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Jebilet Guemassa - Hajar, Draa Sfar, Kettara, Khwadra; Assif El Mal; Jbel Aouam - Tighza

Morocco

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The Hajar massive sulphide and the Tighza and Assif El Mal vein sulphide occurrences are some of many base metal deposits distributed over an interval of ~1000 km within the Western Mesata area of Morocco, which is on the southern margin of the European late Palaeozoic Hercynian orogenic zone.   The Western Mesata is separated from the Eastern Mesata by the Middle and High Atlas and Rif domains.   The High Atlas and Rif domain was thrust over the Mesata in the Cenozoic, and the Middle Atlas zone uplifted during the Miocene.

The Hajar mine is located in th south Jebilet-Guemassa district, 35 km south of Marrakesh and has been mined since 1992, processing run-of-mine ore averaging 10.5% zinc, 3% lead, 0.3% copper and 60g/t silver.   The processing plant is currently being expanded to treat Hajar ore blended with material trucked from the company's new Draa Lasfar mine, 15 km NW of Marrakesh, which opened during 2004, exploiting an ore lens 1 to 25 m thick, 525 m long and dipping at 70 to 80° to depth of at least 700 m.

The Mesata domain comprises Palaeozoic sediments and metamorphics unconformably overlain by undeformed Jurassic calcareous rocks and Cretaceous sediments.   The Palaeozoic comprises Cambrian and Ordovician sediments (mainly psammitic and pelitic schists and quartzites), Silurian and Devonian sandstone, limestone and shale, all unconformably overlain by Carboniferous rhyolitic and basaltic lavas and/or intrusions of dolerite, and rhyolite intercalated with siltstones (the Saghlef Formation) and a thick package of turbidites, including some limestones.   The Palaeozoic is intruded by a series of calc-alkaline granitoids, mainly granodiorite, leucogranites and subalkaline monzogranite dated at 330 to 250 Ma.

Massive sulphides are hosted by the Carboniferous volcanic package, and include Hajar, Draa Sfar, Kettara and Khwadra.   These deposits are clustered in the Jebilet-Guemassa district of the Western Mesata and have been correlated with those of the Iberian Pyrite Belt.   Pb-Zn vein deposits are found within the Jbel Aouam district 200 km to the north-east.

At Hajar the host Saghlef Formation comprises:  i). a lower 300 m thick volcano-sedimentary package (mainly siltstone with rhyolite lava domes, volcanic breccias and felsic epiclastic siltstone),  ii). a middle unit up to 100 m thick of massive sulphide intercalated with sandstone and siltstone, and  iii). an upper unit of thin bedded siltstone and sandstone with minor carbonates.

The main ore deposit occurs 120 m below surface, at the contact zone between the lower volcano-sedimentary series and the upper sedimentary formation.   It comprises stockwork and overlying massive ores.   The stockwork comprises clusters of irregular veins a few centimetres thick in chloritised rhyolite lavas, glassy tuff, siltstone and mudstone, containing mainly pyrrhotite, pyrite and chalcopyrite with or without quartz.   These are accompanied by accessory sphalerite and galena.   Chlorite, calcite and rare biotite and K feldspar make up the gangue minerals in the stockwork veins.   The massive ores are lenticular and consist of banded pyrrhotite, pyrite, sphalerite, galena, chalcopyrite, and arsenopyrite which are capped by supergene ores.

Alteration in the stockwork zone includes mainly chlorite with biotite, muscovite and illite, while the massive sulphides are characterised by chlorite and muscovite with rare biotite.

The Assif El Mal zinc-lead (coper-silver) polymetallic vein deposit is located 100 km SW of Marrakech on the northern flank of the High Atlas Range in Morocco, a structural province of the Atlas Range, sandwiched between the Central High Atlas to the east and the Western High Atlas to the west. The host succession comprises the:
Iguer-N-Tgoula Formation, predominantly composed of conglomerate, dark-grey, shell-bearing sandstone and volcaniclastic rocks.
Berkhous Formation, a 2000 m thick dominantly volcanosedimentary package comprising of olive green schist and mudstone with intercalated units of tuff and, locally, volcanic rocks
Assif El Mal Formation, with a maximum thickness of 650 m, unconformably overlying the Berkhous Formation, that consists of a thick (200 to 500 m) sequence of laminated quartz-sericite-chlorite schist which, at the Assif El Mal mine, grades to organic-rich black shale with interbedded fine- to medium-grained massive sandstone/quartzite.
All of these have been overthrust by Jurassic limestone and Cretaceous red sandstone and shale terranes, all of which are overlain by recent alluvial sediments and soils.

These Neoproterozoic to Ordovician rocks have been contact metamorphosed by synorogenic to postorogenic Late Hercynian peraluminous granitoids to produce a metamorphic assemblage of quartz, plagioclase, biotite, muscovite, chlorite, amphibole, chloritoid and garnet. Regional deformation and metamorphism is considered to be the result of two major orogenic events, the ∼300 Ma Hercynian and the 45 to 5 Ma Atlasic orogenies.

The stratigraphic succession hosting the Assif El Mal deposit comprises an Ordovician clastic metasedimentary and metavolcanic sequence locally intruded by small Late Hercynian felsic (quartz-feldsparphyric) microgranite-rhyolite dykes and pods, and numerous dolerite and microdiorite dykes occur in the mine area. Most of these occur in NE- and NW-striking direction but some are E-W striking. These dykes, which have strike lengths of up to 50 m and range from 1 to 3 m wide are brecciated, locally mineralised, and strongly chloritised.

The Zn-Pb (Cu, Ag) mineralisation is primarily localised within two lithologically similar units, at or near contacts between massive quartz-feldspar porphyritic to spherulitic microgranite-rhyolite and surrounding clastic metasedimentary rocks. Hanging-wall and footwall metasedimentary rocks generally comprise interbedded, foliated and/or compositionally banded fine- to medium-grained clastic rocks. The dominant lithologic units are quartz-sericite-chlorite organic-rich black schist, interbedded with minor lenses of lithic tuff and massive sandstone/quartzite. The deformation history is consistent with late Devonian to Early Carboniferous deformation (Prost et al., 1989), and metamorphism is dominantly of low-pressure green schist grade, although rocks adjacent to the igneous intrusions, have been metamorphosed up to amphibolite grade.

The Assif El Mal polymetallic mineralisation consisted of four major subvertical vein sets with predominantly NE to NW strikes, filled with quartz, sulphides and carbonates. They lie mainly within the organic-rich black shale sequence of the Assif El Formation and to a lesser extent along Liassic dolerite-microdiorite dykes. Wall rock alteration surrounding the veins is generally intensive and includes development of hydrothermal carbonate, quartz, muscovite, chlorite and albite. Sulphide mineralisation crosscuts the S1-2 cleavage, and is largely confined to vertical fault-controlled veins or dilation fractures. The veins are typically several mm to more than 2 m thick and extend for 50 to >200 m along strike and to depths of 100 to 200 m. Mineralisation occurs as open-space filling with comb, cockade, breccia and crack-seal textures. The crustiform veins contain several symmetrical repetitive ribbons of quartz, sphalerite, galena and saddle dolomite that formed progressively toward the centre. Ribbons are defined by individual mineral layers that range in thickness from several mm to >10 cm.

Subeconomic disseminated mineralisation occurs within organic-rich black shale up to several metres from veins. The ores are brecciated and display evidence of late Atlasic shearing. Breccia ore consists of angular to subrounded cm-sized wall-rock fragments cemented by carbonate, with quartz and sulphides commonly forming cockade overgrowths around the fragments. Saddle dolomite, siderite and ankerite occur locally and postdate quartz and associated base-metal sulphides. The most common sulphides are dark- and honey-coloured sphalerite and galena, with lesser chalcopyrite, pyrite and tetrahedrite. Quartz and, to a lesser extent, saddle dolomite, siderite, and ankerite are the major non-sulphide minerals.

The Palaeozoic hosts of the Jbel Aouam district comprise Ordovician and Silurian schist (composed of quartz, chlorite and muscovite with trace kaolinite), Devonian carbonates and sandstones and Carboniferous quartzite, schist and carbonates.   Three isolated granites with ages of 287 to 290 Ma are found in the area, fringed by a 3 x 2 km metamorphic aureole.

The five Tighza veins are located in the Jbel Aouam district, ~600 km NE of Marrakesh, hosted by two large ENE-WNW striking strike-slip faults.   The North vein is hosted in the North fault system while the Sidi Ahmed, Ighrem Aouss and Iguer Oujna veins are in the South fault system.   These veins are 1 to 2 km long and persist to depths of more than 600 m.   They cut early scheelite veinlets associated with the granitoid margins and cut one of the granitoid bodies.   The mineral assemblage is simple and similar for all of the veins in this group, namely galena, sphalerite, chalcopyrite, pyrite, arsenopyrite and marcasite, with minor pyrrhotite. The predominant gangue minerals are siderite, ankerite, calcite, barite, and quartz.   One of the veins also also includes tennantite-tetrahedrite, stannite, cassiterite, bismuthinite and native bismuth.   The veins have halos of sericitic- and smectite-altered rocks.   Age dating suggests that the veins were emplace roughly coincidentally with the intrusion of the main granitoid phase at 280 to 275 Ma.

The Hajar massive sulphide deposit contained:
    1.5 Mt Zn, 0.45 Mt Pb, 0.11 Mt Cu, & 900 t Ag.
    Reserves in 2002 - 15 Mt @ 10% Zn, 3% Pb, 0.7% Cu, 60 g/t Ag (Watanabe, 2002; Eddebbi et al., 1998; Hibti et al., 1999).

The Draa Sfar deposit contained (Moreno et al., 2008):
    ~10 Mt @ 5.9 wt.% Zn, 2.25 wt.% Pb, 0.33% Cu.

The Assif El Mal vein type sulphide deposit (Bouabdellah et al.,, 2009) produced :
    ~1 Mt @ 8% Zn, 2% Pb, <1% Cu, 500 to 2300 g/t Ag.

The Tighza vein type sulphide deposit contained (Watanabe, 2002):
    1.0 Mt Pb, 0.3 Mt Zn, and 1000 t Ag.

For more detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2009.     Record last updated: 22/11/2012
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Bouabdellah M, Beaudoin G, Leach D L, Grandia F and Cardellach E,  2009 - Genesis of the Assif El Mal ZnPb (Cu, Ag) vein deposit. An extension-related Mesozoic vein system in the High Atlas of Morocco. Structural, mineralogical, and geochemical evidence: in    Mineralium Deposita   v.44 pp. 689-704
Castorina F and Masi U,  2000 - Sr-isotopic composition of siderite for assessing the origin of mineralizing fluids: the case study from the Jebel Awam deposit (Central Morocco) : in    Ore Geology Reviews   v17 pp 83-89
Moreno C, Saez R, Gonzalez F, Almodovar G, Toscano M, Playford G, Alansari A, Rziki S and Bajddi A,  2008 - Age and depositional environment of the Draa Sfar massive sulfide deposit, Morocco: in    Mineralium Deposita   v.43 pp. 891-911
Watanabe Y  2002 - 40Ar/39Ar geochronologic constraints on the timing of massive sulfide and vein-type Pb-Zn mineralization in the western Meseta of Morocco: in    Econ. Geol.   v97 pp 145-157


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