Rich Pass Gold is an optional upgrade that you can purchase to earn Huge Rewards for a limited amount of time, including a Bonus Chest as a final reward. When you open the Rich Pass window, you can see all of the rewards available including those that are unique to Rich Pass Gold.

Even if you have already unlocked some of the Free Rewards during the current Rich Pass Season, you can still unlock all of the Gold Rewards you passed by upgrading before the season ends.