Compton Martin Ochre Mine

Also within

Somerset County Mendip Hills Scenic Area

Condition (Natural England)

Geology & landscape

Geological Period: Carboniferous, Triassic · Rock Type: Carboniferous Limestone, Limestone

Landscape processes: Volcanic / Igneous

Description

Description Compton Martin Ochre Mine is located on the north side of the Mendip Hills, immediately south west of Compton Martin village. The site comprises a network of underground tunnels and surface exposures on the eastern fringe of Compton Wood. This locality is the largest, best preserved and most accessible of the red ochre workings of the Mendip area. Red ochre is an iron oxide mineral, used in paint making. The site exposes bedded hematitic iron ore red ochre in Triassic Dolomitic Conglomerates which unconformably overlie the Hotwells Limestone, the highest division of the Carboniferous Limestone in the Mendip Hills. The ochre was deposited underwater as a layered mass of iron oxide pellets of various types, probably in an ephemeral lake or pond fed by hot springs when the Mendip area was occupied by a desert environment some 220 million years ago during late Triassic times. The ochre is associated with other minerals such as quartz, which occurs in large rounded nodules termed geodes; and galena lead sulphide which occurs in a thin vein associated with a sedimentary feature known as a neptunian dyke. The full thickness of the ore body is attained underground and is exposed in the old mine workings. Compton Martin Ochre Mine is of national significance and provides the best example of ochre mineralisation in the Mendip area, one of the most important mineralogical provinces in Britain. Apart from the intrinsic mineralogical importance of the site and its relevance to future research and study, it also provides detailed evidence of the environmental conditions prevailing in the Mendip area during late Triassic times which enables geologists to develop a better understanding of the geological evolution of southern Britain. The mines are also used as a hibernation site hibernacula by greater horseshoe bats Rhinolophus ferrumequinum. A rare and endangered species, the greater horseshoe bat is protected under the Wildlife and Countryside Act 1981 and is listed in Annex 11 of the E C's Habitats Directive 1992.

Species mentioned