Tiles with gold on them will produce commerce (profit) provided that someone in the city whose radius the gold deposit lies within is working that tile. To increase commerce on that tile, build roads connecting it with your city, build a mine on same deposit. This will have the effect of increasing your commerce, i.e. your economy will produce more wealth. To check whether or not the tile is being worked double-click on the city in question. Look at the area map of the city, if the tile containing gold has shield, food and commerce icons on it, then it's producing commerce for your empire. Hope that wasn't too confusing.
"do or do not, there is no try."
