By Robb M. Stewart

MELBOURNE--An Australian lawyer working for a mining company in Mongolia has been stopped from leaving the country as authorities probe a case of alleged corruption, her employer, Rio Tinto PLC (RIO) controlled SouthGobi Resources Ltd. (SGQ.T) said Wednesday.

Neither Sarah Armstrong or SouthGobi has been charged and the company continues to cooperate with an ongoing investigation by Mongolia's Independent Authority Against Corruption, SouthGobi spokesman Dave Bartel said in an emailed reply to questions.

The IAAC has been questioning Ms. Armstrong, who was prevented from departing the capital Ulan Bator for Hong Kong but remains free to travel within Mongolia, Mr. Bartel said. He said she is "stressed and concerned, as would be expected."

Ms. Armstrong is the only employee of SouthGobi to be affected by an international travel ban, he said.

Foreign Affairs Minister Bob Carr told the Australian Broadcasting Corp. Ms. Armstrong hadn't been arrested and her passport hadn't been taken. Australia's consul-general in the country, Dave Lawson, has met with Ms. Armstrong and will accompany her to a meeting with authorities, he said.

"The authorities in Ulan Bator are seeking to interview her further--not, I'm advised, about any allegations against her, but about a complex matter between the company she works for, the resources authority of Mongolia and the Mongolia anti-corruption authority," Mr. Carr said in the radio interview.

The travel ban comes amid growing investor concern over the investment environment in Mongolia, a resource-rich country on China's border.

Rio Tinto and majority-owned Turquoise Hill Ltd. (TRQ.T) last week rejected a request from Mongolia's government to renegotiate the investment agreement for the massive Oyu Tolgoi copper and gold mining development in the country's south.

Oyu Tolgoi is 66% owned by Turquoise Hill, with the remainder owned by Mongolia's government. The companies have already invested almost US$6 billion in the project, which is expected to begin commercial production next year.

Plans by Aluminium Corp. of China Ltd., or Chalco, to take a controlling stake in SouthGobi collapsed in August in the face of opposition from the Mongolian government. SouthGobi, whose flagship Ovoot Tolgoi mine is selling coal to customers in China, is majority owned by Turquoise Hill.

A spokeswoman for Rio Tinto declined to comment on Ms. Armstrong's travel ban.

Write to Robb M. Stewart at robb.stewart@wsj.com

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