Geology and Mineralization of the Wadi al Khadra Cu-Ni Ore Prospect, Wadi Bidah District, Southwest Region, Kingdom of Saudi Arabia
Nasir S. Al-Jahdali, Ral A. Escarrachi, Ibrahim Khalil, Eyad H. Jinadi, Turki Bokhari, Alim A. Siddiqui, Ghazzi Kattu, and Omar Al Amoudi
The Wadi al Khadra prospect has syngenetic copper and nickel minerals in a fairly disseminated style within thin-layered, ultramafic to mafic lava flows that range from normal flows to agglomerates. Due to different periods of structural deformation and intrusions, these rocks were metamorphosed from mainly greenschist up to local amphibolite-serpentinite facies. Bedding or foliation is sub-parallel to local structural trends with azimuths of 320° and 60°. However, the dominant north-south structural trend can be observed in folds, faulting, mafic and felsic dikes, as well as abundant large quartz veins. Fractures and folds, along with microfolds in the outcropping Jof and Ras formations, are also aligned with this general trend.
Averaging 227.33 m long, four diamond drillholes with a total length of 909.35 m were completed to localize the mineralized zone at depth, determine its geometry, and to model and quantify the potential resource. Most were oriented at 200°-275° azimuth and with inclinations of 55°-65°. Mineralization occurs in four horizons from near surface to depth of 110 m. The mineralized zones appear to be discontinuous to the north. However, mineralization remains open to the south where the numbers of horizons increase and thicken.
The mineral assemblage mainly consists of copper in oxidized and sulfide form, expressed by chalcopyrite, pyrite, niccolite, and arsenopyrite. Mineralization occurs as veinlets, clusters, patches, and stringers along the foliation or fractures. It may have been subjected to several periods of remobilization due to structural deformation and metamorphism. On the basis of the sulfide content and mineral associations, the mineralized zone is a volcanogenic massive sulfide (VMS) type, which has been highly altered and metamorphosed.
The potential resource of copper and nickel is located along the 250-m-wide shear zone which is a product of early to late tectonic activity. Apparently, mineralization occurs in layered zones in mafic rocks of variable composition. The shear zone strikes 300°-305° azimuth and dips 85° to 90° NE. At this locality, mineralization comprises mainly reddish hematite, goethite, and traces of limonite on the surface. Primary mineralization occurs at depth, expressed by pyrite, chalcopyrite, pentlandite(?), and niccolite, which is a typical mineral assemblage associated with these lithologies. The total potential resource for this mineralized zone is 2.3 Mt containing 19 kt of Cu and 5.7 kt of Ni.
A highly anomalous area located approximately 360 m north of the mineralized zone should be considered for a drilling campaign. Surficial rock sampling has detected an enriched Cu-Ni target. As indicated in the regional map, there is a 40-m x 10-km corridor of gold and copper occurrences some of which have ancient mining excavations and exploration workings. A regional exploration program should be carried out to its north and south. Future studies for target selection should consider remote sensing, geophysical and radiometric surveys, followed by field visits with tactical sampling to define new areas. More surficial exploration and drilling in the south is recommended for increased mineral resource potential. The next steps would be systematic stream sediment and rock sampling programs.
Al-Jahdali, N.S., Escarrachi, R.A., Khalil, I., Jinadi, H.M., Bokhari, T., Siddiqui, A., Kattu, G., and Al-Amoudi O., 2015, Geology and mineralization of the Wadi al Khadra Cu-Ni ore prospect, Wadi Bidah district, southwest region, Kingdom of Saudi Arabia: Saudi Geological Survey Technical Report SGS-TR-2013-15, 39 p., 21 figs., 7 tables, 11 apps.