Kellingley Colliery will close just days before Christmas with the loss of around 450 jobs.
Pit operators UK Coal has announced mining at the pit will end on or around December 15, depending on when they finish the coal face they will be working on.
As part of the proposals, the workers will lose their jobs a week before Christmas.
Keith Poulson, branch officer for National Union of Mineworkers (NUM), said: “UK Coal has told us that we will close between December 11 and December 18 - depending on when we finish the coal face.
“I still think there are some lads who can’t get their heads around the fact that the pit is shutting.
“Some of us have accepted their fate and reality has started to sink in but there are still some who can’t accept it.”
In March, the government said providing a £338m to keep both Kellingley and Thorseby open until 2018 would not be value for money.
Workers at Kellingley also shelved an employee buyout last year which would have seen the pit stay open until 2018.
Mr Poulson said: “I would love to see a knight in shining armour come in and save the pit but you’re looking at a cost of at least £50m before you’ve even started - it’s not going to happen.
“We have got to start preparing for the future now and part of that is accepting that this is the end of the deep coal-mining industry in ths country.”
UK Coal first announced proposals to close Kellingley as part of a managed closure’ plan last year.
The £20m deal, which included £4m from the government along with cash from private investors, was agreed in September.
UK Coal said at the time that the deal helped to prevent an immediate closure of the site, with gradual job losses over a 15-month period.
A spokesman said the closure was planned for between December 11 and 18.
Mr Poulson said the miners would also hold a march through the streets of Knottingley on Saturday, December 19.
It will leave Knottingley Town Hall at 12.30pm.
He said: “We are not going to go down without a fight and will march through the town.”
Give the miners what they deserve:
Pontefract and Castleford MP Yvette Cooper said she is concerned that Kellingley Colliery’s operators may not have enough money to honour its workers redundancy payments.
Ms Cooper has written to Angela Leadsom, the minister of state for energy, and UK Coal, and has also asked the government to offer the miners more opportunities for them to retrain and gain new qualifications.
Ms Cooper said: “We need a guarantee from the government, UK Coal and its administrators that the miners who kept Kellingley and UK Coal alive for so long will get a proper redundancy deal - it is the least they deserve.”
A UK Coal spokesman said: “It is our intention that all employees will receive the agreed pension payments and exit package.”