Azuera serves to introduce the novel's central theme: the illusory ideal, or dream-ideal, which drives all human desire. Note that, although we assume there is really no gold on Azuera, the passage never says so explicitly. There may or may not be gold on Azuera; the matter of importance is the belief in it. The legend is not so much wrong as it is a construct independent of reality, a construct for which, nevertheless, men are willing to labor, die and eternally enslave themselves. Azuera is thus a symbol for all desire. The barrenness of the dream-ideal is expressed by the fact that nothing grows on Azuera; its subjective and illusory nature is suggested by its appearance as "an isolated patch of blue mist"; and when Azuera is described as "blighted by a curse" we may read it as the "curse" of the dream-ideal upon mankind.
Gold in Nostromo symbolizes rulership, which
adds another crucial element to the passage. To Conrad all dream-ideals, no
matter how benevolent, seek rulership in essence, i.e., the imposition of one's
belief on other people. Note that politically, South America has invariably
been subject to foreign rule, which is why those who find the gold of Azuera
must be "gringos of some sort for certain."