Petrography and mineralogy of fault material from the Great Glen Fault

The Great Glen Fault (GGF) of Northern Scotland is a long-studied yet enigmatic fault structure. BGS interest in the movement history of the GGF, as part of a new UK-wide strategic initiative, has been stimulated by the Coire Glas project – a hydro-pumped storage scheme with the capability to double the current electricity storage capacity of Great Britain. This major civil engineering project will involve tunnelling through tectonised rocks associated with the GGF. Here, we outline a workflow for the characterisation of fault rocks using a fault gouge sample taken from the GGF close to the Coire Glas site. Our preliminary results show that the microstructure of the studied sample reflects a complex history of fracturing and related mineralization associated with movement on the GGF. We note that computerized tomography (CT) has proved a useful tool in confirming minimal disruption of the fault gouge material during sample preparation.