Computer aided analysis of X-ray images in mudstone concretions from Budleigh Salterton, Devon

The examination of fine-grained concretions such as the uranium and vanadium enriched mudstones of Budleigh Salterton, Devon presents difficulties because of the sub-micron size of their mineral grains. We have attempted to address this problem by collecting X-ray images of thin sections of these concretions using a Jeol 8600 electron microprobe. Techniques were developed in this study using "Image 1.54" and "Photoshop 3.0" to process individual element maps and produce a composite image in which the degree of opacity of each layer can be varied. This allows rapid determination of the distribution of elements and their associations. The technique does not identify minerals as such, but gives an insight into element relationships from which mineral compositions can be deduced. The concretions, which are of Upper Permian age, were collected from the cliffs of Budleigh Salterton in Devon. They contain moderately high concentrations of uranium, vanadium and copper. They are also cobalt, nickel, lead and arsenic enriched. For example, cobalt occurs in the concretions as an arsenide mineral, a sulphur arsenic mineral, a sulphide and a cobalt nickel sulphide. The observed mineralization occurs as metal-rich coatings around quartz and other primary grains and as a replacement in areas where calcite has dissolved. Examples of other metal sulphides and other associated mineralization are also discussed.