PERTH (miningweekly.com) – A scoping study by ASX-listed Oz Minerals has shown that converting the lower portion of the planned Carrapateena sub-level cave to a block cave, could deliver significant value for the company.

Oz on Wednesday told shareholders that by converting to a block cave from 2026, the company could more than double the mine throughput rate at Carrapateena from 4.25-million tonnes to between 10-million and 12-million tonnes a year, while also increasing the life-of-mine average copper production to between 105 000 t/y and 125 000 t/y from 2026.

This was up from the planned 65 000 t/y copper production currently planned over the project’s 20-year mine life.

“The Carrapateena block cave expansion work showed the conversion to a block cave to be the most value accretive next step for the Carrapateena resource and conceptually for the entire province, as it potentially enables a series of future add-on block caves, which themselves will now be subject of a Carrapateena life of province plan scoping study,” said Oz Minerals CEO Andrew Cole.

He noted that the block cave expansion could occur without impeding the existing sub-level cave delivery, ramp-up or ongoing operation, which is on track for first production by the fourth quarter of this year.

“The Carrapateena block cave expansion scoping study provides a high-level view of how a block cave could be constructed without impeding operation of the Carrapateena sub-level cave currently in construction, or without rework of current construction plans, as underground infrastructure being installed for the sub-level cave contemplates a potential increase in the 4.25-million-tonne-a-year rate,” said Cole.

The scoping study estimated that the block cave expansion would require a pre-production capital spend of between A$1-billion and A$1.3-billion, in addition to the A$916-million cost of the current Carrapateena development.

However, Cole noted that transitioning from a sub-level cave to a block cave expansion would allow Oz to extract higher-grade ore at the top of the orebody, and higher grade material from the bottom of the resource, prioritizing this over the lower-grade central section.

“The potential for the Carrapateena block cave expansion to progressively unlock the Carrapateena life of province more broadly via a controlled, methodical and incremental approach is particularly attractive as it manages risk and capital expenditure while enhancing value for shareholders and other stakeholders.”

A prefeasibility study (PFS) on the block cave expansion has been launched and will be completed by mid-2020.

“The majority of Carrapateena block cave expansion PFS activity will be desktop studies and technical activity,” Cole said.