Questions are being asked about whether mining giant Adani's proposed rail link in north Queensland is eligible for public financing, after a company spokesman admitted federal government support is not critical.

Adani has applied for a $1 billion loan under the Northern Australia Infrastructure Facility (NAIF) to finance the rail line, which will transport coal from its Carmichael mine site to a coal-loading facility at Abbot Point, near Bowen.

To be eligible for financial support, Adani must demonstrate the assistance would be "necessary to enable the project to proceed, or to proceed much earlier than it would otherwise".

But Adani spokesman Ron Watson told Fairfax Media this morning the subsidy was not critical for the company to proceed with the rail line.

"This is something that governments of all political persuasions have done in the past and I assume will do in the future, it doesn't necessarily mean it's make or break for the project," Mr Watson said.

It prompted researcher Tom Swann from the left-leaning think tank The Australia Institute to suggest Adani was putting out "mixed messages".

"[To say that] it's not critical suggests they're just putting their hand out to see whether they can get anything," Mr Swann said.

"If it's not critical, why would the taxpayer fund it in the first place?"

Federal Minister for Resources and Northern Australia Matt Canavan told 612 ABC Brisbane NAIF was assessing the rail project's eligibility for a loan.

"They'll look more closely over the next few months at the figures from Adani and make a decision about whether they would propose financing and then, only then, the Government has to make a decision," Senator Canavan said.

A spokeswoman for Senator Canavan added that NAIF deliberations were a matter for the facility's independent board.

Today, Premier Annastacia Palaszczuk said she had received an "ironclad" guarantee workers for the mega coal mine would be sourced from regional Queensland.

She made the announcement in Townsville as Adani confirmed its regional headquarters would be in the northern city.