Fluid evolution in an unmineralized greisen-tourmaline system in the Ment granite (central Morocco): a fluid-inclusion study
Marignac, Christian; Zouhair, Mohamed
European Journal of Mineralogy Volume 4 Number 5 (1992), p. 949 - 964
published: Oct 14, 1992
manuscript accepted: Feb 6, 1992
manuscript received: Jul 3, 1991
ArtNo. ESP147050405004, Price: 29.00 €
Abstract Of the Hercynian granites of central Morocco, the Ment granite is the only one devoid of significant ore deposits. Hydrothermal alteration is well developed in the Ez-Zirari area to the NW of the Ment massif. There, fissure-like greisens preceded the formation of quartz-tourmaline bodies. Fluid inclusions in quartz from unaltered biotite granites and leucogranites as well as in quartz from greisens with or without tourmaline were studied in order to compare hydrothermal evolution in the Ment and in mineralized granites of central Morocco. Three successive hydrothermal events are recorded by fluid inclusions: 1) a boiling event involving a fluid of magmatic origin, yielding brine and vapour at a temperature of ca. 400 °C under a low hydrostatic pressure of ca. 20 MPa; 2) a greisenization event involving metamorphic fluids of the C-H-O-N-S-Na-Cl system at a lithostatic pressure of ca. 50 MPa and at temperatures higher than 450 °C, which are progressively diluted and cooled down to ca. 400 °C by moderate-salinity aqueous fluids of more superficial derivation; 3) a tourmalinization event involving the dilution of a hot (ca. 400 °C) moderate-salinity (ca. 8.5 wt.% eq. NaCl) aqueous fluid by a cold (ca. 170 °C) low-salinity (< 0.5 wt.% eq. NaCl) aqueous fluid. These three events are interpreted as the expression of a series of distinct hydrothermal systems generated by the late leucogranites of the Ment massif. They bear much similarity to many mineralized hydrothermal systems in the world and in particular to the neighbouring mineralized granites of central Morocco (Zaër, Walmès). Therefore, the lack of mineralization in the Ment area cannot be ascribed to significant differences either in the nature of the fluids involved or in the characteristics of the hydrothermal evolution.