Croft and Huncote Quarry

Also within

Leicestershire County

Condition (Natural England)

Geology & landscape

Geological Feature: Fissure · Mining / Industrial: Quarry · Geological Period: Ordovician, Triassic

Landscape processes: Volcanic / Igneous

Description

Area,33.4 ha82.6 ac Description The quarries at Croft and Huncote are important in exposing tonalitic igneous rocks of Ordovician age together with attendant zeolite mineralisation and much younger manganese mineralisation of Triassic age. The tonalite, dated at 452 million years, is well exposed in the quarries and belongs to the Leicestershire pluton; a suite of poorly exposed igneous rocks in the East Midlands. The suite is calc alkaline in character and is believed to have formed in an island arc setting; as such it is an important element in documenting the growth of the continental crust beneath Central England. The zeolite mineralisation is attributed to the action of late stage hydrothermal fluids within the cooling pluton. The zeolites are found in drusy fissure veins associated with 'rotten' zones of deeply altered tonalite. Two generations of analcite can be distinguished. Other zeolites such as leonhardite are sparsely represented and laumontite is well developed in Huncote Quarry. Much later, in Triassic times, manganese became localised along the eroded unconformity between the tonalite and overlying Triassic wadi fill sediments. The mineralisation takes the form of a quite extensive black wad, up to 10 cm thick, deposited by water percolating downslope along the unconformity and through the sub Triassic regolith.