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.

A small dyke of porphyritic microgranite[note 2] which has "a dog's-leg shape" in plan[7] was intruded into these rocks during the Devonian Period;[6] this formed a plane of weakness which controlled the position of the fault.

[10] The argentiferous galena (lead sulphide, containing small amounts of silver), which the miners sought, occurred as ribs, strings and dispersed pockets throughout the vein.

W. T. Shaw claimed Greenside was being worked by "a party of Dutch Adventurers" (probably meaning German miners) by 1690,[22] but cited no evidence for this, and may have been thinking of other mines in the district.

[23] Samuel Murphy discovered what he considered "the first documentary evidence" in the form of a barrister's brief of 1799, which referred to a Mr. Thompson who was working a mine at Greenside under the Duke of Norfolk.

The remains of a smithy were found lower down, near the base of the middle collapse hole, where there was a flat area at 584 metres AOD, with the foundations of a building and a scattering of coal, coke, slag and iron.

Other provisions sought to mitigate some of the nuisances caused by a working mine in the area, from pollution of the river and the lake, to the state of the roads and the cleanliness of the workers’ accommodation.

[47] World War I in 1914–1918 pushed up demand for lead and the market price, but the output of the mine fell as a result of three factors: poor ore, a shortage of miners, and two very dry summers which severely reduced the water supply to the power house.

In 1936, BMC with a subsidiary of Associated Lead Manufactures Ltd. formed The Basinghall Mining Syndicate Ltd.[note 17] to explore the possibility of purchasing Greenside, believing it had only failed from a lack of working capital.

However, this did not immediately translate into profits because of high development costs, and operating losses continued to be made until 1941[62] World War II had begun in 1939, just as the large-scale working of the mine began.

A contract was agreed in July 1942, under which the Ministry paid for the operating costs of the mine, for all approved development work and for any plant or equipment needed.

The company continued to run the mine on behalf of the Ministry, and in lieu of profits were paid 30 shillings[note 19] for each dry ton of lead concentrates.

To help with the search, an electrical resistivity survey was carried out towards the end of 1943, and trenches were dug to investigate places on Hart Side where there were promising indications.

[69] Just before the mine was due to close, the company was offered a reasonable fee to allow the Atomic Weapons Research Establishment (AWRE) to conduct an experiment in detecting seismic signals from underground explosions as part of Operation Orpheus.

[74][12] The High Horse Level[note 22] had been started before the mine was abandoned in the 1810s,[17][12] from the lowest possible point on the floor of the upper valley beneath Green Side.

In blind headings a fan blast, worked by a boy, was used, or in very long drives a more powerful waterblast drove air down cast iron pipes to within a few yards of the miners at the forehead.

The fault continued in these rocks but it contained no ore. Work on the shaft was stopped and the 217 Fathom Level was developed to draw ore from the rich stopes just above the shale.

A crushing mill was erected in about 1827, probably using a roller crusher powered by a water wheel, although this still required ore to be broken by hand (known as "knocking") into pieces less than 3 inches (76 mm) in size.

Vibrating tables replaced some of the round buddles to treat fine material, and an effort was made to recover some of the zinc blende in the ore, but this seems not to have been successful.

In these, organic oils and acids caused the galena particles to become attached to rising air bubbles to form a grey foam which overflowed a weir at the top.

After a day of heavy rain, winds increased to 90 miles per hour (140 km/h) overnight and at 1.30 am the dam gave way, emptying the tarn and sending a large flood down Glenridding Beck, through the village and into the lake.

[164] Ore processing was the work of independent Washing Masters, who took a bargain for a year or more to carry out a particular job, and were paid a price per ton of lead smelted.

Men employed on the mine transport (filling wagons, driving horses, working at the shafts) as well as timbermen, blacksmiths and surface workers were paid wages at weekly rates.

[184] Poor labour relations at the time led to an unofficial strike in 1942; the men on weekly rates eventually received an increase of 2 shillings per day following a similar settlement in the West Cumberland iron mines.

The biggest obstacle to a treaty was the issue of verifying that all parties complied with it, and the Western powers were determined that any agreement reached could not be violated in a clandestine manner.

The remainder covered the spoil heaps with organic material to encourage vegetation, and demolished the old stone-walled buildings of the Smelt Mill, the Silver Refinery and the Smith's Shop.

[197] The reopening of the Lucy Tongue Level was agreed to in 1993 by the present owners of the mine, the Lake District Special Planning Board (LDSPB), part of the National Park Authority.

Groups of enthusiasts collaborated to dig through the roof of the level from above the original entrance, and installed a large concrete pipe with a lockable manhole cover.

[205] Also in 2014 Eden District Council began a twelve-month environmental investigation of the site involving testing the metal content of soil, grass and water samples.