You can go on to Cornwall Councils online planing register enter The Burrows for the location, it will return a list, the place is on there, then click the map view option, there is a small rectangular building to the side of the property I wonder if that's it.
Further up the Stennack are more shafts on that system, there was a big one just West of the fire station by the side of the road, a local councilor bought the land it's on and had it plugged then built his mansion there.
Lozz.