Working: As of 14/12/2021, patch 1.1.3.0 has fixed the issue with Bank in Morelton already being unlocked.To store 10,000 gold in the bank you must unlock all 8 banks found in the game. Each time you find/unlock a bank in a major town it increases the gold storage limit (500, 800, 1200, 2000, 3000, 5000, 7000, 10000). Once the 8th bank is unlocked you can deposit 10,000 gold to earn the achievement.