LES MINÉRALISATIONS SULFURÉES À CU-FE ET LES ALTÉRATIONS ASSOCIÉES DANS LES OPHIOLITES PROTÉROZOIQUES DE BOU AZZER ET DE KHZAMA (ANTI-ATLAS, MAROC) (Cu-Fe sulfureous mineralisations and the associated alterations in the Bou Azzer and Khzama Proterozoic ophiolites, Anti-Atlas, Maroc)

Abstract

The Panafrican ophiolites of Bou Azzer and Khzama (NE Siroua) contain sheeted dikes of gabbro and diabase. These dikes are accompanied by hydrothermal pockets of epidosite (epidote, quartz) at the base and veins of chlorite, albite, quartz, epidote and sulfides towards the top. Two stage of mineralizations have been recognized in these ophiolites. The first (phase 1) is early pre-orogenic, and the second, (phase 2) is late- to post-orogenic. In the Bou Azzer ophiolite phase 1 includes two successive paragenesis. Paragenesis 1 characterized by high temperature (350°C), high sulfur fugacity (fS), and low oxygen fugacity (fO2), includes cubanite, chalcopyrite, pink bornite, and sphalerite. Paragenesis 2, of lower temperature and higher sulfur and in oxygen fugacity, consists of digenite, covellite, and chalcocite. In the Khzama ophiolite, phase 1 is formed solely of sphalerite and chalcopyrite, the cubanite and the bornite were not observed. Phase 2, in both ophiolites includes veins of pyrite which cut both phase 1 and the foliation. These stockworks formed from hydrothermal paleocirculation in deep Proterozoic oceanic crust parallel to the sheeted dikes. Application of the geothermometer of Cathelineau and Nieva (1985) gives chlorite crystallization temperature of 320° -380°C (greenschist facies).