The Bronchial Arteries -- the Gold of the Puranas

 It is the bronchial arteries that are referred to as "gold" in the puranic texts. Meru is golden because its four "sides," the secondary bronchi, alongwith the summit, the primary bronchus, are "decorated" with the bronchial arteries. It is this "golden" flow (of oxygenated blood) that makes the entire Meru resplendent. 

Note: The four flows that are said to course through and irrigate the four regions of Ilavrta, that have their origin in the four trees mounted on the four buttress mountains of Mt. Meru seem to be the flow of the bronchial arteries. If that is the case then this must mean that the four regions of Ilavrta, Northern, Southern, Eastern and Western, stand for the four secondary bronchi (as the bronchial arteries course along these bronchi).