The deal, struck on the final day before caretaker mode, gives the mining company hopeful an extended lease at a fraction of the usual price.
"This is another slap in the face to Territorians who have been calling for better rules and transparency on mining and fracking," said Naomi Hogan, of the NT Lock the Gate Alliance.
"It is unacceptable that Chief Minister Giles and Minister Tollner were negotiating this dodgy mining deal for 18 months, yet never once brought it to the attention of Territorians.
"Community members want more of a say about what mining and fracking activity happens in their region, yet this deal appears to take away consultation rights.
"This backroom deal goes against everything the Government has been trying to make us believe about their approach to mining. Instead of working through the issue with the community, the Government is doing secret deals to prop up mining companies.
"It is obviously inappropriate for Minister Tollner to sign off on this minerals lease on his last day of political relevance in the Territory.
"The next Government of the Northern Territory should empower themselves to reconsider all mining and fracking deals in the interests of all Territorians," she said.