St Barbara’s mineral resource estimate for its 15-Mile Processing Hub has expanded by 20 percent, or 0.5 million ounces of gold, to 2.5 Moz. The upgrade represents the company’s second major resource increase at Atlantic Operations this year, following environmental permit approvals and the April restart decision for the Touquoy project. The growth stems not from new discoveries but from decades-old drilling data that St Barbara has now validated and incorporated into its geological models for the first time.
The technical driver behind the increase is significant. St Barbara’s team validated 436 historical drill holes totaling 71,000 metres of core samples collected during the 1980s at three deposits: 15-Mile Mine, Old Mitchell Mine, and Old Austen Mine. Atlantic Gold, the prior operator, had never formally included this infill drilling in its resource estimates. St Barbara undertook months of validation work, cross-checking digital records against originals, verifying sampling protocols, running umpire assays, and benchmarking against more recent drilling. The company concluded the data met quality standards for resource estimation.
This validation exercise enabled a methodological upgrade. Previously, St Barbara used Multiple Indicator Kriging to estimate resources given data limitations. The substantially expanded dataset from validated historical drilling now supports the application of Ordinary Kriging, a more precise statistical method that better captures the continuity and geometry of mineralization. For 15-Mile Mine specifically, the available drilling dataset grew from 725 holes spanning 95,000 metres to 844 holes spanning 112,000 metres. That density of spatial information translates into higher confidence in the block model and grade estimates underpinning the resource.
The operational implications unfold over the coming quarters. St Barbara expects an updated ore reserves estimate, the economically mineable portion of the resource, by the end of Q1 in the 2027 financial year. That revised reserve forms the basis for an updated prefeasibility study due around the same timeframe. Later, in Q4 of FY27, the company will incorporate the new resource estimate into a feasibility study for the 15-Mile Processing Hub. Until then, the company is evaluating new drill targets identified at 15-Mile for additional drilling in FY27, potentially opening further upside.
For investors, the upgrade underscores how St Barbara is systematically de-risking Atlantic Operations. A 20 percent increase in a core asset’s resource base, supported by rigorous validation of archived data, strengthens the project economics ahead of the formal feasibility assessment. St Barbara’s group mineral resources now stand at 5.4 Moz, with 2.9 Moz attributable to New Simberi, positioning the company for its largest resource inventory in years. The announcement is price sensitive and has been flagged as material information by the ASX.
View the full ASX announcement (PDF)
About St Barbara Limited (ASX: SBM)
St Barbara Limited is an Australian-based gold mining company with operations in Canada and Papua New Guinea. The company operates the Atlantic Operations in Nova Scotia, Canada, which includes the Touquoy mine, and the Simberi Operations in the province of New Ireland, Papua New Guinea. The company engages in the exploration, development, mining, and sale of gold, with additional interest in silver exploration.
If you would like to discuss this announcement or how it might affect your portfolio, request a callback or call us on 1300 889 603.
