If you mine resources in your research colony you're basically doing something wrong.
That's presumptuous.
Upgrading buildings trades minerals and pop jobs for building slots. If you are not limited by building slots or are limited by mining districts, this is a bad trade. I usually make use of the mining districts on all my worlds, simply because minerals become the limiting factor later in the game.
About the confusing math:
A very productive miner can supply a very productive chemist who may be able to supply 3 gases. In essence you are using one job to do in 3 building slots what could otherwise be done in 6. It is really only one job because if you do it in 6, you require a technician to pay the extra energy upkeep. This is a rough estimate as there are a lot of other things factoring into productivity and efficiency of pops.