Orogenic gold in compressional and transpressional zones: geophysical, remote sensing and field studies on the central segment of the Allaqi-Heiani Suture, Egypt

Abstract

Abstract Geophysical data, multi-sensor satellite imagery, and field structural studies were employed to analyze the geological context and factors influencing gold-bearing quartz veins within the central Neoproterozoic Allaqi-Heiani suture (~ 730–700 Ma) of the Egyptian Nubian Shield. This region is characterized by ophiolite slices, volcaniclastic metasediments, metavolcanic rocks, and syn- and late-tectonic granitoid intrusions. The tectonic evolution comprised four phases: D 1 (N-S shortening) established penetrative cleavage foliation, imbricate thrust faults, and E-W to WNW-ESE folds. D 2 (NE-SW shortening) caused refolding of the suture belt, generating NW–SE folds and a NW-trending sinistral shear zone that overprints earlier thrusts. D 3 (E-W shortening) resulted in upright and inclined refolding around N-trending axes, creating NNW-SSE thrust-dominated strike-slip shear zones through reactivation of NW-trending thrusts and sinistral shear zones, with the Seiga-Shashoba gold mine area developing as a pop-up structure, and NW-trending shear zones anchored in a low-angle crustal detachment, marking a transition from oblique thrusting to transpressional strike-slip and reverse-sense shear zones. D 4 involved refolding around NE-trending axes, forming dextral NE-SW-striking transpressional shear zones. Gold occurrences are primarily located in areas with NW- and N-aligned superimposed foliations, foliation deflection, significant strain partitioning, and doubly plunging folds. The analysis of host structures, supported by geophysical and remote sensing data, indicates that the formation of gold-bearing quartz veins reflects a temporal and spatial evolution from early compression to early transpression, aligning the Allaqi-Heiani suture with global examples of accretionary metallogenic belts.