Kennall Vale, just outside Ponsanooth, north of Penryn, has another Carnmenellis granite quarry said to have supplied granite to the Embankment.  It’s unclear though as it’s also said the quarry is “early 20th century granite quarry”  And the quarry is not on the 1908 map. It’s possible that Kennall Vale supplied granite for the rebuild of the Millbank embankment, or the raising of the Victoria and Albert Embankments after the 1928 floods.
Kennall Vale is more famous as the site of a 19thC gunpowder works powdered by the river that flows through the valley, diverted into numerous channels.
The valley is incredibly beautiful both as a natural temperate rainforest of giant ferns and moss covered beech trees and for the industrial ruins it holds.  Sadly because of this during 2020 it became overcrowded at weekends and people are only recommended to go during the week.  I went mid-week in late July 2021, and there were few people there.
 https://www.gooseygoo.co.uk/site/kennall-vale-gunpowder-works/  https://historicengland.org.uk/listing/the-list/list-entry/1020143  https://www.cornwallwildlifetrust.org.uk/nature-reserves/kennall-vale  https://www.cornwallwildlifetrust.org.uk/news/kennall-vale-coronavirus-side-effects-nature