I've been at the Map Editor again, and here's the result. Inspired by a photo I saw of an open-cast/open-pit mine, I thought "Hmmm, that's the kind of industrial location that units might stumble across while moving across a planet." As is common with many of my maps, the surrounding terrain is more European in style, but that's easily changed by over-riding it from 'grass' to the default.
32x34 OpenCastMine
And then I thought ... "Ooh, what about if it had been abandoned for a while?" ... so I made a variant, with the lowest level flooded, some of the buildings collapsed, a general increase in tree growth, and more rubble due to the collapse of the pit sides.
32x34 OpenCastMineAbandoned
Hope that people like them!
(There is a vague chance that I might decide to raise the water level another layer or two, resulting in a the very deep lakes that tend to result from flooded mine pits and quarries - if I do, then I'll put it up as a reply to this thread.)