Coal showing infinite resources

I am currently playing a map that as far as I know has two coal mines with infinite resources. When I place a mine on them I get the message straight away stating that there aren’t any resources there. That happens with both mines. Is this a bug or what?

No, you’re most likely trying to put an ordinary mine building on them which doesn’t work. You need the t4 infinite mine buildings for infinite resources.

Oh, OK. It took me an age to reach T3, so I guess that is not going to happen real soon.