Eh, I really don't know LOL... he's just based off of a Chaos Space Marine miniature and that one had no Legion/Chapter markings that I could recognize. I know the serpent backpack seems to suggest Alpha Legion, but they aren't really known for sorcery I believe.
Amazing! Its very rare to see moments like this drawn! A Chaos space marine summoning the forces of the warp while humans suround him in awe , hoping to receive a fragment of his unholy powers.. Excelent work sir , very good!