Green gold ore is a crafting component introduced in the Blood and Wine expansion that can be dismantled into green gold, and is needed to craft green gold ingots, which however are quite useless.
Crafting Requirements 
Crafting Requirements
It can be found as random loot or purchased from the following merchants:
- Armorer in Hauteville
- Blacksmith in Belgaard Manor, after he is rescued
- Lazare Lafargue in his workshop
- Trentin in his workshop in Hauteville
Green gold ore can also be obtained by dismantling a few items, almost all of which are much more valuable, but one is a quite common junk item, Toussaint knife.