China, which consumes close to half the world's industrial metals and is therefore key to setting prices, has had a run of worsening economic data, with figures on Monday showing the first monthly fall in factory output in two years.
Benchmark copper on the London Metal Exchange (LME) traded down 0.3 percent at $5,980.50 a tonne in official rings but the metal used in power and construction has tumbled 17.5 percent so far this year - its biggest fall since 2015.
Aluminium, used in transport and packaging, traded up 0.1 percent at $1,846 but was on course to be down 19 percent in 2018 - its weakest performance since 2008 - after Russia's Rusal, the largest producer outside China, agreed a deal in December with US authorities to remove it from a sanctions list and allow its metal onto global markets.
Overall, the LME's index of six major industrial metals was down 18 percent, the largest annual fall since 2015 and giving back around half of its gains over 2016 and 2017.
Price swings are likely to be calmer in 2019, with both demand and supply weak, analysts said.
"It'll be more like a sideways slog (for prices) next year," said INTL FCStone analyst Edward Meir.
"The supply side is tight, but my fear is that with demand weakening it will offset all these supply concerns so we could see inventories begin to pick up."
TRADE TRIGGER
Metals began 2018 on a high, with copper and nickel reaching the highest in more than three years, aluminium hitting a 7-year peak and zinc surging to its priciest in a decade.
Collapse set in over the summer after US President Donald Trump unleashed a trade war with China.
Investors feared trade tariffs would curtail Chinese economic growth, and the uncertainty helped push the dollar to an 18-month high, making metals more expensive for non-US buyers and helping depress demand.
"If the trade war goes away there's room for prices to move higher," said Saxo Bank analyst Ole Hansen, predicting copper would average around $6,500 next year.
Also supporting prices are tight supplies, with global copper, zinc, nickel and aluminium markets in deficit and only zinc expected to see rapid supply growth next year.
Inventories of zinc, copper and aluminium in LME-registered warehouses reached decade-lows this year, though they have recently picked up.
Time spreads have also tightened, with the cost of metal with nearby delivery dates creeping up relative to contracts for later delivery, suggesting traders are finding it tougher to secure the metal they need.
Zinc, used to galvanise steel, on Monday traded up 0.4 percent at $2,450 a tonne, but has dived 26 percent this year, the weakest performer among industrial metals.
With new mine supply expected to come onto the market next year, Capital Economics sees zinc at $2,300 by the end of 2019.
Stainless steel ingredient nickel did not trade but was bid down 0.5 percent on Monday at $10,680 and was 16 percent lower on the year, its biggest fall in three years.
Battery metal lead was bid down 2.1 percent at $2,017 a tonne and was down 19 percent this year, its weakest since 2011. Tin, used for solder, was bid 0.4 percent lower at $19,425 and was almost unchanged for this year, improving on its 5 percent fall in 2017.