The iron (Fe)-oxide deposits of the Lahn-Dill-type are composed of haematite-quartz and rare siderite-haematite ores. These ores formed as marine chemical sediments on top of volcaniclastic rocks near the Middle to Late Devonian boundary (∼ 380 Ma). As such, their trace element fractionation patterns provide key information on venting style, ocean chemistry, particle-solution interaction, and depositional environment at the time of ore formation. This study combines WDXRF and ICP-MS/OES whole-rock geochemistry with complementary in-situ LA-ICP-MS analysis, and TEM element mapping of ore samples from the Fortuna Mine (Rhenish Massif, Germany). In-situ measurments were conducted on quartz-haematite, haematite, and siderite-haematite microdomains. Bulk major element contents of the ores indicate (volcani)clastic contamination and post-depositional hydrothermal alteration. Microdomain trace element distributions reveal four different trace element signatures, which are related to: (1) syngenetic apatite formation due to sorption of P and REY from seawater; (2) Fe-(oxyhydr)oxide-specific trace element scavenging and fractionation within the seawater column; (3) diagenetic Fe(III) reduction and trace element mobilisation in pore water; and (4) simultaneous deposition of (volcani)clastic material and Fe-(oxyhydr)oxides. These results show that Lahn-Dill-type iron ore formation resulted from mixing of a low-temperature vent fluid with ambient seawater at high seawater to vent fluid ratios. This likely was related to an environment in which diffuse venting dominated over focused venting, and in which quick Fe-particle precipitation led to formation of haematite-quartz ores. Local diagenetic Fe(III) reduction resulted in post-depositional siderite-haematite ore formation during which trace elements were partially remobilised in pore water.

拉恩-迪尔型铁 (Fe) 氧化物矿床由赤铁矿-石英和稀有菱铁矿-赤铁矿矿石组成。这些矿石是在中晚泥盆世边界（约 380 Ma）附近的火山碎屑岩顶部形成的海洋化学沉积物。因此，它们的微量元素分馏模式提供了有关喷发类型、海洋化学、颗粒-溶液相互作用以及矿石形成时的沉积环境的关键信息。这项研究将 WDXRF 和 ICP-MS/OES 全岩地球化学与补充的原位 LA-ICP-MS 分析以及 Fortuna 矿（德国莱尼什地块）矿石样品的 TEM 元素测绘相结合。对石英-赤铁矿、赤铁矿和菱铁矿-赤铁矿微区进行了原位测量。矿石的大量主元素含量表明（火山）碎屑污染和沉积后热液蚀变。微域微量元素分布揭示了四种不同的微量元素特征，这些特征与：（1）由于从海水中吸附P和REY而形成同生磷灰石； (2) 海水柱内Fe-(羟基)氧化物特定微量元素的清除和分馏； (3)成岩作用Fe(III)还原和孔隙水中微量元素动员； (4) (火山)碎屑材料和铁(羟基)氧化物的同时沉积。这些结果表明，Lahn-Dill 型铁矿石的形成是由于低温喷口流体与环境海水以高海水与喷口流体比率混合所致。这可能与扩散通风占主导地位的环境有关，并且铁颗粒的快速沉淀导致赤铁矿-石英矿石的形成。 局部成岩作用 Fe(III) 还原导致沉积后菱铁矿-赤铁矿矿石形成，在此过程中微量元素部分重新回到孔隙水中。