The nature of waste associated with closed mines in England and Wales

This report has been prepared for the Environment Agency (EA) to provide information on mineral waste associated with closed mining and quarrying sites in England and Wales as part of the provisions of the EU Mine Waste Directive 2006 (MWD). The Environment Agency is the regulatory body for England and Wales (E&W) responsible for producing an inventory of closed mining waste facilities, including abandoned waste facilities, as required by Article 20 of the European Mine Wastes Directive, by May 2012. The report builds upon the information on non-metalliferous sites from a study of waste from active mineral workings in the UK (Colman et al., 2006) with much additional material on metalliferous mine sites. The report uses BGS and other datasets to provide generalised maps showing the locations of closed mineral workings and hence associated waste tips. Estimates of mineral production for each area are also given. Waste production figures are not available as waste has generally not been recorded in any official statistics; existing figures are generalised from estimated mineral to waste ratios that are highly variable, especially with regard to metalliferous mines. The report summarises the various types of mining in England and Wales and provides generic qualitative characterisation of the waste associated with former workings of the following mineral commodities and deposit types: crushed rock, sand and gravel, building stone, silica sand, clay and shale, fireclay, slate, china clay, ball clay, fuller’s earth, gypsum/anhydrite, salt, potash, fluorspar, barytes, limestone/dolomite, peat, coal and metalliferous deposits. Geoenvironmental models of metalliferous mineralisation are used to classify the types of mineralisation occurring in England and Wales into a small set of mineral deposit types. Each deposit type has certain specific geochemical characteristics that enable broad generalisations to be made concerning each type’s mineral content, host rock and general geological setting. These in turn have relevance to the degree of environmental problems likely to be associated with specific deposit types. Metalliferous mining has been an important industry in many more remote areas of England and Wales, commonly in areas of high scenic value. It has been carried out over thousands of years but the main period of working was between 1700 and 1900 with the exception of tin and copper in southwest England, fluorite and baryte in the Pennine orefields and ironstone which were worked throughout the 20th Century. The minerals worked were generally those of copper, iron, lead and zinc sulphides with substantial amounts of tin (as cassiterite, SnO2), fluorite and baryte. No metal mines are currently active in England and Wales, though minor amounts of lead are recovered from small-scale fluorite and baryte mining in the Southern Pennine Orefield. Large amounts of various iron minerals have also been mined. Mineral wastes are associated, to a greater or lesser extent, with the extraction and processing of almost all of the minerals produced in England and Wales. Chemical hazards associated with closed mine waste facilities may include the toxicity of certain mine spoil and of any other materials which may have been deposited on site. Some sites might have been used for fly-tipping and may have received material more toxic than the spoil itself. Additionally, some mineral processing operations can give rise to slags and ashes, gaseous and particulate emissions through, for example, grinding and ore roasting and smelting. The waste from active non-metalliferous workings, apart from that associated with deep coal mining, was generally not considered to cause significant environmental effects. Slate and china clay waste may give rise to visual and stability problems. At abandoned metalliferous mine sites, acid mine drainage and metal-rich drainage that develops as a consequence of the weathering of sulphide-rich wastes may represent one of the main contaminant sources along with the legacy of past mineral processing activity. The presence of acid drainage from a mine site is largely dependent on the availability of water, presence of pyrite and the absence of a neutralising host/country rock. Pyrite is the main acid producing mineral; other acid forming sulphide minerals include arsenopyrite, marcasite and pyrrhotite. Not all mine sites will generate acid mine drainage as a result of the neutralisation capacity of the host rock containing carbonates, such as limestone, or because pyrite may not be present in significant concentrations. Different orefields are associated with particular suites of minerals and elements and there are large variations in actual concentrations. The most significant elements associated with the major orefields are reported. Metalliferous mineral veins in England and Wales are principally characterised by elevated concentrations of lead and zinc with variable concentration of cadmium, barium and fluorine. Other types of mineralisation such as in SW England have high concentrations of copper and arsenic. Soils and spoils of mine waste facilities will contain concentrations of contaminants derived from the mined ore or commodity which may be considerably elevated above local background concentrations and therefore likely to be present at environmental significant levels. The occurrence of elevated concentrations of harmful or toxic elements in the environment does not, however, indicate that there is a significant risk as this will depend on a number of factors including their chemical form, concentration, behaviour and bioavailability, the size of the mineral particle in which the element occurs, the pH of the water or soil and, very importantly, the presence and type of pathways and receptors.