In November last year the railway won £50,000 funding from the People's Millions Big Lottery Fund for the memorial park at Cortonwood station, picnic lawns, gardens and a museum carriage at Elsecar.
The carriage included a recording studio where former miners could share their stories of life down the pit, in "a living memorial" to generations of South Yorkshire miners.
Some funding was being used to extend the railway line - which runs from Elsecar to Hemingfield - to Cortonwood.
But this week, a member of Barnsley Council, who did not wish to be named, told the Chronicle that he understood there were delays with the memorial park and railway extension scheme.
He said: "I understand they are running close with the funding and also can't do anything else until the rail lines are inspected. They have also got to put in a waiting area from the Hemingfield pit side."
Chairman of the Heritage Railway, Del Tilling, confirmed there had been delays caused by the need for a traffic management plan to cross Tingle Bridge Lane at Hemingfield and Smithy Bridge.
He said the group was due to meet with representatives from the highways department at Tingle Bridge on Monday, but that the issue would delay the project by several months.
"Things have gone quiet until we sign off on the traffic management scheme and the rail line itself. We have done all the hard work at Cortonwood."
According to the railway website, work was progressing well. The group had ballasted the Cortonwood track bed, laid track and fenced the Cortonwood site ahead of the main gardens project.
The museum carriage at Elsecar had been fitted out and the first exhibits and storyboard put in position.
Level crossing motor bases were also mounted at Tingle Bridge Lane and track bed cleared between Smithy Bridge and Hemingfield. In June, the website reported that work on "the main infrastructure" of the railway extension had been finished.
Most read news stories