Anxiety is mounting in Northland over plans by an Australian mining company to prospect for silver and gold north of Whangarei.
De Grey Mining plans to begin test drilling next month in the Puhipuhi hills, near Whakapara.
The area is known geologically for its high mercury levels and was once the site of New Zealand's only mercury mine.
People there say they're worried that mining will release mercury into the waterways and aquifers.
Hikurangi farmer Ben Smith said mercury contamination from mining could put land and livelihoods at risk.
But De Grey Mining says its test drilling sites are well away from the old mercury mine and pose no risk.
Exploration manager Glenn Martin said if a gold and silver mine is developed at Puhipuhi, it's likely to be an underground one, not an open-cast pit.