OZ Minerals has reported positive results from a prefeasibility study (PFS) of developing block cave mining operations in the lower half of the orebody at its Carrapateena copper-gold mine in South Australia. Based on the PFS results, the company has initiated a feasibility study of block cave development.

Carrapateena is located 160 kilometers (km) north of Port Augusta, South Australia. The upper half of the orebody is currently being mined by sublevel caving methods. The mine produced its first copper-gold concentrate in December 2019. The operation is now ramping up to an expected 4.25-million-metric-ton-per-year (mt/y) run rate by the end of 2020 and targeted rates of 4.7 million to 5 million mt/y from 2023.

The block cave PFS considers increasing plant throughput to 12 million mt/y from 2029 at a lower operational cost and cut-off grade than the sublevel cave. The block cave would also bring forward the ability to mine higher-grade ore at the bottom of the orebody. This ore would have been otherwise mined closer to the end of the mine life, using the sublevel cave mining method.

In conjunction with its release of the PFS results, OZ also reported the results of a Carrapateena “Life of Province Scoping Study,” which considers the future potential of resource extensions, satellite deposits, and exploration targets in the Carrapateena district.

Capital investment for block cave development of about A$1.2 billion to A$1.3 billion is weighted toward 2025 to 2027.

OZ Minerals CEO Andrew Cole said, “The prefeasibility study analyzed the whole Carrapateena Province and determined that replacing the lower half of the current sublevel cave with a block cave and expanding the expected annual throughput rate from the 4.7 million mt/y to 5 million mt/y currently planned from 2023 to 12 million mt/y has the potential to create significantly more value than the sublevel cave alone. The block cave would leverage existing underground infrastructure, supported by expanded surface processing capability.

“The study work showed the conversion to a block cave creates significant additional value from the Carrapateena resource and the province more broadly as it potentially enables a series of future add-on block caves, which have been considered in the Life of Province Scoping Study.

“A block cave conversion in the lower portion of the Carrapateena resource has the potential to almost double average production to approximately 110,000 mt/y to 120,000 mt/y of copper and 110,000 oz/y to 120,000 oz/y of gold from 2026, with life-of-mine all-in sustaining costs of approximately US$0.75 to 0.85/lb of copper.

“An incremental, three-phased approach to capital investment in the project provides optionality at various stages, including a decision on whether to proceed to stage one decline development in 2022 and then, at a later date, a decision as to whether to proceed with the block cave itself. How best to expand the process plant can be considered later, again based on available technology and the plant capacity at the time.

“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.