Large Area Mapping Provides Multi-Scale Insights of Geological Samples

Aim

To understand the relationship between mm and µm scale structures in a section of granite to aid in developing an understanding of the rock and the geological history of the area from which it came.

Challenge

When analysing large samples like this rock sample, we often need to understand information from both macro- and microscales in order to develop a full understanding of how the rock has come to be in its current state. The challenge is to acquire this information in an easy and time efficient manner to enable determination of both the mineral assemblage and the texture of the rock - information which is needed to develop an interpretation.

Solution

AZtecLive's Large Area Mapping functionality can automatically map large sample areas with EDS (and/or EBSD) - collecting individual electron images and X-ray spectral maps in a grid pattern. By using this functionality, the user can gain a good understanding of the sample by acquiring data from multiple fields of view, each with sufficiently high resolution to understand what is happening at a µm scale. The acquired maps contain spectra at each pixel, so the acquired data can be further analysed after acquisition.

Figure 1. Large Area Mapping: From an optical sample image used for image registration to a single field map of an area of interest and finally to mm scale large area mapping – all at the level of detail of the single field map

Conclusion

The acquired montaged data across multiple length scales reveals that this sample is an alkali feldspar granite. Some of the identified mineral species include K-feldspar (KAlSi₃O₈), Quartz (SiO₂), Apatite (CaPO₄) and Biotite (K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂).

By using Large Area Mapping combined with an Ultim Max 170 EDS detector, this data was acquired both quickly and efficiently covering 0.74 cm² in 2 hours 15 minutes.

The fact that data was automatically acquired at a high resolution across the sample (map contains 78 fields, each field containing 1024 x 768 pixels, dwell time per pixel 100 μs) means that it can easily be further analysed at a later stage as a data cube has been created.