Genesis of Devonian volcanic-associated Lahn-Dill-type iron ores – part II: trace element fractionation evidences diffuse fluidventing

IF 4.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Leanne Schmitt, Thomas Kirnbauer, Thomas Angerer, Dennis Kraemer, Dieter Garbe-Schoenberg, Thomas Fockenberg, Sabine Klein
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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.

Abstract Image

泥盆纪火山相关拉恩-迪尔型铁矿的成因--第二部分:痕量元素分馏证明弥散流体侵蚀
拉恩-迪尔型氧化铁矿床由赤铁矿-石英和稀有菱铁矿-赤铁矿矿石组成。这些矿石是在泥盆纪中晚期边界(380Ma∼)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矿石形成时的喷发方式、海洋化学、颗粒-溶液相互作用以及沉积环境的关键信息。本研究将 WDXRF 和 ICP-MS/OES 全岩地球化学分析与 LA-ICP-MS 原位分析和 TEM 元素图谱相结合,对福尔图纳矿区(德国莱茵山丘)的矿石样本进行了分析。对石英-赤铁矿、赤铁矿和菱铁矿-赤铁矿微域进行了原位测量。矿石的大量主要元素含量表明存在(火山)碎屑污染和沉积后热液蚀变。微域痕量元素分布显示出四种不同的痕量元素特征,这些特征与以下方面有关:(1) 由于吸附了海水中的 P 和 REY,形成了合成磷灰石;(2) 氧化铁(氧水)在海水柱中的特定微量元素清除和分馏;(3) 成岩铁(III)还原和孔隙水中的微量元素移动;(4) 同时沉积了(火山)碎屑物质和氧化铁(氧水)。这些结果表明,拉恩-迪尔型铁矿石的形成是低温喷口流体与环境海水在高海水与喷口流体比率下混合的结果。这可能与扩散式喷口比集中式喷口占主导地位的环境有关,在这种环境中,铁微粒的快速沉淀导致了血铁矿-石英矿的形成。局部成岩过程中铁(III)的还原导致了沉积后菱铁矿-海泡石矿石的形成,在此期间,孔隙水中的微量元素被部分重新固定。
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来源期刊
Mineralium Deposita
Mineralium Deposita 地学-地球化学与地球物理
CiteScore
11.00
自引率
6.20%
发文量
61
审稿时长
6 months
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.
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