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The mineralogy, surface area and geochemistry of samples from the Wealden Group of southern England

Kemp, S.J.; Wagner, D.; Ingham, M.N.. 2012 The mineralogy, surface area and geochemistry of samples from the Wealden Group of southern England. Nottingham, UK, British Geological Survey, 26pp. (IR/10/079) (Unpublished)

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Abstract/Summary

This report describes the results of mineralogical and geochemical analysis of a suite of mudstones from the Wealden Group of southern England. The work was carried out as part of the ongoing „Ground Shrinkage Hazards‟ project under the Land Use, Planning and Development Programme. The first part of the report gives an introduction to the geology of the Wealden Group and a summary of previous mineralogical studies of these rocks. A summary of analytical methods employed (X-ray diffraction analysis, X-ray fluorescence spectrometry and surface area determinations) is then provided and the results discussed with reference to their likely effect on the engineering performance of the Wealden Group. This study has generally confirmed the findings of previous workers with typical non-clay mineral assemblages are typically composed of quartz, „mica‟, K-feldspar and a range of trace phases. Clay mineral assemblages are generally formed of I/S, illite, kaolinite, chlorite with occasional traces of discrete smectite. Interbedded ironstones are predominantly composed of siderite. However, the geographic and stratigraphic distribution of the analysed samples from both the Weald and Wessex basins has provided important new information which will aid not only interpretation of the engineering behaviour of these rocks but also their diagenetic and geological histories. The engineering properties of the Wealden Group are heavily influenced by its clay mineralogy and the proportion of clay minerals present. This study has shown variations in both the composition of the clay mineral assemblages and the proportion of phyllosilicate/clay mineral content of the mudstones across the Wealden Group outcrop. The Wealden Group in the Wessex Basin contains the most expansible clay mineral (I/S, R0 40%I) detected in this study but these mudstones are more massive, siltier, quartz-rich and clay mineral-poor resulting in relatively low surface areas. In comparison, the Wealden Group mudstones from the Weald Basin are generally laminated, more clay-rich, contain a less expansible I/S (typically R0 80%I) and present higher surface areas. The detected clay mineral assemblages are mostly detrital in origin with a minimal diagenetic overprint. The common presence of pyrite, together with gypsum in the Wealden Group means that concrete engineering sited in these rocks potentially risk acid attack and thaumasite formation.

Item Type: Publication - Report (UNSPECIFIED)
Programmes: BGS Programmes 2010 > Land Use, Planning and Development
Funders/Sponsors: NERC
Additional Information. Not used in RCUK Gateway to Research.: This report made open by author September 2012. This item has been internally reviewed but not externally peer-reviewed
Date made live: 24 Sep 2012 08:26
URI: http://nora.nerc.ac.uk/id/eprint/19698

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