Indonesia is considering imposing a hefty tax on mineral exports to curb over-exploitation of the country’s resources, as companies scramble to beat a 2014 law requiring ores be upgraded on-shore. It’s a rational follow-up to the government’s quasi-nationalisation of the mining industry, announced earlier this year. It would affect London-listed mining companies BHP Billiton, Bumi, Churchill and Rio Tinto, among others.