According to the expansion pre-feasibility study, which was released this week, converting the lower portion of the sub-level cave at the South Australian site will significantly increase its value and mine life.

OZ Minerals chief executive Andrew Cole said the expansion would see Carrapateena’s expected throughput rate of 4.7–5 million tonnes a year from 2023 increased to 12 million tonnes a year.

The block cave conversion also has the potential to nearly double Carrapateena’s average annual production to 110,000–120,000 tonnes of copper and 110,000–120,000 ounces of gold from 2026.

“Transitioning from a sub-level cave to a block cave would allow us to extract the higher-grade ore at the top of the orebody via the sub-level cave, mining from the top down and then a higher-grade material from the bottom of the resource via the block cave mining from the bottom up and leaves the lower-grade central section until later in the mine life,” Cole said.

“The potential for the block cave to progressively unlock the province more broadly via a controlled and incremental approach is particularly attractive as it manages risk and capital expenditure while enhancing value upside for our stakeholders.

“We are in the enviable position of being able to apply the ongoing learnings from the sub-level cave operation and increased ore body knowledge to de-risk and optimise any potential block cave expansion.”

The first stage of the Carrapateena expansion FS is expected to be largely finished by late 2021, with less critical follow-up work to be completed at a later date.

It is expected to cost $7 million, with OZ Minerals planning to release its updated spend guidance in its second quarter production report, to be released next month.