A gravity investigation of the Middleton Granite, near Inverurie, Aberdeenshire

This report describes the results of a gravity survey in the Inverurie area of Aberdeenshire. The primary target was the Middleton Granite, which is associated with molybdenum and tungsten mineralisation. An 8 km2 detailed survey area around this granite was covered at a station density of 30 per square kilometre, while a surrounding area of approximately 120 km2 was surveyed at a station density of about 2 per square kilometre. A distinct residual Bouguer anomaly low is evident over the Middleton Granite. The results indicate a granite subcrop centred slightly to the north-west of its previously mapped location and a shallow granite ridge extending about 1.5 km to the south-south-west. This structure considerably enlarges the target area suitable for further mineral exploration. Modelling indicates that the Middleton Granite is a cupola projecting from the buried roof of the Bennachie component of the Eastern Highlands batholith. It also delineates a north-east-south-west trending feature which is interpreted as the concealed margin between the Bennachie Granite and the more dense and/or thinner granite components to the south-east. A limited magnetic survey located a (Permo-Carboniferous?) basic dyke cross-cutting the Middleton Granite. Trial electrical soundings indicated little contrast in electrical properties between the granite and surrounding Middle Dalradian rocks.