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During game generation
System bodies Mineral composition (accessibility and availability) is determined upon each system generation. More gravity tends to lead to more minerals and lower accessibility. Comets always have moderate amounts of multiple minerals with high accessibility. Homeworlds have a different starting situation with regard to minerals, and start with the team survey flagged as complete.
When a body mineral generated check take place, a roll is made separately for each mineral. If this check is successful, it generates a quantity and accessibility. Duranium has twice the chance of any other mineral to be generated.
During geological survey
The first step for mineral exploitation is obviously to send geo-survey vessels. The second step is to use Geology Teams (aka: geoteams). A team can find hundreds of thousands of tons of minerals on a planet and improve the accessibility, which is a great boon to any empire.
- Geology Teams must be staffed by five Scientists and/or Officers with some degree of survey skill.
- The higher the team's skill, the faster they finish the survey. (The chance of completing a survey team check during one year is based on a combination of planet size and team skill. The formula is
(1000 / BodyRadius^(1/3)) * (TeamSkill / 100))
- The team's skill has no effect on what is found, only on how quickly the survey can be completed.
- While involved in their surveying efforts, members of the team may gain a small amount of experience and survey skill regardless of whether new deposits of minerals are discovered or not. Interestingly enough it seems that when one member of the team learns something, generally all 5 do.
- Ground based Geology surveys are limited only to bodies that have already been surveyed from space.
- Failure to find anything from space does not preclude the ground based team from finding minerals on bodies previously thought to be barren.
- When the team finally completes the job, new minerals are rolled for the body (with 25% of the normal chance to find minerals). For each mineral, if the new quantity is larger than the original quantity then the original quantity is set equal to the new quantity, and if the new accessibility is larger than the original accessibility then the original accessibility is updated to be the new accessibility. If this results in any changes, the team will report them.
In order to survey the mineral resources of a system body, a geological team only has to be dropped or created on the body. Dropping a geological team on a planet will automatically create a new colony if this planet was empty. Obviously, gas giants are not a valid destination. The survey will take place automatically, you don't have to give specific orders to your team.
Once the survey is done, the Geological Team Survey Completed field on the Economy screen (F2 Summary tab, will be set to 'Yes'.
Because the chance of both generating new minerals and finding that those minerals are better than the existing deposits is quite low, it's probably best to send geo teams only to those bodies where the total accessibility is quite high; even if they find new minerals on a body where none were detected before, it's quite unlikely to raise the total accessibility to something you'd be interested in mining.
The quality of the geo-sensor (normal, improved, advanced) and the skill of the team affect only the time required, not the chance of finding minerals. You can't get more than two chances of discovering minerals - one for the orbital search, one for the team.