Kazaks are Muslim...so yeah
Actually, Kazakhstan is a fairly equal mix of Christianity, and Islamic. Christianity being the religion that is on the Northern part of Kazak., closest to Russia. If anything, I would guess that a good majority of the Muslems are coming from Mongolia.

Anyways, there is not pure gene pool anywhere in the world anyways. So, sorry to burst your bubble, but no such thing as 100% slav., but true, the gene pool in places in Russia is probably no where near as dirty as the American gene pool.