I think it's just something that was once made for fun, as far as I know it doesn't do anything.
As a little experiment I tried to make it look like an actual mine, by placing it on top of an ore mine, placed on top of a cliff piece:

In some cases it took a few clicks though, because for some reason it sometimes places the structure under the ore mine instead of on top of it (even though I placed the ore mine first).
All the mines in the image were placed without any starting ore, that was all generated during the game. So as you can see, when you place an ore mine onto the cliffs like this, it will generate a lot less ore (which could be desired for a gem mine for instance).