SYDNEY (Reuters) - An independence referendum in Bougainville has reignited interest in copper mining in the South Pacific island, causing a surge in the shares of the former operator of the mine that sparked the region's war to secede from Papua New Guinea. Shares in Bougainville Copper Ltd (BCL) , the former operator of the giant Panguna gold and copper mine, have more than tripled since early last week to trade at above A$0.40 late on Tuesday. This coincides with the start of a non-binding..