“Everyone loves copper and everyone wants to buy it” has been this year’s mining mantra. Today the ball started rolling. China’s Zijin Mining Group Co. swooped on a huge undeveloped copper mine in Serbia, acting as a white knight to beat out an earlier hostile bid from a Canadian rival. At the same time, BHP Billiton Ltd., the biggest miner, snapped up a stake in one of the world’s biggest undeveloped assets. Glencore Plc also increased its exposure to the metal with a new offtake deal.