C02 question

[Cantclimbtom]

Looking at BGS around Finedon, especially looking a little West -  could it be the area there the ironstone is present in conjunction with Whitby Mudstone? Which they describe (https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=WHM) as "..Medium and dark grey fossiliferous mudstone and siltstone, laminated and bituminous in part.."  the word bituminous jumps out at me for black damp.

Dunno, do we have a tame geologist reading this?  (if not tame, at least vaguely house trained )

 

[mikem]

Of course, in some areas different beds are present / missing. The mudstone is apparently above the ironstone, so gases would be sinking down & could easily collect in pockets:
https://en.m.wikipedia.org/wiki/Whitby_Mudstone

 

[LJR]

Ironstones come in different strata groups. In the coal measures (around 300 million years) there are often ironstone bands in the coal and/or separate ironstone seams. Sometimes the iron was worked with the coal and other times separately. This stuff was generally a hard ore. I can't speak for all coal districts but this was the case in Derbyshire and North Staffs. Then there is the haematite mines of Cumbria, a different type of stone altogether.
Then the ironstones mined in Northampton and Lincolnshire which were Jurassic (200 million years) ores. These have no coal measures associated with them. The ore is really a soft limestone with added iron. Described by our mine geologist as a "ferruginous limestone" , not sure of the spelling there! The iron content was never high, 25% being good. The coal measures stuff was much better, as were the Cleveland ores. Cumbrian ore was the highest quality (I think).
The good thing about the Lincs and Northants stuff was that it had large reserves for opencast and underground mining and could be mechanised for maximum output. The result being the vast areas of pillar and stall workings that we are now discussing.

 

[mikem]

Ferruginous is correct