Geophysical investigations in the Strath Halladale‐Altnabreac District (northeast Scotland) in relation to radioactive waste disposal

Abstract

A series of geophysical studies have been carried out over the Strath Halladale Granite (around Altnabreac, northeast Scotland) as part of a multidisciplinary reasearch programme into the suitability of granitic rocks for radioactive waste disposal. Regional gravity and aeromagnetic data have been interpreted to investigate the structural setting of the Strath Halladale Granite. Ground magnetic and VLF surveys have been carried out to test their effectiveness in defining lithlogical variations, faults, and fracture zones beneath the ubiquitous cover of peat and moraine. Interpretations of the gravity and magnetic data suggest that the granite is a composite body approximately 3–4 km thick, comprising a dominant moderately magnetic variety with a subordinate (more evolved) nonmagnetic variety on the southeast margin. The intrusion apparently extends at shallow depth beneath Moine metasedimentary rocks east of the mapped contact at Altnabreac. The ground magnetic data indicate that the main body of (moderately magnetic) granite is interspersed with zones of less magnetic rock (Moine metasedimentary xenoliths and/or the more evolved variety of granite) and basic intrusions. Prominent lineaments in the magnetic field suggest dipping sheets of magnetically contrasting material, or faulted contacts. The VLF‐EM results indicate a number of anomalies which probably relate to fracture zones or lithological contacts.