The mapping and assessment of aggregate resources in the south Midlands and Welsh Borderland

Abstract

AbstractIt is becoming increasingly important to delimit resources of aggregates, especially near densely populated industrial areas, where the demand is greatest. Knowledge of these resources is needed by both planners and the aggregates industry. The British Geological Survey (BGS) has recently carried out detailed surveys in the south Midlands and Welsh Borderland, under contracts from the Department of the Environment. The areas are covered by the Warwick, Redditch, Tewkesbury, Worcester and Hereford 1:50 000 geological maps, most of which had not previously been geologically surveyed in detail. The most important element in the surveys, therefore, was the 1:10 000 geological mapping, involving studies of the superficial deposits and solid rocks. There are extensive spreads of sand and gravel in all these districts, deposited by glacial, fluvioglacial, periglacial or fluvial activity.In addition to the mapping, boreholes were drilled in some areas to supplement the data already available. The Industrial Minerals Assessment Unit (IMAU) of the BGS also carried out a shallow drilling programme as part of a resource assessment in the Redditch-Rugby area.Between Redditch and Solihull, various drilling, geophysical and remote-sensing techniques were used by IMAU to evaluate their use in assessing sand and gravel resources. The most effective method proved to be shallow resistivity measurements, using an Offset Wenner system, backed up by cable percussion drilling. The same resistivity technique proved to be especially useful, in the Worcester, Hereford and Henley-in-Arden areas, for locating sand and gravel beneath alluvial silts.Gravel deposits near Worcester were investigated using an EM31 conductivity meter. The local geology, comprising river terrace gravels overlying mudstone bedrock, is ideally suited to this method. Thickness variation in the gravel deposits could be obtained quickly by grid traverses, covering the area at a rate of about 1 square kilometre per day.