Geologic, Hydrothermal, and Geochemical Relationships Between Bimodal Magmatism and Massive Sulphide Mineralization in the Central Jebilet-Guemassa Province (Western Moroccan Hercynides)

Abstract

The Jebilet-Guemassa volcanic-hosted massive sulphide (VHMS) province comprises four sheet-like, polymetallic deposits. These are referred to as Kettara (>20 Mt at 0.6 % Cu with traces of Pb and Zn), Hajar (*20 Mt at 10.5 % Zn, 3.2 % Pb, 0.6 % Cu, and 60 g/t Ag), Draa Sfar (*11 Mt at 5.9 % Zn, 2.2 % Pb, and 0.3 % Cu), and Koudiat Aicha (3-5 Mt at 3 % Zn, 1 % Pb, and 0.6 % Cu), which collectively total >80 Mt of Pb-Zn-Cu ore. Host rocks consist predominantly of variably altered, mafic to felsic, submarine volcanic and tuffaceous volcaniclastic rocks within the metasedimentary Visean Sarhlef Series composed of black argillite with interbedded carbonate, siltstone, and sandstone. Hydrothermal alteration is distinctly asymmetric, occurring regionally in rocks of the stratigraphic footwall, immediate footwall, and hanging wall. In order of decreasing abundance, alteration assemblages consist of varying proportions of sericite, chlorite, quartz, carbonates (calcite, siderite, ankerite, and dolomite), talc, and epidote, with minor albite and tremolite-actinolite. These assemblages were controlled mainly by temperature and pH of the hydrothermal fluids. Mass-balance calculations indicate that hydrothermal alteration of the footwall rocks was accompanied by pervasive leaching of K 2 O, Na 2 O, and CaO, moderate loss of SiO 2 , and addition of FeO, MgO, and MnO under a high-temperature (>150°C) regime and high water/rock ratios (>10). In contrast, sericite-and calcite-rich alteration of hanging wall rocks involved lower temperatures (<150°C) and water-rock ratios of <5. Sulphide ores are dominated by pyrrhotite with variable proportions of sphalerite, chalcopyrite, galena, and pyrite ± tetrahedrite ± arsenopyrite ± marcasite ± bismuthinite ± cassiterite ± stannite ± cobaltite ± cubanite ± electrum. Overall, the ore and host rocks were strongly deformed, foliated, and mylonitized under greenschist-facies metamorphic conditions. Lithogeochemistry, alteration mineralogy, mineral chemistry, fluid inclusion data, and stable and radiogenic isotope constraints indicate that the Jebilet-Guemassa VHMS deposits formed in the Upper Visean (*330 Ma) from an evolving hydrothermal system that was initiated by regional-scale convection of magmatic-hydrothermal fluids and ambient seawater. Compared to classical VHMS systems, the Jebilet-Guemassa deposits possess a number of distinctive attributes that set them apart. These include (1) a banded sheet-like morphology, (2) predominance of pyrrhotite (up to 90 vol.%) over pyrite, (2) lack of well-developed stockwork zones, (4) absence of barite, (5) high Zn/Cu ratio, and (6) volumetrically minor igneous rocks.

Mineralization and sustainable development in the West African Craton: from field observations to modelling

“…While most of the values could be compatible with the leached H 2 S derived from magmatic sulfides, the outliers could be explained by H 2 S being supplied and derived from the leaching of sulfides of biogenic origin, i.e. a source of sulfur prevailing in the organic-rich shales recommended as metallic sources (Bouabdellah et al, 2016). massive sulfide deposits in central Jebilet (North of Marrakech, Morocco).…”

“…The mixing of such a fluid with a serpentinite-derived fluid may have led to As and S (Maacha, 1994 ;Maacha et al, 1998 ;Maacha, 2013). It is also suggested that black shale of the Imiter Group could be the source of all metals and As (Bouabdellah et al, 2016). ( 7) The sequence of mineral precipitation with decreasing temperatures and salinities within the advancing paragenetic sequence could also have been driven by the redox-dependent solubility of Co and Ni (Scholten et al, 2018).…”

“…massive sulfide deposits in central Jebilet (North of Marrakech, Morocco). It has been extensively studied using various techniques, from geophysical exploration to geochemistry and petrology (Moreno et al, 2008;Jaffal et al, 2010;Rziki et al, 2012 ;Bouabdellah et al, 2016 ;Bajdi et al, ;Essaifi et al, 2019 ;Soulaimani et al, 2020). Indeed, Cu-rich lenses, in which gold is being recovered profitably as a by-product, are the continuation of the Zn-rich lens representing the northern prolongation of the Draa Sfar volcanogenic massive sulfide deposit.…”

The Moroccan Massive Sulphide Deposits: Evidence for a Polyphase Mineralization

“…To summarize, the past production and total resources of the massive sulphide deposits of the Moroccan Meseta are estimated to be more than 80 Mt [64], with some deposits reaching a depth of 1500 m. Most of these deposits have been classified as VMS deposits [18][19][20][21][22][23]. The dominance of pelitic rocks in the wall rock and the presence of felsic volcanic rocks in the Tazakourt orebody led Marcoux et al [18] to classify the Draa Sfar deposit within the pelitic subgroup of the siliciclastic-felsic type of Franklin et al [3].…”

“…Nevertheless, Marcoux et al [18] and Bouabdellah et al [64] consider that the least radiogenic signatures are similar to those of the Visean igneous rocks of the Iberian Pyrite Belt and the eastern Meseta, and they suggest a major contribution of volcanic rocks as a source of metals. The lead isotope signature of the Cu-rich lens at Draa Sfar plots close to the Zartman and Doe [138] upper crust evolutionary curve, and it suggests that most of the lead is inherited from the hosting Sarhlef Schists [18,64]. A magmatic source of metals is strengthened by the fact that the less radiogenic signatures are recorded in Draa Sfar South and Hajjar deposits, which are associated with volcanic rocks.…”