Customs inspectors at Fangchenggang, in Guangxi province in southern China, said the cargo was reported by a Shanghai-based company as copper concentrates - a feedstock used by copper smelters for making refined copper. 

However, a photo issued with an official statement on October 11, shows customs officials inspecting a big pile of black powder at Fangchenggang.

The black powder was found to be a mixture of copper concentrates and residual slag from solvent extraction electrowinning (SX-EW) processing of copper ore, which is not regarded as a raw material but as waste, according to the customs statement.

The statement did not mention the origin of the 9,954.2-tonne cargo. 

The cargo was impounded on October 3 during the Golden Week national holiday. 

Over the past few months, copper concentrates have been highly sought after, due to tight spot availability - as tracked by Fastmarkets' copper concentrates treatment/refining charges (TC/RCs), which dropped to all-time low of $43.7 per tonne/ 4.37 cents per lb on September 4. 

Lower TC/RCs mean higher procurement costs for raw materials for copper smelters.

Several of China’s major copper smelters ship material through Fangchenggang.