Chance of Discovering Iron

[redplague]

I popped a spot once, does that count?

 

[Willem]

I have a theory that it's not some fixed small percent, but rather that the AI will do this to help in situations (I can't back that up, just my theory).

Well your theory is wrong. There's a 1/10000 chance for each resource type to appear once there's a mine that's being worked. The numbers are there in the BonusInfo file, it's not something that's hidden in the code somewhere.