If prices maintained their current states of affairs, however, a problem is: supply and demand. Lots of supply, demand goes down, price goes down. Subject to a few other variables in the equation regarding cost of mining, distribution, manufacturing subsidiary products, ...
Nevermind that economies are built on real people's labour (ultimately). If we consider the value that this asteroid actually delivers to people, it probably isn't that significant. Iron is already pretty common, Nickel might be cool, gold is mostly specialist, because jewellery doesn't make peoples lives easier in any meaningful way that isn't about social signalling. Now if the asteroid were made from a fairly pure form of aluminium, that would be good. Aluminium is great stuff, and it takes mounds of energy to process.
Please forgive my ignorance, but how does this reach the surface of the earth without causing some form of physical disaster?