Volcanogenic and exhalative mineralisation within Devonian rocks of the South Hams district of Devon

Soil samples were collected from 77 reconnaissance traverses across the outcrop of the Devonian volcanic rocks in the South Barns district of Devon, between the River Yealm in the west and Totnes in the east, and were analysed for at least 15 elements including Cu, Pb, Zn, As, Sb and Ba. Several geochemical anomalies were found, the most extensive and highest amplitude of which comprise a) Ba with smaller amounts of other elements in the Burraton area, b) Ba and other elements in the Higher Ludbrook area and further north-east, c) Sb in the Ladywell area, d) As in the extreme west of the area, e) Cu in association with a diabase near Weeke and f) Zn and Pb around Willing Cross, near Rattery. Several of these anomalies appeared to follow the strike of the volcanic and associated rocks and the first three were investigated further by means of geophysical techniques and drilling. In the Burraton and Higher Ludbrook areas d. c. resistivity, IP, VLF-EM, VLF-R and some detailed gravity surveys were carried out. Around Burraton resistivity anomalies were generally coincident with soil Ba anomalies but there Has no coincident gravity anomaly. In the Higher Ludbrook area a massive carbonate horizon found by drilling is responsible for a zone of high apparent resistivity, detected with the dipole-dipole array, and a residual Bouguer anomaly high; dipole-dipole IP anomalies indicate that disseminated mineralisation may be extensive, although the results of EH and resistivity surveys suggest that the massive pyrite intersected in one of the boreholes is of limited lateral extent. Limited geophysical surveys were also carried out in the vicinity of Ba anomalies around Whetcombe Cross and near Fursdon in an area of diffuse geochemical anomalies. A small amplitude IP anomaly in the Fursdon area indicates a possible zone of disseminated mineralisation.