Smelter outages this year including those owned by Vedanta Ltd, Mitsubishi Materials and Aurubis caused a supply bottleneck, pushing up spot treatment and refining charges and boosting premiums for cathodes.
Analysts expect to see further shortages next year.
"We could be heading for a second year when smelter outages are higher than mine outages which is unusual in copper," said BMO Capital Markets commodities analyst Colin Hamilton, adding that flagged outages would not take the market by surprise.
BMO forecasts a deficit of 250,000 tonnes in 2019 from a largely balanced market this year, which chimes with a shortage of 240,000 tonnes seen by Morgan Stanley.
Benchmark copper on the London Metal Exchange (LME) is down more than 15 percent so far this year to just around$6,100 per tonne, mainly due to concerns that the U.S-China trade dispute would hurt demand.
But stocks of copper in LME approved warehouses have fallen 35 percent to about 120,000 tonnes in 2018 and have slipped more than 17 percent in warehouses monitored by Shanghai Futures Exchange, sitting just above 120,000 tonnes.
"With limited inventory, the lack of mine supply growth is likely to feed through to tighter metal supply next year," Morgan Stanley in a recent note.