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Some New Mines Of Broadfield Down

By Nicks Harding and Richards

Several open mines were discovered during mineralogical fieldwork in November 08 and a return visit was made to explore these holes.

Bourton Combe.

This is an area of intense 18th C lead mining where at least 20 vein structures of various trends (but often c N-S) have been mined from lines of (now infilled) shallow shafts connected by stopes. Some veins reach c 500m in length and where seen consist of an outer crust of columnar calcite followed by cubes or larger masses of galena. The central portion of the vein is filled with white or gingery barite. Specimens collected demonstrate that other vein configurations occur.

In the adjacent Stancombe quarry these veins are periodically well exposed. Near the surface deeply weathered, confused Barite/clay veins follow joints, bedding planes (flats) and solutional hollows in the limestone. Sometimes very large lumps of abraded galena occur in the clay, a situation somewhat analogous to galena occurrences on Mendip. The veins die out with depth and display the lean ordered nature of primary veins.

1)    Mask Mine 5074 6868 on top of the east side of the combe
       L 5m VR 4m
       Shallow cutting in rock with miners walling leads to entrance crawl into a small chamber. Note the N-S < 60 cm calcite/barite vein (with minor galena) in roof.

2)    Conygeare Rift Mine 5094 6808 in ‘The Conygeare’
       L 16m VR 5m
       Mined rift in pecked out vein < 50 cm wide trending NW-SE, Nearby on same rift is a vertical, partly choked, well preserved ‘ginged’ shaft only 40 x 36 cm in cross section which can be seen to intersect the same rift.

3)    Caldera Pit 5109 6809 in ‘The Conygeare’
       Special mention must be made of this impressive spoil heap containing hundreds of cubic metres of waste-likened somewhat to a volcanic cone. A filled shaft is present on the top, and there are two other satellite pits, one of which is 1.5m deep and displays a square cross-section lined with good walling.

Corporation Woods

In woodland on top of the hill north of Wrington.

A large area of 19th C iron mining which extends into the adjacent Ball Wood, King’s Wood and to Cleeve Hill.

A series of >13 rifts expressed on the surface as shallow trenches and/or lines of pits generally of near E-W trend and some 30m in length. The rifts (where seen underground) are 0.5 –1m wide and are lined with c 6 cm of calcite with a central portion of fragmentary siliceous haematite and a little pink barite. There is also much red ochre and deep red soil. Very few are open and represent the underground sections between pits.

1)    Corporation Woods Mine 1
       4632 6411
       L 20m VR 4m
       Roomy passage up to 3m high in <1m wide rift.

2)    Corporation Woods Mine 2
       4621 6415
       L 9m VR 4m
       Roomy passage descends to miners wall.

3)    Corporation Woods Mine 3
       4618 6414
       L 8m VR 3m
       Recent collapse into small chamber with well constructed inclined miners wall and tight extension.

4)    Corporation Woods Mine 4
       4621 6414
       L 4m VR 2m
       Short passage heading east to dead end

5)    Blanco Pit   4601 6440
       L 24m VR 5m
       Just inside Ball Wood. At confluence if forestry tracks behind woodpile.
       Mine in NE-SW rift. Short shaft into roomy passages to NE and SW, both ending in chokes to adjacent filled pits. Earthenware bottles and a tin of ‘Blanco’ found.

Corporation Woods Mine

Note.     This is another short mine described in an earlier edition of the BB