Abstract The Westerwald region is one of the major ceramic clay mining areas of Germany. The mined clays were deposited on the weathered Rhenish massif during Eocene and Oligocene and were protected from erosion by a large alkaline basalt cover. Two Fe-rich bentonite layers exposed in quarries of the Eastern part of the Westerwald were investigated with X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, optical microscopy, scanning electron microscopy, chemical analyses and cation exchange capacity (CEC). In both bentonite layers, the main mineral is a high-charge Fe-rich beidellite containing exchangeable Ca and Mg. Even if they both derive from mafic volcanic rocks, the difference in accessory minerals and trace element content leads to the conclusion that they have a different precursor. The lower bentonite layer also contains talc, saponite, halloysite, goethite and anatase. It is part of the Paleozoic bedrock and results from the weathering of a Lower Carboniferous metabasalt. The upper bentonite layer has Upper Oligocene age and has been derived from the alteration of tuffite with a composition ranging from alkali basalt to trachyte. This bentonite is linked to the first eruptions of the intraplate Cenozoic volcanic activity of the Westerwald.

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两种产自 Westerwald（德国）的富铁膨润土的表征和成因

摘要 韦斯特瓦尔德地区是德国主要的陶瓷粘土矿区之一。开采的粘土在始新世和渐新世期间沉积在风化的莱茵地块上，并被大型碱性玄武岩覆盖层保护免受侵蚀。用 X 射线衍射、热重分析、红外光谱、光学显微镜、扫描电子显微镜、化学分析和阳离子交换能力 (CEC) 研究了 Westerwald 东部采石场中暴露的两个富铁膨润土层。在两个膨润土层中，主要矿物是含有可交换 Ca 和 Mg 的高电荷富铁贝得石。即使它们都来自基性火山岩，但副矿物和微量元素含量的差异导致它们具有不同前体的结论。下部膨润土层还含有滑石、皂石、埃洛石、针铁矿和锐钛矿。它是古生代基岩的一部分，是下石炭纪变玄武岩风化的结果。上部膨润土层具有上渐新世时代，来源于具有从碱性玄武岩到粗面岩的成分的凝灰岩蚀变。这种膨润土与韦斯特瓦尔德板块内新生代火山活动的第一次喷发有关。