This isn't the best source to go by, but the Steam Powered Video Atlas of North America, Northeast US, on page 64 shows the line to New Philadelphia and Middleport via Port Carbon to be in place and operated by Reading & Northern. It also shows that the former RDG line from Mill Creek Jct to St. Clair and the PRR line from N. Pottsville to St. Clair to be missing. Could you restate the line you found in relation to these?
I remember driving through New Phila. about 4 years ago, and the rails were still there, with an obviously missing rail line (I guess PRR) on the road into town.