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

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, N2, 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

Developing the lithotectonic framework and model for sulphide mineralization in the Jebilet Massif, Morocco: implications for regional exploration

The central Jebilet massif, part of the North African Variscan Belt, hosts significant polymetallic sulphide mineralization. It is generally considered syngenetic and has many features of volcanogenic massive sulphide (VMS) mineralization. However, some characteristics are not compatible with a classic VMS model and two alternative scenarios for formation have been proposed. Our preliminary research favours a complex, multi-stage development of the sulphide deposits. Uncertainty as to the critical processes controlling the mineralization and lack of agreement on a genetic model inhibit regional exploration. We identify the key knowledge gaps regarding sulphide mineralization in the central Jebilet and outline a research program to address these, with the ultimate aim of improving regional mineral exploration targeting and unlocking the economic potential of this relatively undeveloped district

Massive sulphide deposits of the Central Jebilet Massif, Morocco

The Central Jebilet massif, in the Marrakech region of Morocco, comprises a block of Carboniferous sedimentary rocks that were extensively deformed and metamorphosed during the Variscan orogeny. This block, and its extension to the south of Marrakech (the Guemassa massif), are characterised by bimodal intrusive magmatism and abundant massive sulphide deposits that represent a major Cu-Pb-Zn resource. Mining is currently taking place at the Draa Sfar and Hajjar mines. Previously worked deposits at Kettara, Roc Blanc and Koudiat Aicha are not currently being exploited, but have extensive reserves remaining, and prospects such as Laachach and Ben Slimane are being explored

Fluid flow and polymetallic sulfide mineralization in the Kettara shear zone (Jebilet Massif, Variscan Belt, Morocco)

The Kettara shear zone is a regional wrench shear zone within the Jebilet massif of Western Morocco, part of the Variscan orogenic belt. This massif is characterized by bimodal magmatism, largely intrusive, and by a number of polymetallic massive sulfide deposits. A syntectonic mafic-ultramafic intrusion and an adjacent, deformed pyrrhotite-rich massive sulfide deposit are located within a ‘compressional jog’ of the shear zone. Hydrothermal alteration in both the intrusion and the wall rocks adjacent to the deposit is characterized by syntectonic replacement processes leading to formation of chlorite-schists and quartz ± calcite veins. Fluid inclusions in mineralized (pyrrhotite-bearing) quartz veins from the wall rocks adjacent to the deposit and in veins associated with chlorite-schists within the intrusion indicate a prevalence of H2O-CO2-CH4-N2 and H2O-salt fluid systems. In the mineralized veins the fluid shows reducing conditions, with gas dominated by CH4 and N2 and salinities around 7.5 wt% NaCl, whereas in the chlorite shear zones fluid is CO2 dominated and salinities are higher than 23 wt% NaCl. Hydrogen and oxygen isotopic compositions of chlorite and quartz are similar and demonstrate involvement of metamorphic water in both the deposit and the intrusion. The data are consistent with a regional metamorphic fluid flow through the Kettara shear zone. The migrating metamorphic fluids were reduced in the organic matter-rich host rocks leading to deposition of sulfides in the mineralized veins. There are two possible hypotheses for the origin of these mineralized veins: either they were formed during deformation and remobilization of a syn-sedimentary massive sulfide deposit, or they were formed synchronously with the sulfide deposit during development of the Kettara shear zone

Oligo-Miocene thinning of the Beni Bousera peridotites and their Variscan crustal host rocks, Internal Rif, Morocco†

International audienceDeciphering Variscan versus Alpine history in the internal Rif system is a key to constraining the tectonic evolution of the Alboran domain and hence the geodynamics of the western Mediterranean system during the Cenozoic. This study focuses on the evolution of the metamorphic envelope of the Beni Bousera massif and its relation to the underlying peridotites. Combining structural geology, metamorphic petrology, and LA-ICP-MS U-Th-Pb dating of monazite, this study contributes to the understanding of the tectonic history of the western internal Rif. The regional foliation (S2) is characterized by LP/HT mineral assemblages and obliterates a former foliation (S1) developed along a barrovian (MP/MT) metamorphic gradient. The dating of some metamorphic monazite grains from a micaschist and a migmatitic gneiss demonstrates that the crustal envelope of the peridotite recorded two distinct tectonometamorphic episodes. Data from monazite inclusions in S1 garnet suggest that the first event, D1, is older than 250-170 Ma and likely related to the Variscan collision, in agreement with the barrovian type of the metamorphic gradient. The second event, D2, is Alpine in age (at circa 21 Ma) and corresponds to a strong lithosphere thinning allowing subsequent subcontinental mantle exhumation. Such a tectonic context provides an explanation for the LP/HT metamorphic gradient that is recorded in the regional foliation of the western Betic-Rif system. This extension is probably related to a subduction slab roll-back in the western end of the Mediterranean realm during the Oligo-Miocene times. No evidences for a Tertiary HP/LT metamorphism have been identified in the studied are

The Moroccan Massive Sulphide deposits: evidence for a polyphase mineralization

This work provides an overview of the geological, geochemical, and metallogenic data available up to date on the Moroccan massive sulphide deposits, including some new results, and then discusses the evidences for the epigenetic and syngenetic hypotheses. All of the ore deposits are located within a crustal block located at the intersection between two major shear zones and are characterized by a sustained and long-lived magmatic activity. The ore deposits are located within second-order shear zones, which played an important role in controlling the geometry of the mineralization. The mineralization lacks the unequivocal textural and structural features that are indicative of a sedimentary or diagenetic origin, and a syntectonic to late-tectonic pyrite-rich assemblage is superimposed on an earlier, pretectonic to syntectonic pyrrhotite-rich mineralization. Each deposit has a distinctive pyrrhotite sulfur isotopic signature, while the sulfur isotopic signature of pyrite is similar in all deposits. Lead isotopes suggest a shift from a magmatic source during the pyrrhotite-rich mineralization to a source that is inherited from the host shales during the pyrite-rich mineralization. The O/H isotopic signatures record a predominance of fluids of metamorphic derivation. These results are consistent with a model in which an earlier pyrrhotite-rich mineralization, which formed during transtension, was deformed and then remobilized to pyrite-rich mineralization during transpressio