Chief executive Matthew Hill has confirmed to RNZ the sale is going ahead but declined to comment further, other than to say a plan is to package the site up with other assets owned by the company and sell shares in it.
The deal is subject to approval by the regulator New Zealand Petroleum and Minerals.
The company said the mine has had consistent profitable production for 21 years, and Australian media report the deal is worth $750,000.
Coromandel Watchdog of Hauraki chairperson Catherine Delahunty said the existing mine has only been allowed to operate with a special permit and New Talisman was buying the mine as a "Trojan horse".
"It's pretty outrageous, so this is Schedule 4 DoC land which has supposedly got the highest level of protection, getting inside the heart of the most protected part of the DoC estate by buying up this licence with the hope that they will be able to explore further and mine in Schedule 4.
"The Puketui is a beautiful forest and river near Tairua which is very popular for walking, swimming and camping."
Delahunty said she expected the Department of Conservation to prevent any expansion of the mine's operations, "otherwise, what is the point of Schedule 4".
She said the group would protest any changes, and that Prime Minister Jacinda Ardern joined 30,000 other people marching against proposed mining in Schedule 4 land in 2010.
Department of Conservation permissions manager Judi Brennan said it has not received any application to change what was currently authorised at the site.
The permit allows the holder to use pre-existing roads and access tracks to reach the site, remove rock and old timber, install mine support such as wooden bracing and beams, use a small rail track for the removal of material using a non-powered barrow, erect a small hut near the entry to the mine, and enter existing holes in the ground to conduct prospecting.
The Ministry for Business, Innovation, and Employment said the special purposes mining permit allowed the demonstration of historical mining methods.
It said no application has been made to NZ Petroleum and Minerals for a transfer of interest or change of control in either of the Broken Hill permits.
New Talisman Gold Mines said the Broken Hills mine was the sole privately owned underground gold mine in New Zealand, and has been owned by the Rabone family for more than two decades.
Hill said Broken Hills was a significant asset.
The company said it has maintained high levels of environmental standards over the many years of operation, and it would continue to do so in compliance with permit conditions in the same manner as over the last 21 years of operation.
Mining at the site began at the end of the 1800s, ceasing in 1923. The current mine was redeveloped in 1991.
All ore mined has been processed at a Waihi plant.
