well, gold mine has some hard-coded behaviour when peasants/peons are involved. but if you don't need both resources, i have an idea (complicated, yet ellegant - just like me): switch gold and lumber!
1) make a gold mine by simply taking a tree and changing its stats (change aoe spells to make sure they cant take the tree down)!
2) give that tree gold mine model and set pathing size to the appropriate size so that peons are on correct distance when "chopping" gold
3) give the tree 10000 or 20000 hit points - peons chop wood by taking down it's hp...
4) open game interface dialog in advanced menu. find the lumber icon (as displayed on top of the screen) and gold icon and swap their paths!
5) find tooltips that refer to gold and lumber in text section of game interface dialog and exchange those tooltips (for example "Not enough gold.").
6) see that all purchasable stuff in your map (weapons, potions) cost 0 gold and x lumber. (since you exchanged the icons, players won't know the difference)
ta-daa...