Ellen, R. and Callaghan, E. 2015. Geodiversity Audit of Spireslack and Mainshill Wood Surface Coal Mines. British Geological Survey Commerical Report CR/15/126. 70pp.
Spireslack Locality 2: Palaeogene dyke intruding mudstones and ironstones
NGR: [274539 630416]
| Key category of interest | Rarity | Quality |
|---|---|---|
| 1. Igneous rocks | 4 | 5 |
| 2. 3D visualization | 4 | 4 |
| 3. Stratigraphy | 3 | 4 |
| 4. Sedimenrary rocks | 1 | 2 |
| 5. Structural geology | 2 | 2 |
Access: Good access to base of exposure, easily accessible from roadway.
Current safety: Potential loose overhanging blocks above section.
Measures to enhance site: Viewing platform 5 m away, level spoil at base of section.
Key categories in order of interest (1 = primary interest); Rarity, 5 = only example in Spireslack, 1 = many examples in Spireslack; Quality 5 = exceptional preservation in Spireslack, easy access/viewing potential 1 = average preservation in Spireslack, difficult access/viewing potential
Photograph overview with polygon boundary
© Getmapping: Licence Number UKP2006/01
Site description
Geology
An exceptionally well exposed Palaeogene quartz dolerite dyke intrudes the Limestone Coal Formation at this locality. The intrusive contact with the Limestone Coal Formation displays chilled margins, mineralisation and alteration of the surrounding mudstone units. The Limestone Coal Formation is also slightly offset across the dyke. Movement along fracture planes within the mudstone, associated with a nearby fault, has caused polishing of the mudstone. There are also small thrust faults developed within the sequence, highlighted by the stronger ironstone layers. The same dyke is also exposed in the scarp (inaccessible), and whilst the dyke itself has been dug out of the void during coal extraction, this location provides an important reference point for providing an indication of orientation, scale and 3D sense of the intrusion. See also Locality 14 for description of geology surrounding dyke exposure in the scarp.
Access and enhancement suggestions
The dyke is easily accessible on foot from roadways and would provide hands on access as a teaching locality. However, there are loose blocks in the face and the mudstone is liable to weathering — this would require inspection by qualified personnel if the site is to be used for close inspection. Alternatively a viewing platform 5 m from the base of the section would also provide a good viewpoint.