page_title: Greenside Mine
section_title: The ore deposit
hierarchical_section_title: Greenside Mine / The ore deposit
caption_attribution_description: English: A piece of ore found on the spoil heaps of Greenside Lead Mine, Glenridding, containing barite, galena and quartz
context_page_description: Greenside Mine was a successful lead mine in the Lake District of England. Between 1825 and 1961 the mine produced 156,000 long tons of lead and 1,600,000 ounces of silver, from around 2 million tons of ore. During the 1940s it was the largest producer of lead ore in the UK. Unusually for a 19th-century metalliferous mine in Britain there are very full records of its activities, dating back to 1825.
  The mine probably opened during the second half of the 1700s but had closed by 1819. In 1825 the Greenside Mining Company was formed and reopened the mine. They made good profits until 1880, when the price of lead fell. Many other lead mines closed at that time, but the company reduced its costs and continued to work Greenside until 1935. Electricity was introduced to the mine in the 1890s, and it became the first metalliferous mine in Britain to use electric winding engines and an electric locomotive. In 1936 the Basinghall Mining Syndicate Ltd. acquired the mine and turned it into a high volume lead producer. The mine closed in 1962 after lead reserves had been exhausted.
context_section_description: The entire production of the Greenside Mine came from a single mineral vein, which filled a north-south oriented fault running through the east ridge of the Green Side mountain.
  Green Side is composed of andesite rock, part of the Borrowdale Volcanic Group, formed during the Ordovician Period, roughly 450 million years ago. This rests on shales of the older Skiddaw Group, which were encountered in the lowest levels of the mine. A small dyke of porphyritic microgranite which has "a dog's-leg shape" in plan was intruded into these rocks during the Devonian Period; this formed a plane of weakness which controlled the position of the fault.
  The Greenside fault is a normal fault with an average dip of 70° to the east. A fault plane is not a flat surface and the actual dip of the Greenside fault varies between 58° east and vertical; in one place it was 83° west. As the rock fractured and the two sides moved against each other, cavities were created, partly filled with broken rock (fault breccia and fault gouge). Hydrothermal circulation of sea water at temperatures of 110–130 °C, probably during the Carboniferous Period, led to mineralisation of the fault cavities. The metal content is believed to have been leached out of rocks of the Skiddaw Group, or the underlying granite batholith. The mineralisation of the fault shows some vertical zonation, with baryte (barium sulphate) in the upper part of the vein, and small amounts of both blende (sphalerite, zinc sulphide) and chalcopyrite (copper-iron sulphide) at deeper levels.
  The argentiferous galena (lead sulphide, containing small amounts of silver), which the miners sought, occurred as ribs, strings and dispersed pockets throughout the vein. Many strings of galena, varying in thickness between 1/8 of an inch (2 mm) and about three inches (76 mm), were interspersed through the vein, and sometimes spread into the rock on the east side of the vein (the hanging wall of the fault). The mineralised parts of the vein were mostly found in four areas, known as "ore shoots." Their position was determined by the steepness of the fault plane. In general, areas where the fault dipped at more than 70°, were mineralised, but where the dip was less than 70° the vein was barren, filled with the light coloured soft fault breccia which the miners called "chunk." The mineralised parts of the vein, at least in the lower part of the mine, had an average lead content of 7%.
  The width of the vein varied from a fraction of an inch up to 30 feet (9.1 m) or more. Barren sections were generally 5 to 7 feet (1.5 to 2.1 m) wide; worked areas varied from 6 feet (1.8 m) to as much as 40 or 50 feet (12 or 15 m). In the upper part of the mine, where strings of lead had penetrated the hanging wall, it was sometimes worth cutting away an opening 30 to 60 feet (9.1 to 18.3 m) wide, but in the lower workings during the 1950s stopes averaged 6 feet (1.8 m) wide. Two branch veins occurred in connection with the microgranite dyke. At higher levels the vein divided and ran along both sides of the dyke. At greater depth, where the vein was within andesite to the west of the dyke, an East Branch was found in contact with the dyke.
  At its southern end the vein came to an end as it approached the east-west Clay Vein by splitting into a number of small stringers, described as "a horsetail structure". All attempts to find the vein south of the Clay Vein were unsuccessful. The northern end of the vein was never determined, but all searches for lead beyond the limit of the northernmost ore shoot (about 3,600 feet (1,100 m) from the southern end) were also unsuccessful. The vertical extent of the vein was traced and worked from the top of Green Side down to the upper boundary of the Skiddaw Group, a distance of 2,600 feet (790 m). Although lead veins have been found in rocks of the Skiddaw Group elsewhere in the Lake District, the strata at Green Side were unfavourable for mineralisation; these strata therefore marked the bottom of the mine.
caption: Ore from the Greenside Vein, containing baryte (white), galena (grey) and quartz (pale brown). The penny has a diameter of 20.3 mm.
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