Discovering ore on undiscovered tiles

[Nicholas288]

So i was planing on digging out part of a mountain to build a barn for the dozen animals i got when i got the "builders will mine valuable ore" message when placing the blueprints for the wall even though the tile the ore was on is undiscovered and i shouldn't know there is ore there.
Because of this "bug"(oversight really) i now have a reliable way of detecting ore on undiscovered tiles.

I tested this on an ore vein that i knew about and the message didnt show up so im thinking the ore vein must be undiscovered