A Canadian company hoping to drill for gold and silver in the Sperrin Mountains said it would welcome a public inquiry into the plan, which they claim would bring a 1,000-job boost to the economy.
Dalradian Gold wants to open a mine near Greencastle along with a plant which will use cyanide to remove the precious metals from locally mined ore.
However, the proposal has met with strong opposition from residents in Co Tyrone.
A record 10,000 objections have now been lodged and on Saturday a protester chained himself to an exploratory drill rig for seven hours at the site.
Cormac McAleer, chairman of the Save Our Sperrins protest group, said he believed his intervention was necessary to highlight community opposition.
"It shouldn't be happening. If the authorities aren't going to do anything, then we have to. I attached myself to the drill rig with chains and a padlock so that it would cause a halt to the activity," he said.
"I intend to continue the protest again, someone has to stand up to them."
But Dalradian said such incidents are preventing them from carrying out "completely lawful company business".
A spokesperson said: "This is the latest example in a series of escalating incidents which have included trespass, intimidation, harassment, criminal damage and verbal abuse directed at employees, contractors and Northern Ireland Environment Agency staff.
"Dalradian's activities are lawful and we operate under an Exploration Licence granted by the relevant authorities in line with the policies of the NI Executive. The company has been operating in Northern Ireland since 2010 and has assisted in the hiring and training of many local people in exploration drilling.
"Dalradian is proposing a safe project which will meet and exceed strict environmental regulations. Those who wish to raise issues about the project may do so through the planning process. Dalradian also supports calls for a public inquiry which would provide another opportunity for the public and planning experts to further scrutinise the proposals."
The latest protest came after Michelle O'Neill reiterated her party's opposition to the proposed mining.
"We are opposed to the use of cyanide in mining due to its environmental and health implications," she said.
"That is why Sinn Fein's former Infrastructure Minister Chris Hazzard MP made it clear that any planning application should be subject to an independent public inquiry before a final decision is taken. That remains our position."
Ms O'Neill, who met with company officials last Friday, said Sinn Fein will also be submitting co-ordinated motions to four local councils opposing the Dalradian plan.
A spokesperson for Dalradian said: "The project will create 1,000 direct, indirect and induced jobs, and support a $1bn spend on the project's supply chain over its 20-25 year lifespan."
The spokesperson added that the "once-in-a-generation opportunity" would use processes akin to those at Tara mine in Navan, Co Meath.