As I understand it, Tregoning's shaft was also known as Old Sump/Engine Shaft and then following some firkyfoodling and for reasons either mentioned by Trounson or some other book I have, New Sump was sunk alongside. It is marked on the OS map as "New Shaft". Which I think is the one with that engine house. I'm pretty sure Tregonings/Old sump is nearby in the undergrowth. Both shafts are slabbed over. Dines has no mention of either, but mentions Tregonings (off the top of my head). A plan I have (which sadly can't be copied and slung up) shows New Sump and Old Sump shafts, then Hawke's and West Shaft on North Lode. The other shaft on the strike of that lode, but I'm not sure if it links up or not is Wheal Vor engine shaft......
Hope that helps. Would appreciate knowing if I'm wrong or not. I think the info is in Trounson (Cornwall's Future mines). 99.9% sure. Either that or Acton/Brown's guide.
My plan is lifted from the last working.....I gather. Stu