Investigations at Polyphant, near Launceston, Cornwall

Abstract

A geophysical survey was conducted in the vicinity of the Carrock tungsten mine, Cumbria. The object of the survey was to establish an optimum geophysical exploration procedure for the location of the style of mineralisation known at Carrock. The VLF-EM method recorded only weak or indistinct anomalies over much of the known mineralisation but a weak anomaly coincident with the Emerson vein was traced northwards for one km. Several similar linear features were recorded in the area on trends favourable for mineralisation and two, at Poddy Gill in the east and Arm o’ Grain in the west, are coincident for part of their strike with exposed mineralisation. Resistivity measurements indicated that most fault structures have coincident low resistivity zones; a detailed traverse across the Emerson vein showed a minor high resistivity peak within the low zone. Induced polarisation, magnetic and self potential anomalies were recorded only within the gabbro on the extrapolated positions of the Smith and Wilson lodes. It is concluded that these anomalies are caused by discontinuous near-surface lenses of pyrrhotite which have little VLF response. The VLF method is identified as the best tool for the location of structures which may carry mineralisation in this environment. Incidentally to the main objectives of the work, three VLF anomalies are identified which appear to warrant investigation by drilling; the Arm o’ Grain anomaly, the Emerson vein extension and the Poddy Gill feature