Deep in the Atlan hills, Reynosan miners discovered a large vein of pure mithril. From 382 YC to 389 YC, people flocked to the nearby town of Tarkon to mine the valuable metal. This period in history is referred to as the Mithril Rush.
Before this event, all mithril-made tools, arms, and armor found in the realms predated the Shattering. The development and mining of this vein led to the first mithril forging in nearly 4 centuries.