These are usually not standalone files but parts of uuencoded (Unix-to-Unix encoded) binary data or PGP signatures embedded in plain text reports.
A real 7-Zip file should start with the hex signature: 37 7A BC AF 27 1C . Use 7z l B7.7z to list the contents without extracting. These are usually not standalone files but parts
It appears in indices for geological surveys (e.g., Alaska state mineral reports) as a coordinate or sample identifier. These are usually not standalone files but parts