Application of SEM-based quantitative mineralogical analysis in the development of proxies for provenance and transport mechanisms of modern stream sediments

Provenance analyses of stream sediments mostly rely on analytical methods such as bulk sediment geochemistry, mineralogy (provided by XRD) and single grain analysis. In this study, we focus on automated mineralogy by Mineral Liberation Analyser (MLA), as a potentially powerful tool for sediment provenance studies. The MLA combines backscattered electron (BSE) imaging with energy dispersive X-ray spectrometry (EDS) generating compositional data for all measured sediment particles (in this study, i.e. 20000 to 60000 grains and the including sub-grains). Resultant data include particle and mineral grain parameters (i.e. size and shape) as well as the mineralogical composition and properties (e.g. elemental composition, density) of each particle and its individual constituting mineral grains. Necessary, robust statistical analyses are part of the study, to maximize the use of the voluminous set of data provided by MLA. These statistical analyses unveil trends and dependencies in suites of related samples. This is illustrated here in a case study. We combine bulk geochemistry, XRD and MLA analyses. On the one hand, in order to make a comparison of the selected methods, and on the other hand, to ensure the quality and to critically assess the benefit of MLA data.
The study area is located in the Vogtland region of the Free State of Saxony (Germany). The bedrock mainly consists of Variscanaged basement rocks. These rocks comprise plutonic (i.e. different types of granite) and metamorphic units (mica schists, phyllites and quartzites), which are very well studied.
With first results of the study, it becomes apparent that changes in provenance and transport features of the unconsolidated sediments are easily identified, based on the modal mineralogy, geochemical changes and grain-parameter patterns. Using the MLA we can detect and calculate the relative composition and amount of anthropogenic contamination within the sediment. Furthermore, mixing of the material is calculated with respect to the relationship between lithological changes and the river path. The examination of shape features on single grains, such as potential marks of corrosion, leaching, abrasion and fractionation, provide the possibility to implement efficient proxies, which can be related to weathering and transport mechanisms.