I spent a weeks holiday once a year in a house along the line for the last 3 or 4 years of the Ballinacourty workings. As you say, the dolomite trains were more frequent. Two loads a day were brought into the plant, in daylight hours. The magnesite train travelled once a day, and I think it was usually at night. I have a CIE working timetable from that era, and I must check it to see. As already mentioned, The A class with a short rake of oil tanks was a very regular day time movement any time I was there. I think this train was to keep the factory supplied with oil during high consumption periods, and supplemented the oil brought in on the oil/magnesite train. And yes, as far as I know the magnesite was exported from Tivoli.
I was never fortunate enough to travel on the trains though!
Apologies to Patrick, for hi-jacking his thread.....