Sedimentology, Metallographic Characteristics and Geodynamic Evolution of the Merija Copper Deposit (Marginal Folds Basin, Eastern High Atlas, Morocco)

Abstract

The Merija copper deposit is located in the Marginal Folds of the Moroccan Eastern High Atlas. It is a stratiform deposit hosted in sandstone-conglomerate formations of the Infra-Cenomanian, consisting of copper carbonate and sulphide mineralization (malachite, azurite, traces of chalcopyrite, chalcocite, and covellite). This mineralization exhibits different forms: dissemination in the sandstone-conglomerate host rocks and fillings of centimetric veins, sometimes with calcite. Moreover, microscopic examination shows that the mineralization is disseminated in the carbonate matrix, filling of the inter-granular spaces of the sandstone-conglomeratic material. The mineralogical association is composed of: a primary paragenesis with chalcopyrite ، a secondary cementation paragenesis with chalcocite and covellite and a secondary oxidation paragenesis with malachite. This latter is the most dominant mineral presenting a micro-fibrous texture surrounding the sulphides of the primary and secondary paragenesis, composed of chalcopyrite, chalcocite and covelite. It is associated with a quartz-calcite gangue. The copper mineralization at Merija is heterogeneously distributed within the surrounding sandstone-conglomerate formation due to the diversity of paleocurrents carrying the leached copper. The rich paleocurrents trends S, SW, and SE, whereas the poor ones present an N and NW directions. These paleocurrents are derived from a fluvio-deltaic channel system that controlled sedimentary deposition in the area during the Infra-Cenomanian. This sedimentary type mineralization is probably related to a process of alteration and deposition of detrital materials loaded with copper minerals and derived from a protore copper-bearing. This alteration process gave rise to the malachite and azurite mineralization resulting from the replacement phenomenon of chalcopyrite, chalcocite and covellite.