US miner Peabody Energy will close its Metropolitan mine at Helensburgh on January 4, saying the closure will last for eight weeks.
The company says the decision to close - or "idle" the mine - had been made because of the poor state of the coal market this year.
The company plans to re-open the mine after the eight weeks but if the market is still unfavourable this is not guaranteed.
Peabody employs about 250 people at Metropolitan, with the workforce traditionally having been drawn from Helensburgh and nearby.
Some of these workers may stay on to maintain the mine during the closure, but the majority may have to use some of their leave.
"Due to challenging coal market conditions Peabody has decided to idle its Metropolitan Mine for an eight-week period beginning January 4, 2021," a company spokeswoman said.
"The COVID-19 pandemic has presented tremendous challenges to coal miners and, while a slow global recovery is under way, including in steelmaking and industrial activity, this recovery is in very early stages.
"As a result, global coal demand and pricing remain under intense pressure and are weighing heavily on the current economic position of the mine.
"Mine managers have openly conveyed this decision to our employees, including the ability for them to access paid leave for the idle period."
The Mercury asked whether Peabody could guarantee it would re-open but the question was not addressed.
"Peabody thanks all employees of Metropolitan for their efforts throughout this challenging year," the spokeswoman said.
"The company is offering employee assistance and counselling services to our workforce and their families should they need help dealing with these tough times for our sector."
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