Paragenesis and supergene evolution of the Cu-Ba±Pb-Amethyst mineralization from Baba Joua Ali, Eastern Anti-Atlas, Morocco: Exploration application

Abstract

The Baba Joua Ali (BJA) ore mineralization is situated in the Maider basin at the Eastern Anti-Atlas. In this area, the mineralization is hosted within the Ktaoua group and the Second Bani Formation of the Upper Ordovician. The upper Ordovician terrane display ductile deformation, characterized by a succession of synclinal and anticlinal structures. From north to south, the Ordovician formations show a WNW-ESE trend syncline at Jbel El Machhot. The veins ore mineralization is controlled by N-S to NE-SW trending faults. These faults are linked to the Variscan orogeny and kinematic indicators suggesting left-lateral and right-lateral motions, respectively. Based on the metallographic relationship between minerals from outcrop to microscopic observation, two major mineralizing stages are proposed for the precipitation of ore mineralization. The first is a hypogene stage with a banded texture, it comprises colorless quartz with sulfides, amethyst with iron oxide, and finally barite and sulfides. Microthermometric analysis of fluid inclusions was carried out on colorless quartz and amethyst. Primary fluid inclusions trapped in colorless quartz indicate temperatures from 120 to 140 °C and salinity between 14.46 and 19.84 wt% NaCl eq. This fluid is characterized by Te ranging from −32 to −22 °C, interpreted as a NaCl-H₂O system. The fluid inclusion from amethyst indicates a temperature from 100 °C to 110 °C and salinity between 13 and 14 wt% NaCl eq. The banded texture of the primary mineralization (border to center: colorless quartz, amethyst, and barite) reflects the extension context and may correspond to fluid percolation in the Variscan orogeny fault during the Triassic extension (CAMP). The second major stage is characterized by the formation of covellite, chalcocite, malachite, hematite, chrysocolla, cuprite and native copper. This assemblage is linked to the supergene process, the percolation of meteoric acidic water is favored by the intense fracturing in upper Ordovician quartzite, cavities, and fractures crosscutting quartz, amethyst, and barite. The copper and iron oxide with copper carbonate observed at BJA correspond to oxidized zone.