I don't know about those but Antique mantels around here are in serious demand and go for thousands of pounds.
A huge local house owned by the council was closed and for sale ready to be converted to a hotel, well somehow somebody got around the huge 10 foot fence and into the main drive which is clear to the main road and stole 8 sold marble fire places, around 150 years old. Estimated value $120k.
The ppl who bought my pops house restored it to its original style and bought an original 100 year old marble fireplace and paid around $10k for it.
Should be worth at least a few hundred bucks if you restore them nicely.