The blood-pumping organ of a greedy/
selfish moocher/fortune-hunter who only yearns for
gold; i.e., his main goal in life is to be given money to either hoard or spend frivolously.
In the 1937 comedy-film "Way Out West", Laurel and Hardy play a couple of witless buddies who unknowingly deliver a deed for a gold mine to the wrong woman; the recipient is actually the heiress's devious guardian with a "heart of
gold"...
Laurel naively "hits home" by telling her, "Now that you own a mine, I
bet you'll be a swell gold-digger".