Clay Mineralogy and Chemical Composition of Bentonites from the Gourougou Volcanic Massif (Northeast Morocco)

Abstract

The Gourougou volcanic massif (northeastern Morocco) is actively prospected for bentonite deposits. Five bentonites originating from different environments were selected for the present study: hydrothermal alteration of obsidian perlite glass inside the volcanoes themselves (Providencia and Tribia deposits); alteration of pyroclastic flows in a marine shallow water to lagoonal lacustrine environment (Ibourhardayn deposit); ash falls in marine or lacustrine systems (Moulay Rachid and Melg el Ouidan (formerly Camp Berteau) deposits). All of these bentonites were probably formed from volcanic glass originating from a rhyolitic magma at different stages of differentiation as shown by slight variations of REE and incompatible element abundances. The crystal-chemical characteristics of the smectite vary according to alteration conditions: beidellite predominates in hydrothermal systems, whereas montmorillonite predominates in lagoonal and lacustrine environments, and mixed-layer beidellite-montmorillonite in the sea-water-altered pyroclastic flows. All these dioctahedral smectites exhibit a heterogeneous distribution of charge as shown by the presence of partially expandable (1 EG) or non- expandable (0 EG) layers in the K-saturation state. The proportion of the collapsed or partially expandable layers is not related to the average layer charge or to the cation exchange capacity. This militates for an overall heterogeneous charge distribution. Compared to other natural or experimental alteration systems of similar rhyolitic glass, the formation of beidellite or montmorillonite appears to be controlled by the amounts of Mg in the system.

Geologic and Metallogenic Framework of North Africa

“…The origin of the bentonite deposits is attributed to: (1) hydrothermal alteration of perlitic glass inside of the volcanoes, (2) hydrothermal alteration of pyroclastic flows in a shallow marine to lagoonal lacustrine environment, and/or (3) hydrothermally altered ash falls in marine or lacustrine settings. All of these deposits are interpreted as having formed from a parent rhyolitic magma at different stages of differentiation (Ddani et al 2005). Similar bentonite deposits of the same age and geological environment occur in Algeria (Maghnia and Mostaghanem deposits; Abdelouahab et al 1988) and northern Tunisia (Nefza region; Sghaier et al 2014), on the eastern extension of the Moroccan volcanic province.…”

Bentonitas da Formação Irati no setor sul da Bacia do Paraná

“…Esse comportamento identifica a argila como uma esmectita, sendo esse o único mineral observado na amostra. A análise do parâmetro-b da esmectita 1A exibe o pico 1.500 Å (Figura 4b), o que a identifica com esmectita do tipo montmorilonitas, dioctaédrica saturada de Ca (Ddani et al, 2005).…”

“…A razão da mudança de comportamento resulta da ação de vários fatores, entre os quais diferenças na cristalinidade, variações no grau de hidratação e no tipo de cátions predominantes na posição interfoliar (Ddani et al, 2005). Para avaliar melhor essas propriedades, as amostras 1G (folhelho) e 1A (argilito) foram saturadas com CaCl 2 1N.…”

Evaluating the Diagenetic Alteration and Structural Integrity of Volcanic Ash Beds within the Eagle Ford Shale

“…Depositional environment might be variable. Ddani et al (2005) tracked an ash bed through a variety of depositional conditions and demonstrated the changing structure of the clay, depending on water depth and composition. The kaolinite-rich beds could be indicative of changing water temperature, shallow depth, or other conditions that allowed specific diagenesis to prevail.…”