Geophysical investigations in Swaledale, north Yorkshire

An airborne geophysical survey was carried out over part of upper Swaledale and the adjacent moorland. The area has a long history of mining and the geology and style of mineralisation are representative of most of the north Pennine orefield. The survey employed magnetic, electromagnetic and radiometric methods, and provided a test of the applicability of airborne geophysical exploration in this environment. Eleven airborne electromagnetic anomalies were followed up with detailed ground surveys; more limited surveys were employed to check several smaller airborne indications. At two sites the follow-up surveys recorded anomalies sufficiently significant to be considered possible indications of mineralisation. One of these, at Oxnop Gill, was tested by core drilling, but no evidence of significant mineralisation was found. The other site, Whirley Gill, was not drilled, and the anomalies, although promising, remain unexplained. Of the remaining airborne anomalies, some were not detectable on the ground and others were considered to be due to stratigraphical or artificial conductors. It is concluded that the particular airborne EM system employed is not an effective tool in exploration for new mineral veins of the kind known in the northern Pennines.