gold bug

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several North American beetles, especially Charidotella sexpunctata, having a golden metallic luster.
• noun A supporter of the gold standard.
• noun A speculator in or a purchaser of gold.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun finance A person with a particularly great enthusiasm for investing in gold (the metal), an enthusiasm which to others is likely to seem excessive, especially if gold prices are stagnant or falling.