The Queensland government’s resources investment commissioner has said Adani will have to “go back to the drawing board” to satisfy outstanding environmental conditions, and that the approval process could take up to two years.

Caoilin Chestnutt, a former coal executive with Anglo-American whose job is to encourage resources investment in Queensland, reportedly made the comments after speaking at the Coaltrans conference in New Dehli on Wednesday.

Queensland government officials have been increasingly cautious when speaking publicly about the Adani Carmichael mine, and none has previously put a timeframe on the approval process.

Late on Thursday, the Department of Natural Resources, Mines and Energy released a brief statement distancing the government from Chestnutt’s comments, which it said were not sanctioned.

“She is not authorised to speak about any specific environmental approvals as the Department of Environment and Science is the appropriate organisation,” a spokesman said.

Guardian Australia understands Chestnutt gave a presentation about resources opportunities, including in the Galilee Basin, and did not field questions on stage. Afterwards she spoke with a Reuters reporter, Sudarshan Varadhan, who asked about the outstanding approvals for the Carmichael mine.

“I would guess, but it is an absolute mess, [it will take] six months to two years,” Chestnutt said.

“They [Department of Environment and Science] have said [Adani] have to go back to the drawing board and draft a management plan.”

Adani has to gain approval for two management plans in order to satisfy the environmental conditions attached to its mining approval. It requires Queensland government approval for a management plan for the endangered black-throated finch. The company said on Wednesday it would simply reject the findings of an independent report, commissioned by the Queensland government, that has not yet been released.

Adani also requires federal and state approval for a groundwater dependent ecosystems management plan, to protect local water resources. The CSIRO and Geosciences Australia are reviewing the company’s draft groundwater plan, which is understood to require significant revisions.

Queensland ministers and government officials make only carefully-worded statements about Adani, as the company ramps up attacks on scientists, government officials, community groups and others. Those attacks have included a prominent advertising campaign, and threats of legal action against environmentalists.

The Guardian understands there is a growing concern within the Queensland government that Adani could also pursue the state in court if approvals become problematic, or are further delayed. A legal strategy document, leaked to the ABC this week, and prepared by a firm that Adani later hired to conduct commercial litigation, suggested using the legal system to pressure decision-makers.

There is no statutory timeframe for the government to assess Adani’s plans.

Chestnutt also told Reuters protests against the mine were a “hindrance” and that there had been a lot of “misinformation” about the mine that should be challenged.

“I think people just think that coal is dirty and global warming is a major issue, and people just like to blame the coal business for that, CO2 for that.”

A spokesman for Adani told Reuters it expected approvals to be granted more quickly.

“We have provided all required information, data and feedback needed for this process to be completed and accordingly we expect to have these plans approved in the very near term,” a spokesman said.