Mineralogy and Fluid Inclusions of the Kettara Massive Sulphide Deposit (Jebilet Massif, Variscan Belt, Morocco)

Abstract

The Kettara copper deposit is located in the centre of the Jebilet massif, north of Marrakech, and consists of an elongated sub-vertical pyrrhotite-rich massive sulphide lens. The host rocks consist of thin-bedded Visean pelites with sandstones, calcareous beds and doleritic dykes. The host rocks have been folded, foliated, and metamorphosed to low greenschist facies conditions during the Variscan orogeny.

The sulphide mineralization comprises a main lens composed of massive to semi-massive pyrrhotite accompanied by chalcopyrite, magnetite, sphalerite, arsenopyrite, galena and a quartz-chlorite gangue, centimetre-scale mineralized syntectonic replacement veins in the wall rocks with the same mineralogy as the main lens, and a later pyrite-carbonate veins that cut across pyrrhotite mineralization. Microthermometry and Raman analysis indicate that the mineralizing fluids associated with pyrrhotite formation were H₂O, N_2, CH₄ and CO₂-bearing, with low salinities (7.5 wt.%NaCl), typical for low-grade metamorphism. P-T conditions from fluid inclusion studies and chlorite geothermometry indicate that pyrrhotite formation occurred at c. 200-400°C and c. 2 kbar. These characteristics indicate that the genesis of the main mineralization in the Kettara massive sulphide deposit might have taken place in the transition between diagenetic and metamorphic environments or in metamorphic environment under reducing condition.

Keywords: massive sulphide, pyrrhotite, fluid inclusions, deformations.