Non-sulfide zinc deposits of the Moroccan High Atlas: Multi-scale characterization and origin

11The nature and the origin of zinc clays are poorly understood. Based on the example of the 12Bou Arhous Zn-Pb ore deposit in the Moroccan High Atlas, this study presents new advances for the 13 characterization of barren and mineralised clays associated to zinc non-sulphide ores. In the field, white 14 to ochre granular clays are associated with willemite, whilst red smooth clays fill karst-related cavities 15 cutting across the non-sulphide ore bodies. Red clays (kaolinite chlorite, illite and smectite) present 16 evidence of stratification that reflects internal sedimentation processes during karst evolution. White 17 clays contain 7Å-clay mineral/smectite irregular mixed layers with less than 20% of smectite layers. 18The willemite crystals are partially dissolved and are surrounded by authigenic zinc clay minerals. Zinc-rich clays in supergene non-sulfide zinc deposits. 19 56In many supergene zinc deposits, mineralised clay material represents a significant economic range, 60 km to the north-east of Errachidia city (Fig. 1A). The local geology of this deposit has been 81 extensively studied by Leblanc (1968) and recently revisited in Choulet et al. (2014). 82The 4The Jbel Bou Arhous range is one of these ENE-WSW trending faulted anticlines that exhume 90 the Triassic and Lower Jurassic strata (Fig. 1B) (Figs. 1B and 1C). At site of the Bou-Arhous mine located in the footwall of the "Grand 96Accident" thrust, the two limbs of the anticline are vertical ( Fig. 2A) or slightly recumbent and the fold 97 hinge is missing (Fig. 1C). Host rocks of mineralisation include Sinemurian black limestone, locally 98interbedded with thin layers of greyish marls (Fig. 2B), which have experienced slight dolomitisation 99 during diagenesis and emplacement of base metals sulphide lenses (Leblanc 1968). In depth, 100mineralisation is tectonically juxtaposed along the "Grand Accident" thrust to the Triassic variegated 101 shales associated to gypsum (Fig. 2C). 102Following exploration campaigns in the 1960's, the Bou Arhous mine has been exploited by metres. Veins up to 10 metres in width parallel the stratification and dip steeply to the north ( Fig. 2A). 106Non-sulphide zinc-bearing minerals include willemite, hydrozincite, hemimorphite and smithsonite.

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“…1A). The local geology of this deposit has been 81 extensively studied by Leblanc (1968) and recently revisited in Choulet et al (2014). …”

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confidence: 99%

Zinc-rich clays in supergene non-sulfide zinc deposits

et al. 2015

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“…These calamine ores contain a mixture of supergene Zn (with minor Pb) carbonates (smithsonite), hydrated carbonates (hydrozincite), silicates (willemite) and hydrated silicates (hemimorphite, Zn clays) that cap the primary sulphide orebodies. Unlike most North African MVTs, this type of non-sulphide Zn ore deposits is largely confined to the central and eastern High Atlas Mountains (Goulet et al 2014; present study). Such deposits are being extensively prospected by the mineral industry because (Sangster 2003): (1) environment impacts from mining are minimal owing to a characteristic lack of Pb, S, and other deleterious elements, (2) a potential for low-energy recovery of zinc, and (3) a generally higher in situ economic value (Borg 2002).…”

Section: Ore Mineralogy Textures and Paragenesismentioning

confidence: 70%

“…Calamine ores occur both as cavity fillings and as partial to massive replacements of host carbonates in the upper levels of the exploited orebodies. It seems that their genesis benefited from the interplay among weathering, uplift, and erosion and that there is no apparent relationship to the present water table (Goulet et al 2014). …”

Section: Ore Mineralogy Textures and Paragenesismentioning

confidence: 99%

Geology, Geochemistry, and Current Genetic Models for Major Mississippi Valley-Type Pb–Zn Deposits of Morocco

Bouabdellah¹,

Sangster²

2016

Mineral Resource Reviews

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Morocco has been for the past two centuries one of the top ten Pb-Zn producers with two thirds of base-metal production derived from three major Mississippi Valley-type districts (Touissit-Bou Beker, Upper Moulouya, and Jbel Bou Dahar). Collectively, these districts have produced more than 100 Mt of ore at an average grade of *3 wt% Zn and 4 wt% Pb. At the present time, none of the three districts is active. favorable fluid channels for metal-bearing brines into permeable host rocks and dissolution structures. The geometry of the orebodies that parallel the major alpine faults, coupled with lead isotopic constraints, suggest that the MVT mineralizing event occurred during midle Tertiary time (i.e., Cretaceous to Miocene) coincident with closing stages of the Alpine orogeny in the Atlasic orogenic belt. Alpine mineralization is thought to have been promoted by the mixing of older, high-temperature, rock-buffered, dense brines stored within the Paleozoic basement, and a downwelling, cooler fluid probably of meteoric origin. The resulting mixed brines were centered mainly on the basement high structure and its flanks, then flowed laterally away from the basement high and giving rise to the lower grade mineralization of the distal prospects. Fluid migration towards the ore districts could have been achieved either by a gravity-driven system (Touissit-Bou Beker, Mibladen, and Jbel Bou Dahar) or sediment compaction in the foredeep (Jbel Bou Dahar), or a combination of both. An alternative buoyancy-driven fluid convection model is proposed for the Touissit-Bou Beker MVT mineralization.

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“…A large portion of the exploited ores corresponds to the non-sulfide secondary Pb-Zn mineralization studied in detail by Choulet et al (2014). These supergene minerals formed as a result of the oxidation of sulfides by meteoric water during the last 20 Ma (Choulet et al, 2014). The first abundant oxide assemblage, consisting of calamine ( Fig.…”

Section: Mineralization and Paragenetic Sequencementioning

confidence: 99%

The Bou Dahar Jurassic carbonate-hosted Pb–Zn–Ba deposits (Oriental High Atlas, Morocco): Fluid-inclusion and C–O–S–Pb isotope studies

Rddad

Bouhlel

2016

Ore Geology Reviews

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The Bou Dahar Pb-Zn-Ba (±Sr) is hosted in the Lower and Middle Liassic carbonate platform in the oriental High Atlas of Morocco. The paragenetic sequence includes quartz-pyrite-melnicovite-sphalerite-galenacalcite-barite ± fluorite-± celestite. Fluid-inclusion studies were conducted on sphalerite (early mineralizing stage) and barite, and celestite (late mineralizing stage). These studies reveal two end-member fluids, a hot (~143°C) and saline fluid (~23 wt.% NaCl eq.) and a cooler (b 50°C) and diluted fluid (~5 wt.% NaCl eq.). Based on fluid-inclusion and CO -S isotope studies, a conclusion is reached that the Bou Dahar ore deposits were formed by the mixing of two fluid-a diluted, SO 2− 4-rich fluid, and an 18 O-enriched basinal brine that carried Pb, Zn, and Ba. The sulfur required for the precipitation of sulfides was generated by the thermochemical sulfate reduction of dissolved sulfate (SO 4 2−) of the Mesozoic seawaters, and delivered to the site of ore deposition. The sulfur of sulfate minerals was derived directly from these dissolved SO 4 2. The Pb isotope compositions are homogenous with 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios ranging from 18.124 to 18.183, 15.630 to 15.634, and 38.325 to 38.440 respectively. This Pb isotope composition is indicative of an upper crust and orogene reservoirs as the source of lead and other metals. The emplacement of mineralization occurred during the Eocene-Miocene Alpine orogeny, and tectonic burial and compression were the driving forces behind the circulation of the orogenic-brines. These ore-forming fluids migrated, along thrusting regional E-W and NE-SW deep-seated faults, to the confined carbonate-Liassic reservoir.

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Non-sulfide zinc deposits of the Moroccan High Atlas: Multi-scale characterization and origin

Cited by 41 publications

References 72 publications

Zinc-rich clays in supergene non-sulfide zinc deposits

Zinc-rich clays in supergene non-sulfide zinc deposits

Geology, Geochemistry, and Current Genetic Models for Major Mississippi Valley-Type Pb–Zn Deposits of Morocco

The Bou Dahar Jurassic carbonate-hosted Pb–Zn–Ba deposits (Oriental High Atlas, Morocco): Fluid-inclusion and C–O–S–Pb isotope studies

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