Journal of Tethys: Vol. 2, No. 4, 287–313 ISSN: 2345 –2471 ©2014 Bhilisse et al., 2014 287 Available online at http://jtethys.org Geochemical and Mineralogical Characteristics of Serpentinite and Carbonated Serpentinite: case of Magnesite (Bou Azzer inlier, Central Anti-Atlas, Morocco) Mohamed Bhilisse 1* , Amina Wafik 1 , Hassan Admou 1 , Lhou Maacha 2 , Marc Constantin 3 1- Department of Geology. Faculty of Sciences-Semlalia, Cadi Ayyad University, Marrakesh, Morocco. 2- Managem mining Company (SA), Twin Center, Casablanca, Morocco. 3- University of Laval, Quebec, Canada. * Corresponding Author: mohamed.bhilisse@edu.uca.ma Abstract Ultramafic rocks are essentially constituted by silicates of magnesium: forsterite, and/or Diopside- enstatite; who’s the most common hydrothermal alteration are the serpentinization. To Bou Azzer, the serpentinisation affected almost all of the ultrabasic rocks. Among the phenomena bound to the serpentinisation observed on the ground, we distinguish the magnesium deposits (Carbonated serpentinite). These magnesian deposits correspond to veins taken in serpentinized peridotites either realizes the contact between serpentinites and ultrabasic and basic cumulats. These veins of some centimeters a few meters away from power concentrate essentially in the regions of Ait Ahmane, Ingujjem and Ambed and are formed by massive or brecciated magnesite or in cauliflower. The petrography ic and mineralogical studies of the deposits of magnesite of Bou Azzer, reveal mainly two different mechanisms: The replacement metasomatic in situ of the serpentine and the filling of fracture by circulation of a hydrothermal mineralizing fluid. A geochemical study of magnesites and serpentinites of Bou Azzer showed magnesite to be enriched in SiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, MnO and Sr and depleted in Na 2 O, P 2 O 5 , K 2 O and CaO relative to the hosted serpentinite. It is suggested that the ascent of hydrothermal fluids rich in CO 2 pulls the change of the serpentine and the streaming of meteoric waters are at the origin of the magnesite. The latter gradually and partially replace the original serpentine, but occasionally total replacement occurs. Given the geological, structural, petrographic, and geochemical characteristics, the magnesite of Bou Azzer is of type Kraubath. Keywords: Bou Azzer, Magnesite, Carbonated serpentinite, Serpentinisation, Kraubath. 1–Introduction The Bou Azzer inlier of the Anti Atlas of Morocco represents a geological window into the proterozoic basement surrounded by a discordantly overlying infra-cambrien to paleozoic cover sequence. The serpentinization at Bou Azzer occured in two phases: i) a pseudomorphic oceanic serpentinisation materialized by the isotropic serpophite preserving the primary form of olivine crystals with needles antigorite fibro-struck orbrucite as inclusions in the serpentine; ii) and tectonic serpentinization during the obduction of ophiolite with lizardite and chrysotile as a common serpentine mineral products. Magnesite is a rare rock forming mineral occurring in different marine and non-marine geological settings due to the geochemical relations of silicon, iron and calcium. However, magnesite deposits have been formed since the Archean either as carbonated ultramafic rocksor as sedimentary beds. Moreover, major magnesite deposits occur in the Precambrian, and thick magnesite dominated sequences are unknown in the Phanerozoic (Abu-Jaber and