Could it be limestone dust? Stone delivered via train like the coal? I think the stone would be used with the ore and coal in steel production.

Actually, 'darkness', a leaf spring does the same job as a coil spring in that they bear the weight of the vehicle on to the axle. The shock absorbers are related but their job is to dampen the movement to avoid bouncing.

I find it quite admirable that you explore these places that interest you while making efforts for minimal disturbance of the sites and to discourage theft and vandalism.
Also, the bits of history you've included are quite interesting. Even though your photos are interesting in themselves, I find the history of the places adds alot overall.
Awesome photos. Well done, Mr. Motts.