A Taste of the Peak District

Accommodation, activities and attractions of the Peak District of the UK

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The Peak District was the first region in the UK to be designated as a National Park. Read a little about the mineralisation of the area here. Details about the exploitation of lead and copper can be found in the mining section.

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Click here for the official Peak District National Park web site.

Click here for the Open University Geology East Midlands branch web site.

Peak District mineralisation

One of the major industries in the Peak District has been the extraction of metal bearing minerals but how did they get there in the first place?

The mineral deposits are mainly hydrothermal, occurring in veins of varying thickness in the rocks. Mineralisation is exclusive to the Limestone area which suggests that it was could be related to the vulcanism that the region experienced during Carboniferous times rather than a later event. So, at one time, a large mass of granite, deeply buried and not yet discovered, was postulated to explain the Peak District mineral field. However, The Peak District metalliferous minerals are mesothermic in origin i.e. created at moderate depths, pressure and temperature as the mineralogy is galena and sphalerite. In the Castleton area, the unique Blue-John (a form of fluorite) and barytes exist, together with some galena. This sort of mineralogy suggests an epithermic origin i.e. closer to the surface.

After much research and debate, it is now generally accepted that the source of the circulating groundwater was the deep water basins surrounding the limestone shelf areas. It is thought for example, that hydrothermal solutions picked up minerals from the basin clays to the north. These hydrothermal solutions then penetrated the limestones, through joints and faults where minerals such as galena and sphalerite were deposited in fissures along the edge of the St George’s Land shelf. The Odin mine is one such example of this. It is a fault (slickenslides can be seen in the walls) that was mineralised. There is still some mineralisation on the walls of the fault. The Odin mine was worked in the 13th century.  Many of the local rakes and their subsidiary scrins (vertical mineral veins) are wrench faults.

In places, the mineral deposits have a sedimentary origin. Underground watercourses eroded hydrothermal deposits and deposited the detritus in caves, providing rich and easy pickings for miners e.g. in the Millclose mine. Such deposits were easy to extract as they were unconsolidated and the caves were large. The original veins of course were much more difficult to mine as they were effectively part of the rock and also generally quite narrow.

Two types of mineral vein are recognised. Firstly, where the junction between mineral and rock is very clear and sharp, it is clear that hydrothermal deposition has taken place. Here minerals simply precipitated onto the sides of a joint or other fissure underground. In the other type of vein, the junction is not clear and the mineral appears to penetrate the rock. Veins of this nature have been created by metasomatism. This is a type of metamorphism where the circulating hydrothermal solutions have altered the host rock to form the mineral. Elements that were not present in the original rock are introduced by the hydrothermal solution. These elements could originate either from water associated with the magma that powers the hydrothermal activity or be picked up locally. Whichever the case may be, the hot water under high pressure can travel large distances  until conditions were right for precipitation. There appear to be two sources of such solutions in the Peak District. The majority of mineralisation is lead with some zinc but in the Ecton region, rich copper deposits were mined. These formed the basis of the fortune of the Dukes of Devonshire and paid for the erection of the grand buildings of Buxton.

Until recent times, the non metal minerals (apart from Blue-John or course) formed under epithermal conditions were simply regarded as gangue and were discarded. These are now needed in large quantities for the paper industry amongst others and are currently mined, both underground and open cast. Also, in the 1960s and 70s, there was a great deal of reworking of spoil heaps in order to recover the fluorite and barytes.

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