In that picture of mining equipment, is that cylindrical thing the same one the gals were talking about?
THAT is a boiler, or steam generator. A flame tube sheet type, similar to and probably derived from a railroad locomotive.
See those holes at the end? That's a tube sheet and those "holes" are the ends of flame tubes. The firebox would be at one end and the smokestack at the other and flames would flow through the tubes.
The water jacket is the round part around the tubes. The water in the water jacket would get heated by the flames flowing through the tubes and produce steam to run an engine.
In this case it was probably a "donkey" engine that would power stationary driven equipment. See the big flywheel next to the boiler? Or maybe it was an electrical generator, or a water pump. I can't see the engine very well.