An assurance has been given that no cyanide will be used in the proposed mining of gold in Co Tyrone.
Mining company Dalradian has applied to extract gold in the Sperrin Mountains.
It has been working on the Curraghinalt site near Greencastle since 2009 and has applied to develop an underground gold mine.
The Planning Appeals Commission and Water Appeals Commission inquiry into the controversial gold mine planning application is being held at Strule Arts Centre in Omagh (Liam McBurney/PA)
There has been opposition to the proposal, which involves an Area of Outstanding Natural Beauty, in terms of its impact on health and the environment.
However, some local people are in favour of the investment and creation of jobs in the area.
Dalradian has said the project could bring 1,000 jobs and deliver £5 billion to the economy in Northern Ireland.
The application is being examined by Planning Appeals Commission and Water Appeals Commission at the inquiry, which opened at the Strule Arts Centre in Omagh on Monday.
In an earlier plan, Dalradian had proposed using cyanide in the mining process but said that had been removed in 2019.
Senior commissioner Jacqueline McParland opened the proceedings (Liam McBurney/PA)
This was questioned during Monday’s hearing, with those against the proposed mine expressing concern that cyanide could be reintroduced to the proposed process and seeking an explanation of how it was removed.
A representative for Dalradian said it had been removed from the plans for the Co Tyrone mine, adding: “There is absolutely no intention of using cyanide.”
Earlier, senior commissioner Jacqueline McParland, from the Planning Appeals and Water Appeals Commissions, opened proceedings, accompanied by two other commissioners.
She said they have been tasked with considering the representations received in respect of the eight applications made for the gold mine and will prepare a report for the referring authority which it must take into account before reaching its final decision.
Stormont ministers will take the final decision on whether to allow the gold mining applications.
Protesters gathered outside the Strule Arts Centre in Omagh ahead of the public inquiry (Rebecca Black/PA)
The inquiries will continue until the end of March, covering strategic matters and the principle of development, as well as hearing evidence around air quality, noise, vibration and water, among other topics.
Activists from the Save Our Sperrins group, which is opposed to the mine, staged a colourful protest with dancing and singing outside the building before proceedings got under way.
Some of the members also held small black coffins with “RIP clean air” and “RIP clean water” written on them, while another was dressed as the Grim Reaper.