The largest and most productive mine in Saudi Arabia in ancient and modern times has been Mand adh Dhahab. Country rocks in the district are pyroclastic and clastic rocks that belong to the Halaban group of late Precambrian age. From oldest to youngest, the units are: andesite, lower agglomerate, lower tuff, upper agglomerate, and upper tuff. These units have been tilted northerly forming a homocline and are complexly broken by six sets of faults; three of these sets, which strike N.25°-30°W., N.10°W. to N.20°E., and N.30°-60°E. contain productive quartz veins.
The principal ore minerals are native gold and silver, pyrite, chalcopyrite, sphalerite, and galena, plus minor tetrahedrite and argentite. The gold and silver are finely disseminated in the veins and in the altered selvages of the veins. Widespread potassic and propylitic alteration accompanied ore formation.
Early widespread propylitic and potassic alteration and sulfide and quartz precipitation are believed to have taken place at temperatures below 350°C, based on K-feldspar stability and sulfur isotope data . Most of the quartz and precious metals precipitated in the range 200°-150°C, based on studies of fluid inclusions. The isotopic data indicate that sulfur and carbon came from a deep-seated source, but that the water, especially in the later stages, was meteoric.
