A Dartmoor mine closing has put up to 200 jobs at risk.
Australian firm Wolf Minerals (UK) has gone into voluntary administration after talks with international backers seeking further finance failed.
Lorry drivers have been reported to have been sent home from Drakelands mine at Hemerdon, near Plymouth, in Devon, which reopened in 2015.
However, industry analysts said the mine was expected to re-open "after renegotiations with creditors".
Wolf, which had spent £130m in start-up expenses alone, had hoped to produce about 3,000 tonnes of tungsten and tin a year after reopening the mine
It was working to exploit what was said to be the world's fourth-largest deposit of tungsten.
Devon and Cornwall Police were called to the mine at 13:35 BST to reports of a "civil dispute" over equipment, the force said.
The company released a statement on Tuesday saying that, if longstanding talks on refinancing did not reach a positive conclusion within two days, it would run out of short-term working capital.
BBC South West Business Correspondent Neil Gallacher said the statement had shown "either sheer brinkmanship, or it's a sign that Wolf fears its international backers may really be about to decide against a further refinancing".
He said: "The puzzle is that, after such a long and bumpy ride, this would be a curious time for the backers to run out of patience.
"Recent signals from the mine have suggested tungsten output is improving after early teething problems; and the metal's value globally has risen strongly in the last couple of years."
Mining analyst John Meyer, of SP Angel, said it was expected the mine would restart "once the administrator has agreed settlement with creditors and found a suitable buyer for the business".
He added it was hoped administrators would "keep the mills turning" to "enable a quick restart".
But it is not known how it would affect staff in the meantime.