oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Textures and Rare Earth Elements Composition of Banded Iron Formations (BIF) at Njweng Prospect, Mbalam Iron Ore District, Southern Cameroon  [PDF]
Dieudonne Charles Isidore Ilouga, Cheo Emmanuel Suh, Ghogomu Richard Tanwi
International Journal of Geosciences (IJG) , 2013, DOI: 10.4236/ijg.2013.41014
Abstract:

The REE signature of banded iron formations (BIF) and martite-goethite mineralization of the Njweng ridge (South Cameroon) are used here to decipher the nature of the ocean during the period of BIF precipitation. The textures of typical BIF categories are also presented as the only sedimentary feature. Two types of BIF facies are present at Njweng: the oxide and silicate facies. These facies show two stages of phase transformations. The first is the transformation of the original magnetite mineral into martite by oxidation resulting in trellis texture; the second is a simultaneous transformation by hydration into goethite and dehydration into martite. The samples typically show LREE depleted patterns relative to HREE, a characteristic similar to that of modern seawater. Also the strong positive Eu anomalies from the samples indicate the involvement of hydrothermal plumes of volcanic origin such as at mid ocean ridges (MOR). Yttrium (Y) has a strong positive anomaly pointing to the transportation of REEs as aqueous complexes within these ancient seas. The BIF samples have no positive Ce anomalies, suggesting that the oceans at that time were more reducing with no Ce fractionation than in present day oceans. The martite-goethite mineralization rather shows a positive Ce anomaly that derived from the enrichment in REE during the weathering of REE-bearing minerals. These results are integrated into existing literature on REE in BIFs worldwide and provide new insights into these heretofore unstudied BIFs of the northern edge of the Congo Craton.

Analytic expressions for interface terms in general dispersed two–phase flow laden with arbitrary–shaped dispersed elements Expresiones análiticas para los términos interfaciales en flujos bifásicos dispersos generales cargados con elementos dispersos de forma arbitraria  [cached]
Santiago Laín,Ricardo Aliod
Ingeniería y Ciencia , 2008,
Abstract: This paper presents the methodology of the indicator function–discrete elementsprobability density function statistical average applied to Two–phaseflow modelling. This formulation allows to consider particles of arbitrary shapeand size and it can be applied to any laminar or turbulent flow. In the case ofequal sized spherical dispersed elements, the most common case found in theliterature, the final expression for the interaction terms (contributions thatdescribe the effect of the second phase on the continuous one) are obtainedwithout great difficulties due to the high isotropy of the spherical shape. Thistask, in the general case of non–spherical non–equal particles is no longerstraightforward and the derivation of the appropriate general interaction termsis presented in §4. In the case that the dispersed elements are small enough,some simplifications can be further introduced leading to a final presentation that remembers that obtained for the simplest case of spherical particles, butwhere some of the quantities must be adequately redefined. Este artículo presenta la aplicación al modelado de flujos bifásicos de la metodología de promediado estadístico utilizando la combinación de la función indicadora de fase y la función densidad de probabilidad de los elementos dispersos. Esta formulación permite considerar partículas de forma y tama o arbitrarios y puede aplicarse a flujo laminar o turbulento. En el caso de elementos dispersos esféricos de igual tama o, el más frecuente reportado en la literatura, la expresión final de los términos de interacción (contribuciones que describen el efecto de la segunda fase sobre la fase continua) se obtiene sin mayores dificultades debido a la isotropía de la forma esférica. En el caso general, sin embargo, la tarea es más complicada por lo que la derivación de los términos de interacción generales se aborda en §4. Si los elementos dispersos son suficientemente peque os se pueden introducir simplificaciones adicionales permitiendo obtener una expresión final que recuerda la obtenida para el caso más simple de partículas no esféricas, aunque algunas cantidades deben redefinirse adecuadamente.
Characteristics of Rare Earth Elements and Trace Elements in Hanwang Neo-Archaean Banded Iron Formations, Shandong Province
山东韩旺新太古代条带状铁矿的 稀土和微量元素特征

SHEN Qi-han,SONG Hui-xia,ZHAO Zi-ran,
沈其韩
,宋会侠,赵子然

地球学报 , 2009,
Abstract: Hanwang banded iron formations (BIF) in Shandong Province constitute a large iron deposit of Anshan type formed in Neo-Archaean. In this paper, petrology and petrochemistry of Hanwang BIF were studied and a comparison was made with other BIF in the world. Petrological studies show that the BIF suffered greenschist facies to low amphibolite facies metamorphism and part of the magnetite was recrystallized whereas the other part of the magnetite preserved the characteristics of chemical sediments. In the diagram of TFe-(CaO+MgO)-SiO2, Hanwang BIF has a consistent distribution area with Wutaishan BIF and other BIF in the world. The REE contents of Hanwang BIF are low, showing characteristics of marine sediments in Archean. In the PAAS-normalized REE pattern, LREE are depleted and HREE are enriched relatively, with strong Eu positive anomaly, obvious Y positive anomaly and no visible Ce anomaly. These Hanwang BIF characteristics are itentical with characteristics of Gongchangling, Wu-taishan and many other Archean BIF in the world. As for trace elements, contents of Ti, V, Co, Ni, Mn, Sr and Ba are low. In trace elements distribution diagram normalized by primary mantle, U, Ta, La, Ce and P have positive anoma-lies, whereas things are just the opposite for K, Nb, Sr, Hf and Zr. The ratios of Sr/Ba, Ti/V and some other elements are also considered in this paper. A comprehensive study of Hanwang BIF shows that its ferruginous material was associated with volcanic hydrothermal solution and was formed in a marine chemical sedimentary environment.
Thèmes et significations dans le poème apollinairien Signe
Alexandrina Must??ea
Studii si Cercetari Filologice : Seria Limbi Romanice , 2008,
Abstract: La macrostructure sémantique textuelle ou le thème est une des catégories majeures de l’institution littéraire. Déterminer quel est le thème d’un texte permet au lecteur de le comprendre et de l’interpréter, en surmontant ses éventuelles lacunes, et en ne retenant des interprétations possibles que celles qui y renvoient. Cependant, il est rare qu’un texte littéraire développe un thème unique. Le plus souvent il s’agit d’entrelacement ou de superposition thématique. Ce phénomène est particulièrement marqué dans le texte poétique. C’est ce que notre analyse du poème Signe se propose de démontrer, tout en essayant d’en souligner les conséquences pour l’interprétation des significations poétiques.
Simulación del comportamiento elastoplástico de estructuras bifásicas policristalinas de aceros “Dual-phase”  [cached]
Bonifaz, E. A.,Martín Meizoso, A.,Martínez Esnaola, J. M.,Gil Sevillano, J.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 2000,
Abstract: In order to model the elasto-plastic behaviour of polycrystalline dual-phase steel microstructures (ferrite/martensite), uniaxial tension is simulated using a 3-D finite element code. Calculations are performed for a representative dual-phase cubic volume discretised in 3375 elements, using either plane or free-face boundary conditions. The effects of morphology and grain number on the stress-strain macroscopic curve and on the strain distribution are analised. The results confirm the efficiency of the method for predicting the elasto-plastic behaviour of dual-phase steels. The simulations are aimed to be used for the microstructural design of new dual-phase steels. Mediante el Método de los Elementos Finitos (MEF) se han realizado simulaciones del comportamiento elastoplástico de estructuras bifásicas policristalinas con un mismo comportamiento elástico y diferente comportamiento plástico, representativas de aceros bifásicos tipo “dual-phase” (ferrita/martensita). Las simulaciones se realizan en 3 dimensiones, con diferentes condiciones de contorno: caras planas, y caras libres. Se analiza el efecto de la morfología y del número de los granos de ambas fases contenidos en la muestra analizada sobre la curva macroscópica tensión-deformación y sobre varios aspectos micromecánicos de la predicción, tales como la distribución de las deformaciones en las dos fases, la heterogeneidad de las deformaciones locales o las tensiones residuales a escala mesoscópica. Los resultados orientan sobre los métodos más eficientes para la simulación a diferentes escalas del comportamiento plástico de materiales bifásicos y pueden servir de ayuda para el dise o microestructural de nuevos materiales.
中国BIF型铁矿床地质特征和资源远景  [PDF]
沈保丰
地质学报 , 2012,
Abstract: BIF型铁矿床是中国最重要的铁矿床类型,占全国总查明资源储量55.2%。BIF型铁矿床主要分布在华北陆块,其次在扬子陆块。在华北陆块鞍山―本溪,密怀―冀东,五台―吕梁矿集区中铁矿床尤为集中,约占全国铁总探明储量41.5%。BIF型铁矿床在古太古代、中太古代、新太古代、古元古代和新元古代均有产出,但主要在新太古代―古元古代。BIF型铁矿床可划分为阿尔戈马型和苏必利尔湖型两类,其中以新太古代阿尔戈马型最为重要。BIF型铁矿床主要是贫铁矿石,富铁矿石极少。富铁矿均产在贫铁矿体中,以(火山)沉积-热液交代改造型最为重要。BIF形成与海底热液喷流作用有关。在中国BIF型铁矿的资源潜力大,远景可观。
Thermal Analysis and Phase Diagram of the LiF-BiF3 System  [PDF]
G. H. G. Nakamura,D. Klimm,S. L. Baldochi
Physics , 2012,
Abstract: Differential thermal analysis up to complete melting was performed for the complete pseudobinary system LiF-BiF3. Melts with high bismuth fluoride concentration show severe evaporation, nevertheless even pure BiF3 could be molten at 655 deg. C. The system contains one intermediate compound BiLiF4 which melts by peritectic decomposition under the formation of LiF at 415 deg. C. The eutectic between BiLiF4 and BiF3 melts at 415 deg. C. By thermodynamic assessment the following parameters were found for BiLiF4: \Delta H=-1514900 J/mol, S=158.5 J/mol K, c_p=166.173 -0.01072 T (in J/mol K). The melt has negative excess Gibbs free energy.
Geochemistry and Tectonic Significance of Chlorite Amphibolite in Nanfen BIF, Benxi Area, Northeastern China  [PDF]
Ende Wang, Changik Han, Jianming Xia, Sunggi Yun
Journal of Geoscience and Environment Protection (GEP) , 2015, DOI: 10.4236/gep.2015.35007
Abstract:

Benxi area, Northeastern China, is the main distribution area of Archean BIF-hosted iron deposits in China. In this area, Nanfen iron deposit is well known as the largest open-pit iron deposit not only in China but also in Asia. So far, the tectonic nature during Archean BIF formation period in Benxi area has been long disputed and the tectonic setting of Nanfen BIF had not been found. In this study, the geochemical characters of chlorite amphibolites closely associated with BIF have been investigated for the tectonic environment of Nanfen BIF. Chlortie amphibolites show the geochemical affinity to the back-arc basin basalt (BABB), indicating that the tectonic environment of Nanfen BIF is the back-arc basin. In conjunction with geological evidence of other BIFs at Benxi area, it is identified that BIF in Benxi area might be formed in the subduction-related back-arc basin, which provides a favorable sedimentary environment of Algoma-type BIF.

利用BIF尾矿制备轻质墙体材料的试验研究  [PDF]
李学金, 郑乐平, 蒋有义, 常前发
金属矿山 , 2007,
Abstract: 在综合分析BIF尾矿基本特性的基础上,以BIF尾矿为主要原料,选择不同的粘结剂制备轻质墙体材料。研究结果表明,最佳工艺参数为铁尾矿、无机粘结剂和碱液改性生物质粘结剂的质量比90∶5∶5、烧结温度1200±10℃、烧结时间30min。在最佳条件下制备的产品,体积密度1.314g/cm3、显气孔率30.98%、抗压强度达到MU7.5标准。
西澳皮尔巴拉地块BIF型铁矿遥感地质特征与找矿研究  [PDF]
郐开富,徐文斌,黄智才,李素
国土资源遥感 , 2015, DOI: 10.6046/gtzyyg.2015.04.15
Abstract: 为了从遥感角度对西澳大利亚哈默斯利盆地的沉积变质条带状含铁建造(bandedironformation,BIF)型铁矿进行深入研究,利用ETM图像对皮尔巴拉地块进行地质矿产解译,采用ASTER图像对目标区域进行矿化蚀变信息提取;结合传统地质矿产理论及相关文献,对区内BIF型铁矿的遥感地质特征及其成矿机理进行深入解剖、对比和研究,在此基础上建立了BIF型铁矿的遥感地质找矿模型;并圈定了找矿远景区,以期能在BIF型铁矿找矿(前期)技术方面取得突破,为寻找BIF型铁矿提供技术支持与帮助。具有现实验证意义的是,在所圈定的找矿远景区进行野外调查时发现,澳大利亚力拓集团已经在纽曼—必和必拓C区远景区内筹建一处大型铁矿,前期平地工作已基本完成。
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.