I think small scale , rather than industrial a la Teague , Crawshay,etc would be a safe assumption.

"""The Forest of Dean has a unique system of Free Mining dating back to mediaeval period when they were granted privileges listing in the ‘Book of Dennis’ during the reign of King Edward I. These rights granted in ‘tyme out of mynde’ include rights to graze sheep and swine in the Forest have been retained, relatively unchanged. This unique set of customs was granted by the Court of Mine Law and Crown officials, namely the Gaveller and Constable of St. Briavels Castle. Although the world has changed beyond recognition since this right was granted, it is a custom which has never been withdrawn – and would probably meet a hostile reaction from the free miners if ever such a threat were made.

The Free Miners were involved in small scale charcoal burning, iron mining and coal mining and had sole rights to mine within the Forest boundaries.

An early court was founded in the Forest including the Court of Attachment, also referred to as the Verderers’ Court or Speech Court which met every 40 days at the Kensley Lodge until it was replaced by the Speech House in 1676, which still exists although is now a hotel. The role of the Verderers was to protect the ‘vert’ and ‘venison’ of the Forest on behalf of the King. The court continues to meet today at the Speech House.

In order to apply for registration as a Free Miner, a man (no rights for women!) must be 21 or over, have been born within the ‘Hundred of St. Briavels’ and to have worked at least a year and a day in a coal or iron or mine within the Hundred. Each Free Miner had to be approved by the King’s Gaveller and had to pay a weekly and quarterly fee to the King in return for which he had the right to claim a ‘gale’ from the Crown, ie place to mine for coal or iron ore anywhere within the Forest. The King had a share in any new mine and could send a ‘King’s Man’, ie one of his own workers into the mine without bearing any of the overhead expenses of the mine. The landowner would also have the right to send one of his own workmen, the ‘Lord’s Man’ down with the same rights as the King’s Man. A miner could own up to three gales and these could be sold or the free miner could lease his gales and obtain a royalty on any coal or iron ore mined."""

There was a level, known as Pluckpenny, above the left hand side of the road from Nailbridge to Ruardean, about 300 yards from Nailbridge, which was still being worked at the end of the 1940s.
Gerry Meek