The value of Western Australia's resources industry has plunged almost 20 per cent in the past year as iron ore and oil prices slumped.

Sales in the state’s all-important minerals and petroleum industry fell by $22.5 billion, or 19 per cent, to $99.5 billion in 2014/15 after reaching a record $122 billion in 2013/14, statistics released by the West Australian Department of Mines and Petroleum (DMP) show. And while the state has an estimated…