Can metal transmit signals? I would think yes but how useful those signals are for detection by various practical means is the big question.
Atoms have electrons and metals are good conductors and I agree with Esteban that larger metal objects are easier to detect because of their extra mass.
I have an old TR detector and it will go surprisingly deep on large objects but much less on small objects.
OK, I am still skeptical of LRLs, someone send me me a working model -free- and I will check it out....but don't bother though with the mechanical type
........those with a built-in BFO, I will give room that they might work.