While a long-time possession, the Cardassians lacked the resources to mine the mineral until 2371.
After the disastrous joint Obsidian Order/Tal Shiar assault on he Dominion, thirty-four Romulan consultants were still in Cardassian space. They were immediately arrested, and a place to hide them from prying eyes needed to be found. As most were engineers, the Order decided to take Hekiss' mineral wealth for themselves as well as put the Romulans out of easy reach or their political enemies.
The Romulan miners were soon joined by many other political prisoners the Order had hidden away.
During the Dominion War, it was turned into a Prisoner of War Camp under Gul Kuart Jelot and Vorta advisor Br'enn.
While Kuart oversaw the prisoners' mining efforts, a similar job he had performed almost twenty-years earlier on Terok Nor, Br'enn delved into genetic experiments using the prisoners' DNA. This led to the creation of the Alpha Jem'Hadar.