Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane

Abstract

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.

Geology and Metallogenesis of the Sediment-Hosted Cu-Ag Deposit of Tizert (Igherm Inlier, Anti-Atlas Copperbelt, Morocco)

“…Hence the disseminated style of mineralization was rapidly followed by the Late Carboniferous compression and the onset of the vein-style mineralization. On this basis, it appears that copper mineralization of Tizert is largely a Paleozoic event, most likely of Carboniferous age, contemporaneous with the polymetallic sulphide mineralization event in the Moroccan Meseta [82][83][84][85][86][87].…”

Heavy Metal Contamination and Mobility at the Mine Area of Draa Lasfar (Morocco)

“…Location of Draa Lasfar mine. minerals [24]. Industrial activity stopped in March 1981, although activity restarted in 1999 due to its great resource of poly-metallic components (As, Cd, Cu, Fe, Pb, Zn).…”

Apport du modèle géologique et géophysique 3D dans le développement du gisement polymétallique de Draa Sfar (Massif hercynien des Jebilet centrales, Maroc)

“…Le gisement de Draa Sfar appartient à la province métallogénique des amas sulfurés à pyrrhotite dominante du massif hercynien des Jebilet-Guemassa (Huvelin, 1977;Bernard et al, 1988;Souaré,1988;Ben aissi, 2001;Hibti, 2001;Rziki, 2006;Belkabir et al, 2008;Moreno et al, 2008;Marcoux et al, 2008). Les corps minéralisés de Draa Sfar sont encaissés dans la série de Sarhlef qui couvre la majeure partie des Jebilet central ( fig.…”