Why have Fortescue shares lost 36% since May?

Fortescue Ltd (ASX: FMG) shares are up largely flat in Tuesday afternoon trade, at $14.59 each. Today’s slump means the shares have now fallen 36% since reaching an annual high of $22.99 in mid-May. It’s been a long and pretty consistent tumble, too. Fortescue shares are now down 34% for the year-to-date. It made me wonder, what’s going on with the ASX iron ore miner’s share price? And what can we expect next? What headwinds are pushing Fortescue shares lower over the past five months? The ASX mining shares have been smashed by a falling iron ore price this year….