Ore controls at the Mahd adh Dhahab gold mine, Kingdom of Saudi Arabia

Mahd adh Dhahab is the largest of numerous ancient gold mines scattered through the Precambrian shield of Saudi Arabia and the only one with recent production. Free gold and silver, tellurides, pyrite, galena, sphalerite, and chalcopyrite are in and associated with quartz veins and quartz veinlet stockworks. Country rocks consist of a sequence of pyroclastic and transported pyroclastic rocks of the Halaban Group that are locally highly silicified and potassium-feldspathized.

Two known ore zones occur in a north-trending zone of quartz veins and breccias, faults, alteration, and metallization approximately 400 m wide and 1,000 m long. The ancient and recent workings are located in the northern part of this zone, and a significant new discovery, the southern mineralized zone, is in the southern part. A potential resource of 1.1 million tons of 27 g/t Au and 73 g/t Ag ore is contained in the southern mineralized zone.

Geologic setting of ore bodies is similar in both zones. Significant mineralization occurs only within altered and fractured agglomerate directly beneath a cap of fine-grained tuff and sedimentary rock where the layered rocks are cut by metalliferous quartz veins. Ore was localized by four interacting controls; depth, an impervious cap, metalliferous quartz veins and a receptive host rock.