The global demand for iron is being pushed in part by China's insatiable appetite for natural resources. That is causing exploration companies to revisit Arizona's iron ore deposits.
The Transition Zone across the state is home to a variety of Precambrian deposits of hematite and magnetite, which seem to be the primary sources of iron ore in the region. AZGS Bulletin 180 [right] and US Bureau of Mines Circular 8236 are the best references.
There are numerous known deposits with 10 -100 million tons (small circles in figure) and a few over 100 million tons (large circles). Many deposits range from 30-65% Fe (pure hematite has ~70% Fe).
Companies have been exploring Arizona's iron deposits for many decades. Hurdles to development have been the economics, transportation, and the presence of trace elements in some areas that could present problems in the metallurgical process.
Thanks to Mike Conway and Nyal Niemuth at AZGS for updating me on this topic.