(ShareCast News) - Even in a country that accounted for 20% of the global population and 13% of its gross domestic product, private consumers in the People's Republic of China could not be expected to consume half the world's copper as the government-led investment drive cooled, Goldman Sachs told clients in a research note.On top of that, the consensus was mistaken in its view that base supply is set to stop growing. At the spot price of copper prevailing at the time, the bank's analysts expected approximately 3 million tons of additional supply to come online.Hence, the market was set to remain in surplus over the medium term, the bank added.It lowered its price forecasts for copper in 2015, 2016, 2017 and for the longer-term to $5,670, $4,725, $4,500 and $5,000 per metric tonne, from $5,724, $5825, $7,000 and $6,000 previously.In parallel, the team of analysts led by Eugene King removed Glencore and First Quantum Minerals from its Conviction But list, while simultaneously downgrading shares of both companies to neutral.Antofagasta and Anglo American were kept at 'sell' while coverage of Kazhakmys was started at 'sell'.