Portway Mine
Also within
Condition (Natural England)
| Unit | Feature | Condition | Area (ha) | Assessed |
|---|---|---|---|---|
| SK128811 | — | Favourable | 4.19 | 2008-03-27 |
Geology & landscape
Geological Period: Carboniferous, Quaternary · Rock Type: Carboniferous Limestone, Limestone
Description
Area, 4.2 ha. 10.4 ac. Description The excavation at Portway Mine has exposed a chaotic blocky infill of a hollow in the Carboniferous Limestone which was formed as a result of the collapse of a solution cavity some distance below the surface. Many of the blocks show excellent examples of pipe vein mineralisation. Examination of the blocks shows that ancient cavities in the rock were lined with baryte which developed in multiple layers showing a variety of forms and colours. Yellow fluorite occurs interbanded with the baryte and the centres of the cavities often show large corroded calcite crystals in the form of scalenohedra. Juxtaposed with the baryte blocks are blocks of quartz rock, reflecting metasomatic replacement of the limestone and the available evidence suggests that this replacement occurred at an earlier stage than the bulk of the mineralisation. The precise age of the collapse structure is difficult to determine, but is at least partly Pleistocene in age, as loess clays, which blanket the deposit, have also penetrated downwards and form the final infill of baryte lined cavities.