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电子探针测年方法应用于晶质铀矿的成因类型探讨 总被引：7，自引：4，他引：3
电子探针Th-U-Pb测年因其高分辨率与高精度的优势,在独居石、锆石等定年矿物中得到了推广,但在Th、U、Pb含量高的晶质铀矿、沥青铀矿等矿物中则应用较少。本文在铁矿床变质岩绿泥石、阳起石黑云母蚀变岩首次发现U含量高的晶质铀矿,基于此,结合该铁矿床地区的地质背景,利用偏光显微镜与电子探针等分析测试手段,将镜下蚀变现象、年龄计算与其他相关元素分析相结合,重点对晶质铀矿的成矿年龄及成矿规律进行探讨。研究发现:通过镜下观察判断,晶质铀矿的成因类型与澳大利亚著名的变质型铀矿相似,均为古老的变质型,且周围的脉石矿物均为绿泥石,绿泥石皆由黑云母退变质而成,铀矿的赋存位置显示其与黑云母、绿泥石之间有紧密联系,其成矿年龄与黑云母、绿泥石形成年龄息息相关。继而根据电子探针数据计算成矿年龄,判断成矿期次,得出主要成矿期在(1654±17)Ma~(1805±17)Ma,为中元古代中期,且主要成矿期与热液蚀变作用黑云母化有关,后期活化富集时期在(657±17)Ma~(807±17)Ma,为新元古代南华纪时期,此阶段是热液侵入、绿泥石化广泛发育的时期;选取较大颗粒对晶质铀矿的环带年龄进行计算,从年龄分布上证实后期有强烈的流体活动的发生,且主要与绿泥石化相关。另外,对比变质型与沉积型铀矿中Y2O3与UO2含量发现,两者之间存在负相关关系,此关系对判断铀矿成因即是否为变质型或沉积型可能有指示意义,但缺乏大量的数据佐证,需进一步研究。 相似文献
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Geochemical analysis of fine grained (<20 μm) tephra found in ice cores is inherently difficult, due to the typically low number and small size of available particles. Ice core tephra samples require specialized sample preparation techniques to maximize the amount of information that can be gained from these logistically limited samples that may provide important chronology to an ice record, as well as linking glacial, marine and terrestrial sediments. We have developed a flexible workflow for preparation of tephra and cryptotephra samples to allow accurate and robust geochemical fingerprinting, which is fundamental to tephrochronology. The samples can be prepared so that secondary electron imagery can be obtained for morphological characterization of the samples to ensure that the sample is tephra-bearing and then the sample can be further prepared for quantitative electron microprobe analysis using wavelength dispersive techniques (EMP-WDS), scanning electron microscopy with energy dispersive spectrometry (SEM-EDS), laser ablation inductively coupled mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS). Some samples may be too small for typical instrumentation conditions to be used (i.e. 20 μm beam on the EMP) to analyze for geochemistry and we present other techniques that can be employed to obtain accurate, although less precise, geochemistry. Methods include analyzing unpolished tephra shards less than 5 μm in diameter with a 1 μm beam on an SEM; using the “broad beam overlap” EMP method on irregular particles less than 20 μm in diameter, and analyzing microlitic shards as well as aphyric shards using EMP to increase the number of analyzed shards in low abundance tephra layers. The methods presented are flexible enough to be employed in other geological environments (terrestrial, marine and glacial) which will help maximize and integrate multiple environments into the overall tephra framework. 相似文献
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For the first time synchrotron radiation X-ray fluorescence (SR-XRF) microanalysis was performed throughout the total length of 4 single barbs from the primaries and secondaries of a snow petrel (Pagodroma Nivea) collected in the Antarctica. Thirteen elements (S, Mg, K, Ca, Fe, Ni, Cu, Zn, Se, Sr, Ba, Hg and Pb) were detected somewhere in the barbs. Variations in levels of these elements within and among the barbs were obvious, indicating nonuniform microscale distributions. Factors influencing the fluctuations of the levels of the elements were investigated using a multivariate statistical analysis method. Five factors (F1 being associated with high loadings of Ca, Sr, and Ni, F2 with high loadings of Fe and Ba, F3 with high loadings of Se and Hg, F4 with high loadings of Ca and K, and F5 with high loadings of Zn and Pb) were found to explain about 80% of the total variance. Results from the factor analysis suggested external contamination of Fe, Ba, Pb, Zn and Hg on the feathers of the snow petrel. 相似文献
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金矿尾矿是砷污染的重要来源,不同冶炼工艺形成的尾矿中砷的赋存状态有很大差异,不同的砷形态会直接影响其在环境中的迁移转化行为,确认砷的存在形态是修复砷污染场地研究中的重要内容。本文针对浮选法和生物氧化法两种不同浸金方法的尾矿,采用pH计和氧化还原电位自动测定仪测量尾矿的物理性质(pH、氧化还原电位),采用X射线衍射和X射线荧光光谱分析尾矿的矿物物相和主要成分,电子探针分析砷的存在形态。表征结果表明,浮选法尾矿和生物氧化法尾矿的物理性质都会因堆置环境的变化而变化,其Eh、pH和零电荷点都大致相同,pH≈8.5,样品零电荷点(pHPZC)大约为8.5。由于两种尾矿都属于碱性环境,因此在修复方法的选择上也受到限制,如只适合在酸性条件下进行的电动修复法就不适用于这两种尾矿,修复试剂的选择也以碱性物质和铁的氧化物(氢氧化物)为主。浮选法尾矿的主要矿物类型为石英、白云石和黏土矿物,化学主要成分是Si和Al,尾矿呈灰白色,其中砷的含量约为754μg/g左右,主要以毒砂(FeAsS)形式存在;而生物氧化法尾矿的主要矿物类型为石膏,化学主要成分是Fe、Ca和S,尾矿呈红棕色,其中砷的含量约为26350μg/g,主要以毒砂(FeAsS)和五氧化二砷(As2O5)形式存在。两种浸金工艺每一道工序的不同,都会造成两种尾矿在矿物相、主要成分和其中砷存在形态上的差异。因此在进行尾矿原位修复工作时,应考虑不同浸金方法对尾矿堆置环境和砷存在形态的影响,从而选择出一种更加合适、廉价、高效的修复方法和试剂。 相似文献
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Authigenesis of iron-rich phosphate nodules occurs in iron-rich cold-seep sediments (MD052911 core) at Yung-An Ridge offshore southwestern Taiwan. Raman, FTIR, and quantitative X-ray energy-dispersive spectroscopic analyses indicate that the phosphate mineral is vivianite (or barićite) and shows Fe/Mg molar ratios spanning from ca. 0.6 to 4.0 and a general down core trend of increasing Fe/Mg ratios. The formation of vivianite is limited to a depth interval of 13–17 mbsf (meters below seafloor) and is most prominent at ∼16 mbsf in association with high dissolved iron concentrations and depleted dissolved sulfide below a peak sulfidization zone (enriched in mackinawite and greigite). Alternate growths of vivianite and iron monosulfides and compositional zoning with Mg enriched towards the peripheries of individual nodules occur in the transition from the zone of vivianite mineralization to the sulfidization zone. The crystallization of vivianite below the sulfidization front could have been favored by scavenging of downward diffusive dissolved sulfide from pore waters in the sulfidization zone. Alternate growths and overlapping of the zones of iron monosulfides and vivianite can be attributed to fluctuations of the sulfidization front and methane flux. The discovery of vivianite in the Yung-An Ridge sediments implies that authigenic vivianite can be an important sink for phosphorus burial in cold-seep sediments that have high reactive-iron contents and high sedimentation rates. 相似文献
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喷流沉积型矿床是矿床地质学研究的前沿课题,查明矿石中重要组分(镍和钼)的赋存状态是该类矿床地质学研究的重要内容。湘黔地区天鹅山-黄家湾、大坪-大浒镍钼矿带是典型的海底喷流沉积矿床,本文采集该矿区的样品,应用化学和光谱定量分析、偏光显微镜和X射线衍射、扫描电镜、电子探针等大型现代仪器相结合的分析手段,研究了矿石中镍和钼的赋存状态。化学和光谱分析确定矿石中镍含量为3.76％,钼含量为4.99％;偏光显微镜下观察发现金属矿物零星分布,颗粒细小,结晶程度差,光学特征极不明显,晶体形貌特征难以观察,初步推断矿石矿物以胶状形式存在,但在光学显微镜下很难为这些矿物定名和描述;X射线衍射分析验证了偏光显微镜鉴定结果,印证了样品中存在很多非晶质矿物,仅有钨钼钙矿和镍黄铁矿两种矿物含有镍钼,且矿物含量很低(分别为0.4%和0.8%),对比化学分析结果,可推断样品还存在其他富含镍钼元素的矿物。进一步对富集镍钼元素的区域进行电子探针分析,最终确定了镍除了赋存于辉砷镍矿、方硫镍矿中,在胶状黄铁矿和磁黄铁矿边缘呈蠕虫状花边的镍黄铁矿中也有富集;钼主要赋存于碳硫钼矿中。矿石中的镍钼主要赋存于由胶态向结晶态过渡的金属矿物中,研究成果为该类矿床的矿石矿物学研究、选矿、冶炼及矿石综合利用提供重要的信息和依据。 相似文献
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单个流体包裹体成分无损分析进展 总被引：8，自引：0，他引：8
原位无损分析是流体包裹体成分研究的前沿课题,简要总结了单个流体包裹体成分分析方法,评述了原位无损分析方法中微束质子诱发X射线法、同步辐射X射线荧光光谱、显微拉曼光谱、显微红外光谱和红外显微镜分析流体包裹体成分的原理、应用范围、存在问题和研究进展。选择研究流体包裹体成分的方法时,需要考虑分析方法的特点、所测组分及其含量的估计范围、所测流体包裹体的大小、距薄片表面的深度、基体矿物的性质和仪器性能。 相似文献
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广东莲花山断裂带西南段分布有棉洋-双华(Ⅰ)、北山嶂-九龙嶂(Ⅱ)、五指嶂-锅子嶂(Ⅲ)、梅陇-鲘门-观音山(Ⅳ)4条韧性剪切带,呈巨型构造透镜体沿北东向展布。已有研究表明韧性剪切带与本区钨、锡、铜多金属成矿作用关系密切,控制着矿床的空间分布,是重要含矿、控矿构造。按照变质程度和矿物组成,区内韧性剪切带由核部至边部可以划分为石英透镜体→石榴子石(堇青石)糜棱岩→糜棱片岩→片岩→原岩等;通过对其中的石榴子石、黑云母等典型矿物进行电子探针分析(EPMA),并利用石榴石-黑云母地质温压计估算了 4条韧性剪切带形成的温压条件,它们分别为484～526℃/4.92～7.72kbar、458～469℃/2.17 ～2.67kbar、536～551 ℃/1.28～1.67kbar、512～516℃/4.38 ～4.87kbar,与区内变质岩野外地质变形、变质特征相吻合,且火山岩为主的地区变质压力明显高于花岗岩为主的地区。研究显示,变质条件对区内变质分带和多金属成矿作用有明显的控制,棉洋-双华和梅陇-鲘门-观音山韧性剪切带的压力条件相对较高,金属成矿以钨、锡多金属成矿为主;而北山嶂-九龙嶂和五指嶂-锅子嶂韧性剪切带的压力相对较低,金属成矿则以铜、铅、锌成矿为主。 相似文献
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