Second stanza of The Convergence of the Twain by Thomas Hardy:
Steel chambers, late the pyres
Of her salamandrine fires,
Cold currents thrid, and turn to rhythmic tidal lyres.
Can ‘late’ be used as a preposition and what does it mean in the above lines?
It is not a preposition. Prepositions are used to indicate relation between two (or more) separate objects; here the pyres and the steel chambers are the same objects (However, "of" is a preposition, showing relationship between the pyres/steel chambers and the fires, which are separate objects, with the former containing the latter).
I would argue it is an adverb, modifying an omitted and implied verb "were", with "late" being used in a manner equivalent to "formerly" (See adverb definition 3 here: https://www.lexico.com/en/definition/late). I’d argue a less poetical equivalent sentence would be:
Steel chambers, (which were) formerly the pyres/ Of her salamander-like fires/ pass through cold currents, and become rhythmic tidal musical instruments