Copper futures fell sharply on Thursday, with the US benchmark falling $2.00 to $9.40 per pound.
The futures are down about 10 cents in a day since a close of $11.40.
They are also down about 20 cents in less than two weeks.
The slump comes after a run of high-profile moves by China, where the price of copper fell in 2018.
The copper futures are also one of the few bright spots in the US dollar index, which has been in a slump.
The dollar index is down about 15 per cent against the Japanese yen since the start of the year.
The steep fall in the copper price has been a boon for the global economy and for global exports of copper and other minerals, as well as for miners in the United States.
The plunging copper prices also could be good for investors as they will likely raise the dollar to more attractive levels, which will benefit the economy.
However, they could also prove a drag on other global markets, as it will further erode their purchasing power and raise the risk of another global economic recession.