Anti-mining groups are on alert in Northland as an exploration company prepares to start test-drilling north of Whangarei.
De Grey Mining, an Australian company, has high hopes of finding gold and silver in the Puhipuhi Hills.
Rev Thelma Connor of Ngati Hau is keeping watch for the company's arrival, saying tangata whenua, farmers and other supporters intend to show the company it's not wanted.
She says there are high mercury levels in the area and mining could poison farmland by releasing the element into waterways.
But De Grey Mining says there is no way the drilling programme could release mercury and if a mine were to be built it would be underground, not open-cast.
Whangarei MP Phil Heatley says a gold mine at Puhipuhi, north of the city, could be the key to unlocking the mineral wealth of Northland.
Mr Heatley said he understands people's fears, but modern mining companies operate under strict environmental conditions.
He said the potential economic benefits for Northland are immense.