An appeal against the approval of an iron ore mine in Tasmania's north-west has heard increased traffic would not necessarily affect Tasmanian devils in the area.

Conservation group the Tarkine National Coalition is opposing Venture Minerals Riley Creek mine on the grounds its environmental impact was not properly assessed.

The coalition has taken its case to the Resource Management and Planning Appeals Tribunal in the hope it will overturn approvals given by the Environment Protection Authority.

The Riley iron ore mine is close to two other mining leases.

Group spokesman Scott Jordan says the EPA did not properly assess the full impact of the mines.

"What it actually did was only assess the Riley Creek impact and we're arguing that they breach their own project assessment guidelines in this project and the whole thing should be sent back."

The tribunal has heard evidence focused on the impact of the proposed iron ore mine on Tasmanian devils.

Biologist Nick Mooney told the heairng the facial tumour disease may already be in that area, which he described as having a low to very low devil population.

He said the population could withstand a 10 per cent increase in their natural mortality rate.

He believed the travelling speed of cars between dawn and dusk, and not the level of traffic, would have the most impact devil numbers.

The coalition, also known as Save the Tarkine, won an appeal against the approval of Shree Minerals' iron ore mine earlier this month.

The Federal Court ruled the company had not properly considered the impact on the endangered Tasmanian devil.

The Riley mine is the smaller of Venture's two proposals.

It has a life span of two years and will employ 60 people.

The company wants to spend $200 million developing a much larger tin and tungsten mine at nearby Mount Lindsay.

The hearing continues.