Modelling the distribution and quality of sand and gravel resources in the Reading area in 3D

Introduction

Surface and subsurface expression of geological formation

Aggregates, such as crushed rock, sand and gravel, are the most commonly used construction minerals in the UK. The construction industry is a critical sector of the UK economy and our society's level of affluence and aspirations depend upon having infrastructure of the right quality and in the right places — all of which requires aggregates for construction.

However, minerals can only be worked where they occur, and with increased pressure on land-use in England, it is imperative that these resources are not needlessly sterilised by other development, leaving insufficient supplies for future generations. This means that not only do we need to understand the distribution of potential resources in three dimensions below ground, but we also need to have a better understanding of the quality and characteristics of the resource, e.g. what is the grain size, how thick is the deposit, how thick is the overlying material? All of these factors need to be considered when making strategic plans for safeguarding mineral deposits for future generations.

3D modelling using IMAU data

Drilling by the Industrial Minerals Assessment Unit (IMAU).

In the 1970s and 80s, BGS's Industrial Minerals Assessment Unit (IMAU) undertook major surveys of sand and gravel resources in England, Scotland and Wales. The surveys produced hundreds of maps and reports and thousands of detailed borehole interpretations, including over 54 000 particle size distribution analyses. These data are now being used in modern 3D modelling packages (GOCAD-SKUA) to assess the distribution of four different mineral gradings: gravel (> 4 mm), coarse sand (≤4 mm to > 2 mm), fine sand (≤ 2 mm to > 0.063 mm) and fines (≤ 0.063 mm).

The pilot study area is a 60 km by 40 km area around Reading, but only extends at most to 30 m below the ground surface as the sand and gravel deposits are shallow superficial deposits.

Stochastic geostatistical techniques are used to interpolate the predicted distributions of the four mineral gradings at every cell within the grid, based on the measured IMAU mineral grading analyses. The sum of the four categories at any point in the grid will always add up to 100 per cent.

Strategic planning

Development of such models builds upon earlier studies by using the borehole data and results from the original IMAU surveys to provide revised and updated baseline information on the sand and gravel resources of the area. The availability of such information will assist in safeguarding them for the future.

(Left) The distribution of IMAU boreholes across the Reading study area. The distribution of boreholes reflects the mapped extent of sand and gravel deposits. (Right) A regular grid of 1km x 1km in area and by 1m depth is created for statistical interpolation. NB. Any cell more than 3 km from a borehole is removed.
3D model showing the probable distribution of gravels within the Reading study area.

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