Since announcing an upgrade of inferred gold estimated resource at Waihi in August, to a total 339,000oz, Oceana had recently completed another total 10km of test drilling.
The drilling was at multiple points along two underground drives along sections of the Martha, Royal, Empire, Dreadnought and Rex gold veins.
Oceana chief executive Mick Wilkes said the latest underground test drilling results "continue to increase our confidence" in the potential gold resource at Waihi and continued to identify areas of "high-grade mineralisation", which sit deeper and laterally to exploration targets.
"We’re confident of defining a sizeable resource that will further support the extension of the mine life at Waihi," Mr Wilkes said in a market update.
He has in the past estimated adding a decade to Waihi’s mine life.
Oceana is several months into the consenting process for the Martha underground project, which could potentially be operational by 2020.
As with some previous underground operations, some of the proposed tunnelling would be under the Waihi township.
While noting exploration targets were "conceptual in nature", Mr Wilkes estimated there was a potential volume of between 5million and 8million tonnes of ore within the target at a grade of between 4-6 grammes of gold per tonne of ore.
"Recent drilling has intersected significant gold mineralisation both deeper in the central Martha area and eastward towards the current mining fronts approximately 200 metres away on the Empire vein," he said.
Last week Oceana announced strong third quarter production and upgraded its expected calendar year production, to between 515,000oz and 545,000oz.
As with Waihi, recent encouraging drilling results at its mainstay Macraes mine in East Otago has prompted the company to consider starting a second underground operation there.
