Higher silver and zinc prices have led Horizon Minerals to dust off the mothballed Nimbus project that sits adjacent to its flagship Boorara gold operation, some 17km from the historic gold mining town of Kalgoorlie in Western Australia’s Eastern Goldfields region.
The company has set a big exploration target to chase in a drilling campaign planned for next year as it looks to ramp up its resources for an upcoming feasibility study. Horizon says the project already has a resource of 12.1 million tonnes grading 52 grams per tonne silver for 20.24 million ounces and 0.9 per cent zinc for 106,000 tonnes of contained metal.
A defined higher-grade resource comprises 260,000 tonnes at a stellar 774g/t silver for 6.4 million ounces and an equally impressive 12.8 per cent zinc for 33,000 tonnes.
Management believes that with the price of silver back above US$30 (AU$44) per ounce and zinc trading at US$2934 (AU$4320) per tonne, the time is right to revisit the economics of the project. Nimbus has been held by Horizon since 2011, with a plan to home in on higher-grade mineralisation encountered below the historic Discovery open pit.
A 2022 review commissioned by the company involved the appointment of renowned mining specialists Australian Mining Consultants (AMC) and Sedgmen in a move designed to assess all historical data, metallurgical test results and mine optimisation planning to determine the best path forward to mine the ore. The review concluded that the best plan is to mine high-grade lodes in the fresh material below the pit and generate a silver-zinc concentrate.
Some remnant, near-surface material will still be mined by an open-pit cutback.
Depending on cash flows from its gold operations, Horizon plans to begin a drill campaign in the first half of next year, with the benefit of a program of works (POW) already approved.
An ambitious exploration target has been set by the company in a bid to bolster its level of resources at the site, with the intention of having its own concentrator to maximise efficiency and provide the material to potential future offtakers.
Horizon Resources managing director and chief executive officer Grant Haywood said: “We see the potential to grow the higher-grade core within the Nimbus resource at depth down-plunge and along strike. Whilst we are firmly focussed on delivering on gold production at Boorara and Phillips Find, the Company will continue working to develop a longer-term production profile at Nimbus.”
Management notes that Nimbus features several advantages, with the project sitting across two granted mining leases some 2km east of the Boorara operation and offers easy access to the site via sealed and unsealed roads.
The project has an interesting history that includes previous production of 318,000 tonnes at a noteworthy 353g/t silver for 3.6 million ounces. It was classified as a contaminated site in 2006 and eventually placed on care and maintenance the following year.
After the 2011 acquisition from MacPhersons (which merged with Intermin Resources to form Horizon), the company initially spent funds to upgrade plant infrastructure. However, it was placed on the back-burner in 2019 at the time of the merger.
Horizon began clean-up works shortly afterwards, with completion in 2022 amid plans to have the site re-classified. It now plans to submit all necessary paperwork to the Department of Water and Environmental Regulation (DWER) for the purposes of reclassification.
The site still has a mine office and some infrastructure operating on grid-power.
In 2015, CSA Global was engaged to model and estimate the mineral resource. Interestingly, it says the deposit is made up of four distinctive styles of mineralisation – high-grade combined silver-zinc lodes, separate silver and zinc lodes, and gold lodes.
The estimated mineral resource contains an additional 0.2g/t gold.
With an exploration target of between 550,000 tonnes and 700,000 tonnes and grades ranging from 3.4 per cent to 3.6 per cent zinc, 140g/t to 210g/t silver – accompanied by a modest 0.45 per cent to 0.65 per cent lead – Horizon will be hoping the drill bit unearths results that at a minimum, equal those numbers and propel the project to the forefront while it continues to focus also on its Boorara gold operation.
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By Craig Nolan
