Chinese copper demand has been so strong in the past few months that top producer Codelco has almost sold out of supplies for next year, well ahead of schedule, according to the chairman of the Chilean state-owned company. Mining companies and investors are increasingly bullish on copper because of limited supply and falling global stockpiles. Codelco has locked in copper-cathode supply contracts with European buyers at a premium of $ 98 a metric ton over benchmark prices, the highest since 2015. Premiums for contracts signed this year with clients in China and the U.S. are also up by 15 to 17 percent. Codelco plans to keep its annual output at 1.7 million tons of copper a year, Benavides said. But as its giant century-old operations age and ore grades decline, it needs to invest billions in so-called structural projects to upgrade mines and avoid a decline in production.