I set up one of my geologist with all possible iron skills. Lucky Find lv1 with 15% chance. Iron Mining Surplus lv3 with 24% chance. Two Iron in One lv3 with 24% chance. My goal however was not to make an iron deposit skills overloaded geologist, but to find the extra iron deposit. I tried for 1 month, then I wrote ticket to support and I was not explained the skills are mutually exclusive and I was told just to "try harder". So I did and I noticed why Lucky Find skill is not functioning and why notoriously I can not find the extra iron deposit.
When I had one iron deposit cleared and sent geologist, then more or less 24% of the times I had in mail 30-50 iron ores. This was Iron Mining Surplus skill in work. I never found a single extra iron deposit.
When I had two iron deposits cleared and sent geologist, then more or less 24% of the times I found 2 iron deposits instead of 1 iron deposit. This was Two Iron in One skill in work. I never found a single extra iron deposit. I never also received any found by geologist iron ore in mail.
So it looks like, when you skill your geologist with Iron Mining Surplus skill, then you can not find the extra iron deposit with your Lucky Find skill. When you skill your geologist with Two Iron in One, then you need to have exactly 1 iron deposit left to discover for Lucky Find to function.
I dunno why it is so, but it is so. I would assume all skills on geologist should work, once I have them skilled up on a geologist, but it is not so. Apparently you can not have one skill with another skill. You have to pick one iron skill only for that skill to work for iron deposits. I have no idea if this is a planned game mechanics or a bug, but I found over last 2 months this is exactly how it works and nobody bothered to tell me about it or explain it anywhere. Re-skilling geologist costs 1550 gems or alternatively on re-skilling geologist you will lose around 5 manuals, 5 tomes and 6 codex. It is a costly mistake to fix.