As I discussed in the post linked below, olivine requires more heating than would be expected at the furtherest reaches of the solar system where comets were proposed to form. This is the reason why a formation in the Neptune/Uranus region is being suggested instead.
However, this probably would not be enough to explain the presence of carbonate and clay, which require liquid water. An explanation that would explain all these would be internal radiogenic heating:

Re: Carbonate and clay in comet Tempel I raises the possibility of life.
Posted by Robert Clark on 9/18/2005 8:21:18 AM
http://habitablezone.com/space/messages/396387.html

Bob Clark