Gypsum is in great demand by the building industry to make plaster and plasterboard, both essential for internal walls. In its natural state, it is a rock found in seams, which are several feet thick and it is crushed into powder to make the finished product. In this country, most of the mining is carried out by British Gypsum Ltd, who have mines in the Northern Pennines, Midlands and Sussex.
The only surviving working mines in Sussex trace their history back to a meeting of the British Association for the Advancement of Science, held at Brighton in 1872. The geologists at this gathering resolved to sink a borehole, as deep as could be made, through the oldest rocks visible at the surface in South East England. These were the Purbeck Beds at Limekiln Wood near Mountfield. A subscription was raised and it is likely that the project attracted more than scientific interest and support as there was a possibility that the coal seams worked in Somerset and Belgium might also be found at this spot.
After a number of accidents and false starts, the borehole eventually reached a depth of 1,905ft in 1876 when the drilling rods broke and the project was stopped. No coal was found but there was a greater than expected thickness of younger rocks. The investment of £6,000 was not devoid of commercial interest, however, since several thick seams of gypsum had been found at depths between 130-160ft. The Sub-Wealden Gypsum Co. Ltd was formed on 10th May 1876 and mining commenced by sinking a shaft about 60yds from the borehole. Progress was difficult and slow on account of the isolated location, until a railway link had been constructed to the main line at Robertsbridge.
An early description of the operations in 1881 refers to beds of gypsum from 6-7ft high, into which headings of a similar width were driven by drilling and blasting. These were all connected by a network of underground rails to carry the gypsum to the shaft bottom, where it was hoisted to the surface by a steam winding engine. During the 1880s, the mine was a small but significant contributor to the total U.K. production, raising about 8/000 tons per annum with a value (at the mine) of about £9,000.
A curious result of the opening of this mine was that the H.M. Inspector of Mines could no longer ignore the South East of England, as had been the case up to this point. This was hardly surprising in view of the national publicity arising from the experimental boring, laying of a railway track and creation of a deep mine. All underground workings for minerals, other than coal or iron, had been subject since 1872 to inspection and other requirements under the Metalliferous Mines Regulations Act of that year. Although bureaucratic tidiness had placed the south-eastern counties in a mining inspection district, they had been tagged onto that for Manchester & Ireland! It was not until 1882 that the Inspector started to take a serious interest in Sussex, Surrey and Kent, despite the fact that a number of small mines had been at work for many years.
In 1890, Sussex was transferred to the North Wales & Isle of Man District under an exceptionally able and diligent Inspector who made a point of keeping a very close eye on what were at times very slapdash methods. During the 1890s, the gypsum mine”s workforce gradually rose from 15 to 27 men underground and from 22 to 60 on the surface. This reflected the development of a processing plant at the mine, whose main market was plaster for building purposes. Output of gypsum during the same period increased from 6,000 to 18,000 tons per annum but the value only increased from £3,000 to £6,000, from which it appears that the market price of gypsum was in decline and the mine”s profits questionable. Perhaps for these reasons the original company was wound up in 1903. After a ”short stoppage” of production in 1906-7, during which working methods were thoroughly overhauled, mining resumed on a larger (and presumably more profitable) scale.
Production increased again immediately after the Second World War and the winding shaft was replaced by a sloping adit with an electrically operated railway system. In the early 1950s there was further development, with the opening of a second larger mine at Brightling. In view of the scenic value of the surrounding countryside and of the unsuitability of local roads for heavy freight, the two mines were linked by an overhead cableway generally well hidden amongst the trees. This allowed gypsum from the Brightling Mine to be taken to the processing plant at Mountfield Mine and the cableway has recently been replaced by an updated conveyor belt system. Gypsum is sent away from the plant by rail for similar reasons.
The mines today are extensive, with pillar and stall operations on a scale several times larger than the 6ft x 7ft tunnels made in earlier years. The modern miners travel to their working places underground by Landrover and the newly-blasted gypsum is extracted using enormous scraper-loader machines, crushing plant and conveyor belts. Surveyed reserves of gypsum appear to guarantee the enterprise for the foreseeable future.