Large Area Mapping of Mineralogical Samples

Large Area Mapping (Hypermaps) using a SEM can be hampered by the slow movement of a standard SEM stage. In addition, there are potential X-ray signal intensity artifacts at low magnification due to the variance of the electron beam and sample interaction during analysis. This is particularly relevant for WDS analysis and can also be observed in BSE images or EDS element intensity maps.

The Rapid Stage is specifically designed for SEMs to enable large area mapping over millimeter (mm) to centimeter (cm) scales. This will eliminate potential SEM X-ray intensity variation artifacts associated with low magnification mapping and thus enhance elemental and mineralogical information in a timeous manor that was previously not possible. The Rapid Stage also operates in conjunction with the micro-XRF.

The Rapid Stage has a maximum analytical area of 50 mm x 50 mm, which can be expanded in combination with the SEM stage to encompass the maximum possible spacial area allowed within any SEM chamber. Traditional large area analysis using a SEM is based on mosaicing numerous fields of view together to create the large area map, where each individual field is mapped by rastering the beam. The source X-ray beam that interacts with the sample is in a fixed position, and therefore cannot be controlled to raster as a standard SEM e-beam.

Consequently, all mapping is via stage control (that is stage movement). Thus the Rapid Stage enables large areas to be mapped almost an order of magnitude faster than if moving the SEM-stage from point to point. Examples are shown in Fig. 1 (concrete), Fig. 2 (exotic Cu), and Fig. 3 (soil bedrock).

Fig. 1: Example of the analysis of a concrete sample using the Rapid Stage in combination with the SEM stage. The concrete block is 61.8 x 74.4 mm². The sample is analysed in four Rapid Stage maps which are subsequently stitched. Left: Mosaic BSE image of the concrete sample using the SEM Stage (14 x 22 individual images). Middle top: Optical image; middle bottom: Total X-ray Intensity image. Right: Mixed element image from micro-XRF analysis combined with Rapid Stage with Fe (green), Ca (blue), and Si (red).

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Fig. 2: Sample from the exotic Cu mine "El Tesoro" in northern Chile. The Cu occurs in many different forms, including Cu-Silicates (e.g. chrysocolla), Cu-Phosphates (e.g. brochantite), Cu-Sulphates (e.g. chalcanthite), Cu-Carbonates (e.g. malachite), Cu-Sulphides (e.g. chalcopyrite), and Cu-Halides (e.g. atacamite). Important deposit and source of Cu. Unusual geological formation and uncertain origins. Analytical area: 40 x 20 mm².

Fig. 3: Soil bedrock sample. This sample shows a range of heavy metals in the bedrock that often occur as contaminants and toxins as soils. Analytical area: 40 x 30 mm².