Mining explosives company Orica has paid $US640 million ($966 million) for a US chemical company specialising in gold purification, doubling the size of its chemical business to cash in on boom times in the gold sector.

The acquisition of Cyanco, a sodium cyanide business with plants in Nevada and Texas, will combine with Orica’s existing sodium cyanide factory in Queensland to create the biggest producer globally. Sodium cyanide is used in mining to extract gold from ore.