TOKYO (Reuters) -Japan, Spain and South Korea issued a rare joint statement on Wednesday expressing deep concerns over tumbling copper treatment and refining charges (TC/RCs), warning both smelters and miners cannot develop sustainably under current conditions.

Copper smelters worldwide are grappling with falling processing fees and shrinking margins amid tight concentrate supply and expanding smelting capacity in China. In June, some Chinese smelters agreed to process copper for Chilean miner Antofagasta ( ANFGF ) at no charge.

"We are deeply concerned that this deterioration in TC/RCs is prompting a reassessment of copper smelting operations worldwide, with several companies already indicating intentions to scale down or withdraw from copper concentrate smelting," the three countries' industry ministries said after an online meeting.

TC/RCs, a key source of revenue for smelters, are fees paid by miners when they sell concentrate, or semi-processed ore, to be refined into metal. But in some spot deals this year, TC/RCs have turned negative, forcing smelters to pay miners to provide smelting services.

The ministries said the current market environment prevents copper smelting from developing sustainably alongside mining in resource-producing countries and warned that growing dependence on specific countries is undesirable for both resource-producing and smelting countries.

"We hope TC/RCs will return to sustainable levels for copper concentrate trading," they said, adding they will continue engaging with relevant countries and stakeholders to establish a resilient and sustainable copper supply chain.

Naoki Kobayashi, deputy director of the mineral resources department at Japan's industry ministry, said the three countries -- all importers of copper concentrate with domestic smelting operations -- wanted to raise the issue during the metals industry gathering LME Week in London. 

Japan's major copper smelters, JX Advanced Metals and Mitsubishi Materials ( MIMTF ), have said they plan to scale back copper concentrate processing as declining fees erode margins.