The iron ore collapse has pushed producers to the brink of survival, according to the head of the world’s second-biggest mining company. “There are a lot of producers that we believed would leave the market that are hanging on by their fingernails,” Sam Walsh, chief executive officer of Rio Tinto Group, said in an interview with Bloomberg’s Jonathan Ferro in London. While his competitors are floundering, Walsh said Rio is “well positioned” for what will be another tough year in 2016 because the company has the lowest debt in the industry.