Renac,C. and Assassi,F.(2009): Formation of non-expandable 7Å halloysite during Eocene-Miocene continental weathering at Djebel Debbagh, Algeria: A geochemical and stable-isotope study. Sedimentary Geology, 217, 140-153.

『アルジェリアのDjebel Debbaghでの始新世〜中新世大陸風化期における非膨潤性７Åハロイサイトの形成』

『Abstract
　In north-eastern Algeria, autochthonous limestone units at Djebel Debbagh varying in age from Aptian to Cenomanian underwent burial diagenesis followed by deformation during the alpine orogeny. Karst windows formed during Oligocene to Miocene times, and are now filled with clay minerals, which currently help to sustain a local mineral industry. The largest karst window at Djebel Debbagh contains substantial volumes of 7Å halloysite ore. Mineralogical investigations on the 7Å halloysite indicate a non-expandable material, with measured water contents varying from 14.1 to 15.5 wt.％ H2O. Non-expandable 7Å halloysite showed limited hydrogen-exchange capacity during a 24-month laboratory experiment, suggesting that hydrogen and oxygen isotopes had not exchanged since equilibrium at the time of halloysite formation. Therefore, stable-isotope data were used to calculate reliable temperature profiles and to determine fluid composition. It is suggested on the basis of geochemical and mineralogical data that 7Å halloysite formed between 25℃ and 40℃ in equilibrium with meteoric water during Eocene to Miocene times. Estimates of supergene temperatures and calculated stable-isotope values for rainfall correspond to continental climate conditions during Miocene times, coeval with the closure of the Liguro oceanic basin.

Keywords: Karst deposit; Non-expandable 7Å halloysite; Stable isotopes; Exchange experiments and palaeotemperatures』

1. Introduction
2. Geological setting
　2.1. Comparison with Tunisia
　2.2. Regional setting
　2.3. Mining area setting
　2.4. Sampling of Karst 46
3. Analytical methods
　3.1. Petrography, mineralogy, and chemistry
　3.2. Fluid inclusion microthermometry
　3.3. Stable isotopes
　　3.3.1. Hydrogen-exchange experiments
4. Results
　4.1. Present day, and ancient thermal fluid circulation, in host limestone
　4.2. Large kaolin deposit (Karst 46) with ferruginous cap-rock
　4.3. Stable-isotope results and exchange experiments
5. Discussion
　5.1. Fluids in the sedimentary pile
　5.2. Chemical composition of fluids producing non-expandable 7Å halloysite
　5.3. Thermal conditions for the formation of karst deposit no.46
6. Summary and conclusions
Acknowledgements
References

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