The origin of fluorite deposits in the Bou-Izourane district (Central High Atlas of Morocco) and its relationships with the Tamazeght magmatic complex

• Published in: Ore geology reviews Vol. 160; no. 105596; p. 105596
• Main Authors: Achmani, Jamal, Blaise, Thomas, Chraibi, Ilham, Barbarand, Jocelyn, Brigaud, Benjamin, Bounajma, Hassan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2023; Elsevier
• Subjects: Applied geology; Bou-Izourane deposits; Earth Sciences; Fluid inclusions; Fluorite mineralization; Geochemistry; Late magmatic fluid; Mineralogy; Moroccan High Atlas; Petrography; Sciences of the Universe; Tamazeght carbonatite; Bou-Izourane deposits; Late magmatic fluid; Tamazeght carbonatite; Fluorite mineralization; Moroccan High Atlas; Fluid inclusions
• ISSN: 0169-1368; 1872-7360
• DOI: 10.1016/j.oregeorev.2023.105596

[Display omitted] •The seven deposits of the Bou-Izourane district show similar characteristics in terms of paragenesis, geochemistry and emplacement temperature, except for the site of Bou-Imetssene.•Both late magmatic fluids and meteoric waters are identified as mineralizing fluids.•The fluids have interacted with the rocks of the Tamazeght complex, which also acts as a heat source and a driving mechanism for fluid flows.•F is provided from the partial leaching of various minerals from the Tamazeght complex, while Ca is sourced mainly from the host sedimentary rocks. Fluorite deposits in the Bou-Izourane district of the High Atlas in Morocco are distributed over seven known mineralized sites near the Middle Eocene Tamazeght magmatic complex and hosted in sedimentary rocks (limestones and marls) of the Lower Jurassic (Bou-Izourane, Takkat, Bou-Kharouba and Tabja deposits), magmatic rocks (Bou-Imetssene and Meghsan deposits) and skarns (Tamazeght and Bou-Imetssene deposits). This paper examines the origin of the mineralizing fluids and the relationship between the Tamazegth complex and fluorite deposits. Fluorspar occurs in veins oriented according to three families (N20, N50-80 and N120), in karst cavities and as stratabound deposits. Three stages are identified in the mineralization: (1) fluorite emplacement associated with the dissolution of the host rocks; (2) fracturing and sealing by calcite and finally (3) silicification associated with the partial dissolution of fluorite and calcite. Fluid inclusions in fluorite hosted in marls and carbonates of the Lower Jurassic have low salinities (1.5 to 3 wt% equiv. NaCl) and homogenization temperatures between 91 °C and 159 °C. Fluid inclusions in the Tabja, Tamazeght and Meghsan fluorites exhibit the same salinity range, but with increased homogenization temperatures, ranging from 99 °C to 241 °C, with a vapour phase containing CO2. Secondary solid daughter phases, such as nahcolite, calcite and strontianite are identified. Only Bou-Imtessene fluorite has high salinity fluid inclusions (∼18 wt% equiv. NaCl) and intermediate homogenization temperatures between 126 °C and 187 °C. These high local salinities and the presence of nahcolite and secondary carbonates in the fluid inclusions of the Tabja, Tamazeght and Meghsan fluorites may reflect the involvement of late-magmatic fluids. The δ18O isotopic composition of the fluid that precipitated calcites from Tabja (highest Th) and Bou-Izourane (lowest Th) indicates a meteoric origin. Fluorite has a broadly similar REE distribution to that of the Tamazeght carbonatites, suggesting that REE are derived from: i) carbonatites by hydrothermal alteration (e.g., Bou-Izourane, Bou-Kharouba and Takkat), and ii) carbonatitic (late-magmatic) fluids (e.g., Tabja, Tamazeght, Meghsan and Bou-Imtessene). Our data shows that fluorite mineralization in the Bou-Izourane district and the spatially associated middle Eocene Tamazeght magmatism have a direct genetic relationship through the contribution of late-magmatic F-rich fluids in close proximity to the complex. Fluorite mineralization farther from the complex is formed by per descensum circulation of meteoric waters along fractures resulting in fluorine leaching. The Tamazeght complex acts as a heat source and driving mechanism for fluid flows. The dissolution and recrystallization reactions are made possible by a strong geothermal gradient persisting after the complex was emplaced. The upwelling of these hydrothermal fluids into the calcium-rich host rocks (limestone and marl) leads to the precipitation of fluorite.