you can get sapphires as a bonus when digging after tier 1 resources.
Seeing how there are
no tier one gems, it seem improbable.
Maybe you mean tier 2, but not having any real information in game/forum about the chances and seeing the results so far, I doubt it is working.
I know somewhere in the changes notes it is written that you have a chance to get one of the special gems as a drop, based on how you set the slider, but then it was changed as it modify the chance of successfully mine the regular gems.
So again, we have no real, up to date, informations from one of the developers on how it work.