Regarding radioactivity the full text is bertter :-
But if the indigenous people killed everyone, then why were some of the clothes of the victims contaminated with radioactivity? A possible explanation can be found in the diaries. Lyuda wrote: ‘After breakfast, some of the lads, headed by Yuri Yudin, our well-known geologist, went to look for local minerals. They didn’t find anything except pyrite and quartz veins in the rock.’ Pyrite is a mineral regularly found in the Urals. But it isn’t only pyrite, gold and silver that are found in these mountains. There is also uranium ore, which gives off radioactivity, and which most likely fouled the hikers’ trousers and sweaters with radioactive dust. In the notebooks of journalist Grygoriev, who took part in the rescue operation, there is the following entry: All the backpacks have bits and pieces of rocks … Vishnevsky told me that they were for striking fire in case their matches got damp. I disagreed because I saw that they were rocks taken from the 2nd Severny camp.
Oss, Svetlana. Don't Go There: Post Mortem (pp. 206-207). LiberWriter.com. Kindle Edition.