The Snelston Ridge: evidence for a concealed ridge of mineralized Dinantian rocks to the south of the Derbyshire Dome

Abstract

SUMMARY Little is known of the southern continuation of the Lower Carboniferous (Dinantian) rocks of the Derbyshire Dome where they lie concealed beneath Triassic rocks at the margin of the Needwood Basin. Evidence from regional Bouguer gravity anomaly surveys pointed to the existence of a ridge of shallow Dinantian rocks, here called the Snelston Ridge, largely concealed by Triassic strata apart from two small inliers. The NNW–SSE trending ridge was proved by a borehole which intersected (Dinantian) Widmerpool Formation rocks at a depth of 61 m. Evidence from a seismic reflection profile indicates that the ridge, at least at Birchwoodpark (Snelston), is probably an asymmetrical, fault-controlled anticline. There is, however, no evidence for any significant changes in the thickness of Dinantian rocks hereabouts. The base metal potential of the Snelston Ridge was investigated using detailed geophysical and geochemical surveys and drilling. A borehole on the top of the mineralized mudmound that forms the Limestone Hill Inlier proved minor replacement galena–sphalerite–baryte mineralization with up to 10% Pb over an intersection of about 11 m. Two boreholes on the flanks of the feature revealed little sign of mineralization, indicating that it is restricted to the exposed dolomitized summit of the mudmound.