Libertarians are opposed to fiat money, in line with their general dislike of government regulation. If you reject paper money, where to next? Gold has a lot of very nice properties that made it useful as a medium of exchange in the past, so why not go back to something that worked? If you can explain away the problems with the old gold standard as a consequence of poor financial planning, then the rational choice seems to be the gold standard. Electronic currencies, like Bitcoin, have various issues of security and not really "existing" that just don't apply to physical objects.

How to resolve this with cornucopianism of natural resources? Honestly, I haven't seen any libertarian works addressing this question. It seems to me that the big push for gold has mostly historical reasons.

You see this contradiction in Ayn Rand's novel Atlas Shrugged, where the Operating Objectivists can create mountains of goods - copper, coal, steel, petroleum, wheat, etc. - when they live under a proper political order. But they mysteriously can't seem to do this trick for gold.

The gold standard has an interesting history. The World Wars and the Great Depression uncovered many practical problems with the gold standard and Rand lived to see the various debates and policy shifts that arose during this time. The emphasis on gold in Atlas Shrugged is likely a yearning for the good old days before contemporary politicians mucked everything up.