Through integration of Pb-Zn ± Cu non-sulfide mineralogy, texture, and stable isotope (C, O, S) geochemistry, the world-class Touissit- Bou Beker and Jbel Bou Dahar Mississippi Valley-type districts of the Moroccan Atlasic system have been investigated in order to gain insights into the origin and processes that contributed to the formation of the base metal non-sulfide mineralization. In both districts, direct replacement (“red calamine”) and wallrock replacement (“white calamine”) ores are observed. Based on the mineral assemblages, ore textures, and crosscutting relations, three distinct mineralizing stages are recognized. The earliest, pre-non-sulfide gossanous stage was a prerequisite for the following supergene stages and constituted the driving force that ultimately promoted the leaching of most base metals such as Zn and Cu and alkalis from their rock sources. The following two stages, referred to as the main supergene “red calamine” and late “white calamine” ore stages, generated the bulk of mineable “calamine” ores in the Touissit-Bou Beker and Jbel Bou Dahar districts. Stable isotope compositions (δ¹³C_V-PDB, δ¹⁸O_V-SMOW, δ³⁴S_CDT) support a three-stage model whereby metals were released by supergene acidic fluids and then precipitated by bacteria and archaea-mediated metal-rich meteoric fluids due to a decrease in temperature and/or increase of f_O2. Oxygen isotope thermometry indicates decreasing precipitation temperatures with advancing paragenetic sequence from 33° to 18 °C, with wet to semi-arid to arid climatic conditions. The close spatial relationships between coexisting sulfide and non-sulfide mineralization along with stable isotope constraints suggest that the oxidation of sulfides occurred concurrently after the main stage of the Alpine orogeny between 15 Ma and the present. More importantly, the current data show for the first time the involvement of biologically controlled activity as the major driving process that triggered both oxidation and deposition of supergene mineralization at Jbel Bou Dahar and Touissit-Bou Beker districts. Conclusions drawn from this study therefore have implications for supergene Mississippi Valley-type (MVT) -derived non-sulfide deposits worldwide and account for the prominent role of biological processes in the genesis of this category of ore deposits.

The Oumjrane copper deposit in eastern Anti-Atlas is one of the top three major copper producers in North Africa with an annual production exceeding 260,000 tons at an average grade of 1.4% Cu. Current inferred resources are estimated at 5 million metric tons grading 1.5% Cu. Host rocks consist of a succession of Ordovician carbonate-free siliciclastic metasediments comprising sandstone- and quartzite-dominated rocks with cherty beds and phosphate nodules, conformably overlain by Silurian organic-rich black-shales. In the mine area, high-grade ores were recovered from open pits and underground workings of three major roughly continuous, subparallel, and steeply dipping vein systems referred to as Bou N’Hass, Bou Kerzia, and Zagora Graben over a strike length exceeding 10 km. The veins extend vertically for as much as 300 m, and their widths vary from ~2 m to ~15 m averaging 4m. The paragenetic sequence comprises two main stages of alteration and related mineralization. The earliest stage, referred to as the main Cu-rich stage I, is economically the most productive consisting of ore-related quartz together with chalcopyrite and reddish to orange apatite (i.e., Ap-1). The later Pb-Zn-Ba-rich stage II consists of variable proportions of galena and sphalerite enclosed in a matrix of barite as the main gangue minerals. Texturally, this stage ends with the development of well-developed green apatite crystals (i.e., Ap-2) up to 12 cm across. In addition to its potential for U–Pb dating, the REE+Y chemistry of the paragenetically well-constrained ore-related apatite (i.e., Ap-1, Ap-2) could provide insights into fluid chemistry, fluid-rock conditions, and fluid-rock interaction processes that prevailed during ore deposition of both ore stages. In this respect, EMPA analyses show that Ap-1 is almost pure hydroxyapatite, (XF=0.198-0.334, XCl=0.001-0.078, XOH=0.642-0.795), whereas Ap-2 is fluorapatite (XF=0.190-0.227, XCl=0.066-0.101, XOH=0.672-0.743). More importantly, LA-ICP-MS analyses indicate that Ap-1 is characterized by ∑REE+Y contents ranging from 962 to 2435 ppm and shows bell-shaped PAAS-normalized patterns with prominent negative Y anomaly Conversely, Ap-2 yields on average the highest ΣREE+Y concentrations at 8473 ppm, and shows negative sloped pattern with no Eu anomaly. The Y/Ho values are variable, but are generally distributed between 15 and 18 for Ap-1, and 23 and 26 for Ap-2. Overall, these geochemical characteristics indicate that there are two temporally distinct mineralizing events. The earlier Zn-rich stage is thought to have occurred in response to hydrothermal circulation of basinal brines and extensive fluid-rock interaction with the phosphate-rich lithologies. Conversely, the late Pb-Zn-Ba stage is linked to mixing between basinal brines and mantle-derived fluids, likely derived from the synchronous Middle Jurassic–Lower Cretaceous alkaline magmatic series. Ongoing U-Pb geochronology of both apatite types is performed to constrain the timing of mineralization and to trace back the ore-forming source(s) and processe(s).

Unusual Ag-(Ni-Co-Sb-As-Hg ± Bi)-bearing fault-fill vein ore shoot mineralization set in a gangue of quartz, fluorite, and barite has been identified in Morocco’s Aouli deposit. The Paleozoic host rocks consist of a succession of Cambrian to Ordovician-aged folded and low- to medium-grade metasediments and metavolcaniclastic rocks with tuff interbeds and amphibolite sills, locally intruded by late Visean calc-alkaline to alkaline granitoid intrusions. Paragenetic relationships indicate that the sequence of ore precipitation comprises a succession of Ni-Co-Fe arsenides, followed by Pb-Sb-As-Ag-Hg sulfarsenides/sulfosalts and then Zn-Pb-Fe sulfides. Results indicate that the ore shoot mineralization formed from episodic stages of fracturing and subsequent fluid migration. Precipitation of ore phases is thought to have occurred as a result of isothermal mixing and subsequent fluid–rock interactions. The timing of mineralization is thought to have occurred between Late Triassic and Late Miocene, coinciding with major crustal extension and Middle Jurassic–Upper Cretaceous alkaline magmatism. Thermal convection and seismic pumping are proposed as the main driving force for the large-scale migration of the ore-forming brines. This research bears directly upon the potential for new exploration targets in Pb-Zn ± fluorite ± barite deposits hosted in Variscan inliers throughout North Africa.

The Beni Snassen belt (northeastern Morocco) hosts several Mississippi Valley-type Pb-Zn ± Cu occurrences localized along the Variscan basement/Lower Liassic carbonate interface within the Atlasic foreland system. This study integrates geological observations with organic petrography and C-O-S-Pb isotopic systematics to constrain the origin of mineralizing fluids, metal source, and ore-forming processes within a basin-scale metallogenic system. The host sequence consists of unmetamorphosed, dolomitized Pliensbachian carbonates with marl interbeds and organic-rich black shales. Mineralization is structurally focused along ENE-WSW and E-W faults and occurs as massive calcite-galena veins, “en échelon” tension gashes, vug fillings, and solution-collapse breccias. Ore-stage calcite exhibits restricted isotopic variability (δ¹³C = −4.7 to +1.2‰; δ¹⁸O = 14.9 to 19.7‰), consistent with rock-buffered basinal fluids and extensive fluid–carbonate interaction. Calculated δ¹⁸OH₂O values indicate precipitation from evolved saline brines variably mixed with meteoric waters. Galena δ³⁴S values (−20.9‰ to +10.3‰) reflect thermochemical sulfate reduction (TSR) under fluctuating redox conditions. Pb isotope compositions define a tight linear cluster between upper crust and orogene growth curves, indicating a predominantly upper crustal metal source, notably Triassic dolerite–diabase lithologies, with a possible contribution from organic-rich black shales. High-reflectance pyrobitumen (VR₀ up to 4%) indicates thermal conditions exceeding those predicted by local burial history, supporting long-distance migration of hydrocarbon-bearing metalliferous fluids from overpressured basin compartments, most plausibly the adjacent Neogene Guercif Basin. Fault reactivation during Late Miocene transtension fostered basin-scale fluid focusing and ore deposition. Hence, the Beni Snassen district represents a basin-integrated MVT system involving crustal metal leaching, organic-assisted metal transport, TSR-mediated sulfur reduction, and structurally focused fluid flow. These results refine metallogenic models for the Atlasic belts and highlight the exploration potential of structurally reactivated foreland basins hosting coupled hydrocarbon-hydrothermal systems.