Only aluminum is showing a similar movement but there is no sign of China having any import appetite for the other base metals.

The interval includes a higher-grade 45-metre interval of 1.18% copper, 1.01 g/t gold and 4 g/t silver (2.13% copper-equivalent) from 401 metres.

The take-private deal is subject to court approval and a shareholder vote in December or early January.

Diamond exports from the world's second-biggest producer dropped 42% in the first nine months.

Chile's world-leading copper industry could see some of its mines put out of business if an early stage bill to protect glaciers continues its march through Congress.