Caegwernog Mine exploited several well-mineralised veins of limited length that cut through the Clogau Shales near the head of the Wrin Valley. These veins contained galena, sphalerite, pyrite, and arsenopyrite.

The mine was first opened around 1842–43, with three adits driven—two of them by 1846—alongside a shaft and several exploratory workings. Operations continued on and off until 1905, when the mine was last operated by the St David’s Mining Development Company Ltd.