Sulfur and lead isotopic compositions of ore sulfides and mining economic potential of the High Atlas Mississippi Valley-type ore province, Morocco
Graphical abstract
Introduction
The Northwest African Atlas extends over a large distance (>2000 km) from the Moroccan Atlantic Ocean to the Tunisian Mediterranean coast. It corresponds to an intra-continental basin filled with Mesozoic to Cenozoic sediments. The Moroccan High Atlas range contains several PbZn (Ba-Sr-Fe) mines and prospects (Ovtracht, 1978), the majority of which are Mississippi Valley-type ore deposits. These ore deposits belong to the Circum-Mediterranean PbZn province (Rouvier et al., 1985). Among the most productive ore deposits are the Touissit Bou Beker and EL Abded in the Moroccan-Algerian confines (Bouabdellah and Sangster, 2016), the Moroccan High Atlas, and the diapiric zones of Tunisia and Algeria. The Pb-Zn-(Ba-Sr-Fe) ore deposits of the High Atlas form an important mining province that consists of medium- to large- size orebodies and small uneconomic prospects (Ovtracht, 1978). Several zones in the High Atlas are not yet explored and investigated for potential ore deposits of economic interest. Hence, the present work addresses the mining economic potential of the High Atlas MVT ore province in Morocco using sulfur and lead isotopic composition of sulfides. Several studies have also used these isotopes for ore exploration (Gulson, 1986; Sangster, 1990; Leach et al., 2005; Leach et al., 2010). Assessing the mining potential of the many Jurassic carbonate-hosted-Pb-Zn (Ba-Sr-Fe) ore deposits of the Moroccan High Atlas (Fig. 1) raises the question of whether size differences reflect (i) different processes of sulfur reduction, (ii) source/availability of metals and sulfur, and/or (iii) the different processes of ore precipitation. The development of large-sized ore deposits of economic interest requires a large amount of sulfur and metals among other factors. The generation of sulfur through TSR and/or BSR depends on the availability of a great quantity of dissolved sulfates. Similarly, a potential metal reservoir is required to supply metals such as Pb, Zn, Fe, Ba, and Sr for the sulfide and sulfate precipitation. In that respect, the analysis of S and Pb isotopes of sulfides provides insight into possible sources of sulfate and metal reservoirs.
A limited number of the aforementioned ore deposits were thoroughly studied (Mouguina, 2004; Adil et al., 2004; Rddad and Bouhlel, 2016; Rddad et al., 2018; Rddad, 2019). Previous sulfur isotope data have been interpreted as a result of the thermochemical sulfate reduction (TSR) from the Triassic-Jurassic sulfates and/or coeval pore water sulfates (Bou Dahar, Rddad and Bouhlel, 2016; Bouabdellah and Sangster, 2016; Ali Ou Daoud, Rddad et al., 2018) or by a combination of both TSR and bacterial sulfate reduction (BSR) (Bou Dahar; Rddad and Bouhlel, 2016; Bouabdellah and Sangster, 2016). Based on the Pb isotope data, the Paleozoic basement was considered the main source of lead and by inference other metals (Rddad and Bouhlel, 2016; Rddad et al., 2018). Fluid inclusion studies reveal that the ore-bearing fluids are basinal brines with a salinity range (3–28 wt% NaCl equiv.) and a temperature range (40° - 180 °C), which fall within those of MVT ore deposits (Mouguina, 2004; Adil et al., 2004; Rddad and Bouhlel, 2016; Rddad et al., 2018). Besides these geochemical attributes, the High Atlas ore deposits are epigenetic and stratabound (ore-bearing faults and fractures are confined to Jurassic carbonates), which further confirm their integration into the MVT ore deposits class. The metalliferous basement-derived fluids ascended through the major faults toward the Jurassic carbonates where they mixed with the reduced sulfur and/or dissolved Triassic-Jurassic sulfates (Rddad and Bouhlel, 2016; Rddad et al., 2018; Rddad, 2019). This fluid-mixing process is proposed to be the primary mechanism for ore precipitation for Bou Dahar (Adil et al., 2004; Rddad and Bouhlel, 2016), Tazoult (Mouguina, 2004), Ali Ou Daoud (Mouguina, 2004; Rddad et al., 2018), and Tigrinine-Taabast (Rddad, 2019). The formation of the ores took place during the Eocene-Miocene time in relation to the Alpine orogeny (PbZn (BaSr) Bou Dahar ore deposits, Rddad and Bouhlel, 2016; Bouabdellah and Sangster, 2016, PbZn Tigrinine-Taabast ore deposits, Rddad, 2019) and the Late Jurassic-early Cretaceous in relation to the extensional tectonic activity (e.g., Ali Ou Daoud and Tazoult ore deposits, Mouguina, 2004, Ali Ou Daoud, Rddad et al., 2018). Although fluid inclusion and PbS isotopic studies were carried out on few ore deposits in the High Atlas (Mouguina, 2004; Adil et al., 2004; Rddad and Bouhlel, 2016; Rddad et al., 2018; Rddad, 2019), no comprehensive Pb and S isotope study were carried out regionally at different localities of the High Atlas basin. The purpose of this paper is twofold: (i) constraining the source of sulfur and metals through the analysis of S and Pb isotopes of sulfide ores from representative ore deposits and (ii) addressing the question of the determinant factor(s) responsible for the formation of medium- to large-size orebodies of economic importance in this metallogenic province.
Section snippets
Regional geologic background
The Atlas Mountains are subdivided into the NE-SW-trending Middle Atlas and the ENE- WSW-trending High Atlas (Fig. 1). The High Atlas is subdivided into the Western (occidental), Central, and Eastern (oriental) High Atlas (OCHA, CHA, and OHA, respectively). The term High Atlas, thereafter, refers to the Central and Oriental High Atlas, which are the main focus of this study. The High Atlas consists of Mesozoic to Cenozoic sedimentary rocks covering the Precambrian to Paleozoic basement which is
Ore deposit geology
The Moroccan High Atlas PbZn (Ba-Sr-Fe) metallogenic province is one of the most important provinces in North Africa. The ore deposits are hosted in the Jurassic carbonates and occur along the Jurassic ridges intruded by the Triassic evaporites (diapirs) and the Jurassic igneous intrusions (e.g., Tazoult, Fig. 2A), the southern border (e.g., Bou Dahar; Tirginine-Taabast), norther border (e.g., Aoudine, Sidi Belghite), and western border near the Paleozoic paleohigh (e.g., Tadagaste) (Fig. 1,
Analytical methods
For sulfur and lead isotope analyses, mineral separates were prepared under a binocular microscope by handpicking or by the use of a micro-drill. Sulfur isotope analyses were carried out on samples of sphalerite (n = 15), galena (n = 31), and pyrite (n = 4) from different ore styles at the Spectrometry facility of the Department of Engineering, University of Nevada. The sulfur isotope compositions were measured on a Eurovector elemental analyzer interfaced to a Micromass Isoprime stable isotope
Sulfur isotopes
The sulfur isotopic compositions of sphalerite, galena, and pyrite are reported in Table 2 and Fig. 6, Fig. 7. The studied ore deposits in the High Atlas basin show a large variation in δ34S values ranging from −18.6 to 22.2‰. The Aoudine and Sidi Belghite ore deposits, located in the northern part of the High Atlas basin (NZ), show negative δ34S values that range from −18.6 to −15.2‰ (avg. = −16.9‰). Conversely, the ore deposits that are located in the center of the High Atlas basin (CZ)
Source of sulfur
The sulfur isotopic compositions of sulfides in the High Atlas ore deposits are highly variable ranging from −18.6 to 22.2‰ (Fig. 7). Previously published data of sulfur isotopic compositions of barite and celestite in Bou Dahar (δ34S ~ 15–20‰) (Rddad and Bouhlel, 2016) fall within the range of the Mesozoic seawater sulfates (e.g., Triassic seawater: 11 to 20‰; Jurassic seawater: 14 to 18‰) (Claypool et al., 1980). These δ34S values of sulfates also fall within those of the Triassic evaporites
Concluding remarks
On the basis of the geologic study and the sulfur and lead isotopic data of sulfide ores from the ore deposits in different zones (NZ, WZ, SZ, CZ) in the central and oriental High Atlas, salient conclusions can be drawn.
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Sulfide ore samples display concrete sulfur isotopic composition zonation with δ34Savg. values of 14.3‰, −16.9‰, −9.1‰, and 4.4‰ in the CZ, NZ, WZ, and SZ, respectively. This zonation reflects the predominance of the isotopically heavy sulfur (TSR) and the bacteriogenic sulfur
Declaration of competing interest
The authors confirm that all the claims, statements, and conclusions are true and that there is not conflict of interest.
Acknowledgment
The first author would like to thank the Professional Staff Congress of the City University of New York (PSC/CUNY) for the partial funding of this project. We are also grateful to Dr. Francis Albarède for his insightful comments and suggestions that improve the quality of this manuscript. We would also like to express our gratitude to the associate editor and the Editor-in-Chief Dr. Stefano Albanese for handling this paper.
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2022, Ore Geology ReviewsCitation Excerpt :Hence, pyrite trace element geochemistry has been used as an indicator to trace the metallogenic processes (Maslennikov et al., 2009; Mukherjee and Large, 2017; Basril et al., 2018; Gregory et al., 2019). For pyrite with well-defined generations, in-situ sulfur isotope analysis is also more widely used for interpreting ore-forming fluid source and evolution (Fan et al., 2018; Xie et al., 2018; Lin et al., 2021), and for fingerprinting different types of deposits, including those of porphyry-type (Zhang et al., 2016; Liu et al., 2020a,b; Sheng et al., 2022), volcanogenic massive sulfide (VMS) (Keith et al., 2016; Basril et al., 2018; Caruso et al., 2018; Liu et al., 2020a,b; Yu et al., 2020; Wang et al., 2021a,b; Zhang et al., 2021), orogenic-type (Tang et al., 2019; Wu et al., 2019; Zoheir et al., 2019; Zhai et al., 2021), iron oxide-copper–gold (IOCG) (Pal et al., 2011; Li et al., 2018; Adam et al., 2020; Dora et al., 2020; Liang et al., 2021), Carlin-type (Yan et al., 2018; Wei et al., 2020; Chen et al., 2021; He et al., 2021; Li et al., 2021; Song et al. 2022), sedimentary exhalative (SEDEX) (Jiang et al. 2021; Zhang et al., 2022; Zhang et al., 2022), and Mississippian Valley Type (MVT) (Li et al., 2015; Rddad and Mouguina, 2021). Although some workers consider that base metal vein-type mineralization is part of porphyry-related magmatic-hydrothermal system (e.g., Morococha District, Peru) (Sillitoe, 2010; Catchpole et al., 2015a, Catchpole et al., 2015b), the ore-fluid evolution from porphyry-type to vein-type mineralization is still poorly understood.