The most-traded October copper contract on the Shanghai Futures Exchange rallied 1.22 percent to close at 50,550 yuan ($8,200) a tonne on Wednesday fuelled by short covering and bottlenecks in supply, although sluggish global growth eroded demand prospects and signalled gains may prove tough to sustain. But given slowing growth and rising regulation in China, the heat has been taken out of copper demand, said analyst Natalie Rampono at ANZ in Melbourne. "We don't think copper's gains are sustainable," she said.