"The Gold Mine produces gold. Upgrade it to boost its production and gold storage capacity." - Clash of Clans
The gold mine collects gold from an unlimited underground reserve (called the Ley Line) and stores it until collected by the player and placed into a Gold Storage. When the mine is full, production will be stopped until it is collected. The production rate and capacity depends on the level of the Gold Mine. One can estimate the amount of resources in the mine by looking at the bin on the right side of the mine.
A percentage of uncollected gold left in the gold mine can be stolen by attackers. An annoyance with mines is that, even though the cost to upgrade them is low, the time taken to complete them is relatively long.