The silver has been mined in Roc Blanc deposit. (Huvelin et al. 1978; El Arbaoui et al. 2015). In Koudiat- el-Hamra, the ore deposit consists of four mineralized.
Geochronology and mineralogical evolution of the Koudiat-El-Hamra silver ore veins deposit (Central Jebilet, Morocco) Amal El Arbaoui, Amina Wafik, Abderrahim Essaifi and Abdelmajid Jarni Cadi Ayyad University, Morocco Lou Maacha Managem Mining Company Abstract. In the Hercynian Central Jebilet Massif, the Agrich Koudiat-el-Hamra Pb-Zn-Cu-Co-As-Sb-Sn vein ore deposit is hosted in the visean volcanosedimentary sarhlef series. The principal ore vein is generally subparallel to the regional schistosity. This vein was fragmented and extruded during the syn-schist deformation indicating probably that the mineralization pre-main deformation. Textural relationships indicate that stock metal deposit forming the Koudiat El Hamra mineralization was carried out in a single stage marked by assemblages of quartz-chlorite-carbonate. Silver minerals are freibergite, miargyrite, pyrargyrite, polybasite, argentopyrite, and native silver. The sulfides minerals are pyrite, pyrrhotite, arsenopyrite, galena, sphalerite and chalcopyrite with Ag-Pb-Sb sulfosalts that are inclusions in galena. The geochronology and mineralogical evolution of the Koudiat-el-Hamra ore deposit may be linked to the Bamega Tabouchennt granite. The paragenetic minerals could be explained by the mineralogical and geochemical differentiation followed by more advanced remobilization attested by the mineralized veins recovery in new folded stage, a temperature lowering and supergene weathering conditions.
of the Pb-Zn-Cu-Co-As-Sb-Sn and the Koudiat-elHamra hydrothermal system.
2 Geological setting The Jebilet massif, 7 km north of Marrakech in north central Morocco, forms a component of the Western Meseta, part of the North African Variscan Belt (Fig. 1A). The massif, 170 km long and 40 km wide, is dominated by a succession of sedimentary rocks, deposited in the shallow marine environment of a Devonian-Carboniferous, continental margin, transtensional rift basin (Huvelin 1977; Aarab and Beauchamp 1987; Moreno et al. 2008). The Jebilet massif consists of three tectono-stratigraphic units subdivided as Eastern, Central and Western Jebilet (Huvelin 1977; Bordonaro et al. 1979). Their original sedimentary relationships are masked by complex tectonized contacts. The Western Meseta Shear Zone separates the western and central units (Pique et al. 1980) and the Marrakesh Shear Zone separates the Central and Eastern units (Lagarde and Choukroune 1982).
1 Introduction The Koudiat-el-Hamra Ag-rich Pb-Zn-Cu-Co-As-Sb-Sn vein deposit, situated 26 km north western Marrakech (Fig. 1), is hosted in the visean volcano sedimentary sarhlef series (Huvelin 1977) that is affected by both regional and contact metamorphism. The silver has been mined in Roc Blanc deposit (Huvelin et al. 1978; El Arbaoui et al. 2015). In Koudiatel-Hamra, the ore deposit consists of four mineralized veins having direction ranging from 120°E to 170°E. The veins are hosted in the Sarhlef formation. Detailed microscopic description shows that KoudiatEl-Hamra ore is composed primarily of pyrite, arsenopyrite, sphalerite, pyrrhotite, chalcopyrite, galena, silver minerals, Pb-Ag-Sb sulfosalts and native silver. The gangue mineral includes quartz, chlorite dolomite, siderite and barite. These minerals form a single paragenesis and they precipitate in a single mineralizing fluid. This paper describes the geological and mineralogical characteristics of the Koudiat-el-Hamra Pb-Zn-Ag deposit. Various aspects of the mineralization have been discussed previously by (Huvelin 1977, Huvelin et al. 1978, Huvelin et al. 1980). This preliminary information is integrated with additional data on the geological setting, ore mineralogy and geochemistry, with a view to understanding the genesis GS01 – General session
Figure 1. a Geographical location of the Jebilet massif and study area. b Geological map of Central Jebilet Massif (Huvelin 1977).
The Western unit consists of weakly deformed and metamorphosed Cambrian and Ordovician rocks, whereas the Central unit is a block of low-grade metamorphosed, schistose, marine visean shale (Sarhlef schist). The Eastern unit is composed of Visean rocks including allochtoneous terranes of Ordovician to Devonian age. The Central unit of the Jebilet Massif, which hosts the Koudiat-El-Hamra deposit, includes several pyrrhotite-rich massive sulfide deposits. Syn1523
tectonic magmatism comprising an ultramafic to granitoid bimodal association (>65% mafic-ultramafic, the remainder is felsic) is widespread, associated with peraluminous granodiorites emplaced at ca. 330 Ma, intruded by younger (300 Ma) leucogranites (Fig. 1B). The bimodal plutonism occurs principally in three lineaments parallel to shear zones (Essaifi et al. 2014). The Koudiat-el-Hamra deposit is hosted within the Sarhlef series. These series consists of pellite and sandstone intercalations, bioclastic limestones, finely banded calcareous and massive sulphide deposits (Kettara pyrrhotite, Koudiat Aicha and Draa Sfar deposits). The study area contains many intrusive bodies of gabbros and dolerite, it was intersected by long veins of microdiorite, and finally by numerous quartzcarbonate veins with sulphide paragenesis (veins of Jbel Sarhlef ‘‘Pb-Zn’’) (Fig. 2).
4 Paragenetic sequences The Koudiat-el-Hamra mineralization corresponds quite accurately to a classical paragenetic type: the zinc-lead
3 Morphology of mineralized veins The quartz-chlorite veins had generally small size. Their thickness and their extension vary from few mm to a many decameters and are frequently grouped into anastomosing networks. These veins are generally subparallel to the regional schistosity intersecting clearly the corresponding folds. This is particularly the casealong the main Koudiat-el-Hamra and Jbel Sarhlef veins trips that are both sub-meridian having East dip. Silver-mineralized veins (Fig. 2) are less abundantin the area. These veins were fragmented and extruded during the syn-schist deformation. The main Koudiat-elHamra vein is by far the most mineralized. This vein is staked approximately along 300m by the ancient works. It has an average of 45° E dips, substantially the same as that of the schistosity, but with a slightly inclined direction. The opening exceeds rarely 50 cm, and is found often between 10 and 30 cm, with rapid variations. The mineralization is very complex and is mainly composed of sulphide hosted in an irregular gangue composed of chlorite, quartz, and carbonates (siderite, dolomite and calcite). However, because of its richness in silver, it has been the subject of quite developed mining work (Huvelin 1977), particularly from 1930 to 1948. Between the 25 and 45m depth levels, the ore is banded having irregular thickness, varying from 1 to 25 cm (10 cm average), generally located outside a filling of pyrite and quartz. It can be located also at the wall, at the roof rat both sides (Clariond 1932). Across the entire deposit, the reduced sulphide thickness was estimated at 5 cm around the 45 m level. In contrast to the main Koudiat-el-Hamra vein deposit and to that of Jbel Ergab-el-Beida, other veins (Fig. 2, map of the area) are clearly oblique to the schistosity. These are Madeleine vein having a 75° NE dips; the vein A with 15° to 45 ° ENE dips and the vein B, at 200 m SE of vein A at 35° to 45° E dips (Fig. 2).The works, which concerns the Madeleine vein, seem to have followed a recent break with quartz, barite and galena filling (Fig. 2), of the same type as that of the Jbel Sarhlef lead mine, but also highlighted Ag-rich ores in a quartz gangue accompanied by chlorite.
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Figure 2. Geological map of the Koudiat-El-Hamra area (this study).
paragenesis with copper and silver that have magmatic originas defined by (Oelsner 1965). According to this author paragenesis features in its variant of high temperature are: (1) massif ore vein without banded texture; (2) significant grade of iron sulphide in the mineralization; (3) initial deposition of Fe-rich minerals that are arsenopyrite, pyrrhotite and pyrite accompanied by Cassiterite, then sphalerite-chalcopyrite group minerals including stannite, and finally galenatetrahedrite Ag-rich group minerals; (4) exsolution phenomenon reflecting the high crystallization temperature of the sulphides: pyrrhotite and chalcopyrite exsolutions in sphalerite and pyrite exsolution in chalcopyrite. This lets say that for the most part of the stock metal deposit constituting the Koudiat-el-Hamra mineralization was carried out in a single stage. Subsequent processes as recovery vein in new folding phases and lowering temperature have led to limited ore transformations particularly in its mineralogical expression mode.
5 Koudiat-el-Hamra mineralization features Among mineralizations known in the central Jebilet, a detailed metallographic study shows two sulphide mineralizations that are comparable to that of Koudiatel-Hamra. The Roc Blanc mineralization and this of
Mineral Resources to Discover - 14th SGA Biennial Meeting 2017, Volume 4
North Draa Sfar mine (Table 1). Table 1. Comparison of the primary sulphide parageneses of the Koudiat-el-Hamra, North Draa Sfar mine and Roc Blanc deposits.
We note that for many characters, the Koudiat-elHamra mineralization is intermediate between the Roc Blanc and the North Draa Sfar mine mineralization. The character that seems decisive corresponds to the pyrrhotite-pyrite ratio for the first generation associated with arsenopyrite reflecting different degrees of sulphidation ores. The North Draa Sfar mine dominantpyrrhotite appears to be significant in sulfur, relatively to metals, in contrast to the Roc Blanc deposit where pyrrhotite veins filling cm-scale (0.1-20 cm) crosscut metapelite (El Arbaoui et al, 2015). According to this character, at the North Draa Sfar mine, the tin is in the oxidized form [SnO2], while in Koudiat-el-Hamra, we note the oxidized tin (Cassiterite) and sulfide tin (Stannite) association. At the Roc Blanc deposit, tin was detected only in its sulphide form (traces in sphalerite), and that the germanium is expressed in sulphide form (Argyrodite) [Ag8GeS6]. This gradation is in agreement with an increasing sulphidation potential of the ore-generating environment. In addition, we note also: (1) The individualization of cobalt (cobaltite) at north Draa Sfar mine, while it is expressed only in the Co-rich arsenopyrite and ullmannite form in Koudiat-el-Hamra deposit, variety which is occurs in Co-rich ullmannite at the Roc Blanc deposits; (2) The content of Bi, Se, Au and Ag at more expression in the North Draa Sfar mine in contrast to the other two deposits; (3) The increasing abundance of silver and antimony-bearing minerals in the Roc Blanc and Koudiat-el-Hamra deposits, and a decreasing abundance of copper bearing minerals, in the North Draa Sfar and the Roc Blanc deposits. The comparative paragenetic study of these three mineralizations allows obtaining a coherent ensemble of mineralogical and geochemical gradients. At the Fe/S ratio variation, explained by pyrrhotite-pyrite ratio of the first generation, correspond variations in the minor or trace elements content, in particular Ag and Cu. There may be a useful guide to determine which ones are the most likely to have interesting silver or copper content.
6 Conclusion and discussion The Koudiat-el-Hamra Ag-rich veins deposits constitute a special case, because their establishment in the hercynian Central Jebilet orogeny and gitology remains to be discussed. A tectonic point of view, these veins are extruded and fragmented. In addition, they are affected by late folding and a Kink bound schistosity (S2) that is clearly post contact-metamorphism. This is justified by the presence of crystallization tail and pressure shadow areas of andalusite following the main schistosity (S1). Gitologic point of view, Koudiat-el-Hamra Ag-rich
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veins deposits present certain analogy with those of North Draa Sfar mine (Huvelin et al. 1978), and Roc Blanc veins deposits that are linked to BramramTabouchant-Bamega granite (BTB) (Huvelin et al. 1980; El Arbaoui et al. 2015). According to these observations, one as sumption could be convincingly. This hypothesis stipulates that the stock metal constituting the Koudiat-el-Hamra mineralization was carried out in a single stage. The paragenetic succession evolution could be explained by mineralogical and geochemical differentiation followed by more advanced remobilization attested by the mineralized veins recovery in new folded stage, a temperature lowering and supergene weathering conditions.
Reference Clariond L, (1932) Note concernant les travaux exécutés par le BRPM sur les filons argentifères de Koudiat el Hamra, Rapport BRPM, Rabat, inédit. El Arbaoui A, Wafik A, Ndiaye I, Maacha L, Zouhair M, Ouadjou A, Radnaoui, A, (2015) Mineralogical Evolution of the Polymetallic Vein Mineralization at the Roc Blanc Silver Deposit (Jebilet Massif, Variscan Belt, Morocco). Mineral Resources in a Sustainable World. 13th Biennial SGA-SEG Meeting, Nancy-France, August 2015. Proceedings, Volume 2, pp. 449-452. Essaifi A, Samson S, Goodenough K, (2014) Geochemical and Sr– Nd isotopic constraints on the petrogenesis and geodynamic significance of the Jebilet magmatism (Variscan Belt, Morocco). Geological Magazine 151, 666–691. Huvelin P, (1977) Etude géologique et gîtologique du massif hercynien des Jebilets (Maroc occidental). Note et Mémoires du Service Géologique du Maroc, 232 bis, 307pp. Huvelin P, MOELO Y, PERMINGEAT F. & PICOT P, (1978) Sur la mineralisation du champ filonien polymetallifere du Roc Blanc (Jebilet centrales, Maroc). Notes Serv. Geol. Maroc, t. 40, n° 275, 239-248. Huvelin P, Ortelli L, Permingeat, F, Picot, P, (1980) Présence de filons stannifères dans le granite hercynien du BaramramTabouchennt (Jebilet centrales, Maroc). Notes Serv. Geol. Maroc, t. 41, n° 285, 231-236. Lagarde JL, Choukroune P, (1982) Cisaillement ductile et granitoïdes syntectoniques: l’exemple du massif hercynien des Jebilet (Maroc). Bull SocGéol Fr 24:299–307. Moreno C, Sáez R, González F, Almodóvar G, Toscano M, Playford G, Alansari A, Rziki S, Bajddi A (2008) Age and depositional environment of the Draa Sfar massive sulphide deposit, Morocco. Miner Deposita 43:891-911. Oelsner (1965) Atlas des principales paragenèses minérales vues au microscope (traduit par R. Mignon). Gauthier-Villars Paris. Edition Leipzig. Piqué A, Jeannette D, Michard A, (1980) The Western Meseta shear zone, a major and permanent feature of the Hercynian belt of Morocco. J StructGeol 2:55–61.
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