- 01Staged $75m Halls Creek plan shares Onedin plant.
- 02Targets copper, zinc and silver over ~11 years.
- 03Pre-tax NPV $317m; IRR 47%; LOM cash flow $681m.
An updated scoping study by Cobalt Blue Holdings (ASX: COB) for its Halls Creek base metals project in Western Australia has outlined an integrated development strategy with material from the Onedin and Sandiego deposits treated through a common processing plant to recover copper, zinc, and silver.
The update—which supercedes the original study released in mid-2025—assesses a $75 million staged development using a processing plant at Onedin, with initial cash flow assumed to fund the subsequent development of Sandiego.
Incorporating silver recovery from both deposits for the first time, the study delivers a pre-tax net present value of approximately $317m and a 47% pre-tax internal rate of return on a 100% project basis to generate $681m in life-of-mine free cash flow.
Silver recovery is expected to establish a significant third revenue stream from metal already contained within both deposits.
Cobalt Blue currently has a 51% stake in Halls Creek under a joint venture agreement with AuKing Mining (ASX: AKN) subsidiary Koongie Park, and has exercised an option to increase its interest to 75% by incurring an additional $1.5m in exploration expenditure before June 2028.
Open-Cut and Underground Mining
The updated scoping study outlines a staged development of Onedin and Sandiego, comprising an initial 12-month construction period followed by approximately 11 years of production.
Underpinned by existing mineral resource estimates, the development will progressively unlock the value of both deposits through shared infrastructure and a common processing pathway.
The operation will comprise an open-cut mine at Onedin followed by underground mining at Sandiego, with Sandiego feed trucked via the Great Northern Highway to Onedin, where ore from each deposit will be stacked on a separate heap leach pad at a rate of approximately 55,000 tonnes per month.
Pregnant leach solution from both heaps will be treated at a common processing plant based at the Onedin site designed to sequentially recover silver, copper cathode, and zinc oxide, with solution recycled to the respective heaps following metal recovery.
The combined Onedin and Sandiego operations have been estimated to produce an average of 4,000 tonnes per annum of copper as cathode, 13,000tpa of contained zinc as zinc oxide, and 130,000 ounces per annum of contained silver.
Capital-Efficient Pathway
Cobalt Blue chief executive officer Dr Andrew Tong said the new development scenario was a significant progression for Halls Creek.
“This update brings silver into the picture from Onedin and Sandiego alongside copper and zinc with a single processing plant and a staged development, which makes for a simpler, more capital-efficient pathway to three saleable metals, with a lower external funding requirement,” he said.
“Using a common processing plant also provides a platform for district-scale growth, and we will assess opportunities to identify additional feedstock across the broader Halls Creek district with the potential to increase production scale, extend mine life and further improve project economics.”
Dr Tong said the refreshed approach would employ the intellectual property and capabilities of Cobalt Blue’s Broken Hill Technology Centre in New South Wales to optimise the project and its commodities.
Preliminary Feasibility Study
Cobalt Blue has turned its focus to advancing the proposed Halls Creek integrated development scenario through a preliminary feasibility study targeted for completion by mid-2028.
Workstreams will include metallurgical validation and variability testing of Sandiego heap leach performance, silver recovery and zinc oxide product quality, as well as heap leach design and supporting geotechnical, geochemical and hydrogeological investigations.
Other work will feature refinement of mine designs, production schedules, and common process plant engineering, environmental baseline studies, heritage assessments, Native Title engagement, and progression of approvals pathways, along with product marketing, refinement of capital and operating cost estimates, and assessment of funding options.
The company also plans to advance broader exploration initiatives targeting additional mineral resources amenable to treatment through the Onedin plant, promoting an extended operating life, increasing utilisation of shared infrastructure, and improving capital efficiencies.
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