Towards a Minerals Local Plan for Derbyshire and Derby

Towards a Strategy for Vein Minerals

Introduction

1          Introduction and Background

What are Vein Minerals?

1.1       In simple terms, veins are narrow bands of one type of rock/mineral set inside a wider band of the main type of rock found in the area. Veins are formed when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. In Derbyshire these veins are found mainly within limestone as the host rock. The primary varieties which remain available in the County in commercial quantities are fluorspar and barytes.

Uses of Vein Minerals

1.2       Vein minerals are very important resources due to the specialised industrial uses that can be made of them. Fluorspar is the principal industrial source of the element fluorine and is most commonly used in the manufacture of hydrofluoric acid. It is used as a flux in the manufacture of steel and to a lesser extent in the ceramics industry. It is also used in the manufacture of a wide range of fluorine based chemicals used in the production of aluminium, aerosols, refrigerants and solar panels1.

1.3       Barytes is used mainly in the offshore oil and gas industries as a weighing agent in drilling fluid, which has accounted for up to 85% of overall production. It is also used as a high quality filler and extender in the plastics, rubber and paint industries2.

1.4       Calcite is mainly used as a decorative element in building products such as reconstituted stone, terrazzo tiles and drive surfacing.

 

Sources of Vein Minerals

1.5       Fluorspar rarely occurs as a pure mineral in nature. It is often present as an ore in a host rock and commonly contains other minerals such as barytes. The percentage of mineral within the host rock can vary considerably (20% to 70% is not uncommon) and extracted stone has to be processed to obtain the required mineral in a usable form. The proportion of host rock in the raw material has a direct effect on transport costs whereby quarries and processing plants are usually located close together. It is not normally economical to transport the raw material over long distances although the final processed material is a commodity which is used world-wide.

1.6       In the United Kingdom, fluorspar-barytes-lead mineralisation occurs mainly in two areas; the Southern Pennine Orefield and the Northern Pennine Orefield. Derby City does not contain any resources of vein minerals so although this paper has been jointly prepared with the City Council, reference is made to Derbyshire only (excluding the Peak District National Park area) as this is the part of the Plan area where the resource is found. In Derbyshire, vein minerals are associated with extensive lead-zinc mineralisation in the Carboniferous Limestone. Locally, the majority of vein mineral deposits occur within the Peak District National Park area. In the part of Derbyshire outside the Peak District National Park, vein mineral deposits lie within the areas of high landscape value3 bordering the National Park, limited mainly to a line along the eastern edge of the Carboniferous Limestone around Matlock, Wirksworth and Brassington.

1.7      In the last thirty years vein mineral extraction has mainly been from sites in the Peak District National Park, with limited working in the Plan area. Fluorspar operations in the Peak District National Park were largely focused on the sites operated by the former Glebe Mines Ltd., who operated the country’s only processing plant at Cavendish Mill near Stoney Middleton. Ownership of this business and sites has changed several times. British Flourspar Ltd, the current owner, currently extracts from the Bow Rake/High Rake site on Longstone Edge where production levels are expected to be around 65,000 tonnes per year of fluorspar and 10,000 tonnes of barytes. The company has also recently invested in the refurbishment of the Cavendish Mill processing plant. Fluorspar ore is also extracted from the Milldam Mine near Great Hucklow where planning permission has recently been granted by the Peak Park Authority to extend operations until 2028. The last active vein mineral operation of substance in Derbyshire outside the Peak Park was at Milltown Quarry near Ashover, which closed in 2005.

How are Vein Minerals Extracted?

1.8       Where vein minerals were evident at the surface, working has tended to move along the rakes, extracting the shallower veins using a hydraulic machine or dragline (a machine with a long, lasso-like device which is dragged across the ground to extract the mineral).

1.9      As the shallower minerals become worked out, the remaining mineral at greater depth has been worked by methods more akin to the other hard rock quarries in the County. The deeper vein minerals were often lying within host limestone deposits which were also extracted to enable access to the veins. This method was particularly evident where the veins tended to be found in non-vertical columns, often crossing, leading to extensive areas of extraction relative to the volume of the vein mineral that was obtained. The resultant extraction areas appeared as traditional limestone quarries, with quarry faces and benches and the associated activities of blasting etc. Truly underground working resulted in large overburden mounds and a potential for subsidence. In addition, small scale working of fluorspar and barytes from old lead and zinc workings and waste tips has also taken place.

National Production and Demand

1.10    In comparison to other minerals, the quantities of fluorspar and barytes which have been extracted and used in the United Kingdom are very small. Information from British Geological Society indicates that from 1874 to 2009 a total of 8.86 million tonnes of fluorspar was produced in the United Kingdom. Production expanded considerably during the late 1960s and early 1970s due to increasing demand from the chemical and steel industries. Peak output of 235,000 tonnes was achieved in 1975 but this dropped to only around 25,000 tonnes by 2009. With the exception of very limited working for mineral specimens, domestic production of fluorspar then ceased in 2010, with all supplies being met from imported sources. Whilst extraction and processing in Derbyshire has recently recommenced, production levels are very low.

1.11    The future of the industry is very unpredictable and at present it is not possible to provide a reliable estimate of the future level of demand for fluorspar in the United Kingdom, either from imported or domestic sources.

1.12    The demand for barytes is a direct function of the oil and gas exploration industries. In 2004, 80% of the total sales in the United Kingdom of some 61,000 tonnes were derived from Foss Mine in Aberfledy, Scotland. Following the closure in 2000 and 2002 of sites in Durham and Cumbria, production in England came solely from the Cavendish Mill operation and therefore the closure of this facility in 2010 resulted in the cessation, albeit temporarily, of domestic production. Current production levels are expected to be around 10,000 tonnes per year.

Further more detailed information about vein minerals resources, the methods of extraction and the availability of resources is available in the Vein Minerals Supporting Paper, April 2016.