I remember 2 malachite veins in the Well Cave almost at the end of that cave (at the right side), not so far from where Zagan is, but after stones blocking you way back... you can't get to them. Right ? (I'm not totally sure because I have discovered that the door to the Well Cave via High Hall is after killing Zagan still open, so maybe you can make it to the veins, still ... ? )

But sorry, I can't make screenshots (Xbox) ...

On 7th of february 2015 : I start a new adventure in the Divinity world of Original Sin,
it's a Fantastic Freaking Fabulous Funny ... it's my All Time Favorite One !