Leanne Schmitt, Thomas Kirnbauer, Thomas Angerer, Dennis Kraemer, Dieter Garbe-Schoenberg, Thomas Fockenberg, Sabine Klein
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引用次数: 0
Abstract
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.
期刊介绍:
The journal Mineralium Deposita introduces new observations, principles, and interpretations from the field of economic geology, including nonmetallic mineral deposits, experimental and applied geochemistry, with emphasis on mineral deposits. It offers short and comprehensive articles, review papers, brief original papers, scientific discussions and news, as well as reports on meetings of importance to mineral research. The emphasis is on high-quality content and form for all articles and on international coverage of subject matter.