I suspect you'll find that the SP's react when there is news that impacts long term iron ore price expectations, it just so happens that same news will impact the short term price as well. In recent months the two bits of long term news that have moved iron ore stocks around are:
The pollution story - caused a short term sell off in the iron ore price but caused analyst to downgrade long term margins for lower quality iron ore.
S&P upgrading long term iron ore price forecasts a few weeks ago is what ignited the rally in BHP and RIO in particular.
Outside of that the iron ore price is volatile and large short term swings is BAU - it's when news gets into long term expectations that the market reacts, notably.
FMG Price at posting:
$21.20 Sentiment: None Disclosure: Held
A personalised tool to help users track selected stocks. Delivering real-time notifications on price updates, announcements, and performance stats on each to help make informed investment decisions.
(20min delay)