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Journal of the Geological Society; 1996; v. 153; issue.6; p. 839-852;
DOI: 10.1144/gsjgs.153.6.0839
© 1996 Geological Society of London

Article

Hydrogeochemistry as an aid to geological interpretation: the Glen Roy area, Scotland

W. M. EDMUNDS1 & R. M. KEY2

1 Hydrogeology Group, British Geological Survey, Wallingford OX10 8BB, UK
2 British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3 LA, UK

The hydrochemistry of first and second order streams, sampled at a density of 1 km2, has been used to investigate ways of enhancing information obtained during regional geological mapping. The Glen Roy area of Scotland is a pristine area with large variations in bedrock geology, ranging from Dalradian metasediments (including carbonates), to granite, granodiorite and appinite rocks (coarse-grained lamprophyre) but with relatively minor drift.

Alkalinity (HCO3,) is used to determine the extent of water-rock interaction with both silicate and carbonate rocks. The ratio Na/Cl is also used to measure the extent of silicate reaction: dolomitic facies are picked out in areas with carbonate by Mg. Mn, Fe and Y are useful indicators of the weathering of biotite and garnet. A strong and well defined hydrogeochemical anomaly of Ba, Sr and K outline the outcrops of the appinites. Together with HCO3, these three elements define an extended NW–SE lineament (Strath Ossian Lineament) which includes possible concealed areas of appinite, the bicarbonate probably reflecting the presence of a carbonate aureole derived from mantle CO2. In particular the bedrock characteristics in poorly exposed ground can be inferred and information obtained on the volume of bedrock through which the water has passed.


Keywords: Dalradian, Scotland, geochemistry, hydrogeology, trace elements.