when you walk down from great market to lanlinor lane right after the 5 runes that are on the wall you wil see a statue that will ask for a password (the order to solve it is to activate 5 handles throughout Aleroth) then you have acces to the sewers if you go in there and make a left turn you'll see a melachite vein;)
Oh, that one. I have that listed in my guide. It's FoV vein #3.
