Vancouver-based Amerigo said this week its phase two expansion of the MVC plant was scheduled to reach full production in the December quarter, lifting annual output to 85-90Mlb at a projected $1.45/lb cash cost.

"Production results in Q2-2018 met expectations and MVC is nearing completion of the phase two expansion project which will increase production and lower cash costs," CEO Rob Henderson said.

"Amerigo remains well positioned for a strong close of the year, fully leveraged to the price of copper."

Copper prices have been falling on US-China trade war fears. The current price around US$2.86/lb (US$6,308.09/t) is off the 12-month high of US$3.29/lb.

BHP this week said the world's biggest copper mine, Escondida in Chile, produced 113,700t in May, up 4.1% month-on-month and its highest monthly output since mid-2015.

Amerigo also expects to produce 1.5Mlbpa of molybdenum at its expanded production rate.

Henderson said Amerigo would release its latest financial results at the end of this month.