Grosmont Ironworks When Grosmont Railway Tunnel was dug in 1836, ironstone was discovered. Within 30 years there were three mines producing 70,000 tons of iron ore per year. In order to progress the ore locally blast furnaces were built on this site. The brick structure in front of you is part of the overhead conveyor which brought the ironstone from the min to the smelter. By 1880 steel was being made from cheaper but superior imported iron ore. Grosmon's importance declined and the mines and furnaces finally closed in 1915.