also from wikipedia

There are three options for mining:

1. Bring back raw asteroidal material.
2. Process it on-site to bring back only processed materials, and perhaps produce fuel propellant for the return trip.
3. Transport the asteroid to a safe orbit around the Moon or Earth. This can hypothetically allow for most materials to be used and not wasted.

Processing in situ for the purpose of extracting high-value minerals will reduce the energy requirements for transporting the materials, although the processing facilities must first be transported to the mining site.

Mining operations require special equipment to handle the extraction and processing of ore in outer space. The machinery will need to be anchored to the body, but once emplaced the ore can be moved about more readily due to the lack of gravity. Docking with an asteroid can be performed using a harpoon-like process, where a projectile penetrates the surface to serve as an anchor then an attached cable is used to winch the vehicle to the surface, if the asteroid is rigid enough for a harpoon to be effective.

There are several options for material extraction:

1. Material is successively scraped off the surface in a process comparable to strip mining. There is strong evidence that many asteroids consist of rubble piles,[8] making this approach feasible.
2. Asteroids with a high metal content may be covered in loose grains that can be gathered by means of a magnet.[9]
3. For volatile materials in extinct comets, heat can be used to melt and vaporize the matrix.[10]
4. A mine can be dug into the asteroid, and the material extracted through the shaft. This requires a transportation system to carry the ore to the processing facility.

Due to the distance from Earth to an asteroid selected for mining, the round-trip time for communications will be several minutes or more, except during occasional close approaches to Earth by near-Earth asteroids. Thus any mining equipment will either need to be highly automated, or a human presence will be needed nearby. Humans would also be useful for troubleshooting problems and for maintaining the equipment. On the other hand, multi-minute communications delays have not prevented the success of robotic exploration of Mars, and automated systems would be much less expensive to build and deploy

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Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets is a book by John S. Lewis which discusses the development of interplanetary space within our solar system.

Lewis makes a prediction that the abundant resources of the solar system, including effectively-limitless solar energy, could support a vast civilization of 1016 people. He argues that shortage of resources is "...an illusion born of ignorance."

Lewis calculated the value of M-type asteroid 3554 Amun at US$20 trillion: US$8 trillion worth of iron and nickel, US$6 trillion worth of cobalt, and US$6 trillion in platinum-group metals.[1] Since the book was published, the value of platinum, for example, has tripled