Ma’aden Gold and Base Metals company (MGBM), a wholly owned subsidiary of Maaden Saudi Arabian Mining Co. (Ma’aden), operates five gold mines, i.e. Mahd Ad-Dahab, Al-Amar, Bulghah, As-Suq and Ad-Duwayhi and a processing plant at Sukhaybarat.
Summary:
Mine area rocks are composed of a mafic to felsic volcanic-sedimentary sequence. The volcanic sequence consists of a Lower Andesite overlain by the Lower Agglomerate unit, a Lower Tuff, the Upper Agglomerate, and Upper Tuff units. A rhyolite porphyry stock occurs to the north of the mine and is exposed in the SAMS area. This stock may be part of a much larger intrusive body at depth.
The rock sequence forms an east trending homoclinal structure trending east with a northerly dip from 30° to 75°. At depth the sequence is sub-vertical to overturned. These rocks have been complexly faulted by steeply dipping north to north-northwest and northwest trending faults. Vein complexes trend north-northwest to north with some veins trending northwest.
Mineralisation is associated with multiphase quartz veining and silicification developed along predominant north to north-northwest trending faults. Some veins are developed along northeast and northwest trends. Quartz veining is associated with intense silicification, massive, laminated and brecciated veins. Veins are vertical to sub-vertical. Major vein systems can be traced across the mine area and are preferentially developed in the Lower and Upper Agglomerate Units. Veins are more poorly developed in the andesite and tuff units. Economic gold mineralisation is associated with quartz, pyrite, chalcopyrite, sphalerite, galena and silver.
Moderate to intense sericite and chlorite alteration is associated with the vein systems. Carbonate alteration and quartz veinlets form at the peripheries of the vein systems. Near surface mineralisation is oxidized to a depth of 10m grading into a transitional zone that extends to depths of 20m to 60m.
Mineralisation occurs in epithermal to mesothermal vein systems. Typically mineralisation is zoned according to the temperature and boiling point of hydrothermal fluids. Often lower temperature zones or epithermal environments are associated with high levels of gold mineralisation. Mesothermal environments are associated with massive metal sulphides and possibly a lower tenor of gold mineralisation. In a general overview of the upper regions of Mahd Ad’Dahab, vein systems show epithermal characteristics and are associated with high grade gold mineralisation. The deeper regions of the vein systems may represent a higher temperature regime and thus are associated with massive sulphide mineralisation with lower gold grades. Fluid inclusion studies indicate that veining occurred in epithermal to low mesothermal temperatures.
Mafic dykes intrude quartz veins. Dykes are believed to be post or contemporaneous with mineralisation.
Quartz and massive sulphide vein system at Mahd Ad’Dahab are subdivided into four zones comprising:
- SAMS: comprising 70% of ore currently mined, economic veins include veins 1, 4, 8, 14, 15, 16, 17 and D complex (veins D1 to D4);
- Western Zone: comprising 4 complex, 3 west, 2 west, F, F1, F2 and a number of narrow high grade veins from 0.4m to 0.5m wide including veins S, 10 West, 8 West, 6 West, 7 West, diluted grade of narrow veins about 10g/t Au;
- Eastern Zone: comprising 10 East, 11 East veins and the M vein complex;
- Northern Zone: comprising the Northern, 678, 345, T veins and the two vein complex, the near surface mineralisation of vein 678 was mined out as high grade mineralisation extracted through a small open-pit operation.
The mineralization occurs within an area about 900 metres by 900 metres in size. Mineralization is associated with multiple phases of quartz veining and silicification related to north to northwest trending faults. The high grade gold mineralization occurs as steeply dipping, narrow (0.5 metres to 2.0 metres) quartz and massive sulphide vein systems in four zones; SAMS, Western Zone, Eastern Zone and Northern Zone; and in larger stockwork veined zones up to 20 metres in width in the Eastern Zone.