When your geologists find a deposit (e.g. copper) you can see it on the map, when you place on top of this deposit a mine and destroy the mine before settler starts to build it, you lost the deposit too. I have full building queue and I want to clear it (copper mine was 3rd in the queue) I clicked on "X" to cancel it from building queue but after this deposit has been lost too, so I had to use geologists again..
Thank you for further comments to this topic.