Now Human Services Minister, Mr Robert is a "close personal friend" of Mr Marks, who has donated $2 million to the Liberal Party in recent years. The minister also owns shares in Mr Marks' Evolution mining company, according to his register of interests. Human Services Minister Stuart Robert is under fire over a secretive China trip. Credit:Andrew Meares Labor defence spokesman Stephen Conroy accused Mr Robert of "appalling lack of judgment" and an apparent conflict of interest. "There is a prima facie case of a breach of the ministerial code of conduct," he told reporters in Canberra on Monday. "Every minister knows you are not allowed to use your office for your personal benefit." Senator Conroy said Mr Robert wasn't invited to the ceremony as an average shareholder but because he is a minister. "He implies he is speaking on behalf of the Australian government in endorsing this project."

Prime Minister Malcolm Turnbull must demand a full explanation from Mr Robert and a transcript of his remarks at the ceremony, Senator Conroy said. Stuart Robert at the signing ceremony. Credit:Minmetals And if the explanation isn't good enough, he should be sacked, he said. "If all of the facts are that Stuart Robert has used his position as a minister to promote a company that has made major donations to the Liberal Party, and that he's a personal investor in, then he has to go," Senator Conroy said. Stuart Robert at one of the formal meetings. Credit:Minmetals

The revelation comes just weeks after Mr Turnbull lost two ministers in Jamie Briggs and Mal Brough. At the ceremony the two companies agreed to set up an "exploration technical committee" for a mineral project in western NSW. The Minmetals website says Mr Robert spoke "on behalf of the Department of Defence", presented a medal to one Chinese official and a "letter of appointment" to another. Stuart Robert with Prime Minister Malcolm Turnbull at family day at The Lodge on Sunday. Credit:Alex Ellinghausen An ordinarily avid user of social media, Mr Robert did not make any posts about his China trip. Labor frontbencher Doug Cameron said: "If you stop posting on Facebook when you're a prolific Facebook poster you've obviously got something to hide."

But Foreign Affairs Minister Julie Bishop said Mr Robert's trip was "perfectly acceptable". "I don't know how you can make a secret visit to China anyway," she told the Seven Network. "China knows a great deal of what is going on when it comes to its borders." Education Minister Simon Birmingham noted the trip occurred quite some time ago. "I'm sure Mr Robert will have something to say in terms of making sure that it is clearly understood that it was a private capacity and the way in which that occurred," he told Sky News. Follow us on Twitter