Sulfide disseminations and hydrothermal alteration haloes in the Gabal Monqul area, Egypt: Field, mineralogical, and remote sensing studies

Field and mineralogical studies are integrated with multispectral and radar satellite data to unravel the occurrence of sulfide dissemination in the Gabal Monqul area (Eastern Desert, Egypt). This study was motivated by the strong belief that the widespread hydrothermal alteration haloes and sulfide disseminations in this area were ambiguously deciphered as a porphyry-style mineralisation. NE-Elongate bodies of silicified and sulfidized rocks frequently occur at the contacts between andesite-dacite, granodiorite, and porphyritic biotite granite intrusions. Hydrothermal alteration zones are best identified and outlined by employing band ratios (BR) and independent component analysis (ICA) techniques for the distinction between ferric and ferrous iron minerals. If fused with the clay and OH-bearing minerals maps, ferric iron oxides may characterise epithermal and porphyry mineralisation in which ore formation occurs under oxidising conditions. Iron-hydroxide, copper hydro-carbonate (malachite), and hydrous copper phosphate (pseudomalachite) are supergene mineral phases. The resultant processed images show that alteration extends beyond unit boundaries and overlaps different crosscutting lithologies. This observation implies that hydrothermal alteration of the host rock represents a secondary overprint, yet gypsum (±anhydrite) and barite in association with iron oxides and pyrite disseminations pinpoint a porphyry-related alteration assemblage. The poor metal endowment in the potassic alteration zones goes against the supergene enrichment typical of the porphyry mineralisation system and is coupled with the lack of hydrothermal breccia bodies, implying a rather epithermal sulfidation genesis. However, a thorough assay program is required to outline the potential metal-rich lithological unit(s) using XRD and remote sensing investigations that point to zonal alteration anomalies.