The Moroccan Massive Sulphide Deposits: Evidence for a Polyphase Mineralization

Abstract

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 transpression.

Sidi M'Barek: a representative example of the Moroccan massive sulfide deposits

“…Figure 14. Lead and sulphur isotopic compositions of the Draa Sfar ores (data from Marcoux et al 2008;Essaifi et al 2019). The lead isotopic compositions of the IPB VMS deposits (Blue field; Marcoux 1998) are also shown for comparison.…”

“…A less radiogenic source (with 206 Pb/ 204 Pb close to 18.28) dominated in the Zn-rich lens, and a more radiogenic source ( 206 Pb/ 204 Pb ~ 19.01) was predominant in the Cu-rich lenses (Marcoux et al 2008). The most radiogenic lead isotope signatures are recorded in the syn-to late-tectonic pyrite veins crosscutting pyrrhotite at Sidi M'Barek, and mark a contribution of radiogenic lead during the syn-metamorphic mineralization, coeval with low-grade metamorphism (Essaifi et al 2019), while the less radiogenic Pb isotopic values are represented by the Zn-rich ore of Tazakourt, and suggest a major contribution of volcanic rocks as source of metals (Marcoux et al 2008;Bouabdellah et al 2016). The other data points form a mixing trend suggesting that the advent of the Cu-mineralization resulted in a radiogenic Pb component being added to the isotopically less radiogenic Zn-rich mineralization.…”

“…Ore mineralogy and textural relationships were studied by transmitted and Whole-rock geochemical data were determined at the Reminex Research Centre by ICP-AES method using the same procedures as those described by Oummouch et al (2017). Sulphur isotopes of pyrrhotite, chalcopyrite and pyrite for the Sidi M'Barek samples have been determined by Essaifi et al (2019) while lead isotopes of sulphide samples have been determined by Marcoux et al (2008).…”

“…They are typically pyrrhotitedominated, vertical or steeply dipping, and most of them have been classified as VHMS (Bernard et al 1988;Zouhry 1998;Belkabir et al 2008;Marcoux et al 2008;Moreno et al 2008;Lotfi et al 2008). They are affected by Variscan deformation (Bernard et al 1988;Marcoux et al 2008;N'diaye et al 2016;Admou et al 2018) and show a polyphase mineralization (Lusty et al 2015;Essaifi et al, 2019). According to the geochemical classification of VHMS deposits (Franklin et al 1981;Large 1992), the major massive sulphide deposits of Central Jebilet belong either to the Pb-Zn-Cu type (Tazakourt, Koudiat Aicha) or the Cu-type (Kettara, Sidi M'Barek) (Essaifi et al 2019).…”

“…There is an ongoing debate on the genesis of these deposits, with a syngenetic hypothesis that classifies the deposits as VMS deposits formed at or below the seafloor in an anoxic basin (Belkabir et al 2008;Marcoux et al 2008;Moreno et al 2008) and an epigenetic hypothesis implying that the deposits formed during regional deformation and metamorphism (Essaifi & Hibti 2008;N'diaye et al 2016). In addition, a multistage evolution of the Moroccan massive sulphide deposits has recently been proposed (Essaifi et al 2019).…”