Environmentalists including the Bob Brown Foundation oppose Venture Minerals Limited's Riley iron ore mine in the Tarkine.

The Bob Brown Foundation on Thursday morning said activists locked themselves to machinery and a gate to stop site works and "prevent further destruction".

"Riley Creek is in an area of known Tasmanian devil and spotted tail quoll habitat, in a region that has been independently verified as having both national heritage and world heritage values", Bob Brown Foundation takayna/Tarkine campaigner Scott Jordan said.

"With question marks over the validity of Venture's permits, the federal and state environment ministers should be here to stop this mine and defend the heritage values of takayna.

"As they are not, we have gathered in a peaceful vigil with members of the public who will."

"Venture's investors should understand that public opposition to their planned ecological vandalism will not go away."

Venture, which recently decided to proceed to mining at Riley, maintains it is compliant with all its regulatory obligations.