There is a bug with the geologist.
The case is when you have a depleted mine (say, copper), but it has not been demolished yet. You send out a geologist to find copper, and THEN demolish the old mine. The geologist will return with nothing; doesnt find any copper.
My guess is that the return value of the geologist is determined when he is sent out, instead of when the survey timer runs out. I think this should be the reverse.
I hope other people can replicate this case and report the same.
Kind regards,
Sir_Lederhosen