The value of gold is mostly the cost of labour etc. to extract it; to the extent that it's just the value of the land that it was dug out of, sure, I'd support taxing it. Most Georgists support extending the land value tax to other kinds of economic land e.g. slices of radio spectrum. But physical land is the big one that affects society (particularly because everyone needs some land to live on), so it's the most important one to tax.
But it's important to note that this is a different question than if the roads have tolls on them. (Not that you implied that in any way, but it is a confusion that happens!)
Rather, the tax on the land of the roads is an accounting mechanism to ensure that the land is being used for greater economic efficiency, rather than, say, a way forward wealthy people who live far away to get the public to subsidize the transport to their large mansions.
