http://en.wikipedia.org/wiki/Asteroid_mining#Purpose,
http://science.howstuffworks.com/asteroid-mining.htm
http://www.space.com/19462-asteroid-mining-deep-space-industries-birth.html
http://www.forbes.com/sites/kitconews/2013/01/25/asteroid-mining-becoming-more-of-a-reality
http://www.telegraph.co.uk/news/worldnews/northamerica/usa/9844423/As-asteroid-heads-for-Earth-near-miss-space-mining-companies-prepare-to-boldly-dig.html