Anti-mining groups are challenging the right of an Australian mining company to begin drilling on Puhipuhi mountain, north of Whangarei.
Evolution Mining announced this week it will begin exploring for gold and silver in the area after several months of geo-technical surveys.
Representatives of the tangata whenua Ngati Hau and the lobby group Minewatch Northland have called for a hikoi to the drill site tomorrow, in protest.
Spokesperson Dr Benjamin Pittman said the group did not accept Evolution's assurances of safety, if mining did eventually go ahead.
He said gold-mining created toxic waste, and the company should be told to leave.
Meanwhile, Evolution says the presence of mercury in local streams is no threat to health or the environment.
Evolution has paid for independent testing of waterways at Puhipuhi in response to local concerns about the heavy metal in creeks near an old mercury mine.
The company's chief geologist Roric Smith said mercury was present in stream sediment in some places but it was inert and will not dissolve into the water.
The mercury was also at very low levels, and at two parts per billion was well within acceptable limits, he said.
There was no way that Evolution's drilling exploration programme could release mercury into aquifers, as some local people feared, he said.
The mining company was setting up the drilling rig and platform for its first test bore on private farmland at Puhipuhi this weekend.