Located within Carboniferous limestone, which has been altered to dolomite in some areas, with mudstone bands present. The main lode trends NNE, containing lead and copper ores, with cerussite and malachite as secondary oxidation products.

The mine features a cavernous entrance, leading to a network of narrow galleries that connect to small chambers. Many of these passages are now choked with waste material. The 19th-century shaft, which connects to the central Shaft Chamber, was not originally accessible from the entrance chamber. Over time, earlier narrow workings were widened through multiple phases of extraction.

Some evidence of lead smelting has been suggested by historical reports of bole hills on the hilltop, but these features were destroyed during the development of the golf course.

The Llanymynech Ogof mine has been associated with lead and copper extraction across multiple periods, including the Roman era and possibly immediately pre-Roman times. While no direct evidence of prehistoric mining was found, researchers suggest the mine has characteristic features of Roman and perhaps pre-Roman origin.

In the 19th century, the site was reworked, with a shaft sunk in 1823, linking to a central main chamber (Shaft Chamber). Many of the earliest narrow workings were later expanded in at least two additional phases of extraction. Shot-holes identified in the Shaft Chamber suggest later blasting techniques were used.

Scheduled Monument