the moon - Is extraterrestrial mining more difficult or impractical for bodies without plate tectonics?

I vaguely remember my dad talking about this.

Uranium and other heavy elements are dense. When the celestial body was molten (early in it's life) all the heavy elements sank to the core of the body. Now, with tectonics, the heavy elements are brought back up to the surface. This is why we can mine Uranium on Earth near the surface: the Uranium was brought back up due to convention current on Earth.
In conclusion, it's not worth it at all to mine on a non-tectonically active planet/moon

If anyone can extend this, please do.