Late-Hercynian intrusion-related gold deposits: An integrated model on the Tighza polymetallic district, central Morocco

•Study describes the first R-IRG deposit in North-Africa to our knowledge.•Detailed mineralogical, isotopic (Pb, Sr–Nd), chronological and fluid inclusions data are given.•Original structural context with pre-granitic corridors explained the shape of the deposits.•3D model is proposed, discarding a genetic relationship of Pb–Ag veins with gold deposits. Gold have been recently recognized in the Tighza (formerly Jebel Aouam) district, in the Hercynian belt of central Morocco. This district has long been known for its W mineralization, as well as major Pb–Ag–Zn, and minor Sb–Ba deposits, all geographically associated with late-Hercynian calc-alkaline magmatism. Gold mineralization in the district is mainly hosted by thick W–Au quartz veins located around the “Mine granite” small granitic plug. Within the veins, gold grade is highest (up to 70g/t) close to the granite but rapidly decreases going outward from the granite, defining a perigranitic zoning. Anomalous gold grades have also been measured in hydrothermal skarn layers close to two other granitic plugs (Kaolin granite and Mispickel granite), associated with disseminated As–Fe sulfides. The paragenetic sequence for the W–Au quartz veins shows three stages: (1) an early oxidized stage with wolframite-scheelite associated with early quartz (Q1), (2) an intermediate Bi–As–Te–Mo–Au sulfide stage with loellingite, bismuth minerals and native gold with a later quartz (Q2), restricted to a narrow distance from the granite, and (3) a late lower temperature As–Cu–Zn–(Pb) stage with abundant massive pyrrhotite, arsenopyrite and sphalerite, locally forming independent veins (“pyrrhotite vein”). Both Q1 hyaline and Q2 saccharoidal gold-bearing quartz display aqua-carbonic fluids with minor H2S and Cu and an homogeneous composition (81mole% H2O, 18mole% CO2 and about 1mole% NaCl). The trapping pressure is estimated to 1.5–2kbar with temperature ranging from 300 to 350°C. Q1 inclusions have exploded indicating an uplift of the Tighza block, that lead to saccharoidal Q2 quartz deposition with multiphase NaCl-saturated fluid inclusions. 40Ar/39Ar dating demonstrates that the “Mine granite”, tungsten skarnoid, scheelite-molybdenite veins, and very likely gold-bearing veins are coeval, emplaced at 286±1Ma. Multiple and widespread metal sources are indicated by radiogenic isotope studies. Nd and Sr isotope compositions of scheelite and granites suggest the participation of a juvenile component while lead isotopes demonstr