Rio Tinto Alcan will be investigated by the Northern Territory Government over an industrial spill on one of its alumina mine and refinery on east Arnhem Land coast.

An anonymous source disclosed to ABC that Rio Tinto Alcan executives authorized its workers to dump at least 88 tonnes of alumina into Grove Harbour this month.

The source added that a ship loader was seen working at night on April 12, carrying at least 88 tonnes of material, and instructed its workers to dump the said contents into the harbour.

The workers, who disobeyed the command, were forced by their superiors to dump the materials into the water.

Representative of Rio Tinto Alcan is yet to respond over the allegations on its illegal activities.

Meanwhile, the Department of Resources was disappointed because it was not informed when the incident took place.

Rio Tinto Alcan said it will conduct an insider investigation on the matter.

"Rio Tinto Alcan is conducting an investigation into the reports that as yet undetermined quantity of alumina was spilled into the harbor at the Gove refinery last week," Rio Tinto Alcan said.

Rio Tinto believes that the incident happened following a breakdown of the ship loading conveyor.

Alumina, as described by the company, is an inert material to produce aluminum and does not cause any negative effects to animals or plants.

The Dhimurru Aboriginal Corporation in Nhulunbuy stated that the company was not informed over the spill into Gove Harbor. Dhimurru currently runs a Sea Ranger program near Arhnem Land.

On the other hand, authorities of the Environment Department will closely monitor any loading operations of the company.

An air quality test will be conducted during the mineral transfer.

Rio Tinto Alcan is an aluminum subsidy of Rio Tinto.