Edough-Cap de Fer Polymetallic District, Northeast Algeria: II. Metallogenic Evolution of a Late Miocene Metamorphic Core Complex in the Alpine Maghrebide Belt

Abstract

During the late Oligocene-early Miocene, three main hydrothermal events formed polymetallic deposits of the Edoug-Cap de Fer in the Edough massif of the Alpine Maghrebide belt. At ca. 17 Ma, the Karézas As (löllingite)-F (fluorite)-W (scheelite) deposit formed at a depth of ca. 2 km and temperatures of ca. 450-500°C, from mixing between magmatichydrothermal hypersaline fluids issued from a concealed rare-metal granite and several metamorphic fluids derived from the metamorphic core complex. Slightly later, at ca. 16 Ma, the intrusion of microgranites produced high-enthalpy, liquid-dominated geothermal fields at the basement-Kabylian flysch boundary, with Numidian flysch acting as an impermeable lid and host for "mesothermal" polymetallic vein fields (Aïn Barbar, Mellaha, Saf-Saf). Temperatures as high as ca. 350-375°C were attained in the deep parts of the Aïn Barbar field, at depths of ca. 1.3-1.5 km, accompanied by massive input of sodium that formed metasomatic plagioclase-rich hornfels (Chaïba domain); higher in the Cretaceous flysch aquifer, influx of hydrothermal fluids (300-270°C) produced hydrothermal metamorphic assemblages of quartz-chlorite, calcite-chlorite, wairakitechlorite, and epidote. The source of these hot fluids was a basement of the Edough type, in which heat advection was likely related to emplacement of a

Isotopic and geochemical constraints on lead and fluid sources of the PbZnAg mineralization in the polymetallic Tighza-Jbel Aouam district (central Morocco), and relationships with the geodynamic context

“…(2015) consider the Pb-Zn-Ag mineralization to be the last stage of a reduced intrusion-related gold deposit, with fluid focusing at the top of the solidified and cold intrusion. The hydrothermal activity associated with the Pb-Zn-Ag deposit was recently dated at 254 ± 16 Ma (Tarrieu, 2014;Cheilletz et al, 2015;Rossi et al, 2016), demonstrating the disconnection between the Pb-Zn-Ag mineralization and the W-Au mineralization. A new metallogenic model, based on the disconnection from spatially associated granites, needs to be considered for the TJAD.…”

“…The high-K calc-alkaline signature of all of these intrusive bodies is observed in most Moroccan Variscan granites and reflects either an enriched mantle or a lower crustal component (Gasquet et al, 1996;El Hadi et al, 2006). The monzogranite stocks have been dated at 320-300 Ma by Tarrieu (2014) and Rossi et al (2016).The three southernmost stocks are surrounded by a large and well-delimited biotitic alteration halo related to the W-Au mineralizing event (Figure 2; Cheilletz, 1984;Cheilletz and Isnard, 1985). The gravimetric study of El Dursi (2009), carried out on the TJAD, suggests that this hydrothermal alteration halo is associated with a hidden thin and shallow intrusive pluton.…”

“…The currently mined Pb-Zn-Ag mineralization, which crosscuts the W-Au ore (Figure 3), has been dated at 254 ± 16 Ma (Tarrieu, 2014;Cheilletz et al, 2015;Rossi et al, 2016). It developed during a magmatic-hydrothermal episode associated with emplacement of a dense network of late-Permian dikes, found throughout the Moroccan Meseta (Bouloton and Gasquet, 1995;Gasquet and Bouloton, 1995;Rossi et al, 2016). The Pb-Zn-Ag mineralization is filling NE-SW transtensive tension-gashes that developed during a NW-SE compression.…”

“…The polymetallic Tighza-Jbel Aouam district (TJAD; central Meseta, Morocco) displays two main types of mineralization, W-Au and Pb-Zn-Ag, hosted in Paleozoic rocks surrounding late-Carboniferous high-K calc-alkaline granitic stocks (Agard et al, 1958;Cheilletz, 1984;Jébrak, 1984;Nerci, 2006;Marcoux et al, 2015;Rossi et al, 2016). It has long been considered to have a single magmatic-hydrothermal origin due to the spatial zoning of mineralization around a supposed hidden batholith (Agard et al, 1958;Desteucq, 1974).…”

Edough-Cap de Fer Polymetallic District, Northeast Algeria: I. The Late Miocene Paleogeothermal System of Aïn Barbar and Its Cu–Zn–Pb Vein Mineralization

“…Alpine ore fields, mainly of the epithermal type (e.g., Glaçon 1971), occur within some of these core complexes, but appear to be later than the main detachment tectonics; their possible relationships with the host core complex were not examined until now. In eastern Algeria, the Edough-Cap de Fer massif is one of these metal-endowed core complexes (Aïssa et al 1995), displaying a variety of mineralization styles including W-(Sn) skarns, polymetallic Cu-Zn-Pb vein systems, and Sb-As-(Au) veins and replacements (Marignac 1988a;Aïssa et al 1998;Marignac et al 2015).…”