The purpose of Goldcoin is to create a bitcoin like coin which could be exchanged for a set amount of gold, let's say 1 Goldcoin equals 1 ounce of gold.
Lets say I mine 50 Goldcoins, who is going to provide the gold?
Nobody provides you the gold (directly anyways). Since the mining reward is variable based on the price of Goldcoin, then you would be able to sell the 50 Goldcoin on the open market for 50 ounces or more of gold (or equivalent).