An Australian mining firm has struck a gold deposit inland from Dunedin that it believes could be worth billions of dollars.New Age Exploration said the discovery near Lake Mahinerangi was years away from progressing into a mine proposal, but if that were to happen, the company would likely look to the fast-track process to build an underground mine.The company announced its early-stage findings to the Australian Securities Exchange this week.Chief executive Kirby Johnson said shear-hosted gold mineralisation was identified during drilling at the company's Bella prospect, within the wider Lammerlaw Gold-Antimony Project, where it holds an exploration permit.While the company was "only a few drill holes in", he said initial indications were that the deposit could extend more than five kilometres laterally."If you find a million ounces of gold at US$4000 an ounce, these days gold has become incredibly valuable," he said. "Then that can easily translate into $4 billion and so that's definitely our target."The deposit bore similarities to the Macraes deposit in Waitaki, where OceanaGold operated the country's largest gold mine, Johnson said."There's a heck of a lot of work to go yet, before we know genuinely if it could be that big, but that's definitely our aspiration," he said.Asked about the potential environmental impacts of a mining proposal, Johnson said New Zealand's world-class environmental management legislation was a major drawcard for the company.He said the site was agricultural land."There are no wineries," he said. "There is no tourism that I'm aware of, and I feel that agriculture and mining can co-exist."Johnson said the company's strong preference would be for an underground mine."We think that, fundamentally, that's a better way to go, rather than open-cut. An underground mine has a much smaller footprint on the surface and probably more suited to this environment."A New Zealand workforce would also be central to any future proposal, he said."Mining jobs are good jobs, high-paid jobs and profits, tax, they all stay in New Zealand," he said.Nearby, in Central Otago's Dunstan Range, Santana Minerals' application to construct an open-cut gold mine has attracted criticism from opponents, who argue it is too complex and risky for the Fast-track process.Johnson said New Age Exploration viewed the fast-track process as a way to sort through issues quickly, rather than bypass or sidestep them."We really like the fast-track process and we give credit to the New Zealand government," he said. "We're very supportive."It's actually a key attraction for us to be working in New Zealand."Exploration was a risky business and the true likelihood of a mine going ahead was unknown."We think we've got excellent geology here and it's extremely encouraging for us to go forward, but we have to do a lot more drilling to really know," he said."We're still several years away from even thinking about applying for a mining permit."