An integrated structural, mineralogical, and geochemical investigation of a fault-controlled hydrothermal system in Northern Tunisia

Integrated structural observations, XRD mineralogy, whole-rock geochemistry, and stream-sediment analyses from the Sidi Aïssa district (northern Tunisia) document a fault-controlled hydrothermal system developed along the NE–SW Ras El Korane–Thibar Major Fault (RKTMF). The system is characterized by hydrothermal breccias, quartz–carbonate veins, silicification, argillic alteration, and iron-oxide-rich gossans within a broad brittle fault damage zone. Breccias display crackle, mosaic, chaotic, and locally vuggy textures indicative of repeated hydraulic fracturing and fluid circulation. XRD analyses reveal alteration assemblages dominated by quartz, calcite, dolomite, illite, muscovite, clinochlore, and minor kaolinite. Whole-rock geochemistry shows modest Zn–Pb–Ba enrichment in hydrothermal breccias, whereas stream sediments exhibit strong polymetallic anomalies (Zn 58–47,200 ppm, Pb 15.6–8,563 ppm, As 7.6–1,132 ppm, Ba up to 63,100 ppm), well above regional threshold values. Robust Principal Component Analysis (RPCA) identifies a dominant hydrothermal Zn–Pb–As–Cd–Ba association opposed to a contrasting Sb–Ag–Th–Zr–V–P assemblage. The strongest anomalies occur mainly north of the main mapped fault trace, suggesting preferential mineralization within subsidiary structures and concealed feeder zones adjacent to the RKTMF. Intense supergene oxidation has destroyed primary sulfides at surface. Comparison with the nearby Sidi Aïssa Pb–Zn–Ba occurrence, where primary sulfides are preserved at depth, suggests that Cheneg Roha represents the oxidized upper part of a larger fault-controlled hydrothermal system. The observed features are compatible with fault-controlled hydrothermal systems of possible epithermal affinity, although confirmation of the genetic model—including the sulfidation state—requires further petrological, fluid inclusion, and isotopic studies. These results highlight the exploration significance of reactivated crustal-scale faults in the Tunisian Nappe Zone.