The Newcastle Seam occurs in the Early Campanian Newcastle Member of the Upper Cretaceous Pender Formation, Nanaimo Group. The seam occurs 244 metres to 305 metres above the Wellington Seam and on average 18.3 metres below the Douglas Seam. The seam has the most restricted distribution of the three producing seams in the Nanaimo Coalfield and has been mined mainly from the Brechin or Northfield (Brechin), Protection, No. 1 mine (092GSW041), Newcastle, and Fitzwilliam mines. The seam occurs in the area underlying Newcastle and Protection Islands, beneath the town Nanaimo, and is thought to extend towards south Wellington with a short continuation south of the Nanaimo River.
The seam averages 0.9 to 1.2 metres in thickness where worked but thicknesses range from 0.5 to 2.4 metres. The seam is high volatile bituminous with lower carbon and higher oxygen and ash contents than the Wellington and Douglas seams. The coal has mainly been sold as steam coal. The seam is underlain by flaggy or shaly sandstone and overlain by sandy shale to fine conglomerate. The seam does not contain many shale partings (except in the vicinity of faults or rolls) and is more regular than the Wellington or Douglas seams. At the Brechin mine one or more persistent partings occur in the seam which is 0.75 to 1 metre thick in this area.
Mineable coal was worked from the Brechin mine to the No. 1 mine for a distance of approximately 2 miles along strike and for about one mile down dip. The seam extends beneath Newcastle and Protection Islands and for some distance seaward.
The strata generally strike northwest to northeast and dip shallowly predominantly to the northeast and southeast. Minor faulting occurs in some parts of the seam.
The Douglas Seam (20 metres above the Newcastle Seam) outcrops at the Brechin mine but has not been worked.
At the Protection mine the Douglas Seam is approximately 1.5 metres thick under a hard faulted roof rock. Below this seam is the 1.2 metre thick Newcastle Seam. Both seams were mined out under the Northumberland Channel at this mine.
