Don't be too caught up by theories of meteriors causing the mineral deposits. The deposits do not come from outer space but from deep within the earth. They are likely volcanic in origin (looking for diamonds in this area too) but yes in the Sudbury case a meteror caused the magma below surface to flow and leave massive deposits.

The deposits in James Bay lowlands are formed by minerals coming out of molten rock and mixing in some cases with sulphides.

Don't get upset if this is too simple an explaination because of course it's much more complicated and even the experts disagree how these rich deposits came to be. It's enough to know they aren't singular in nature and there will be a lot more found.