Board Thread:Game discussion/@comment-124.6.181.59-20130325072427/@comment-108.243.81.180-20130327132455

from the "spellblade" entry:

"The area of effect slow is not considered part of the "Spellblade" effect, and is instead classified as Icy. If you own both Iceborn Gauntlet and a higher priority Spellblade item (i.e. Lich Bane and Trinity Force), you will trigger the higher priority's damage component while still triggering the area of effect slow."

you won't get the bonus damage from IG but you will get the slow