I've modified the mine from the "Solid Territory Borders"-thread. It was a lumber drilling derrick but looks like some trees. So I've make it with metall instead of lumber and here it is.

preview (http://www.ccj39.de/mine.htm)

And here is a file for those who want it manually in their buildings file. (this file only include one of the 3 mine-views and no other buildings)

Looks cool, but it would be weird in the ancient and middle ages! I wish there were era specific terrain improvement graphics.

thx :)
The problem is that civ3 only work with one mine-picture so you should change manually your minegraphic if you want different mines in the time areas.

Any chance of this being updated for C3C now that some new buildings have beenadded to the terrainbuilldings file by Firaxis?

yes, look at, there is the C3C-update ;)