The clay-with-flints of the western Paris Basin: a potential aggregate resource

Abstract

With future increasing restrictions on extraction of alluvial materials for aggregate production, the Paris basin in particular is faced with the problem of substituting up to 62% (more than 50 Mt/year) of its requirements from other sources. The clay-with-flints formation to the north-west, west and south-east of Paris has been the subject of intense studies aimed at determining its suitability as a potential source of substitute aggregate material. The formation is located much closer to Paris than alternative resources and because the cost of transport constitutes a major factor in the price of aggregates, proximity to consumption centres is of prime importance. Two potential resources targets have been identified within the clay-with-flints. The slope located clay-with-flints (named 'bief à silex' in France), despite being rich in flint, form deposits that are too small for industrial scale exploitation. In addition, the biefs à silex tend to be located in forested areas and subjected to environmental constraints. Where the plateau-located clay-with-flints attains a thickness in excess of 30 m, notably in northern Eure et Loir and southern Eure Departments, an increase in the proportion of flint from 10 m downwards, opens up the possibility of dry processing separation of the fine-grained clayey matrix, either direct from the quarry or after open-air drying. Wet processing has been shown to be unrealistic because of the vast amounts of water that would be required. The plateau deposits show far fewer environmental constraints and the resource potential for substituting a significant part of alluvial material consumption in the Paris basin is excellent.