Mining in Ecclesall Woods

The extent of coal mining in the western parts of Ecclesall Woods and the adjoining areas is often not appreciated. Coal mining went on in areas around Dore, and in the area under the present picnic area the Moss Valley mine extracted coal and ganister. Coal mining went on until World War II. I have heard that the miners were drafted and moved to more productive areas, and the Dore and Moss Valley mines were not re-opened after the war. Certainly the Moss Valley mine was covered with landfill to make the present picnic area, and the stream visible at the far side of Limb Lane, and drainage from the mine shafts and tunnels, together flow out from a large pipe and become the stream which runs past Ryecroft Mill and joins the Limb Brook at the 18th century bridge.

At times, this stream is coloured a deep orange-yellow by oxidised iron compounds.

Mining in Ecclesall Woods

I am grateful to S. Dumpleton, B. Sc., Ph.D., CGeol, for the following authoritative description of the origin and formation of these compounds.

Background
Ochrous discharges into streams and rivers have been known for many decades in the western areas of the exposed Yorkshire-Derbyshire coalfield. Most (though not all) of these discharges are associated with former mining activity. Workings which were de-watered by pumping or drainage tunnels (soughs) become flooded following the rebound of water levels after abandonment.

Pyrite (FeS2) is ubiquitous in Coal Measures rocks and is especially abundant around the horizons of marine bands. During mining operations, oxidation of pyrite to soluble ferrous sulphate occurs in humid (but not flooded) conditions. This reaction is enhanced by bacterial action, principally Thiobacillus ferro-oxidans. When the workings become flooded, the ferrous sulphate is taken into solution. Liberation of protons, H+, results in acidity. If the minewater reaches a surface watercourse, further oxidation occurs to ferric sulphate and ultimately to ferric hydroxide and oxy-hydroxides which precipitate out on to the stream bed, casing the characteristic unsightly orange coating which smothers bottom-dwelling flora and fauna. The reactions are summarised below.

Summary of the processes involved: FeS2 + 7/2 O2 + H2O -> Fe++ + 2 SO4-- + 2 H+       (1) Pyrite oxidation in air in damp (but not flooded) conditions.

Fe++ + 1/4 O2 + H+ -> Fe+++ + 1/2 H2O      (2) Ferrous iron from (1) is oxidised in air to ferric iron.

Fe+++ + 3 H2O <--> Fe(OH)3 + 3 H+        (3) Hydrolysis of ferric iron produces ferric hydroxide (forms insoluble orange-yellow precipitate) and releases additional acidity.

The sum of (1), (2) and (3) gives: FeS2 + 15/4 O2 + 7/2 H2O <--> Fe(OH)3 + 2 SO4-- + 4 H+ So, for each mole of pyrite oxidised, 4 moles of H+ (acidity) are produced.

Limb Valley
The Limb Valley and its surroundings is a well known recreational area, with a nature trail and forms part of the Sheffield Round Walk. It is also close to popular residential areas

The Limb Brook has its source on Namurian ('Millstone Grit') shales at an elevation of about 350 m OD at around SK 287 836, near the village of Ringinglow, about 8 km WSW of Sheffield. It flows in a general easterly direction, picking up a few small tributaries on the way, crossing a succession of Namurian and Lower Coal Measures rocks before joining the River Sheaf at Abbeydale, SK 324 815.

Parts of the area have been affected by mining. Workings in the Ringinglow Coal dating from the early 19th century exist close to the Limb Brook in its upper reaches. Near Ringinglow village, both coal and pyritic shale have been worked, the latter to produce sulphuric acid and 'copperas' (ferrous sulphate) for the dying and tanning industries. Downstream, the Ganister Coal and its underlying fireclay and ganister (siliceous seatearth - valuable for refractory bricks and furnace linings) have been extensively worked from the Moss Ganister Mine. These workings particularly affect the Brick Houses Brook tributary (NB. this is our name; the brook has no official name), drainage from them resulting in a major ochrous discharge (SK 3123 8191).

A further ochrous discharge occurs adjacent to the Limb Brook further downstream (SK 3176 8179) from a small 'well' (Ordnance Survey map, 1875-1906 editions) or 'spring' (Ordnance Survey map, 1923 and later editions, but which old mining plans indicate is most likely an old shaft connecting to Dore Colliery workings. Although the mines have long since been abandoned, mining-induced fractures have enhanced the hydraulic conductivity of the rocks, creating new pathways for groundwater and minewater flow to the surface.

Credits
Horse-drawn tramway. The Forgotten Mines of Sheffield. Ray Battye. Published by Alastair Lofthouse, Sept 2004. This locally produced book is an excellent source on ganister mining and uses. Many thanks for permission to use this picture Coal; www.quietenvironmentalist.com, with thanks
Ganister Rock: thanks to earlscience.blogspot.co.uk

Words: Linda Evans
Design: Jimmy's Garden Services

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