(Sharecast News) - Greatland Resources reported a substantial increase in its group mineral resource base on Monday, driven by significant drilling at its Telfer operation, while also outlining a maiden estimate for the O'Callaghans tungsten project, highlighting the scale of its broader asset portfolio.

In its December group mineral resource update, the AIM-traded company said total resources across Telfer and Havieron rose to 14.9 million ounces of gold and 645,000 tonnes of copper.

The Telfer resource alone increased by 150% to 8.0 million ounces, including a 163% rise in higher-confidence Measured and Indicated resources to 3.8 million ounces, following extensive drilling of around 134,000 metres during 2025.

Greatland said the expansion was achieved at a discovery cost of around $5 per ounce and included a maiden high-grade underground resource at West Dome of 0.6 million ounces.

The West Dome open pit resource increased by 2.8 million ounces to 4.9 million ounces, while the Main Dome underground resource grew by 1.5 million ounces to 2.2 million ounces.

The firm said the increase in higher-confidence resources will support an updated ore reserve estimate targeted for the June quarter, with further drilling planned across the remainder of the financial year and into 2027 to drive additional growth and resource upgrades.

In a separate update, Greatland also published a maiden mineral resource estimate for the O'Callaghans deposit, defining a 70 million tonne polymetallic resource grading 0.35% tungsten trioxide, alongside copper, zinc and lead credits.

The estimate equated to 246,000 tonnes of tungsten trioxide, 207,000 tonnes of copper, 371,000 tonnes of zinc and 182,000 tonnes of lead.

It described O'Callaghans as "one of the largest high-grade tungsten deposits globally," noting its strategic importance amid tightening supply conditions and rising prices for the metal.

Located around 10 kilometres from Telfer, the project was expected to benefit from potential infrastructure synergies.

"O'Callaghans is a globally significant tungsten and base metals deposit that presents latent value and optionality within Greatland's portfolio," said managing director Shaun Day, adding that the high proportion of Indicated resources provides a strong foundation for future development studies.

Greatland said it would continue to prioritise development of its core Telfer and Havieron assets, while assessing options to advance O'Callaghans and unlock further value from the project.

At 1046 BST, shares in Greatland Resources were up 8.47% at 554.3p.

Reporting by Josh White for Sharecast.com.

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