The Umm Matierah gold prospect: Mineralogical and geochemical characteristics of a potential low-sulfidation epithermal gold deposits, southeastern Arabian Shield, Saudi Arabia

Abstract

The Umm Matierah gold prospect is located in the southeastern part of the Arabian Shield, at the northernmost tip of the Jabal Ishmas-Wadi Tathlith gold belt. Detailed mineralogical and geochemical investigations indicated that the studied metavolcanics show lithological varieties of meta-alkali basalt, meta-andesite, meta-trachyandesite, and meta-dacite. These rocks are foliated and hydrothermally altered (bleached), indicating a low-temperature propylitic alteration, affected by breccia veins and veinlets, and irregular stockwork. The Umm Matierah gold deposit is characterized by quartz-adularia-sericite-chlorite-carbonate alteration assemblage. The ore minerals of the Umm Matierah gold prospect are dominated by pyrite and arsenopyrite, with minor amounts of sphalerite. The sulfides have no preferred host rock; however, they are mainly present within the veins and veinlets and at the contacts with host rocks; they are also associated with the quartz-rich breccias. Minute gold grains are traced at the contact between the inner pitted and the outer clear zones of large pyrite crystals. Gold and sulfide enrichment do not exceed 10 vol% of the whole rock and are correlated with the thickness of extensive alteration zones that also show an ultimate association of chlorite with sulfide minerals. Compositionally, the studied rocks show 6.47 ppm average gold, are relatively rich in K, Ag, As, Sb, and W, and are relatively poor in Al, Na, Cu, Cr, Ni, Nb, Y, and Rb. The host rocks range in composition from ultrapotassic, shoshonitic, high-K calk-alkaline, to calk-alkaline end member, with transitional environmental signature from intraplate to oceanic island arc. These compositional features suggest that these rocks may have been derived from island source and subsequently slightly fractionated and contaminated during ascent and/or slightly affected by hydrothermal alteration. The host rocks display strong positive Eu, and negative Th, Nb, and Sr anomalies in keeping with the upper continental crustal pattern. There is a general enrichment of the LILEs and the LREEs relative to the MREEs. Collectively, our data, suggest that gold mineralization at Umm Matierah gold prospect, is a possible candidate for a low-sulfidation epithermal style of mineralization, spatially associated with the distal intrusion.