"Because China has little high-quality ore of its own"  This is also true of worlds 3rd largest economy-Japan-which attacked U.S. 12-7-41 to pre-empt the raw materials it needed for its industrial economy. Japan is still preparing plans to rebuild the northern part destroyed by the tsunami and will be needing ore to do so.

As I've noted China has had an average internal cost of 150/ton (12-13-10 agmetalminer)because of its low quality ore-mining as little as 4% ore underground-so until derivative speculators caused ore to drop in Sept-Oct China's internal cost of 150/ton was considered to be the floor- a floor being approached again.