Miners pay treatment and refining charges (TC/RCs) to smelters to process their copper concentrate into refined metal, offsetting the cost of the ore itself. Charges typically go down when concentrate supply is tight and smelters have to accept lower fees to get feedstock.

China's copper concentrate supply took a hit earlier this year because copper mine operations in key supplier Peru were curtailed by pandemic-induced lockdowns.

"Next year we do have some supply growth, but not really until mid-year," said Colin Hamilton, managing director for commodities research at BMO Capital Markets.

The supply growth, however, from the expansion of Chilean miner Antofagasta PLC Los Pelambres mine, BHP Group Spence mine in Chile and Ivanhoe Mines' Kakula project in the Democratic Republic of Congo is not expected to offset China's demand resurgence.

Hamilton expects next year's TC/RCs at $60 a tonne and 6

cents a pound "with a slight skew to the downside".

The annual TC/RC benchmark - usually agreed between miners and smelters around the turn of a year - is referenced in concentrate supply contracts worldwide, playing a significant role in determining the profitability of miners and processors.

The benchmark has fallen every year since being struck at $107 per tonne and 10.7 cents per pound for 2015. For 2020, it was set at $62 per tonne and 6.2 cents per pound.

Spot TC/RCs - rather than long-term - have been hovering around $51.50 a tonne since late July this year.

Spot TC/RCs are at their lowest since November 2012 because of the mine disruptions and the rapid recovery in copper demand in top consumer China that revived smelter operating rates there after a pandemic-triggered slump.

While TC/RCs will see support from an expected recovery in concentrate supplies next year, with 2020's tightness loosening to a surplus, next year's smelter demand would limit gains.

Chilean miner Antofagasta Plc has already inked concentrate supply deals for the first half of 2021 with China's Jiangxi Copper and Tongling Nonferrous Metals Group at a TC of $60.8 per tonne, Reuters reported in July.

"I estimate it (TC/RC benchmark) will decrease slightly as there will be increasing domestic demand next year," said a copper trader at the sidelines of the China International Copper Forum in the southeastern city of Xiamen.

The most-traded copper contract on the Shanghai Futures Exchange has jumped 33.5% since March due to China's strong construction and infrastructure activities.

By Emily Chow