Now let's see what
National Geographic has to say:
one geoscientist calculated that there are 1.6 quadrillion tons of gold in the core—that’s enough to gild the entire surface of the planet half-a-meter (1.5 feet) thick
Why bother with an asteroid, if the earth's core holds 8800 times more gold?
Wow, yes, it's huge number but we can only dig out a tiny bit...