| The polymetallic Hajar deposit, located 30 km south of Marrakech, represents one of the most important north African volcanogenic massive sulfide deposits. It occurs at a depth of a hundred metres, at the contact between two Dinantian lithostratigraphic units belonging to the Viséan Guemassa massif. The host rocks were deformed during the Hercynian and Alpine orogenies, resulting in important folding and a regional metamorphism attaining the green-schist facies.; From underground mapping and drill holes data, we have refined the stratigraphic column at the deposit scale. Petrologic and geochemical studies show a rhyodacitic felsic lava overlain by andesitic tuffs, succeeded then by massif sulfides, which are in turn overlain by hangingwall turbidites and carbonates. All of these rocks show the effect of hydrothermal alteration affiliated with the Hajar mineralization.; The earliest hydrothermal product consists of thin pyrrhotitic laminae interbedded with tuffs. The massive sulfide mineralization overlying the tuffs is concordant with the sedimentary host-rocks; the eastern portion is predominantly pyrrhotitic, whereas the western portion is pyrititic. Mineral textures consist of banded laminae of pyrrhotite-chalcopyrite overlying a stockwork zone, banded sphalerite-galena mineralization (economic zones), and massive pyrrhotite without sphalerite or galena.; Stockwork mineralization is hosted by in all rocks underlying the ore body. The central part is chalcopyritic and, where it intercepts the pyrrhotitic rythmites, the stockwork mineralization consists of sphalerite. Surrounding the stockwork zone are four zones of silicate alteration: a silicic central zone, succeeded outward by serictic, biotitic and chloritic zones.; Our genetic model for the Hajar mineralization proposes that the pyrrhotitic bands of the footwall rythmites and hangingwall turbidites result from fluids of moderate temperatures which exhaled during accumulation of their hosts. The massive sulfide mineralization was deposited from a hotter fluid with a density is 0.8 g/cc, carrying iron, zinc, lead and copper, injected into the tuffs and turbidites between the lower temperature fluids responsible for the pyrrhotitic rythmites. The dispersion of hot low density ore-forming fluids by an exhaling plume can be prevented by infiltration into unconsolidated sediments. Lead isotopes from Hajar galena suggest the mixing of a fluid from a deep source (Cambrian sediments) with a fluid from the Carboniferous volcanic footwall rocks. Sulfur isotopes indicate a sulfur source in Viséan seawater or from leaching of Viséan volcanic and sedimentary units. |
