Crucible was also a captive mine (of the Crucible Steel Company) however they never had a prep plant on this side, just the dump. And they didn't have a conveyor belt to bring it over, they had a skip, or as they call it on a mine map an "Aerial Tramway", basically like a ski lift but for buckets of mine waste. The mine opened in the early 1910s but they must have dumped on their own side for awhile.
It wasn't there in 1939.
It was in 1959. Probably nearing the end of the mine's life, it shut down by the early 1960s.
So what's left today? Well I haven't been to the other side but the dump is still there.
While not the biggest slate dump around in area, these "twin peaks" sure are tall! Also note the bottom has largely turned to "red dog", a byproduct once used to cover rural roads, today that's the job of gravel. There aren't many "red dog" roads left, probably due to environmental concerns.
No idea how the overhead skip worked but this must be what's left of it, there's no other reason cables like this would be just hanging out on the top of this pile. Presumably they had bulldozers or something on this side to even the pile out from time to time.