The most-traded January copper contract on the Shanghai Futures Exchange dropped 1.1 percent to close at 43,670 yuan ($6,357) a tonne on Thursday as the dollar stayed near a 13-1/2-year high, pulling the industrial metal further away from its strongest level since June 2015 after a rally that many doubt could be sustained. Among underperformers, Shanghai zinc slid 3.6 percent to 20,570 yuan a tonne and aluminium dropped 2.1 percent to 13,430 yuan.