Deformation-assisted fluid flow and massive sulfide evolution in a ductile shear zone: insights from the Kettara mining district (Central Jebilet, Morocco).

The Kettara mining district (Central Jebilet, Morocco) hosts a pyrrhotite-rich massive sulfide lens enclosed within the low-grade metamorphosed Sarhlef volcano-sedimentary sequence and spatially associated with a syntectonic mafic–ultramafic intrusion. The deposit lies within a dextral strike-slip shear zone of the Variscan belt. The main objective of this study is to evaluate the structural role of the Kettara shear zone in the genesis, architecture, and redistribution of the massive sulfide lens, and to determine whether it represents a pre-existing sulfide accumulation subsequently remobilized during ductile deformation or a syntectonic sulfide formation linked to shear-zone activity.

Structural observations reveal an increasing deformation gradient from the volcano-sedimentary wall rocks toward the ore lens, with maximum strain at the ore–host interface. Deformation produced several structural generations: an early S1 foliation with a general N45 orientation associated with anisopachous P1 folds; a penetrative S2 foliation accompanied by tight isoclinal P2 folds; and late chevron P3 folds, observed exclusively within the ore body, which has been tectonically rotated and progressively steepened to a subvertical attitude in direct response to shear-zone deformation. Localized shear corridors exhibit well-developed C/S fabrics, indicating strain partitioning and a strong simple-shear component. These structures acted as preferential pathways for fluid flow, locally accommodating transient porosity through grain-size reduction and recrystallization.

Microscopic studies reveal a mineral paragenesis characterized by two distinct metallogenic stages. The first stage corresponds to a silica- and sulfur-rich fluid, dominated by massive pyrrhotite displaying textures indicative of syn-metamorphic remobilization and recrystallization, accompanied by subordinate pyrite, chalcopyrite, galena, and sphalerite, with chlorite as the main gangue phase. The second stage is characterized by fissuring of pre-existing sulfides and the infiltration of Cu–Zn–Fe-rich fluids, causing disseminated precipitation of pyrrhotite, chalcopyrite, galena, and quartz–carbonates, while reorganizing the minerals under the influence of ductile deformation and the preferential flow of fluids along the structural conduits of the shear zone. Collectively, these stages record the transition from an early Fe-rich massive sulfide accumulation to later fluid-mediated mineral precipitation.

These observations highlight the first-order structural control exerted by the Kettara dextral shear zone on hydrothermal fluid transfer. Although available data do not allow a definitive distinction between metamorphic remobilization of a pre-existing sulfide mineralization and the intervention of magmatic–hydrothermal fluids derived from the syntectonic intrusion, the structural control remains unequivocal. At all scales, the mineralization is strongly guided by the shear-zone architecture, forming anisotropic, high-permeability conduits that control fluid ingress, fluid–rock reactions, and the coupled chemical–mechanical evolution of the deforming rock mass.

Kettara thus represents a natural example of deformation-assisted fluid migration and shear-zone-controlled metallogenesis in an orogenic setting. Complementary petro-structural, geochronological, and isotope geochemistry investigations are needed to constrain the timing, sources, and physico-chemical conditions of the fluids involved.

Keywords: massive sulfides, C/S fabrics, ductile shear zones, fluid flow, remobilization, Kettara.