"Tunguska researchers have always believed that the TSB sub- stance is still preserved somewhere in the taiga and may be found. The only exception is probably Lincoln La Paz and his antimatter hypothesis, according to which the Tunguska meteorite was com- pletely annihilated in the terrestrial atmosphere. But this is an extreme viewpoint. A piece of antimatter would hardly have pene- trated Earth’s atmosphere so deeply – it would have been annihi- lated at a higher altitude. "
http://t2mh.com/space/Tunguska%20Mystery.pdf
The above is not accurate though. My understanding is that Tsilokovsky was a proponent of the "anti-matter / matter" collision theory. I am having difficulty finding the father of space science's original work, but here's a more recent citaiton:
Title:
The Possible Antimatter Nature of Micrometeorites
Authors:
Konstantinov, B. P.; Bredov, M. M.; Belyaevskii, A. I.; Sokolov, I. A.
Publication:
Cosmic Research, Vol. 4, p.58 (CosRe Homepage)
Publication Date:
01/1966