Thanks to the magick of beta units there is actually a solution - in fact quite a few. Firstly, you can block the gold mines off - using invisible cliffs (map copy and rotate cliffs), rocks, whatever. If you want the gold to be accessible, you could use a different unit instead of the goldmine - for this you can map copy from a utility (there are a few - "Map tricks", "New Units" etc). The best solution though is to download GeniEd2.
There are 3 units available. Firstly there is a pile of gold (named just that) that only has 1 gold. This is real gold, and the pile will disappear very quickly. This is suitably named, but if you don't want the player's villies to be picking up 1 gold mines, you may want to use one of the others.
There's also the Porex mine - this is like pile of gold, but it makes the villager disappear. It may not be suitable for this reason, but it's worth learning about anyway. I believe it also has 1 gold, but the resource though it can be dropped off does not seem to be the same resource as gold.
The last gold mine-like unit is the OREMN (sp?) - this looks like a gold mine but cannot be mined at all - ideal for appearance only, but might be a little difficult for newbies to deal with - like moths flying against a window.
If you need more help Berserker Jerker will likely have more information. To get him to come you must sing this rhyme:Ho! Berserker Jerker, Berserker Jerkerillo!
By water, wood and hill, by the reed and willow,
By fire, sun and moon, harken now and hear us!
Come, Berserker Jerker, for our need is near us!