Copper closed above $12,000 a tonne for the first time on Tuesday, extending a rally driven by transmission-grid construction on three continents and the slowest mine-supply growth in a decade.
Benchmark three-month copper touched $12,085 on the London Metal Exchange before settling at $12,020, up 34 percent this year. Analysts pointed to grid build-outs in the United States, India and Brazil, where utilities are contracting years of cable and transformer supply in advance.
Smelters, meanwhile, warned that treatment charges have collapsed as concentrate supply tightens, squeezing margins even as the metal's price climbs. Two Chinese smelter groups said they would bring forward maintenance shutdowns in September.