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Geology, mineralogy, and geochemistry of the Zarloukh Bentonite −Tuff deposit, Hemrin South Mountain, northern Iraq: implications for genesis and geotectonics

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The Quaternary Zarloukh Bentonite –Tuff (ZBT) deposit occurs within the Hemrin South Mountain, northern Iraq. The ZBT deposit occurs as depression-filling exposed on the erosional surface of the siliciclastic Pliocene Muqdadiya Formation and covered by an overburden of recent sediments. The thickness of the studied industrial bentonite bed is ~80−100 cm, occurring at the bottom of these depressions, covered by ~3−4 m thick bedded volcanic tuff, which also contains many 10–12 cm thick bentonite layers along its bedding planes. The volcanic ash at the bottom of lakes/swamps with shallow water content acted as basins for the deposition of falling volcanic ash, which immersed in water and devitrified to bentonite at a later stage by hydration and chemical interactions, meanwhile the continued fallen ash consolidated as tuff beds protecting the bentonite formed at the bottom of the depressions. | Turkish Journal of Earth Sciences Turkish J Earth Sci 2021 30 973-989 http journals.tubitak.gov.tr earth TÜBİTAK Research Article doi 10.3906 yer-2104-3 Geology mineralogy and geochemistry of the Zarloukh Bentonite Tuff deposit Hemrin South Mountain northern Iraq implications for genesis and geotectonics Yawooz A. KETTANAH Department of Earth and Environmental Sciences Dalhousie University Halifax Canada Received 04.04.2021 Accepted Published Online 06.11.2021 Final Version 22.11.2021 Abstract The Quaternary Zarloukh Bentonite Tuff ZBT deposit occurs within the Hemrin South Mountain northern Iraq. The ZBT deposit occurs as depression-filling exposed on the erosional surface of the siliciclastic Pliocene Muqdadiya Formation and covered by an overburden of recent sediments. The thickness of the studied industrial bentonite bed is 80 100 cm occurring at the bottom of these depressions covered by 3 4 m thick bedded volcanic tuff which also contains many 10 12 cm thick bentonite layers along its bedding planes. The volcanic ash at the bottom of lakes swamps with shallow water content acted as basins for the deposition of falling volcanic ash which immersed in water and devitrified to bentonite at a later stage by hydration and chemical interactions meanwhile the continued fallen ash consolidated as tuff beds protecting the bentonite formed at the bottom of the depressions. The bentonite bed shows mini-scale trough crossbedding as a sign for its formation within a low energy shallow agitated water in lakes swamps. The bentonite and its precursor tuff show some differences in the concentration of Ca Mg Na and K representing the exchangeable elements in smectite montmorillonite which is the predominant clay mineral in bentonite because of the probable gain of bentonite for these elements during the process of bentonitization of volcanic ash which also formed the tuff. The ZBT has most probably the same origin as the Hemrin Basalt located NW of ZBT deposit. The .