Aqueous and hydrocarbon inclusions in dolomite fromTouissit-Bou Beker district, Eastern Morocco: a Jurassic carbonate hosted Pb [sbnd]Zn (Cu) deposit

Abstract

Within the Touissit-Bou Beker area several Mississippi Valley-type (MVT) deposits occur forming a word-class mining district, in northeastern Morocco and adjacent Algeria. The Pb Zn deposit occurs exclusively within dolomitic Aaléno-Bajocian condensed series, which overlies unconformably paleozoic substratum formed of crystalline Carboniferous rock (rhyodacites and granodiorites) and low-grade schists. Fluid characteristics in the different layers and sectors of the district (Oued Mekta, Hassi Ennyag, Beddiane, Bou Beker,Soltena, Tiouli, Tazoughart) have been specified by a survey of inclusions in the sphalerite and quartz associated with galena, and in synore recrystallized dolomites observed next to the ore deposits. The hydrothermal recrystallized dolomite is characterized by the presence of abundant small size (≤ 15 μm) aqueous and few hydrocarbon fluid inclusions that dominantly have an equant shape of primary origin. The occurrence of three-phase aqueous and hydrocarbon inclusions, indicative of heterogeneous trapping, indicates contemporanety of aqueous and hydrocarbon inclusions. The aqueous inclusions have a high salinity (20–26 wt.% eq. NaCl), NaCl/(NaCl+CaCI 2) ratio of 0.4 to 0.5, and Na/Ca ratio of 4 to 5. Homogenization temperatures range from 70 to 135 °C. Hydrocarbon inclusions, which occur as isolated population, are monophase liquid; rarely, two-phases. Homogenization temperatures range from 35 to 48 °C. Analyses by Raman spectrometry and Fourier transform infrared (FT-IR) spectroscopy indicate 100% ethane liquid inclusions. The fluid inclusion data indicate that the mineralization occurred at ambient condition of 100–135 °C and pressures of 150–200 bar, as constrained for the two inclusion types. The liquid hydrocarbon is considered to have been generated by thermogenic processes via interaction of the heated, high saline mineralizing fluid with organic-rich beds within the paleozoic substratum and the dolomitic series, and was subsequently entrained as an immiscible phase within the aqueous fluid.