The bottom line, page-19

should regain control of the iron ore sector over the next few years as higher cost producers fall victim to lower commodity prices.

The only problem is that as soon as the price rises a bit, the Chinese mines which were shut down reopen. To make sure they remain permanently closed, the big 4 (including Vale) would need to ensure IO price remains at this level ad infinitum. But doing so is reducing their profits. Effectively they are capping their own knees. I seriously don't think the Big 4 are flooding the market to take out the higher cost producers, more like if I don't increase supply, the other three will. If it is an oligopoly it is a very weak one.