The strike entered its fifth day on Monday, as the union awaited a decision by labor authorities over whether substitute workers the company called in are legal.
Like gold, fewer and fewer large copper deposits are being discovered, and the time between discovery and production has lengthened over the years as costs rise.
Shanghai copper price registered a second consecutive month of gains on Monday as prices firmed on a potential supply threat in Chile and massive US infrastructure spending plans.
China plans to strengthen controls in industries such as steel and aluminum which involve high energy use and produce high emissions, in an effort to promote low-carbon developments.
Chinese rebar and hot-rolled coil futures also jumped after the market recorded heavy losses over the past few weeks following the government's vow to stabilise commodity prices.