One of the more interesting asteroids is called 433 Eros. It is the second closest Near Earth Orbit (NEO) asteroid, about 34km x 11km x 11km in size. Data from the Near Earth Asteroid Rendezvous spacecraft in 1998 indicates that it could have as much as 20,000 billion kilograms of gold and more importantly, platinum group metals.
https://en.wikipedia.org/wiki/433_Eros
It also has a substantial amount of aluminum, which while of little value by itself, could be used to create the mining infrastructure needed to collect and refine the more valuable metals.
One additional note is that, in addition to the orbits of the asteroids, a spaceship from Earth might also be able to hitch a ride on a comet, either from Earth or returning to Earth, saving a lot of fuel.
Interesting!