Potential for stratiform massive sulphide mineralisation in south-west England

This study provides an assessment of the potential for stratiform massive sulphide mineralisation in two parts of south-west England, the Central Area between Bodmin Moor and Dartmoor, and North Devon. The Central Area was selected on the basis of its tectonic, stratigraphical and lithological similarities with the Iberian Pyrite Belt (IPB) where numerous volcanogenic massive sulphide (VMS) deposits occur. North Devon is considered prospective on account of its similarities to the Harz Massif in Germany that hosts the major polymetallic sedimentary exhalative (Sedex) deposit at Rammelsberg. More than 60 stratiform mineral occurrences are known in the two areas and previous exploration, including extensive drainage geochemical surveys, geophysical surveying and drilling, has revealed stratiform mineralisation at some localities, including at Egloskerry, near Bodmin Moor, where up to 10% Pb over 4·5 m was recorded. In North Devon, stratiform mineralisation has been recorded from a borehole at Honeymead Farm, and further evidence of potential is provided by a distinct aeromagnetic anomaly parallel to the regional strike over the upland areas of Exmoor. The potential for the occurrence of stratiform sulphide deposits in North Devon and the Central Area has been assessed by GIS-based prospectivity analysis software, Arc-Spatial Data Modeller (Arc-SDM), using knowledge-driven and data-driven modelling techniques. This analysis used both new and legacy multivariate datasets including geophysics (aeromagnetic and gravity), geochemical data, mineral occurrences, and digital 1:50 000 geological linework. This has confirmed known occurrences as well as identifying new targets for stratiform mineralisation. Zones of high prospectivity in the Central Area occur along the northern edges of Bodmin Moor and Dartmoor, in the intervening ground underlain by Lower Carboniferous strata, and in the Lower Carboniferous strata on the eastern side of Dartmoor. In North Devon, prospective areas were identified at a number of localities in the Upper Devonian and Lower Carboniferous strata, with the highest potential occurring along strike from Combe Martin near Honeymead Farm.