Origin of rift-induced sediment-hosted barite mineralization in the Early Miocene Musayr Formation, Midyan Basin, northwestern Saudi Arabia

Rift-related faults are widely recognized as key structural pathways that facilitate fluid migration and promote barite mineralization within sedimentary successions. Fracture- and fault-controlled barite mineralization occurs within the Early Miocene Musayr Limestone of the Midyan Basin, northwestern Saudi Arabia; however, its origin and fluid evolution have remained poorly constrained. This study presents the first comprehensive investigation of these barite deposits, integrating field observations, petrography, scanning electron microscopy, X-ray diffraction, whole-rock geochemistry, sulfur isotope analysis, and fluid inclusion microthermometry to constrain the mineralogical characteristics, formation conditions, and genetic controls of the mineralization. Barite occurs predominantly as vein- and fracture-filling mineralization localized along NW–SE–trending faults and fractures associated with the extensional tectonic regime of the Red Sea rift, although local transpressional stresses have led to the development or reactivation of reverse faults that act as fluid pathways. Petrographic observations reveal at least two stages of barite precipitation. The first and most volumetrically significant stage is characterized by coarse, euhedral to subhedral bladed and lath-like crystals forming radiating, fan-shaped, and rosette aggregates that grow into open cavities, indicating open-space growth from hydrothermal fluids. Fluid inclusions trapped in these crystals are predominantly primary, two-phase (liquid and vapor), and yield homogenization temperatures of approximately 68–89 °C. These temperatures fall within the range of both burial diagenetic and low-temperature hydrothermal systems. However, the structurally controlled occurrence, open-space filling textures, and radiating, fan-shaped morphology of the barite are more consistent with precipitation from hydrothermal fluids than with typical burial diagenetic growth. A later stage of barite occurs as platy, fracture-filling tabular crystals that replace earlier gypsum and anhydrite. These textures indicate fluid-mediated replacement under relatively low-temperature conditions, possibly reflecting late-stage fluid circulation distinct from the earlier barite-forming fluids. Sulfur isotope compositions of barite, compared with those of the Middle Miocene Mansiyah evaporites, indicate that sulfate was primarily derived from sulfate-rich basinal or evaporitic brines rather than magmatic sources. Whole-rock mineralogical and geochemical data suggest that barium may have been supplied mainly through leaching of K-bearing minerals in the Proterozoic feldspar-rich basement and the underlying arkosic sandstones of the lower Musayr Formation during fluid–rock interaction. Mixing between ascending Ba-rich hydrothermal fluids and sulfate-rich basinal brines along fault-controlled pathways triggered barite precipitation. Overall, the Musayr barite mineralization represents a structurally controlled, low-temperature hydrothermal fluid system with a late-stage overprint, likely developed under shallow burial conditions (on the order of a few kilometers), consistent with the fluid inclusion temperatures (∼68–89 °C) and basin-scale fluid circulation in an overall rift-related setting. These findings provide new insights into barite formation processes in extensional basins and offer a genetic framework applicable to similar barite occurrences in rifted continental margins worldwide.