The company said the expansion, to start in early 2019, would add an average 60,000 tonnes per annum to its production over the first 15 years of operation.

First output is expected in the second half of 2021.

Copper production will rise from an extra 40,000tpa in the first year to 70,000tpa towards the end of the 15-year period.

Throughput at the plant will be increased to an average 190,000t per day from the current 175,00tpd, with the installation of an additional SAG mill, ball mill and corresponding flotation circuit with six additional cells.

Antofagasta said the cost included $500 million for a desalination plant and water pipeline, which would supply the expansion and any further growth, as well as benefit the existing operation in cases of prolonged or severe drought.

The company said a subsequent phase of expansion could follow to increase production further and add to the mine life by accessing Los Pelambres' undeveloped mineral resources, but this would be dependent on required environmental and regulatory approvals.

CEO Ivan Arriagada said the expansion would advance the company's organic growth pipeline and ensure it remained a first-quartile producer for many years more.

RBC's Tyler Broda said the approval had been expected.

He said while the project was not "particularly cheap", with $18-21 per tonne of copper capital intensity, the $500 million desalination plant impacted this and when spread evenly through the current 300,000t of production, the project's intensity would be around $13,000/t of annual copper, below the global pipeline average of $20,000-25,000/t.

"We would also expect, although no guidance has been given, for unit costs to move lower as well,"Broda said.

He said, with the Centinela expansion feasibility study expected soon, Antofagasta would move towards a phase of growth that would increase production from around 700,000-750,000tpa to around 825,000-875,000tpa.

"The potential for selling the Centinela water assets (and eventually monetising the Pelambres one) should help to reduce cash outflows. With our favourable long-term outlook on copper, growth, further scalability in the assets beyond this announcement and a safe jurisdiction, we see Antofagasta as attractive for long-term investors," Broda said.

RBC kept the company's rating at "outperform" and the target price at £8.80 (US$11.23) per sahare.  

Antofagasta's shares (LSE:ANTO) were up 2% Thursday to £7.77/share.