It makes sense to add minerals to compost (or IM) before adding them
to the soil.
As I noted previously, Phil Nauta in his book Building Soils Naturally
recommends adding rock
dust to the compost pile so that the minerals gets chelated with
organics. He cites a couple sources for amounts: 2-20 pounds per cubic
yard of compost, or 40-50
pounds per cubic yard of compost.
In another part of the book, the (optional) amount he recommends =
50-500 pounds of paramagnetic rock dust (per 1000 sq. ft. of garden
beds), either to the soil or to the compost pile.