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Alkali-metasomatism and/or alkali-metasomatites are commonly recognized in different types of endogenic iron deposit,especially in the contact-metasomatic and porphyrite types in China.Alkali-metasomatites occur at the bottom of the mineralized alteration zone,in the marginal facies of the metallogenetic magmatic masses adiacent to iron ore bodies.They are approximately consistent with the attitudes of the ore bodies.As a result of alkali-metasomatism,great changes have taken place in the source rocks,producing distinet alteration zones with the color becoming lighter and lighter upwards and outwards.The alkali-metesomatic solntion is a kind of pneumato-hydrothermal solution rich in Cl,Si and alkalis.Its main components are alkalis and volatiles(dominantly H2O and Cl).The alkalis are closely related to magmatie source and its subsequent differentiation,while H2O is derived mainly from meteoric waters absorbed by the magma and Cl mainly from magma-mesitized gypsum-salt strata(including ground brines).In essence,alkali-metasomatism is the continuation of magmatic evolution and also an auto-metamorphism within the metallogenetic masses,i.e.,a complex ion-exchange reaction under certain physico-chemical conditions.The whole process of alkali-metasomatism can generally be divided into the Na^ -,Ca^2 -and Na^ -replacement stages.In the Ca^2 -replacement stage iron was largely separated from the source rocks.Alkali-metasomatism and the formation of iron ore deposits are two different forms of expression with respect to the same magmatic process,and both are controlled by and genetically related to magmatism,as is indicated by the facts that some of the oreforming materials are products of the de-iron process during alkali-metasomatism and that alkalis and volatiles have played an active role in the formation of iron and differential fusion of silicate melt. 相似文献
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美国“页岩气革命”引领了页岩气的全球性开发,页岩气作为全球能源结构变革中的“过渡能源”,越来越受到各国政府的青睐.但是,页岩气全球性开发对涉“水”、“陆”、“空”三个层面的国际法规则带来了挑战.笔者认为应从加强国际能源法与国际能源政治良性互动、促进国际能源法专业化以及构建世界能源组织三个方面来加以应对.无论面临何种挑战,都应遵守国际法,秉持可持续发展原则,协调各方利益,积极参与全球能源治理. 相似文献
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六十年代以来,我国相继发现内生铁矿的成矿岩体大多程度不同地发育着一套碱交代岩,它与矽卡岩相比是个直接的找矿评价标志,更能反映铁矿的生因本质。因此,进一步探讨有其理论和实践意义,而且对其他矿种的内生矿床的蚀变交代岩研究也有一定参考价值。 一、碱交代岩的基本地质特征 我国主要内生铁矿类型的碱交代岩皆赋存在靠近铁矿体的成矿岩体的边缘相带内,一般处于矿化蚀变带的根部,与深色蚀变岩带或矽卡岩带毗连,它或构成铁矿体的底板(有时为 相似文献
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