Blue Mountains Friends of the Earth are hosting an information night on the use of cyanide in gold mining at the Carrington Hotel in Katoomba from 6.30 pm tomorrow.

Cyanide is now being transported from Gladstone, where it is produced, to gold mines in Western NSW through the Blue Mountains and Lithgow, Bathurst districts.

"The Blue Mountains is the source of most of Sydney's water supply and a cyanide spill would have significant consequences," Ms Rhiannon said.

"In 2007 I asked the Minister for Climate Change, Environment and Water, about the amount of cyanide being transported by rail and the frequency of its transportation.

“The answer was, 'we don't know'.

"It seems either the NSW Government doesn't know, or the information is part of a secret deal with Orica, the maker of cyanide, and Pacific National, its rail carrier.

"It's estimated that more than 60,000 tonnes of cyanide a year are freighted down the East Coast from Gladstone where Orica makes it, across Sydney and over the Blue Mountains to gold mines in Western NSW.

"The government is currently considering whether to grant approval to expand the controversial Lake Cowal gold mine.

"This will almost double the size of the pit and extend mine's life from 13 to 20 years.

"This means, for just this one mine alone, at least an additional 6000 tonnes a year of cyanide will pass through the Blue Mountains for an extra seven years," Ms Rhiannon said.