Just lately "they" are saying all the Gold found on this Planet "must have come from Space" via meteorites.

Why so? "They" say that if Gold occurred naturally on the Planet, when the Iron core "sank" (as the Planet cooled), the Gold being a very heavy metal would have sunk to the core too.

So how do they explain the huge deposits of Iron ore that have been and still are mined? Did that amount of Iron in/on the crust also arrive via meteorites?

The meteorites of which "they" speak are those which arrived during the periods of bombardment, the last of which was the Late Heavy Bombardment which, it is theorised, lasted from over 4 billion years ago to (depending who you listen to) just under 3 billion years ago.

There was definitely a period of bombardment but how long it lasted is a matter of argument. I suppose that at that time there wasn't much of an atmosphere in which asteroids/meteorites would have been slowed and/or burned up so most of the impacting debris would have hit the Planet full pelt.

As to whether much Gold arrived that way seems a bit unlikely as seams of Gold are found deep within the Earth. Some deep deposits of minerals could easily have been "swallowed" up by movement of the tectonic plates but it seems a bit far fetched to claim all the Gold mined up to date arrived from "out there"?