Just spoken to one of my work colleagues. He suggested it may have been taken from the site of the old lime kilns (where the old Pine Chip Plant was subsequently built) looking south across the car-park towards the river.
If so, that provides evidence of another small 2' gauge tramway, of which I wasn't previously aware. That makes the third at the mill site, the first and best known being the billet mule train network that ran from the old billet yard, west of the new Pine Chipper, south along the mill internal road to loop through the the Grinder Room with branches east to the old log deck behind the CCS. The second was a small internal tramway in the basement of the old Woodmill that was used by push carts to collect and shift sawdust and chips and so on. It would be interesting to know how extensive this limestone tramway was?