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Willemite (ZnSiO) usually reported in hypogene non-sulfide deposits is described as the main ore mineral in the carbonate-hosted Bou Arhous zinc deposit. This deposit is located in the High Atlas intracontinental range that formed during the Tertiary. Based on a set of microscopic observations, it was possible to establish that willemite replaces primary sphalerite. On the basis of cathodoluminescence imaging, three successive generations of willemite are distinguished, with evidence of dissolution-reprecipitation processes. Willemite is also variably enriched in Ge (up to 1000 ppm), while Ge contents lower than 100 ppm are reported in the primary sulfide minerals. Depending on the willemite generation, this substitution was positively or negatively correlated to the Zn-Pb substitution. According to the nature of zoning (sector versus oscillatory), the incorporation of Ge was either controlled by crystallographic factors or by the nature of the mineralizing fluids. Willemite is associated with other oxidation-related mineral species, like cerussite (PbCO) but is not in isotopic equilibrium and therefore not considered to be cogenetic. Oxygen isotope compositions support the formation of willemite at temperatures below 130 °C, from mixed meteoric and deeper, hydrothermal fluids. The formation of the High Atlas Belt during the Tertiary has contributed to the exhumation of the sulfide minerals and the development of vertical conduits for percolation of meteoric water and ascending hydrothermal fluids. In addition to a local contribution of silicate minerals of the host limestone, hydrothermal fluids probably transported Si and Ge that are incorporated in willemite. [ABSTRACT FROM AUTHOR]

Draa Sfar is a polymetallic (Zn-Pb-Cu) volcanogenic massive sulfide deposit with an actual resource of 13 Mt at 4.0% Zn and 1.3% Pb. It is part of the central Jbilets area known for its several Cu-Zn ore deposits. The ore is hosted in the upper Visean-Namurien sedimentary formation. Owing to the complexity of the geology of the ore deposits, numerical simulation approach was attempted to shed light into the temperature distribution, the circulation of the hydrothermal fluid and the genesis of massive sulfide ore bodies by evaluating the permeability, porosity, and thermal conductivity. On the basis of this simulation approach, the ore is predicted to be deposited at a temperature ranging between 230 and 290 °C. This temperature range is dependent on the pre-existing temperature of the discharge area where a metal-rich fluid precipitated the ore. The duration of the Draa Sfar ore body formation is predicted to be 15, 000 to 50, 000 years. Based on geological studies of Draa Sfar deposit together with the aforementioned results of the simulation approach, an ore genetic model for the massive sulfide ore bodies is proposed. In this model, the supply of ore-forming fluids is ensured by the combination of seawater and magmatic waters. Magma that generated rhyodacite dome acted as the heat source that remobilized the circulation of these ore-bearing fluids. The NW-SE trending faults acted as potential pathways for both the downward and upward migration of the ore-forming fluids. Due to their high permeability, the ignimbritic facies, host rocks of Draa Sfar ore bodies, have favored the circulation of the fluids. The mixing between the ore-forming fluids of magmatic origin and the descending seawaters and/or in situ pore waters led to the formation the ore bodies in 35,000 years. The position and size of the ore body, determined by the simulation approach, is consistent with the actual field geological data. [ABSTRACT FROM AUTHOR]

The study performed on the host rocks of the Tighardine deposit allows proposing a new lithostratigraphic succession, mainly constituted of three volcanic and volcano-sedimentary units and dolomitic bed and lenses. Volcanic rocks consist mainly of basalt, andesite, and less common dacites. They are characterized by a FeO/MgO ratio range of 0.8-10.0, TiO2 contents ranging between 0.6 and 3.2 wt%, and high values of Zr/Y (7.1 to 9.9), Nb/Y (0.5 to 1.1), and Nb/La (0.7 to 1.1) ratios, providing good evidence of intracontinental tholeiitic character with a subalkaline affinity. They have no Nb anomaly and high Ti/Yb ratios (> 4000), suggesting their derivation from an enriched source and emplacement in an extensional continental setting. Fractional crystallization is the main differentiation mechanism of these rocks, and crustal contamination may have contributed to their final geochemical signature. U/Pb dating these volcanic rocks revealed ages of 603.5 ± 3.3 and 596.1 ± 3.3 Ma. These early Ediacaran ages chronologically correlate to the age of the Lower Ouarzazate Supergroup located in the Precambrian area of the Moroccan Anti-Atlas. The Tighardine formations underwent superimposed polyphase metamorphism. Mineralogical investigations show evidence of local intense thermal metamorphism and hydrothermalism evidenced by andalusite and cordierite in pelites; diopside, tremolite, and actinolite in dolomite; and by actinolite in volcanic rocks. Late brown biotite may overgrow early metamorphic minerals in all facies. Hydrothermal transformation is particularly confined in the crossings of N-S and N70 to E-W faults. The local thermal metamorphism and hydrothermalism result from a hypothetical granitic intrusion at depth. The early disseminated polymetallic mineralization (Cu-Pb-Zn) is confined in the Ediacaran volcanic and volcanosedimentary formation of Tighardine. This volcanic activity contributes to the genesis of the Tighardine ore deposit. The economic ore deposit is related to the recrystallization and brecciation of this early-disseminated polymetallic mineralization, during the Variscan event or later. [ABSTRACT FROM AUTHOR]