The geology of Quaternary Silica Sand Resources in Cheshire - a Fresh Analysis
A Thompson
2022
Abstract
The Quaternary sand deposits in the eastern part of Cheshire have, for many decades, been relied upon as a major source of silica sand for glass-making and other industrial applications. With the overall level of demand for such material being maintained by an increasingly wide range of specialist end-uses, there is concern for the continued availability of suitable resources and a need for these to be adequately managed. This paper summarises the geological aspects of a detailed study undertaken in 2019 as part of that process, to inform the Minerals and Waste Local Plan for Cheshire East Council.
The Cheshire plain is underlain by extensive Quaternary sand and gravel deposits which are largely of glacio-fluvial origin, laid down by meltwater streams and rivers associated with the advance and retreat of ice sheets during the Late Devensian glaciation. Such deposits occur extensively at the surface in the area around Delamere Forest and more sporadically elsewhere, where they are interspersed with or overlain by other glacial sediments.
In the eastern part of Cheshire, however, these glacigenic sediments are often underlain by older sand deposits which have quite different characteristics. These are of fluvial, rather than glacio-fluvial origin, and appear to have been laid down within a series of low-angled alluvial fans extending westwards across the Cheshire plain from higher ground to the east.
It is these deposits which are the origin of Cheshire’s silica sand resources. They are generally not seen at the surface (and therefore not easily mapped) but are revealed in existing and former quarries and in sub-surface borehole investigations. By comparison with the glacio-fluvial sediments, these older sands are characterised by a relatively tight grain size distribution and a relatively high degree of grain roundness and sphericity. Of critical importance, in terms of their suitability as industrial sands, they also tend to have a high silica content (generally more than 96%) and relatively low levels of impurities.
In addition to the areas of concealed resources (where the silica sands are overlain by glacigenic sediments), there are also areas where glacial and post-glacial processes have redistributed the material, producing either mixed deposits or thinner spreads of near-surface silica sand, with little or no overburden.
Drawing on both public and confidential borehole information, as well as published reports and areas of recent prospecting identified by individual operators, the study was able to refine the previously mapped area of silica sand in eastern Cheshire and to demonstrate that substantial unworked deposits are likely to remain.