Answer:
The spanish words in Nina Morena by Duncan Browne (Streets of Fire album, Logo 1979) are the final stanza from a Pablo Neruda's poem titled En su llama mortal (In its mortal flame), included in Veinte poemas de amor (Twenty Love Poems). Here's text and an attempt at translating it in English:
Oh grandiosa y fecunda y magnética esclava
del circulo que en negro y dorado sucede:
erguida, trata y logra una creacion tan viva
que sucumben sus flores, y llena es de tristeza.
Oh magnificent and fertile and magnetic slave
of circle that in black and gold changes:
proud, she strives and gets so living a creation
that its flowers die, and she is filled with sadness.