Gold refineries are running at about 1/3 production capacity currently. Known reserves are growing year over year and quite adequate, and the "whisper numbers" for the real reserves (as opposed to published reserves) are an integer factor larger than published. The cost of producing an ounce of gold is falling year over year in current dollars.
An interesting fact is that a very significant chunk of gold mining production in a given year does not come from published reserves. In a nutshell, there is no shortage in supply or refinery capacity, and the reserves are significantly understated. There will be no real gold shortage for the foreseeable future.
I'll just add that I would be far more inclined to buy platinum group metals than gold if I wanted to store value in metals. Even silver would be better in many ways, though that is more volatile because a lot of the silver produced is not mined as a primary ore but as a secondary product of copper, gold, and lead mining (among others), meaning that supply is dependent on the production of other metals.
What would you estimate the max. possible increase in supply per year would be?