1) North-country spellings of ‘bank’, that is a working section of the coal-face.
The OED reference is to narrow ‘roads along the benk faces’, used in a paragraph which dealt with the way in which a colliery was being worked in 1797. However, the word features regularly in earlier colliery accounts: 1690 for a benke feying
1718 five bencks turning in
1720 Titus lad [worked] 2 days in the down benck, Farnley .