Copper snapped a four-day losing streak to end firmer on Tuesday, as extended labour action at the world's largest mine backed market-wide expectations of a supply shortfall this year. In New York, the key September COMEX contract rallied 7.15 cents, or 1.6 percent, to settle at $4.4780 per lb. Escondida, which produces nearly 7 percent of the world's mined copper, stands to lose production of about 3,000 tonnes per day during the strike.