User blog comment:Xilinoc/Ch. 541 - THE BLADE AND ME 2/@comment-2211792-20130612103127/@comment-10630156-20130612104138

It was probably reishi he had used to seal the real zanpakuto rather than being because of being a fire style Zanpakuto. The Zanpakuto is likely to be near to his old zanpakuto due to that one not being a spirit weapon.

if it does have a type it will probably be demonic seeings to the BGT and the Moon reference in the name "Zangetsu" (Slaying Moon)