Detailed Exploration and Assessment of the Jabal al-Khawar East Gold Prospect
Eyad Jennadi, Zaben Al Harbi, and Islam Dourgham, with the collaboration of Alim A. Siddiqui
Numerous ancient workings on the mineralized quartz veins hosted by dioritic rocks in Jabal Al-Khawar gold prospect have been recorded. The ancient miners’ activities were apparently in the quest for gold as confirmed by the proximity of the extension of the open pits to the elongation of the auriferous quartz veins, which are nearly impoverished in all other metals except gold. A few exposures of parts of the mineralized quartz veins are available for further detailed examination. The area is subdivided into 3 main sites named A, B, and C. In each site, the mineralization is represented by a network of discontinuously exposed quartz veins arising from either discontinuities in the mineralized quartz veins actually separated by considerable distances or discontinuous surface exposure of the same long quartz vein. This assumption is confirmed by the almost the same structural trend of the three sites. The 123 samples collected from the different sites in the prospect gave encouraging results, particularly in the 3 main sites. The highest gold value, recorded in site A, reached up to 12.6 ppm. The samples collected from the trenches have low gold content. Unfortunately, the project was abruptly stopped before the drilling stage because of logistical problems. Thus, assessment for the mineralized ore bodies at prospect was not made. Nevertheless, the work accomplished enabled formulation of ideas about the mode of mineralization and occurrence style, extension of the mineralized quartz vein, and the associated alteration zones, as well as the geochemistry of mineralization. With reference to the accumulation of all the necessary agents required for gold precipitation processes, the gold mineralization style at the Jabal Al-Khawar prospect represents a perfect localization of gold. The mineralized zones are restricted inside the dioritic mass which constitutes the common host rock type especially in the Afif terrane. The dioritic bodies show major structure that reflects a regional tectonic framework where a contrast in the rheology of the competent granitoid intrusions and the surrounding supracrustal rocks of the Hulayfah and Murdama groups causes a spacing that acts as conduits for the hot active fluids bearing gold and associated ore mineral assemblages. One major tectonic movement caused the orientation of all rock units in the area and also produced brittle deformations, and such that sites A and B are arranged along one line while site C is displaced toward the west due to later strike-slip fault crossing the mineralized zone. All sites are confined within a deep-seated fault zone. The ore mineral assemblage associated with the gold mineralization at the different sites comprises, in addition to gold, chalcopyrite, galena, sphalerite, altaite, and covellite. The intergranular and mutual relationships indicate that gold was co-precipitated with galena, sphalerite, and chalcopyrite and that gold was formed in the mesothermal zone and in the temperature range suitable for gold accumulation. The hydrothermally carbonitized diorite wall rock are depleted in gold. Moreover, circular sericite is sometimes well-developed into muscovite laths or even flakes (hypogene type). Alteration may have changed into silicification, chloritization and carbonatization with increasing depth. These alteration types represent suitable environments for gold accumulation. There is close relation between gold and quartz veins at the Jabal Al-Khawar prospect. The mineralization style shows a spatial and temporal relationship with the auriferous quartz veins indicating silicification. Mapping, grid sampling, and trenching were carried out in the three vein clusters A, B, and C and at some sites forming dendritic branches from the main auriferous quartz veins. The correlation matrix of the analyzed elements shows concordant values which demonstrate that the gold in the three sites were precipitated during the same event and that the gold mineralization belongs to one phase. The majority of the collected data at Jabal Al-Khawar strongly confirms a mesothermal ore style.
Jennadi, E.H., Al Harbi, Z.M., and Dourgham, I.A., 2013, Detailed exploration and assessment of the Jabal Al-Khawar east gold prospect with the collaboration of Siddiqui, A.A.: Saudi Geological Survey Open-File Report SGS-OF-2013-1, 43 p., 29 figs., 10 tables, 1 app., 2 pls.