3O8.7类似，属等轴晶系。两个新矿物相均产于蒙山矿中的微裂隙和熔融交代海绵边中，呈斑点状、蠕虫状、微脉状，组成元素复杂，不同颗粒分析点成分有差异，且在同一微脉中成分也有变化，反映了这两种新矿物相是非平衡的交代一结晶产物。从矿物的产出关系和成分的特征来看，它们的形成与地幔流体交代作用有关。  相似文献   

碎裂蚀变花岗岩型铀矿的赋矿岩石特征     

冯明月 《铀矿地质》1997,(2)

本文着重论述了碎裂蚀变花岗岩型铀矿的赋矿岩石特征：即岩石原始铀含量高；岩石碎裂强度大；岩石蚀变强烈；岩石组分简单，有利于铀的浸出（有害元素含量低）。这些特征可以作为识别与寻找该类型铀矿床的岩石学依据。  相似文献   

地质学家重视研究深部（变质）CO_2对古气候的影响   总被引：5，自引：0，他引：5  

王焰新  文冬光 《地学前缘》1996,3(4):274-281

地质学家重视研究深部（变质）ＣＯ２对古气候的影响贾跃明（中国地质矿产信息研究院，北京，１０００３７）近几年来，随着过去全球变化研究的兴起，地质学家越来越重视地质历史时期影响大气ＣＯ２浓度的因素的调查。不少人认为，变质作用和火山活动可能是过去大气中ＣＯ...  相似文献   

Modelling of soil temperature profiles using data from the pilot experiment at Anand     

B Joseph  P Goswami 《Journal of Earth System Science》1996,105(2):191-195

We present some preliminary results from a multi-layer soil temperature finite-difference model using the data set obtained during the pilot experiment on land surface processes at Anand. We hope that the present results will prove useful during the final field experiments scheduled for the coming monsoon season.  相似文献