Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn-Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe 7 S 8 , and its absolute magnetic susceptibility is 2.10 − 3 SI/g. Ar-Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile-brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, ( 206 Pb/ 204 Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member ( 206 Pb/ 204 Pb 18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO 2 conditions and neither a high temperature nor a low aH 2 S (below 10 − 3 ) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds. Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.
Draa Sfar is a siliciclastic-felsic, volcanogenic massive sulphide (VMS) Zn-Pb-Cu deposit located 15 km north of Marrakesh within the Jebilet massif of the western Moroccan Meseta. The Draa Sfar deposit occurs within the Sarhlef series, a volcano-sedimentary succession that hosts other massive sulphide deposits (e.g., Hajar, Kettara) within the dominantly siliciclastic sedimentary succession of the lower Central Jebilet. At Draa Sfar, the footwall lithofacies are dominated by grey to black argillite, carbonaceous argillite and intercalated siltstone with localized rhyodacitic flows and domes, associated in situ and transported autoclastic deposits, and lesser dykes of aphanitic basalt and gabbro. Thin-to thick-bedded, black carbonaceous argillite, minor intercalated siltstone, and a large gabbro sill dominate the hanging wall lithofacies. The main lithologies strike NNE-SSW, parallel to a pronounced S1 foliation, and have a low-grade, chlorite-muscovite-quartz-albite-oligoclase metamorphic assemblage. The Draa Sfar deposit consists of two stratabound sulphide orebodies, Tazakourt to the south and Sidi M'Barek to the north. Both orebodies are hosted by argillite in the upper part of the lower volcano-sedimentary unit. The Tazakourt and Sidi M'Barek orebodies are highly deformed, sheet-like bodies of massive pyrrhotite (up to 95% pyrrhotite) with lesser sphalerite, galena, chalcopyrite, and pyrite. The Draa Sfar deposit formed within a restricted, sediment-starved, fault-controlled, anoxic, volcano-sedimentary rift basin. The deposit formed at and below the seafloor within anoxic, pelagic muds.The argillaceous sedimentary rocks that surround the Draa Sfar orebodies are characterized by a pronounced zonation of alteration assemblages and geochemical patterns. In the more proximal volcanic area to the south, the abundance of medium to dark green chlorite progressively increases within the argillite toward the base of the Tazakourt orebody. Chlorite alteration is manifested by the replacement of feldspar and a decrease in muscovite abundance related to a net addition of Fe and Mg and a loss of K and Na. In the volcanically distal and northern Sidi M'Barek orebody alteration within the footwall argillite is characterized by a modal increase of sericite relative to chlorite. A calcite-quartz-muscovite assemblage and a pronounced decrease in chlorite characterize argillite within the immediate hanging wall to the entire Draa Sfar deposit. The sympathetic lateral change from predominantly sericite to chlorite alteration within the footwall argillite with increasing volcanic proximity suggests that the higher temperature part of the hydrothermal system is coincident with a volcanic vent defined by localized rhyodacitic flow/domes within the footwall succession.
Koudiat Aïcha is a Visean stratiform, volcanogenic massive sulphide (VMS) zinc-copperlead deposit, situated northwest of Marrakech, within the Central Domain of the Jebilet massif of the Western Moroccan Meseta. The Central Domain is formed mainly of sedimentary (argillite, siltstone, sandstone, carbonate) and magmatic (gabbro and rhyodacite) rocks that host numerous massive sulphide deposits (e.g., Koudiat Aïcha, Kettara and Draa Sfar) in a thick grayish argillite sequence (rhythmic metapelite). The deposit is stratabound and consists of highly deformed, sheet-like lenses of massive sulphide located structurally on the eastern flank of a large anticline. Prior to metamorphism, the country rocks were subjected to hydrothermal alteration which is particularly pronounced in the immediate vicinity of the sulphide deposits where chloritization and sericitization are prevalent. Hydrothermal alteration extends into both the stratigraphic footwall and the stratigraphic hanging wall. The footwall lacks an obvious pipe zone (sulphide stringers or vent complex) beneath the sulphide mineralization, but is characterized by an increase in the modal proportion of Mg-chlorite and by the breakdown of feldspar and sericite. Chloritization, the most extensive and readily recognizable alteration useful in mineral exploration, is evident for more than 60 m above the subcropping sulphide deposits. The hanging wall rocks show a pervasive sericitization (over 30 m wide) and a weak chlorite alteration accompanied by disseminated nodules of pyrrhotite stretched parallel to the S 1 foliation. Because chlorite and sericite are metamorphic minerals that also occur in unaltered rocks surrounding the sulphide deposits, abundant Mg-rich chlorite and the absence of feldspar in the footwall are used to distinguish hydrothermal alteration facies from metamorphic facies. The chlorite geothermometer reveals temperatures between 250 and 330 °C. Higher temperatures (up to 300 °C) are associated with chlorite located in and adjacent to sulphide mineralization, whereas lower temperatures correlate with distal chlorite in both the footwall and hanging wall rocks.Chemical trends in altered footwall rocks are shown by absolute mass gains for Fe 2 O 3total , MnO and MgO, by absolute mass losses for CaO, K 2 O and Na 2 O, and by a moderate loss in SiO 2 . Oxygen and hydrogen isotope compositions of Koudiat Aïcha lithofacies (6.2-12.4‰ for oxygen and −51‰ to −36‰ for hydrogen) have also been used to determine the temperature and origin of metalliferous fluids. The couple plagioclase-amphibole of gabbros provides equilibrium temperatures between 310 and 380 °C and suggests that the heat source for the ore-forming fluid system may have been igneous. On the other hand, oxygen and hydrogen isotope ratios cluster between normal values for sedimentary and magmatic rocks, suggesting a magmatic-metamorphic origin for the ore fluid.
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