Seven Hidden Mines

Seven Hidden Mines was a location in YGGDRASIL that contained deposits of prismatic ores.

Background
Ainz Ooal Gown once possessed a monopoly on the entirety of the Seven Hidden Mines. They discovered that the mines contained a wealth of celestial uranium. After mining the ore until the mines were depleted and later stockpiling it, the clan came across an unexpected turn of events. Apparently, the celestial uranium had transformed into Caloric Stone.

The Seven Hidden Mines were later taken by a rival guild. Through the use of Ouroboros, a World Item, they banished Ainz Ooal Gown from the world in which the mine were situated. Each of the seven mines then came under the control of several independent guilds.

Trivia

 * Under normal circumstances, a guild that found a new mine would thoroughly exploit it first before selling its ores on the market. If the mines were tapped-out, they would slowly recover and be ready for further harvesting.
 * Ainz Ooal Gown had once schemed to reclaim the mines, and Punitto Moe suggested they spill information of the mines' potential to produce Caloric Stone, a World Item to Trinity and 2ch Alliance and spark a guild war.