I have a copy of the Irish Rail Working Timetabe 11th Dec 05- 9th Dec '06. In it it sates that all liners are limited to 780 tons at 36 TEU max. Exceptions being 1,000 ton cement trains only to be hauled by 071 or 201 class. (2x 141/181) not permitted. The 1,000 tons train are only permitted with special permission between Platin and Northwall and Northwall to Cork.
I don't see anything in it about Tara Mine train weight limits other than the max weight of a laden wagon is 75 tons.
Actually just found it, max tara weight limit of 12 wagons is 942 tons.
Cement trains were 900 max, the 1,000 limit was worst case with a dead loco in tow if needs be.