The appeal fund for the families of the four miners killed in the Gleision colliery tragedy in the Swansea Valley now stands at £970,000.
Trustees expect the fund to top £1m before they officially wind up the appeal, but no date has been given.
They told BBC Wales a large sum has been invested in a high interest account with cheques still coming in.
David Powell, 50, Charles Breslin, 62, Philip Hill, 44, and Garry Jenkins, 39, died when the mine flooded last year.
Three others escaped during the incident at the drift mine, near Pontardawe, on 15 September.
Wayne Thomas, trustee of the Swansea Valley Miners' Appeal Fund, described the current total as "phenomenal".
"We need to be careful how we manage this fund," he told BBC Wales after trustees met on Thursday.
He said they have started talks with legal experts about things like setting up trust funds for families and the children involved.
"There are still substantial amounts coming into the fund still," said Mr Thomas.
"I honestly think it will make the million."
The fund has received several donations over the Christmas period, including a big pledge from the pantomime at Swansea's Grand Theatre, along with £6,000 this week alone.
Two payouts have already been made. One was to the families to help with funeral costs.
The other to the daughter of one of the men who died. She is disabled, and has used the money to buy an electric wheelchair and a specially adapted car.
The fund is expected to be wound up later this year.
An investigation into the mine incident is being carried out by the Health and Safety Executive (HSE) and South Wales Police.