A Ngati Hau group has sent another invitation to Prime Minister John Key and senior Cabinet members asking them to listen to local concerns about proposed mining at Puhipuhi.

Ngati Hau Trust Board's resource management unit is ramping up its efforts to have the Government acknowledge the potential dangers of having the area's high mercury deposits disturbed.

The resource management unit made its latest invitation by open letter, saying it is unsure whether previous invitations were received as they were never replied to.

In August, the trust invited Mr Key and Economic Minister Stephen Joyce, along with opposition and local politicians, and other interested parties, to a hui at Whakapara Marae to discuss economic development alternatives to mining.


Government representatives were absent at what trust member Allan Halliday said was "a useful discussion of economic development alternatives to mining for the area".

The trust's open letter sent to the Government and media on Tuesday included findings from the Waiariki Stream Baseline Survey in June 2012, by Bioresearches Group, showing the majority of metals in stream sediments were below quality guidelines with the exception of antimony and mercury.

That mercury concentration, at 1.94 mg/kg dry weight, was almost twice the ANZECC (Australian and New Zealand Guidelines for Fresh and Marine Water Quality) high limit of 1.0 mg/kg dry weight.

"This result indicates that adverse effects on sediment biota due to the presence of mercury are likely to occur frequently," Mr Halliday said.

"We believe it would be reasonable to assume that any additional disturbance, whatever the scale, will increase the risk and magnitude of that risk. Even exploratory drilling will inevitably cause some disturbance within that area."

Ngati Hau's letter stressed a strategic plan to bring jobs and incomes to the district.

Possibilities Ngati Hau have put forward include eel farming, a dam to store Hikurangi catchment floods, and a small power station.

"We would like you, Prime Minister, and senior Minister Hon Steven Joyce, to visit us so we can talk about our concerns [and] put forward our alternative solutions for future jobs in Northland.

"We are making this invitation in the form of an open letter as we are not sure that your office registered the nature of our most recent invitation to you to discuss this matter."