Copper prices are tumbling just as miners in the top producing nation gird to fight for bigger bonuses, setting the stage for labor strife that raises the risk of supply disruptions. Workers at several mines in Chile are being emboldened by surging company profits and a bumper bonus package agreed to last week at the giant Escondida operation. But the market for bonuses is also linked to the price of copper, which on Thursday fell back below $9,000 a metric ton and is now about 15% off May’s record high. The opposing factors create a tough environment for labor talks in a country that accounts for more than a quarter ... (full story)