**** man, idk... I just read the poem and it seems to be about how some young men will die young, probably in battle. "they carry back bright to the coiner the mintage of man" sounds like they're going to meet their maker (the coiner) still in their 'mint' condition. But the elbow line is weird. All I can think of is, in the last stanza:
"But now you may stare as you like and there’s nothing to scan;
And brushing your elbow unguessed-at and not to be told
They carry back bright to the coiner the mintage of man, 15
The lads that will die in their glory and never be old."
Maybe 'They' are angels or spirits, carrying the men back to the 'coiner' in heaven, and if they brush your elbow they are "unguessed-at" because they're invisible ("There's nothing to scan" = nothing to see).
Sounds far-fetched but that's the only thing I could think of.