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Shardlow & Donnington |
There was an early start (9 for 9.30 am) for this very full day, which began at the offices at Shardlow Quarry, just off the A50 near Castle Donington. This is a sand and gravel quarry operated by Hanson Aggregates. 550,000 tonnes of mineral are extracted annually, mostly for use in ready mix concrete production. The morning’s tour of the site was led by Bob Woodbridge, Hanson Regional Geologist, and Paul Lagram, Quarry Manager.
Geology Shardlow’s sands and gravels are extracted from unconsolidated drift deposits laid down by the River Trent. These deposits date from about the last 50,000 years, the climax of the Devensian glaciation. Very large river deposits were formed during glacial and interglacial periods, when meltwaters caused much more vigorous river activity than today. The deposits of sand and gravel are 3-7m thick—although over 13m have been recorded in places. They are overlain by 0.5-3m of silty clay and soils, and rest unconformably on about 95m of the Triassic Mercia Mudstone Group. These mudstones are useful as an impermeable barrier in the land restoration process, which follows extraction, although the presence of up to 2m thick bands of permeable “skerry” (green-grey dolomitic sandstone/siltstone) is sometimes a handicap.
Bob described the gravels and sand as: “The gravels at Shardlow consist of sub-rounded—sub-angular quartzite and vein quartz with subordinate sedimentary, igneous, and metamorphic rock types. Many of these are derived from the reworking of Triassic rocks belonging to the Sherwood Sandstone Group within the catchment area of the River Trent. The sand is fairly well sorted, comprising coarse to medium grained quartzitic material.”
Generally, over 60% of the mineral is gravel (varying sizes, but mainly from 10-40mm), 35% is sand and 5% is silt. The quartz and quartzite are high-grade, durable material, ideal for use in structural concrete. Lignite is also present in varying quantities throughout the mineral and, because of its softness, can have an adverse effect on the quality of the cement product if it is not removed during processing.
Quarry Operations The tour of the site enabled Bob and Paul to give us a comprehensive picture of how the quarry works and of the way in which current planning and environmental legislation affects what is done. The whole operation, from planning, through extraction, to land restoration is closely monitored by the Environment Agency. There is close liaison with Severn Trent Water, Network Rail, British Waterways (the Trent and Mersey Canal runs along one of the quarry boundaries, a railway line along another) and the Civil Aviation Authority (concerned about collisions between water fowl and planes at nearby East Midlands Airport if pits are water-filled rather than land-filled and restored to the original agricultural use).
The amount of restrictions/hazards made us wonder how they managed to do any extraction and make a profit at all. Each extraction phase has to be completely restored before the next phase can begin. Restoration involves lots of physical work entailing a geologically impermeable layer covered by inert landfill and topsoil, as well as inevitable delays and uncertainties caused by bureaucracy.
Other considerations include wildlife eg work is suspended in one area until autumn as there is a colony of sand martins in residence. Water voles, badgers and Great Crested Newts all have to be given special attention. The nearby River Trent floods the site annually—last time it happened 200,000 cubic metres of water had to be pumped out of the quarry. The sand and gravel themselves are an aquifer and so constant pumping is required to prevent flooding. Some of this water is used to clean the extracted material, the rest goes into the Trent. Despite all this, production is profitable. Most (two-thirds) is sold locally in Notts/Derbys, with the rest sold to Leics and Northants. I live in Daventry in Northants, where our District Council and West Northants Development Corporation are planning to build over 6000 new houses as well as offices, warehouses and roads, so some of Shardlow’s produce will probably be heading my way. Many thanks to Bob and Paul for giving up their Saturday morning to take us round Shardlow and explain this well-managed operation.
Afternoon localities After a welcome lunch outside in the sunshine at a canal-side pub at Shardlow Wharf, a small group of us, led by Don Cameron, visited a couple of sites in Castle Donington. First stop was in Delven Lane, its name giving a clue to former quarrying activity. Here we examined an outcrop, which was part original rock and part wall. We found a very soft, yellow sandstone. It was fine-grained with both quartz and white mica grains. The mica indicates that the material had not travelled far from its source. There were also some specks in the sandstone, some dark and some light coloured. There was some speculation as to whether these were a barite cement. Although there was some minor cross-bedding, the general conclusion was that these sands were laid down in a quiet environment such as a lake. The sandstone is part of the Triassic Bromsgrove Sandstone Formation.
For our last stop, we parked at the Priest House Hotel. As we walked past the front of the hotel, a jazz band entertaining the guests at a wedding reception, gave us a rousing rendition of Colonel Bogey to send us on our way. We looked at another outcrop of the Bromsgrove Sandstone Formation in King’s Mill Quarry. This example was marginally coarser, harder, horizontally bedded and showed no cross-bedding. The beds were of varying thickness, with some shaly-looking intervals.
Don then led us to a nearby stream where he gave some willing volunteers some expert tuition in panning for heavy minerals (definitely no gold, before you get too excited!). The idea was to see which minerals were present to give a clue to the source of the material. We were all successful in obtaining a concentrate from the panning process. The concentrates contained a tail of dark coloured and clear minerals for identification later. Possible minerals could be epidote, various iron oxides, zircon, and cinnabar. A big thank you to Don for organising and leading a very informative and enjoyable day.
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