The deputy prime minister, Barnaby Joyce, has declared the Adani mine needs to proceed, and he’s endorsed giving the project a concessional loan in order to “get the thing built and get the money flowing”.

Joyce used Wednesday’s worse-than-expected GDP figures to urge Queenslanders to “show the same spunk you had when you developed the coalfields in the past, built international airports at Cairns, built the Wivenhoe dam, sealed the roads out west, built the Gold Coast”.

His enthusiastic backing for the contentious project contrasted with more obvious caution expressed by the treasurer, Scott Morrison, on Wednesday.

Morrison told reporters in Canberra he did not intend to join commentary about whether the project should win support from the government’s Northern Australia Infrastructure Fund.

He said the independent advisory board of the fund needed to be left alone to do its job. “I agree that it was set up to make independent assessments about the proposals.

“They are the people to make those calls and I don’t intend to join in in any commentary about what they should or shouldn’t do, that would compromise the fundamental purpose of those people who have to make those assessments,” the treasurer said.

During the federal election, the government’s position on the Adani project was that it should proceed, or not, on a commercial basis.

But since the election, senior Nationals have pushed to have the project allocated $1bn from the Northern Australia Infrastructure Fund to bankroll a 388km railway line associated with the Carmichael mine.

On Monday, the prime minister, Malcolm Turnbull, met the Adani Group chairman, Gautam Adani, in Melbourne to discuss the project.

Joyce used a speech in Brisbane on Wednesday to sing the praises of the controversial project, declaring Queensland needed to return to its pioneering spirit.

The deputy prime minister seized on news that Australia’s economy slipped backwards in the September quarter by a greater than expected 0.5%, to argue Australia needed development.

“When I hear people standing up against the development of central Queensland coalfields, the Adani mine, where is your alternate source of income going to come from?” Joyce said.

“We have had in this quarter negative growth. People say that’s terrible. Let’s talk about the solution. If you don’t want that wealth, where is your alternate form of wealth going to come from? How are you going to do it?

“Will it become manifest on a tree in the botanic gardens? It won’t.

“You have to show the same spunk you had when you developed the coalfields in the past, built international airports at Cairns, built the Wivenhoe dam, sealed the roads out west, built the Gold Coast.

“That’s the spunk Queenslanders have to show again and they’ve got to have that drive and that vision and that enthusiasm to take the next step.”