Use the console command:
/spawn_patch size type
size can be tiny, small, medium, big, huge, or colossal.
type can be crude-oil, coal, stone, iron-ore, copper-ore, uranium-ore, water or tree-09.
Ore patches come out perfectly square and the spawn point is the player, with the player at the bottom left corner of the spawned patch.
Any tile where ore is spawned will have whatever is already there removed from existence.
The command will not disable achievements.
I only know this because I delved into the code and then tested it out.
