That the one that went off at the station then down an incline towards the old wharfs across the main road and a swing bridge?
Route is certainly shown on my 1970's 1" OS map.
The swing bridge is still standing and has rails on it, and I seem to remember there were still some rails in the wharfs.
There is an info board at the bottom of the incline, where the sand drag was.
You can walk a good length along the old Pool that is full of poisonous mud, past various info boards and old buildings.
Check the Middleton Book for the area, as I expect that has plans and photos.
Loads were probably china clay and coal for the old Power Station inwards.
(Daughter lived in Hayle last year!
There is a member on here who lives in Lelant, he may know more)