The Deputy Prime Minister is cheering over the possibility the controversial Shenhua coal mine may not go ahead.

Doubts have been cast over the future of the project, near the NSW regional town of Gunnedah, after the Chinese operator indicated plunging demand for coal this year due to low prices and market oversupply.

Mr Joyce, who faces a tough political campaign for his seat over the issue, said he had been aware of the project’s uncertain future “in the background” for a while.

“You don’t have to be Pythagoras to work that one out, because the prices are way below the cost of production,” he told AAP in Scone on Tuesday.

“It’s something that advances the process of stopping the mine, which I’ve always wanted to do.”

The agriculture minister faced several questions over the proposed mine from locals angry about the project’s potential impact on groundwater as he campaigned in his seat of New England on Tuesday.

There is also fresh pressure over the issue from political rival, former independent MP Tony Windsor, who’s running for his old seat.

Mr Joyce was happy Mr Windsor could be denied that attack line.

“One of the big issues of the election is probably dead.”

The Greens candidate for New England, Mercurius Goldstein, said it proved Mr Joyce had been ineffective in his attempts to stop the mine.

“The mine is completely out of his hands and, in the end, it’s proven the decision will be made by bankers and not a democratically elected minister,” he told AAP.

In an interview with local ABC on Wednesday, Mr Joyce followed up on his remarks, saying it appeared economics would beat Shenhua. 

“There’s reports coming from China that the economics of it do not stack up,” he said the local broadcaster.

“I will use any ally I can to bring about the outcome I have been fighting for, which is based on the principle that we shouldn’t have mines on prime agricultural land.

“If, in this instance, economics is the ally, then we will use economics as the point that I’ve been bringing forward a number of times already, saying that with the price of coal at its current level, it’s impossible to make these things stack up.

“It will cost hundreds and hundreds of millions of dollars to build a mine; you don’t build them for free.”

Mr Joyce said that negotiation “happens away from me, between the state government and the proponents”.

“The last discussion at the highest levels about this was nearly a week ago in Macquarie St in Sydney,” he said.

And in Quirindi during another opening stopover, Mr Joyce expanded on it, telling The Leader: “I’m an accountant – if they were going to go forward with that kind of expansion, I can find you a whole range of mines for a lot cheaper somewhere else.”