The Unmailed Letter (1960)

The film is based on the eponymous book by Valery Osipov. Four geologists are searching for diamonds in the wilderness of Siberia. After a long and tiresome journey they manage to find their luck and put the diamond mine on the map. The map must be delivered back to Moscow. But on the day of their departure a terrible forest fire wreaks havoc, and the geologists get trapped in the woods.