Oct 2023
Abstract
World-class gold deposits encompass the top decile of all known gold deposits, containing nearly 90% of the total Au content discovered in the Earth's crust to date. These exceptional deposits contain a minimum of 3.5 Moz, equivalent to ~ 100 metric tons Au, and 'true giants' are those that surpass 10 Moz of Au, approximately 300 metric tons.
In the Arabian-Nubian Shield, the Sukari (> 15 Moz) stands as a colossal ‘giant’ world-class deposit, and discrete ‘sub world-class’ deposits occur in different parts of the shield, e.g., Hassai (Sudan) with 2.3 Moz, Ad Duwayhi (Saudi Arabia) ~1.9 Moz, Tulu Kapi (Ethiopia) ~1.7 Moz, Bisha VMS deposit (Eritrea) with ~ 0.5 Moz. The Sukari mine produces ~ 0.5 Moz of gold annually.
Field, mineralogical and geochronological studies of the Sukari deposit suggest ore formation during the orogenic collapse stage. During this stage, ore deposition from shear-associated, circulating magmatic (± metamorphic) fluids could have been triggered by pressure fluctuation and focused flow at rheologically contrasting interfaces. Not to a lesser importance, buffering of the single- or mixed-source ore fluids was maintained by the interaction with reduced carbon in carbonaceous ophiolitic mélange rocks. In a conceptual model, the Sukari granite (~695 Ma) acted as a rigid body that enabled preferential strain localization and repeated pressure build-up and release, resulting in auriferous quartz veins and low grade sericitized wallrock (~ 623 Ma). The diverse spectrum, ranging from contorted and laminated Au-quartz veins to silica-rich hydrothermal breccia, signifies a protracted mineralization process as the system transitioned from ductile to brittle behavior at intermediate crustal depths (12-5 km).
Considering the ANS's favorable geological attributes and its prolonged orogenic collapse stage, the presence of substantial, as yet undiscovered gold deposits, including those of the > 1 Moz category, is highly plausible. It is imperative to bear in mind that numerous orogenic gold deposits initially commenced as modest discoveries before expanding significantly in size through continued exploration and resource drilling efforts. From a thematic standpoint, the most promising areas for exploration are those characterized by intra-terrane and inter-terrane shears exhibiting distinctive transpression features and delineating high-strain belts from autochthonous basement blocks.
Bio
Basem Zoheir has been a professor of mineralogy and economic geology at Benha University (Egypt) since 2015, an Alexander von Humboldt Fellow since 2017, and a research professor at Kiel University (CAU-Germany) since 2020. He was a DAAD-scholarship holder and obtained a Ph.D. degree from the University of Munich (Germany). Basem was a visiting researcher at the Universities of Tübingen, TU Clausthal, Geneva, Stockholm, Graz, and TU Lulea, and was a Fulbrighter at the U.S. Geological Survey, Denver. He has authored and co-authored more than 85 research articles in international peer-reviewed journals, written several chapters in edited books, and delivered numerous presentations at international conferences and workshops. He serves as a reviewer and associate or guest editor for a number of geoscience journals and as an examiner for several research funding institutions. Aside from the academic work, he has consulted for international exploration and mining companies. His expertise and research highlight the exploration targeting of orogenic gold and massive sulfide deposits in the Arabian-Nubian Shield, rare metal granites and pegmatites in the Hoggar Massif of the Tuereg Shield, and podiform chromite deposits in the Alpine orogenic belts.