They did a plugging programme up there, but actually did quite a good job with the amount of batcastles they put in. From what I can see, the shaft has a concrete "lid" on it, rather than being plugged.
I have a feeling that the council's attitude to plugging has changed and it's only choked shafts which get the plug.
Oddly enough, the only one which got a batcastle on Wheal Buller (of this era) went straight to water, whilst the interesting shafts got "plugged".