BHP Billiton declared its preference for a demerger of its unwanted aluminum, manganese and nickel assets on Friday, setting the stage for the formation of a separate company that one report said could be worth $14 billion. One report said those plans were well advanced and would include the Nickel West business that the world’s biggest miner has been trying to sell. “A demerger of a selection of assets is our preferred option,” the company, which has a market capitalization of $185 billion, said in a statement to the Australian stock exchange.