MARK COLVIN: Environmental authorities in Queensland are racing to prevent a disastrous heavy metals and cyanide spill.

It involves the fear that a series of ponds will overflow from a mining site into a river in the Murray-Darling Basin.

The company behind the silver mine at Texas on the Queensland-New South Wales border has gone broke.

The site and its four large storage ponds containing contaminated water are abandoned.

An internal Government document obtained by the ABC reveals that authorities fear that as little as 40 millimetres of rain could trigger a spill from the site and send contaminated water into the nearby Dumaresq River.

Locals have told the ABC that with the wet season approaching, the Government must act to stop a potential catastrophe.

Mark Willacy has this exclusive report from the site.

MARK WILLACY: It's drenching time on Ron Morris' sheep property near Texas. His place is eight kilometres downstream from the Texas silver mine, which until it went broke in July was employing dozens of locals.

Ron Morris was a supporter of the mine for the jobs and money it brought to the Texas district but now he worries what it could bring to the nearby Dumaresq River which is the lifeblood of this rural community.

RON MORRIS: Well it's very important because to all the irrigators, and not only the irrigators, the cattle people and the sheep people along the river, it's very, very important.

MARK WILLACY: The ABC has obtained an internal Queensland Government document which spells out how the abandoned silver mine poses a threat to the Dumaresq River.

It warns:

INTERNAL QUEENSLAND DOCUMENT (voiceover): A recent site inspection identified significant management issues associated with acid mine drainage and insufficient contaminated mine water storage capacity to cater for wet season inflows.

It is estimated that as little as 40 millimetres of rain my cause a discharge from site. Discharge water from the site would flow about seven kilometres through small drainage lines to the Dumaresq River.

MARK WILLACY: The Queensland Environment Department has confirmed to the ABC that water storage ponds on the mine site contain cyanide and elevated levels of heavy metals such as copper, iron, manganese, zinc and nickel.

For Texas farmer Ron Morris the threat posed by the abandoned silver mine is existential.

RON MORRIS: I think everybody is a bit worried about it, what happens to the mine? What happens up there now? What happens with all the ponds and everything they've left up there?

You know, who manages that? This is what we'd like to know. We get a big storm and it overflows into the Dumaresq River, there'd be a hell of a big mess.

MARK WILLACY: Just upstream from the mine is Tim Ramsay's cattle property. Today he's drafting steers for sale. But most of his business comes from the crops he grows thanks to irrigation from the river. The prospect of a spill from the mine is horrifying.

TIM RAMSAY: You know, if it was to affect the wildlife in the river, or the quality of the produce that we produce, or just the whole ecosystem in general, it would be, you know, catastrophic.

MARK WILLACY: The Queensland Government would like another company to take over the silver mine but so far there are no takers. The state has a $2 million bond from the previous owner but the internal Government document obtained by the ABC says the rehabilitation cost could be as high as $10 million dollars.

But as Texas landholder Ron Morris points out, a spill from the mine could have an even greater cost to the people who live and rely on the Dumaresq River.

RON MORRIS: The whole problem with it is, it flows into the Dumaresq but it doesn't stop there, it's going to flow into the Macintyre and all those big irrigators down around Gundiwindi, you know, it's just going to go on.

So it's not just going to stop here in Texas if those ponds overflow, I think it's a massive problem and, you know, and I'd like to see somebody put their hand up and say, "Well we're going to do something about it."

MARK COLVIN: Texas landholder Ron Morris.