Main parameters influencing the plastic behavior of clays used for traditional ceramics production

This paper investigates the main parameters influencing the plastic behavior of clays used for traditional ceramics production. For this, twenty-six clayey pastes were selected from twelve traditional ceramic plants around the city of Marrakech (Morocco). According to the lithology, six different types of materials are used as raw material in the ceramic industry of this region. Emphasis is placed on the impact of the characteristics of these clayey materials upon the plastic behavior of these clays. The pastes were characterized through their consistency using the Atterberg limits. It has been concluded that the gain size, the mineralogical and the clay mineral composition and content, the effect of diagenesis and the presence of talc-pyrophyllite association play the most important role in the control of the plasticity behavior.

The nature of Zn-phyllosilicates in the nonsulfide Mina Grande and Cristal zinc deposits (Bongará District, Northern Peru): The TEM-HRTEM and AEM perspective

Zn-phyllosilicates are common minerals in nonsulfide Zn deposits and can give crucial information about the genesis of these oxidized mineralizations. They seldom represent the prevailing economic species but might have a significant impact on mineral processing. This study has been carried out on the Mina Grande and Cristal Zn-sulfide/nonsulfide deposits, which occur in the Bongará district (Amazonas region, northern Peru). The Cristal and Mina Grande orebodies are hosted by the sedimentary (prevailingly carbonate) successions of the Pucará Group (Condorsinga formation, Lower Jurassic), in an area affected by Neogene tectonics and characterized by Late Miocene and Pliocene-Early Pleistocene uplift phases (Andean and Quechua tectonic pulses). The Cristal deposit consists of both sulfide (sphalerite with minor pyrite and galena) and nonsulfide concentrations. The nonsulfides consists of smithsonite, hemimorphite, hydrozincite, chalcophanite, goethite, and greenockite, locally associated with Zn-bearing phyllosilicates. The Mina Grande deposit consists almost exclusively of Zn-oxidized minerals in limestone host rocks. The nonsulfides association consists of hydrozincite, hemimorphite, smithsonite, fraipontite, and Fe-(hydr)oxides, also containing a clayey fraction. The study deals with TEM-HRTEM and AEM investigations on clayey materials, to determine their crystal-chemical features and the origin of the complex Zn-clays-bearing parageneses. In both deposits, Zn-bearing illites (1Md and 2M polytypes) and I/S clay minerals (I3) are the main detected phases, with few compositions close to (Zn-bearing) muscovite. In the clayey fraction at Mina Grande, fraipontite, a Zn-bearing mica called K-deficient hendricksite, and (Zn-bearing) kaolinite also occur. Zn-illites and smectites (always containing Zn in variable amounts) characterize the mineral association at Cristal. The investigated compositional gap between di- and tri-octahedral Zn-phyllosilicates gives indications on the genetic relationships between them and advances on the knowledge of these species. The present work gives an insight into the Zn-bearing phyllosilicates systems by determining the amount/mode of metal incorporation in their lattices and understanding the relationships of natural occurring clay-rich complex associations, which can act as models for possible synthetic counterparts.

Geophysical and Petrographical Study of Apatapiti Charnockitic Rock, Akure, Southwestern Nigeria

Geophysical and petrographic evaluation of the earth’s subsurface is of vital concern, especially prior to geotechnical and hydrogeology works. Vertical Electrical Sounding (VES) of Ire-Akari Estate of Apatapiti Community in Akure South was carried out to assess the effects of the petrographic properties of charnockitic rocks on the geotechnical and hydrogeologic systems. The three curve types identified within the study area are AA, KH and HA, with a predominance of KH curve type, which suggests that the predominant geologic sequence comprising the topsoil has a clayey content alternating with laterite. This is underlain by weathered layer and fresh bedrock. Petrographic analyses revealed the presence of plagioclase (Albite-Anorthite), hypersthene, biotite, quartz, hornblende, microcline, pyroxene and dark-coloured minerals, with an average modal composition of 31%, 15%, 11%, 18%, 13%, 1%, 5% and 6%, respectively. A correlation of both results showed that the topsoil is mostly of about 0.4 m to 2 m thick layer of clay, indicative of weathering of feldspars. This is underlain by 0.8 m to 7 m thick layer of lateritic clay which responds as a low resistive layer. However, the mineral composition at location 1 is characterized by rocks that are more resistant to weathering due to the presence of low plagioclase in the rock sample compared to samples from other locations with a higher percentage of plagioclase and hypersthene minerals. This implies that weathering condition at all locations except location 1 could be favorable to hydrogeology if there are interconnected fractures in the parent rock (charnockite). However, since the area is predominantly covered by clayey materials which are established as poor foundational materials, appropriate ground improvement techniques and in-depth geotechnical analyses should be performed to forestall hazards associated with them.

Assessment of clayey materials from Santa Maria (Azores, Portugal) for preparation of peloids

There is growing interest in the use of natural materials as alternatives to medicinal products composed of chemicals. For this reason, it is important to study materials which fill this need (e.g. the formulation of peloids). Historically, the Azores archipelago has long been visited for its mud baths, mainly on São Miguel Island, where volcanic muds demonstrate beneficial properties. The volcanic muds are scarce, however. Thus, residual clay materials of Santa Maria Island were studied to assess their suitability for the formulation of peloids. The results of tests from 20 samples, collected from all over the island, presented evidence that they are very favourable for peloid formulations, due to their mineralogical, chemical and technological properties. The materials showed good potential for blending with the São Miguel volcanic muds. The deposits studied show extensive outcrops.