May be completely wide of the mark but can't see how this could be made from cast iron. The large heating boilers you see in older buildings are normally made up of sections of cast iron that are bolted together, to allow for movement when heating/cooling. Also, the fact it's riveted, cast iron & hammer blows don't get on too well together.
Anyway, a quick test to prove/disprove, would be to take a battery drill & drill a small hole in it, somewhere out of sight. If the cuttings are granular & the bit soon loses it's edge, then it's cast. If the cuttings come out twirly, it's steel.
As to the idea behind it, again could be completely wrong, if the shaft needed to be made safe but not sealed (i.e. capped) & there was an old disused boiler, air receiver, whatever on site, it would be a quick & effective solution.
Just my two-penny worth... 😉
Regards, John...
Huddersfield, best value for money in the country, spend a day there & it'll feel like a week........