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... Bradbury and Baeyens, 1999;Churakov and Dähn, 2012); however, Zn can also substitute for bivalent cations in octahedral sites (Schlegel et al., 2001). When Zn is the dominant cation in the octahedral site, the clay mineral can be a 2:1 Zn smectite (sauconite, Ross, 1946), a Zn chlorite (baileychlore, Rule and Radke, 1988) or a 1:1 serpentine like clay mineral (fraipontite, Fransolet and Bourguignon, 1975). Sauconite is a trioctahedral smectite Applied Clay Science xxx (2016) xxx-xxx ⁎ Corresponding author. ...
... with a structure very similar to saponite and represents the most common clays reported from several Zn deposits in Northern America (Ross, 1946), Peru (Boni et al., 2009;Mondillo et al., 2014Mondillo et al., , 2015, Southern Africa (Kärner, 2006;Terracciano, 2008;Boni et al., 2011) and Iran (Daliran et al., 2007). Fraipontite was discovered in supergene zinc deposits in Belgium (Fransolet and Bourguignon, 1975), and described in many deposits from Iberia (Calvo et al., 2007;Will et al., 2014), Italy (Merlino and Orlandi, 2001) and Kazakhstan (Chukhrov, 1956). ...
... Kärner, 2006;Boni et al., 2009) but only few studies present the detailed clay mineralogy (Kaufhold et al., 2015;Mondillo et al., 2015). Sauconite was described for the first time by Ross (1946). It is a Zn trioctahedral smectite with a saponite like structure; tetrahedral charge is related to the Al-Si substitution, while Zn occupies the octahedral sites. ...
Zn-clay minerals have been found in the non-sulfide deposit of Bou Arhous (High Atlas, Morocco). They occur as white or ochre clays embedding willemite (Zn2SiO4) and are commonly associated to red detrital clays in karstic cavities. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) with Energy Dispersive X-ray (EDX) analyses were combined in order to characterize the clay minerals and to determine the mechanism of their formation. XRD patterns on oriented and powdered clays and Fourier Transform Infrared (FTIR) spectroscopic analyses suggest that fraipontite is the major Zn clay phase (with some smectite interstratifications). SEM observation (back-scattered electron mode) shows that Zn clays are closely associated to willemite; euhedral willemite crystals show partial dissolution that preferably affects edges adjacent to newly formed fraipontite. Zn clays are also present as aggregates of about 50 μm filling the porosity or pervading the detrital clays. Intimate mixtures of Zn clays with detrital micas can also be observed. TEM-EDX analyses were carried out on clay separates but also on TEM foils prepared by Focused Ion Beam (FIB) milling directly on the thin section. Low- and high-resolution transmission electron microscopy images were acquired on selected areas preserving the texture of the sample. Two types of textural sites were selected: the Zn clay aggregates filling the porosity and the detrital clays partially replaced by Zn clay minerals. STEM-EDX map and point analyses confirm the occurrence of fraipontite. Individual particles of clay minerals with about 10% of Zn were analyzed. Structural formulae support the presence of a trioctahedral TO clay mineral like fraipontite. In the analyzed aggregates, the clays are composed of crystals of about 0.5–1 μm in diameter and 10 to 100 nm in thickness. At high magnification, the 0.7 nm layer periodicity was clearly imaged. Double layer periodicity is also common. In some fraipontite crystals, some intercalations with 1 nm layer were imaged. Stable isotope measurements suggest that this Zn clay mineral formed by direct precipitation of fluids which could be meteoritic and/or hydrothermal
... Combinations of the different genetic types may occur together in a given deposit, affecting the texture of ores and providing an intricate mineralogical record. This includes carbonates (smithsonite), hydrated carbonates (hydrozincite), silicates (willemite), hydrated silicates (hemimorphite), and various rare minerals, including clays, such as sauconite, a smectite containing up to 50 wt% of ZnO (Ross 1946), or more rarely fraipontite, a zinc berthierine (Fransolet and Bourguignon 1975). ...
... In the literature, several types of zinc clays were described. Sauconite, a trioctahedral smectite with a saponite-like structure is the most commonly described clay type and was reported in several deposits in Northern America (Ross 1946), Peru (Boni et al. 2009a), Southern Africa (Kärner 2006;Terracciano 2008;Boni et al. 2011), and Iran (Daliran et al. 2009). Fraipontite, a zincian berthierine (7 Å mineral), was found in supergene zinc deposits in Belgium (Fransolet and Bourguignon 1975), Iberia (Calvo et al. 2007;Will et al. 2014), and Italy (Merlino and Orlandi 2001). ...
... Other rare zinc clays, found in hypogene environments, are baileychlore, a zinc chlorite (Rule and Radke 1988), and hendricksite, a zinc mica (Frondel and Ito 1966;Robert and Gasperin 1985). Besides, moresnetite (Ross 1946) and vanuxemite (Frondel 1972) were also described as a mixture of zinc clays and hemimorphite. Zinc-bearing interstratified clay minerals were recently described, such as illite-zincian beidellite interstratified mineral in Peru (Mondillo et al. 2014) and fraipontite-sauconite interstratified minerals in Portugal ; this latter one is very close to the clay mineral described by the present study. ...
The nature and the origin of zinc clays are poorly understood. With the example of the Bou Arhous Zn-Pb ore deposit in the Moroccan High Atlas, this study presents new data for the mineralogical and chemical characterization of barren and zinc clays associated with non-sulfide zinc ores. In the field, white to ocher granular clays are associated with willemite (Zn2SiO4), while red clays fill karst-related cavities cutting across the non-sulfide ore bodies. Red clays (kaolinite, chlorite, illite, and smectite) present evidence of stratification that reflects internal sedimentation processes during the karst evolution. White clays contain 7-Å clay mineral/smectite irregular interstratified minerals with less than 20 % of smectite layers. Willemite is partially dissolved and is surrounded by authigenic zinc clay minerals. Together with XRD results, WDS analyses on newly formed clay aggregates suggest that this interstratified mineral is composed of fraipontite and sauconite. CEC measurements support that zinc is only located within the octahedral sheets. These new results support the following process: (i) dissolution of willemite, leading to release of Si and Zn, (ii) interaction between Zn-Si-rich solutions and residual-detrital clays, and (iii) dissolution of kaolinite and formation of interstratified zinc clay minerals that grew over detrital micas.
... Combinations of the different genetic types may occur together in a given deposit, affecting the texture of ores and providing an intricate mineralogical record. This includes carbonates (smithsonite), hydrated carbonates (hydrozincite), silicates (willemite), hydrated silicates (hemimorphite), and various rare minerals, including clays, such as sauconite, a smectite containing up to 50 wt% of ZnO (Ross 1946), or more rarely fraipontite, a zinc berthierine (Fransolet and Bourguignon 1975). ...
... In the literature, several types of zinc clays were described. Sauconite, a trioctahedral smectite with a saponite-like structure is the most commonly described clay type and was reported in several deposits in Northern America (Ross 1946), Peru (Boni et al. 2009a), Southern Africa (Kärner 2006;Terracciano 2008;Boni et al. 2011), and Iran (Daliran et al. 2009). Fraipontite, a zincian berthierine (7 Å mineral), was found in supergene zinc deposits in Belgium (Fransolet and Bourguignon 1975), Iberia (Calvo et al. 2007;Will et al. 2014), and Italy (Merlino and Orlandi 2001). ...
... Other rare zinc clays, found in hypogene environments, are baileychlore, a zinc chlorite (Rule and Radke 1988), and hendricksite, a zinc mica (Frondel and Ito 1966;Robert and Gasperin 1985). Besides, moresnetite (Ross 1946) and vanuxemite (Frondel 1972) were also described as a mixture of zinc clays and hemimorphite. Zinc-bearing interstratified clay minerals were recently described, such as illite-zincian beidellite interstratified mineral in Peru (Mondillo et al. 2014) and fraipontite-sauconite interstratified minerals in Portugal ; this latter one is very close to the clay mineral described by the present study. ...
... The first attempts, aiming at a definition of the kaolinite structure, date back to 1930, when Pauling, starting from models based on idealized polyhedra, provided a basic description. Later, several studies were devoted to the definition of the space group for this mineral (Gruner, 1932a;Hendricks, 1938;Brindley & Robinson, 1945, 1946. Gruner (1932a) indicated, for kaolinite, a monoclinic Cc symmetry with d 001 ¼ 14.3 Å , corresponding to a two-layer structure. ...
... Gruner (1932a) indicated, for kaolinite, a monoclinic Cc symmetry with d 001 ¼ 14.3 Å , corresponding to a two-layer structure. Brindley & Robinson (1945, 1946 recognized many reflections in the powder pattern that could not be indexed correctly on the basis of a monoclinic structure, and suggested a lowering of layer to the triclinic symmetry. This evidence was also confirmed by Zvyagin (1960), who suggested a rotation of SiO 4 tetrahedra, and by several other authors (e.g. ...
... Sauconite, ideally (M þ x Á nH 2 O)Zn 2þ 3 (Si 4þ 4Àx Al 3þ x )O 10 (OH) 2 , is a Zn-bearing smectite with octahedral Zn cations ranging from 1.48 to 2.89 a.p.f.u. and with the total octahedral occupancy varying from 2.70 to 3.06 a.p.f.u., thus suggesting that layer charge is dependent on tetrahedral substitution (Güven, 1988). Interlayer cations are commonly Ca, Na and K. Ross (1946) reported a monoclinic cell (space group C2/m) and unit-cell parameters a ¼ 5.34, b ¼ 9.32, c ¼ 15.8 Å , and b ¼ 958 for sauconite. Another detailed investigation, also including several determinations at non-ambient temperature conditions is that by Faust (1951). ...
Because of their many novel and advanced applications, there is increasing interest in layer silicates from the scientific and technical communities. Appropriate application of these minerals requires deep understanding of their properties and of the processes where they are involved. This chapter, by providing fundamental definitions and crystal structural and chemical data pertaining to layer silicates, aims to introduce this field to new researchers and technicians, by describing the fundamental features leading to different behaviours of layer silicates in different natural or technical processes. The subject addressed is vast and so the reader is referred in some cases to work already published. The focus here is on layer silicates for which detailed crystal structures are given in the literature and which are likely to be used in an applied way in the future. Layer-silicate minerals fulfilling these requirements are: (1) kaolin-serpentine group (e. g. kaolinite, dickite, nacrite, halloysite, hisingerite, odinite, lizardite, berthierine, amesite, cronstedtite, nepouite, kellyite, fraipontite, brindleyite, guidottiite, bementite, greenalite, caryopilite; minerals of the pyrosmalite series); (2) talc and pyrophyllite groups (e. g. pyrophyllite, ferripyrophyllite, willemseite); (3) mica group (i.e. some recent advances in crystal chemistry and structure of dioctahedral and trioctahedral micas); (4) smectite group (e. g. montmorillonite, saponite, hectorite, sauconite, stevensite, swinefordite); (5) vermiculite group; (6) chlorite group (e. g. trioctahedral chlorite such as clinochlore, di,trioctahedral and dioctahedral chlorites such as cookeite and sudoite); (7) some 2: 1 layer silicates involving a discontinuous octahedral sheet and a modulated tetrahedral sheet such as kalifersite, palygorskite and sepiolite; and (8) imogolite and allophane.
... It has been showed that the precipitation of Zn phases occurs in contaminated soils allowing the retention of Zn in excess to its adsorption capacity (Jacquat et al., 2009). Among the Zn precipitates, Zn with a structure very similar to saponite and represents the most common clays reported from several Zn deposits in Northern America (Ross, 1946), Peru (Boni et al., 2009;Mondillo et al., 2014Mondillo et al., , 2015, Southern Africa (Kärner, 2006;Terracciano, 2008;Boni et al., 2011) and Iran (Daliran et al., 2007). Fraipontite was discovered in supergene zinc deposits in Belgium (Fransolet and Bourguignon, 1975), and described in many deposits from Iberia (Calvo et al., 2007;Will et al., 2014), Italy (Merlino and Orlandi, 2001) and Kazakhstan (Chukhrov, 1956). ...
... Kärner, 2006;Boni et al., 2009) but only few studies present the detailed clay mineralogy (Kaufhold et al., 2015;Mondillo et al., 2015). Sauconite was described for the first time by Ross (1946). It is a Zn trioctahedral smectite with a saponite like structure; tetrahedral charge is related to the Al-Si substitution, while Zn occupies the octahedral sites. ...
... La microscopie conventionnelle ne peut fournir beaucoup plus de pr6cisions. Toutefois, l'existence d'une smectite et d'anomalies en zinc donnent ~ penser que cet 616ment pourrait &re localis6 dans une sauconite (Ross, 1946; Faust, 1951). Mais ~ ce stade, un doute est encore possible car une observation plus fine des photographies r~v61e la pr6sence d'une troisi6me phase (Fig. 6) fi contours irr6guliers, tr6s sensibles au faisceau 61ectronique et semblant amorphe ou tr6s mal organisee. ...
... 13, mais le signal obtenu est faible car la touche 3d de cet 61~ment est satur~e et a une petite section efficace. Cette analyse nous permet donc d'aftirmer que la smectite presente dans le m61ange est une sauconite (Ross, 1946; Faust, 1951) dans laquelle les ions Zn 2 § sont dispos6s dans la couche octaedrique. Phase amorphe. ...
Resume
Le remplissage des cavités karstiques de la région d'Ain Khamouda (Tunisie Centrale) est partiellement constitué d'une argile blanche. Son étude par diffraction X. ATD et analyse chimique traditionnelle montre qu'il s'agit d'un mélange d'halloysite prédominante et de smectite, renfermant plusieurs pourcents de ZnO. Une étude plus détaillée mettant en oeuvre un diffractométre à détecteur linéaire et à ambiance contrôlée, la microscopie électronique à transmission et la microscopie électronique à transmission en balayage (STEM) a permis de préciser les points suivants. En dehors de l'halloysite totalement dépouvue de zinc, il existe deux phases porteuses de ce métal: une sauconite et un hydroxyde de zinc à peu près amorphe. En outre, les faibles quantités (0.2%) de MgO contenues dans l'échantillon sont localisées à l'intérieur des tubes d'halloysite. De plus, ce minéral est présent sous la forme de deux phases, l'une hydratée, l'autre anhydre. Enfin, ces argiles renferment un peu d'argent sous la forme de microparticules de 3 à 10 nm de diamètre.
... The Zn clay sauconite is among the most common minerals found in several samples. According to Ross (1946), sauconite is a Zn-Na trioctahedral smectite. In this paper we use the term " sauconite " as referring to the typical Zn-rich smectite found at Accha, even though we were not able to determine the actual Na wt percent in this clay mineral due to strong Na Kα- Zn Lα peak overlap in both EDS and WDS analyses. ...
... The zinciferous variety of smectite is present at Accha in most samples analyzed. However, it was not always possible to distinguish between typical sauconite (as defined by Ross, 1946) and a Zn-rich smectite. Sauconite occurs in small amounts (<5%) in the samples where smithsonite is predominant but is more abundant (>30%) in the lithotypes that contain detrital quartz and partially weathered K-feldspar. ...
The Accha-Yanque zinc belt is located in the southern Altiplano of Peru, a major zinc-rich metallogenic province hosting a number of economic mineral deposits (porphyry copper and skarn ores). Several nonsulfide-type occurrences, showings, and mineral deposits are situated in a belt, peripheral to the northern, northeastern, and northwestern edge of the Oligocene-(MioceneP) Yauri-Apurimac batholith. Mineralization is hosted in breccias of both sedimentary and tectonic origin in the limestones of the Middle to Upper Cretaceous Fer-robamba Formation. Primary ores belong to the carbonate replacement deposit type and are at least in part structurally controlled. Currently, the Zn mineralization is almost fully oxidized: the Accha deposit can be assigned to both direct replacement and wall-rock replacement types. The mineralized zone (indicated resources 5.1 Mt @ 8.2% Zn and 0.9% Pb) occupies the hinge of an anticlinal dome that has been exposed by erosion. The southern limb of the structure dips about 55° to the south-southwest, whereas its northern limb is truncated by faults. The nonsulfide concentrations, consisting of a mineralized zone 5 to 20 m thick, are continuous along strike to the west for at least 700 m. The mineralogy of the Accha deposit shares many characteristics with that of the typical carbonate-hosted calamine-type nonsulfide Zn ores. The nonsulfide mineral association consists mainly of smithsonite and hemi-morphite replacing both primary ore minerals and carbonate host rocks. Hydrozincite has been detected only in samples near the surface. Smithsonite occurs in zoned concretions with goethite, Mn (hydr)oxides and Zn clays, as well as replacive cement in the limestone intervals. One of the most peculiar nonsulfide Zn minerals at Accha is a sauconite-like, zincian smectite, variably concentrated throughout the deposit. Locally sauconite occurs as replacement of detrital feldspars and/or detrital fragments occurring in marly sediments or in infills of karst cavities. It also replaces both hemimorphite and smithsonite deposited during earlier stages. The age of the supergene products in the whole belt is poorly constrained, although there is geomorphologic evidence that the formation of supergene minerals postdates by more than 10 m.y. the last large-scale secondary enrichment event that terminated with central Andean climatic desiccation at -15 Ma. The age of the Accha deposit may be consistent witb a Pliocene K-Ar date of 3.3 ± 0.2 Ma obtained for supergene alunite from the top part of the leached cap in the nearby Cotabambas Cu deposit.
... en 80 and 100 m in depth, where a high concentration of smithsonite has been detected. Hemimorphite is less abundant and spatially associated with Fe(hydr)oxides, but not always with smithsonite. In fact, this Zn-silicate occurs in two different associations: hemimorphite–smithsonite and hemimorphite–Zn-smectite . Zn-smectites (sauconite-type, cfr. Ross, 1946) are ubiquitous, and locally very abundant. The Accha " sauconite " is a Zn–Na trioctahedral smectite similar to the Zn-clay reported from the Skorpion mine (Borg et al., 2003). Quartz and feldspars have been also detected. The occurrence of K-feldspar in most samples can be commonly correlated with the presence of the clays, which are ...
... Sauconite is one of the most characteristic nonsulfide minerals detected at Accha (Table 2). The SiO 2 content of this trioctahedral smectite ranges here between 30 and 36%, generally higher than the published values (Ross, 1946), and ZnO between 34 and 44%. The Al 2 O 3 value of the most reliable analyses is comprised between 4 and 7%, while FeO, CaO and MgO are below 2%. ...
The Accha deposit in Southern Peru is the first case in which an integrated study between mineralogy, petrography and metallurgical characteristics of a nonsulfide Zn orebody has been carried out. The Accha–Yanque Zinc Belt is located in a major zinc-rich metallogenic province hosting a number of economic mineral deposits, which extends in a zone peripheral to the edge of the Oligocene–Miocene Yauri–Apurímac granite batholith. This belt is comprised of a number of weathering-derived nonsulfides occurrences, showings and mineral deposits. A thorough mineralogical and petrographic study has been carried out on the MET 1, MET 2, MET 3 and MET 4 cores, drilled between 2006 and 2007 for metallurgical purposes. The nonsulfides mineral association in the deposit consists mainly of smithsonite and hemimorphite replacing both primary ore minerals and carbonate host rocks. Smithsonite occurs in zoned concretions with goethite, Mn(hydr)oxides and Zn-clays. One of the most peculiar nonsulfide Zn mineral at Accha is a sauconite-like Zn-smectite, which can be locally very abundant (up to 30%).
... However, these 2 elements can be substituted by iron in its two oxidation states (Fe 3+ and Fe 2+ ) (Stucki, 1988;Finck et al., 2015). Other less common elements that may occupy the octahedral cationic sites are Ti 4+ , Ni 2+ (Bosio et al., 1975;Decarreau et al., 1987), Mn 2+ (Nahon et al., 1982), Cr 3+ (Mackenzie, 1984;Khoury and Al-Zoubi, 2014), Li + (Foshag and Woodford, 1936;Tien et al., 1975), and Zn 2+ (Ross, 1946;Balassone et al., 2017). All these isomorphic substitutions generate a charge deficit in the smectite layer ranging from 0.4 to 1.2 per unit cell (p.u.c.) (Guggenheim et al., 2006). ...
This work focuses on the study of the trace elements allocation in smectites throughout the statistical analysis of geochemical data corresponding to a very wide group of pure or almost bentonite samples. Data of trace elements contents corresponding to both analysed samples and bibliographic references were treated with different statistical analysis such as Partial Least Squares Discriminant Analysis (PLS-DA), Wilcoxon-Mann-Whitney rank sum test (WMW test). A clear relationship between trace elements and smectite crystallochemistry was evidenced from the PLS-DA results because the contents in certain the trace element separated the dioctahedral smectites from the trioctahedral smectites. In addition, the WMW test indicated that dioctahedral smectites preferentially accumulate Er, Eu, Gd, Sm, Tb, Nd, Ga, Dy, Ho, Tm, Be, Y, Yb, La, Pb, Ce, Lu, Pr, Hf, Bi, Zr, Zn, Nb, In, Th, Ta, Sn, and Ge, while trioctahedral smectites preferentially accumulate As. Complementary analysis by X-Ray Micro-Fluorescence and a study of after homoionization were done to help to discuss these results. According to these results, the presence of these elements as interlayer cations or their adsorption at layer edges has been excluded. In addition, external factors such as impurities and the geological origin of bentonites have been discussed and ruled out as influencing factors that could invalidate the obtained results. An evaluation of atomic parameters for trace elements indicates that As, with an effective cationic radius of 33.5 pm for coordination number CN=4, can be allocated in tetrahedral positions, whereas the remaining elements can occupy octahedral positions.
... Sauconite (Ross 1946;Newman and Brown 1987), one of the most common clay minerals in nonsulfide deposits (Large 2001;Hitzman et al. 2003;Boni 2005Boni , 2009aBoni , 2009bMondillo et al. 2014;Boni and Mondillo 2015), is a trioctahedral saponitelike smectite with Zn in octahedral coordination. Experimental studies on its synthesis and stability (i.e., Kloprogge et al. 1999;Higashi et al. 2002;Petit et al. 2008;Pascua et al. 2010) demonstrated that sauconite can precipitate from solutions of silicic acid, variously mixed with Zn-compounds (Zn-chlorides, Zn-oxides, or Zn-hydroxides) and Na-and Al compounds, at a pH interval of 6-12 and temperatures ranging between 20 and 200 °C. ...
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.
... Although not a focus of this study, Zn-bearing clay minerals Choulet et al. 2016) have been observed with smithsonite and hemimorphite in most White Zinc Zone samples (Fig. 8). The dominant clay mineral tentatively is identified as sauconite, the Zn-dominated smectite (Ross 1946). Sauconite typically has a powdery texture and is variably pink, white, ivory, or bright brown. ...
The Sierra Mojada District comprises multiple types of near-surface mineral concentrations ranging from polymetallic sulfide zones, “nonsulfide Zn” (NSZ) deposits, and a silver-rich Pb carbonate deposit hosted by lower Cretaceous carbonate strata. Hypogene concentrations of Fe-Zn-Pb-Cu-Ag sulfides and sulfosalts are locally preserved and are associated with hydrothermal dolomite and silica. Alteration mineralogy and sulfur isotope data suggest primary Zn-Pb-Ag mineralization from circa 200 °C hydrothermal fluids. The NSZ deposits dominantly consist of smithsonite and hemimorphite associated with local Mn-Fe oxides. The Red Zinc Zone consists of strata-bound zones dominantly of hemimorphite that fills pores in residual and resedimented Fe oxides. The White Zinc Zone shows local dissolution features, including internal sediments interbanded with and cemented by smithsonite. Similar Pb isotopic compositions of smithsonite, hemimorphite, and cerussite to Sierra Mojada galena document that the NSZ deposits originated from polymetallic carbonate-replacement sulfide deposits, with flow of metal-bearing groundwater being controlled by local topography and structural features in this extensional terrane. Oxygen isotope values for Sierra Mojada smithsonite are relatively constant (δ¹⁸OVSMOW = 20.9 to 23.3‰) but are unusually low compared to other supergene smithsonites. Using δ¹⁸OVSMOW (− 8‰) of modern groundwater at nearby Cuatrociénegas, smithsonite formational temperatures are calculated to have been between 26 to 35 °C. Smithsonite precipitation was favored by near-neutral conditions typical of carbonate terranes, whereas hemimorphite precipitated by reaction with wallrock silica and locally, or episodically, more acidic conditions resulting from sulfide oxidation. Transition to, and stabilization of, the modern desert climate over the past 9000 years from the Late Pleistocene wetter, cooler climate of northern Mexico resulted in episodic drawdown of the water table and termination of local supergene metal mobilization.
... Sauconite (Ross 1946;Newman and Brown 1987), which is one of the most common clay minerals in nonsulfide deposits, is a trioctahedral saponite-like smectite with Zn in octahedral coordination. Experimental studies on its synthesis and stability (i.e. ...
Zn-clays worldwide occur in various supergene nonsulfide (Zn-Pb) ores, where they can be the prevailing economic minerals or represent minor concentrations in the mineral assemblage. The world-class Zn smectite-rich Skorpion mine (Namibia) is considered one of the most important supergene nonsulfide zinc deposits in the world. At Skorpion, the trioctahedral Zn-bearing smectite predominates over the other Zn-oxidized minerals. This work is focused on microtextural observation and chemical analyses on the clay nano-particles of the supergene nonsulfide ores from Skorpion, carried out for the first time using TEM/HRTEM and AEM investigations. This approach helped to better understand the formation mechanism of the Skorpion Zn-clays and related phases down to the nanoscale. The microtextures of the Skorpion Zn-clays suggest they formed from fluids, meteoric and/or hydrothermal in nature, in two textural contexts: smectites can grow on previously deposited phyllosilicates (mica) (CCP texture), and/or directly nucleate from Zn-rich solutions (PCA texture). The Skorpion sauconite is chemically characterized by a greater homogeneity if compared with natural sauconites from other occurrences; it is quite stoichiometric, with Ca as interlayer cation and limited quantities of Mg and Fe, with an average composition of Ca0.14K0.02(Zn2.7Mg0.09Al0.14Fe0.10)(Si3.4Al0.6)O10(OH)2·nH2O. Contrary to Peru nonsulfide ores (Accha and Yanque), at the micro- and nanoscale the occurrence of Zn-beidellite at Skorpion is very subordinated. Chlorite and baileychlore have been also detected. Detrital micas are commonly the template for epitaxial sauconite growth. Typical supergene processes at ambient temperatures should be considered for the genesis of the Skorpion sauconite-bearing deposit, with some local contribution of low-T hydrothermal fluids. The micro- and nano-features of the Skorpion mineral assemblage confirm the complex mineralogical nature of the smectite-rich nonsulfide (micro)systems, with remarkable implications for mineralogical evaluation and processing.
... Les phyllosilicates sont parmi les minéraux les plus réactifs de l'environnement (Sparks 2003). De nombreuses études ont montré l'importance des phyllosilicates dans la rétention des cations métalliques tels que le Zn soit par adsorption à la surface soit par incorporation dans la structure cristalline de l'argile (Ross 1946 ;Manceau et al. 2000Manceau et al. , 2002bManceau et al. , 2004Lee et al. 2004 ;Panfili et al. 2005). Deux types de surfaces existent pour les phyllosilicates chargés Figure III-7). ...
Les matières en suspension (MES) sont constituées de colloïdes et particules et sont couramment décrites comme des agrégats hétérogènes formées de phases minérales, organiques et biologiques et possédant une forte réactivité de surface. Cette étude vise à étudier l’évolution de composition spatiale et temporelle des MES de la rivière Moselle (Lorraine, France) et également d’étudier la réactivité des MES vis-à-vis de contaminants métalliques. Les MES ont été collectées à différentes stations le long de la rivière Moselle et selon différents régimes hydriques. Des études microscopiques et macroscopiques ont été réalisées dans le but de caractériser les MES. Les résultats ont montré que la composition minérale des MES était relativement constante (1) le long de la Moselle (2) durant différents régimes hydriques et que la géologie du bassin versant contribuait grandement à la composition des MES. Les affluents de la Fensch et de l’Orne, deux rivières impactées par l’héritage industriel ont cependant montré la présence de particules d’origine anthropique. Cette étude a également montré le rôle majeur des MES dans le transport des TMEs et REEs quel que soit le débit. La caractérisation organique des MES a également montré des variations atténuées révélant l’aspect intégrateur d’un bassin versant de cette taille. Des variations saisonnières ont tout de même été observées avec une production autochtone plus élevée durant l’été. L’augmentation du débit a engendré une diminution de la teneur en matière organique ainsi que la présence d’une matière organique plus dégradée. Hormis les stations sur la Fensch et l’Orne, les propriétés de surface des MES sont homogènes, en relation avec la composition des particules. Les études ont également montré que le zinc s’associait de manière différente selon la quantité de zinc en solution. Enfin, l’étude comparée du mode d’association du zinc sur les composés modèles et les MES naturelles a montré la contribution des phyllosilicates dans le transport du zinc
... Chukanov et al. (2003); 52. Ross (1946);53. Smol'yaninova et al. (1961);54. ...
Changes in the mechanisms of formation and global distribution of phyllosilicate clay minerals through 4.567 Ga of planetary
evolution in our solar system reflect evolving tectonic, geochemical, and biological processes. Clay minerals were absent
prior to planetesimal formation ~4.6 billion years ago but today are abundant in all near-surface Earth environments. New
clay mineral species and modes of clay mineral paragenesis occurred as a consequence of major events in Earth’s evolution—notably
the formation of a mafic crust and oceans, the emergence of granite-rooted continents, the initiation of plate tectonics and
subduction, the Great Oxidation Event, and the rise of the terrestrial biosphere. The changing character of clay minerals
through time is thus an important part of Earth’s mineralogical history and exemplifies the principles of mineral evolution.
... The chemical composition of Yanque sauconite has many similarities with the same type of Zn clays reported from Friedensville, USA, Coon Hollow, USA (Faust, 1951), and Skorpion, Namibia (Kärner, 2006; Table 4). In the trioctahedral smectite, zinc is located in the octahedral sites, together with minor amounts of Mg and Fe 3+ , whereas Ca, K, and Na occur as interlayered cations, and aluminium can occur in tetrahedral and octahedral coordination (Ross, 1946;Newman and Brown, 1987). The chemical formulas calculated from the analyses of the Yanque sauconites (Table 4) are very close to the chemical formula for this mineral accepted by the International Mineralogical Association [Na0.3Zn3(Si,Al)4O10(OH)2 ...
The Yanque nonsulfide Pb-Zn deposit (inferred resources 12.5 Mt @ 3.7% Pb and @ 3.5% Zn) is located in the Andahuaylas-Yauri ore province (Cuzco, southern Peru). The deposit occurs within a base metal mineralized district, centered on the medium-sized Dolores porphyry copper. A thorough geological, mineralogical and geochemical study has carried out in order to define: the relationships between the Dolores Cu-porphyry ore and the Yanque Zn-Pb polymetallic mineralization, and the characteristics of the economic nonsulfide concentrations.
Both sedimentary and igneous rocks constitute the backbone of the Yanque-Dolores area. The sedimentary lithologies belong to the Soraya, Mara and Ferrobamba Fms. (upper Jurassic-middle Cretaceous). The Yanque orebody is hosted by the Mara Fm., which prevailingly consists of a siliciclastic sedimentary breccia. The original sulfide mineralization consisted of galena, pyrite and sphalerite. The host rock has been affected by a strong hydrothermal alteration, characterized by prevailing sericite/illite, as in the typical porphyry-related phyllic-argillic alteration stage, and by minor kaolinite, dolomite and quartz. Minor element geochemistry, characterized by Sb, As, Mn, Ag and locally also by Cu, points to magmatic-hydrothermal related mineralizing fluids. The Pb isotopic compositions from Dolores and Yanque sulfides are similar, and are typical of the Tertiary magmatically-derived ores in this part of Peru. The hydrothermally altered rocks at Yanque have the same Pb isotopic compositions as the sulfides, thus confirming the hypothesis that the Yanque primary Zn-Pb mineralization may have been produced by hydrothermal circulation related to the emplacement of the Dolores Cu-porphyry, as it is the case of other porphyry Cu systems associated with polymetallic mineralization elsewhere. However, no simple genetic model for the mineralization involving just one fluid circulation episode is able to explain the data.
The Yanque economic nonsulfide ore association consists of sauconite, hemimorphite, smithsonite and cerussite, which result from the weathering and alteration of the original sulfide mineralization. Zinc is allocated mainly in sauconite (Zn-smectite), rather than in carbonates: a factor strictly related to the prevailing siliciclastic character of the host rock.
Distinctive features of the Yanque orebody are the comparable ore grades for both Pb and Zn (3.5% Zn and 3.7% Pb), and the inverse supergene chemical zoning. In fact, contrary to other supergene ores of this type, zinc prevails in the top zone of the Yanque deposit, whereas lead content increases with depth. Considering the different mobility of the two metals in solution, it may be assumed that most of the primary zinc that was the source for the Yanque nonsulfides was originally located far from the position occupied by the galena mineralization, whose remnants have been observed on site. Zinc sulfides may have been originally contained in the eroded rock volumes that surrounded the actual deposit: the zinc-rich solutions have possibly migrated through the siliciclastic Mara Fm. and precipitated the nonsulfide minerals by porosity filling and replacement processes. In this sense, the Yanque secondary Zn-Pb deposit could be considered as a special type of “Exotic” mineralization.
... Recent investigations of Zn-contaminated soils have renewed interest in the local structural environments of Zn 2+ ions in diand trioctahedral phyllosilicates and other layered structures of environmental relevance (Manceau et al. 2000;Roberts et al. 2002;Scheinost et al. 2002;Voegelin et al. 2002;Juillot et al. 2003). Zn 2+ can form end-members or non-ideal solid solutions with Mg 2+ in trioctahedral phyllosilicates (see, e.g., Brindley and Brown 1980;Bailey 1988 and references therein), as illustrated by the smectite group minerals sauconite (the Zn end-member) and stevensite (the Mg end-member), which form a complete solid solution (Ross 1946;Faust 1951). Zn-rich talcs have been synthesized by Wilkins and Ito (1967), and sauconites have been synthesized at 80 °C by Decarreau (1981Decarreau ( , 1983Decarreau ( , 1985. ...
EXAFS spectroscopy has been used to determine the medium-range structural environment (within a radius of approximate to 7 angstrom) of trace levels of Zn2+ ions within the octahedral sheets of trioctahedral 2:1 phyllosilicates. EXAFS signatures of trace quantities (800-4000 ppm) of Zn in natural and synthetic trioctahedral 2:1 phyllosilicates (talcs and biotite) were analyzed using ab initio FEFF calculations (FEFF 8.10 code) in which various second-neighbor atomic configurations around a Zn-containing octahedral site were examined. Comparison of the results of these model calculations with observed Zn K-edge EXAFS spectra provides constraints on the distribution of Zn within the octahedral sheet. Zn was found to be randomly distributed within the octahedral sheets of the synthetic talc containing 4000 ppm Zn. In the natural biotite containing 800 ppm Zn, the distribution of Zn could not be determined because of significant Fe content, which precluded unambiguous FEFF analysis. Finally, FEFF analysis of single-scattering and multiple-scattering contributions to the EXAFS data of the Zn-dilute talc sample, followed by comparison with EXAFS data from a natural dioctahedral illite sample containing 140 ppm Zn, allowed unambiguous identification of spectral features characteristic of Zn2+ ions incorporated within the octahedral sheets of trioctahedral phyllosilicates. These results indicate that EXAFS spectroscopy can be used to distinguish between incorporation of trace levels of Zn2+ ions within the octahedral sheet of di- or trioctahedral phyllosilicates. They also provide a strong basis for determining the speciation of Zn at trace concentration levels in natural phyllosilicates from Zn-contaminated soils and sediments using Zn K-edge EXAFS spectroscopy. Because the crystal chemistry of other potentially toxic first-row divalent transition elements (i.e., Co2+, Ni2+, and Cu2+) is similar to that of Zn2+, this FEFF-based EXAFS approach could be used to (1) complement existing FTIR and polarized-EXAFS approaches in assessing the distribution of these elements within the octahedral sheets of di- and trioctahedral plyllosilicates and (2) better determine the speciation of these elements in contaminated soils and sediments.
... ons. However, it seems opportune to review briefly the present status of the various members of the montmorillonite group. Ross and Hendricks (1945) described montmorillonite, beidellite and volehonskoite as the dioctahedral members, and saponite and hectorite as the trioctahedral members. None of these names were new; all had been previously used. Ross (1946) later added sauconite, the zinc member, and discussed the relations of iron-rich griffithite. Faust and Murata (1953) added stevensite, a magnesian member, and Chukhrov and Anosov (1950) described medmontite, a copper member. ...
Since the publication of the paper on the minerals of the montmorillonite group by Ross and Hendricks (1945) some species have been added to the group, and minor changes in the acceptable species have become advisable. No radical changes are proposed, but a review of the members and their grouping will be presented. The acceptable dioctahedral members of the group appear to be montmorillonite, nontronite and volchonskoite. Beidellite should be discontinued. The acceptable trioctahedral members of the group appear to include saponite, hectorite, sauconite, stevensite and medmontite. Griffithite is probably a useful term for an iron-rich saponite. Representative chemical analyses and formulas have been assembled to illustrate relationships.
... The name comes from the first discovery of the mineral at the Uberroth Mine in the Saucon Valley, Pennsylvania (Genth, 1875). Sauconite found in nature generally has a saponitelike, Zn-rich smectite structure, i.e. with tetrahedral charge due to Al/Si substitutions in tetrahedral sheets (Ross, 1946;Faust, 1951). Sauconite usually occurs in the oxidation zone of Zn deposits, occasionally associated with hemimorphite (Zn 4 Si 2 O 7 (OH) 2 H 2 O) and smithsonite (ZnCO 3 ). ...
Stevensite-like sauconite, with the general composition: Si4 (Zn3−x□x)O10(OH)2R2x+, where □ is a vacant site, was synthesized. The objective was to study the possible migration of some cations (Li+ and Zn2+) within such trioctahedral smectites, under heating, following the so-called 'Hofmann-Klemen' (HK) effect. The initial gel wasdivided into five aliquots and placed in teflon-coated hydrothermal reactors with distilled water, and these were hydrothermally treated at 80, 100, 120, 150, and 200°C, respectively, over 30 days. X-ray diffraction (XRD) analysis confirmed that the samples synthesized were smectites. The number of vacant sites (x) per half unit cell (O10(OH)2) ranged from nearly 0 to 0.23 but no simple relationship was established between x and the temperature of synthesis. The samples were Li+- and Zn2+- saturated, and heated overnight at 300°C (HK treatment). Cation exchange capacity measurements were made by Fourier transform infrared spectroscopy (FTIR) on NH4+-saturated samples. After LiHK treatment, the structural formula of samples could be expressed as: Si4Zn(3−x)LixO10(OH)2NH4x+, while after ZnHK treatment, it could be expressed as: Si4Zn3O10(OH)2. Analysis by XRD and FTIR showed that the samples moved from a Zn-stevensite-like structure to Zn-talc-like structure after treatment with ZnHK. These results are interpreted as evidence that Zn2+ (and Li+) migrated into the previously vacant sites under HK treatment.
... These (bio)geochemical enrichments generally persist as a result of element immobilization by inorganic solids. For example, field studies and batch experiments on bentonite powders outlined the importance of Zn retention by phyllosilicates, either by sorption on the surface or by incorporation in a clay structure (Ross, 1946;Manceau et al., 2000Manceau et al., , 2002aManceau et al., , 2004Scheinost et al., 2002;Lee et al., 2004;Isaure et al., 2005;Panfili et al., 2005). To better understand the physico-chemical conditions favoring either of these two retention mechanisms, characterization of the reactivity of soil phyllosilicates toward Zn and other trace elements is needed. ...
Zinc uptake in suspensions (63.7 g L À1) of MX80 montmorillonite was investigated at pH 4.0 and 7.3, a total Zn concentration ([Zn] total) of 500 lM, and dissolved Si concentrations ([Si] aq) of $70 and $500 lM in 0.5 M NaCl, by kinetics experiments and polarized extended X-ray absorption fine structure (P-EXAFS) spectroscopy. Differential thermogravimetric analysis verified the cis-vacant character of the montmorillonite. No Zn uptake occurred at pH 4.0, confirming that cation exchange was hampered by the high ionic strength of the sus-pension. At pH 7.3 and low [Si] aq ($70 lM), Zn uptake occurred rapidly during the first hour of reaction, and then leveled off to 50 lmol/g montmorillonite at 168 h. The uptake rate is consistent with Zn sorption on pH-dependent edge sites. At pH 7.3 and high [Si] aq ($500 lM), the initial sorption rate was similar, but Zn sorption continued, reaching 130 lmol/g at 168 h, and was paralleled by Si uptake with a Si/Zn uptake ratio of 1.51(10), suggesting formation of a Zn (hydrous) silicate. P-EXAFS data indicated that the first oxygen coordination shell of sorbed Zn is split into two subshells at 1.97(2) and 2.08(3)–2.12(2) Å for all EXAFS samples. These two distances are assigned to a mixture of tetrahedral (IV Zn) and octahedral (VI Zn) Zn complexes. The proportion of IV Zn was lower in the high [Si] aq samples and decreased with reaction time. Al low [Si] aq and 216 h of reaction, nearest cationic shells of 0.6(4) Al in the film plane and 0.5(4) Si out of the film plane were detected at 3.00(2) and 3.21(2) Å , respectively, and were interpreted as the formation of IV Zn and VI Zn mononuclear complexes at the edges of montmorillonite platelets, in structural continuity to the (Al, Mg) octahedral sheets. At high [Si] aq , in-plane Zn and Al and out-of-plane Si neighbors were detected at 4 h, indicating the formation of Zn phyllosilicate nuclei at the layer edges. At 313 h, Zn–Al pairs were no longer detected, and Zn atoms were surrounded on average by 3.4(5) in-plane Zn at 3.10(1) Å and 1.7(9) out-of-plane Si at 3.30(2) Å , supporting the precipitation of a Zn phyllosilicate. Thus, dioctahedral Al phyllosilicate may act as a nucleating surface for the heterogeneous formation of trioctahedral Zn phyllosilicate at [Si] aq relevant to natural systems.
... Under natural conditions, metal ions are often associated with clay minerals. For example, natural smectites with high Cu 2 + contents (Mosser et al., 1990) and natural Zn 2 + -bearing trioctahedral clay minerals (Ross, 1946;Robert and Gasperin, 1985;Manceau et al., 2000) have been reported in the literature. ...
Physicochemical sequestration of transition metal ions is increasingly promoted as a cost-effective remediation technique for heavily contaminated soils and sediments. In enhanced stabilization/solidification strategies, this sequestration is hypothesized to result from the neoformation of various oxides, hydroxides and silicate minerals. However, more detailed information on the conditions that facilitate these neoformations or on the resulting metal sequestration is needed. In the present experimental study, the fate of selected transition metal ions (Cd2+, Cu2+, Pb2+, and Zn2+) is monitored during the precipitation of a synthetic smectite (hectorite) in a salt solution at 100 °C. X-ray diffraction (XRD) patterns and Fourier transform infrared (FT-IR) spectra confirm the synthesis of well-crystallized hectorite. Electron paramagnetic resonance (EPR) spectroscopy, coupled to NH3 vapor treatment, is used to determine the chemical form and structural location of Cu2+ in coprecipitates with hectorite. A quick extraction with EDTA probes the structural location of Cd2+, Cu2+, Pb2+, and Zn2+, and provides information on the fraction of the transition metal ions that are loosely associated with the external surfaces of the clay mineral. As indicated by the spectroscopic and chemical data, and as expected from the Pauling radii of the four transition metal ions, Cu2+ and Zn2+ are substituted in the mineral structure more significantly than are Cd2+ and Pb2+. The latter metal ions may be too large to be accommodated within layer silicate structures, and therefore represent a greater challenge for stabilization by coprecipitation in clay minerals. The results obtained in this research provide some of the theoretical foundation needed to improve the design of stabilization/solidification technologies.
... Both Zn-HIM and Zn-phyllosilicates (as Zn-kerolite) have been identified in pristine acidic soils Isaure et al., 2005). In saprolite developed from metalliferous mafic rocks and in weathered Zn-bearing ore deposits, several Zn-rich layered precipitates were identified, including fraipontite (Zn-serpentine), sauconite (Zn-smectite), baileychlore (Zn-chlorite) and zaccaganite (Zn-LDH) (Cesàro, 1927;Ross, 1946;Paquet et al., 1986;Rule and Radke, 1988;Merlino and Orlandi, 2001). Supergene alteration of primary Zn-sulfide deposits in limestone may also result in the formation of Zn-(hydroxy) carbonates and hydroxides in addition to Zn-silicates (Takahashi, 1960). ...
In order to better understand the long-term speciation and fractionation of Zn in soils, we investigated three soils naturally enriched in Zn (237–864 mg/kg Zn) from the weathering of Zn-rich limestones (40–207 mg/kg Zn) using extended X-ray absorption fine structure (EXAFS) spectroscopy and sequential extractions. The analysis of bulk EXAFS spectra by linear combination fitting (LCF) indicated that Zn in the oolitic limestones was mainly present as Zn-containing calcite (at site Dornach), Zn-containing goethite (Gurnigel) and Zn-containing goethite and sphalerite (Liestal). Correspondingly, extraction of the powdered rocks with 1 M NH4-acetate at pH 6.0 mobilized only minor fractions of Zn from the Gurnigel and Liestal limestones (<30%), but most Zn from the Dornach rock (81%). In the Dornach soil, part of the Zn released from the dissolving limestone was subsequently incorporated into pedogenic hydroxy-interlayered vermiculite (Zn-HIV, ∼30%) and Zn-containing kaolinite (∼30%) and adsorbed or complexed by soil organic and inorganic components (∼40%). The Gurnigel and Liestal soils contained substantial amounts of Zn-containing goethite (∼50%) stemming from the parent rock, smaller amounts (∼20%) of Zn-containing kaolinite (and possibly Zn-HIV), as well as adsorbed or complexed Zn-species (∼30%). In the soil from Liestal, sphalerite was only found in trace amounts, indicating its dissolution during soil formation. In sequential extractions, large percentages of Zn (∼55–85%) were extracted in recalcitrant extraction steps, confirming that Zn-HIV, Zn-containing kaolinite and Zn-containing goethite are highly resistant to weathering. These Zn-bearing phases thus represent long-term hosts for Zn in soils over thousands of years. The capability of these phases to immobilize Zn in heavily contaminated soils may however be limited by their uptake capacity (especially HIV and kaolinite) or their abundance in soil.
... The weathered products of willemite, a Zn nesosilicate (2112 SiOb), were studied by Koud (1985) According to the definition of Ross (1946). the smectites analyzed are sauconites, i.e. ...
An aluminum-free zinc-bearing smectite (Zn-smectite) was synthesized under hydrothermal conditions, together with its magnesium substituted products. Its layer charge calculated by cation exchange capacity (CEC) is 117.4 mmol/100 g. Powder X-ray diffraction (XRD) revealed turbostratic stacking and showed that the d06l value of the Zn-smectite was >1.525 Å, indicating that it is trioctahedral. Its d001 value increased from ca.12.8 Å to ca. 16.0 Å after ethylene glycol (EG) saturation. The Zn-smectite did not irreversibly collapse after heating the Li+-saturated sample to 300 °C, suggesting that its layer charge was generated from octahedral-site vacancies (defects). The Zn-smectite resembles zincsilite-like minerals with interlayer Na+ and Zn2+. The intralayer structure of zincsilite was confirmed by pair distribution function (PDF) analysis, and the whole crystal structure was built and optimized by DFT calculation in the CASTEP module of the Materials Studio software. Synthetic zincsilite is triclinic, space group P1, and its optimized unit-cell parameters are: a = 5.294 Å, b = 9.162 Å, c = 12.800 Å, α = 90.788°, β = 98.345°, and γ = 90.399°.
A multi-methodical characterization of a sauconite (Zn-bearing trioctahedral smectite) specimen from the Skorpion ore deposit (Namibia) was obtained by combining X-ray powder diffraction (XRPD), Cation Exchange Capacity (CEC) analysis, Differential Thermal Analysis (DTA), Thermogravimetry (TG), Fourier Transform Infrared spectroscopy (FTIR) and Transmission Electron Microscopy (TEM-HRTEM-AEM). The X-ray diffraction powder pattern exhibits the typical features of turbostratic stacking disorder with symmetrical basal 00l reflections and long-tailed hk-bands, confirmed also by TEM observations. Besides sauconite, the sample also contains minor amounts of kaolinite, dioctahedral smectite and quartz. CEC analysis provides a total of Ca (∼69%), Mg (∼26%), Na (∼4%) and K (0.7%) exchangeable cations. Therefore, Zn is located exclusively within the octahedral site of sauconite. TG analysis provides a total mass loss of about 17% in the studied sample. Three endothermic peaks can be observed in the DTA curve, associated to dehydration and dehydroxylation of the material. An exothermic peak at 820°C is also present as a consequence of dissociation and recrystallization phenomena. The infrared spectrum shows the typical Zn3OH stretching signature at 3648 cm-1 , whereas, in the OH/H2O stretching region two bands at 3585 and 3440 cm-1 can be associated to stretching vibrations of the inner hydration sphere of the interlayer cations and to absorbed H2O stretching vibration, respectively. Diagnostic bands of kaolinite impurity at ~3698 and 3620 cm-1 are also found, whereas 2:1 dioctahedral layer silicates may contribute to the 3585 and 3620 cm-1 bands. Finally, using the one layer supercell approach implemented in the BGMN software, a satisfactory XRPD profile fitting model for the Skorpion sauconite was obtained. The findings have implications not only for economic geology/recovery of critical metals but, more generally, in the field of the environmental sciences.
Elements in aqueous solution are the basis of surface geochemistry. Water is the agent of change concerning the materials brought to the surface by geological actions. Rocks containing minerals of high temperature origin interact with water because the constituent rock minerals are unstable under conditions of aqueous abundance where the water contains no more than minor amounts of solutes and is in equilibrium with atmospheric oxygen and CO2. The dissolution of an element into aqueous solutions is the major result of the interaction of surface water and the geologic materials found at the surface of the earth (rocks). The elements have different chemical relations with solids and the aqueous environment according to their chemical characteristics, ranging from essentially cations to oxyanions in solution. The differences in the nature of chemical attraction (ionic or covalent) determine the movement of the elements at the earth’s surface as being associated with solids or remaining in solution. Ionic reactions with aqueous solutions are the basis of surface geochemistry.
The disposal of nuclear waste will create a thermal gradient in the near-field environment, the magnitude of which depends on the cooling delay before disposal, and on the geological environment. For anticipated conditions, such a disposal is expected to have a gradient of 100 to 200°C for 100 to 1000 years during the thermal period of disposal (P.A.G.I.S., 1988). We studied the influence of this thermal gradient on the alteration processes in terms of mass transfer and alteration phases. A simulated French nuclear waste glass (containing 8 cations) was enclosed in a gold tube filled with deionized water and put in a cold-seal vessel submitted to thermal contrasts of 320-280°C and 250-220°C between 95 to 145 days at 130 bars. The new solid phases and their spatial distribution along the tube were studied by SEM observations coupled to EDS analyses, and X-ray microdiffraction. A mineralogical zonation implying mass transfer through the tube was systematically observed whatever the experimental temperature. It allowed us to demonstrate the mass transport of elements either towards the hot or the cold point of the system; indeed, zirconium and calcium moved toward the hot extremity whereas elements of the transition series and aluminium preferentially migrated to the cold one. Moreover, the absolute temperature did not affect the trend of this mass transport and only influenced the nature of the secondary phases : the lowest temperatures favoured amorphous products and phyllosilicates vs. well-crystallized phases. In a similar experiment, the influence of a chemical barrier made of kaolinite was studied. The presence of kaolinite successfully prevented the migration of heavy elements and calcium from the glass, by inducing crystallization of oxides trapping zirconium and calcium, and by favouring precipitation of hydrated amorphous products sealing the pores of the clay. These experiments clearly demonstrate that a thermal gradient might have important consequences for the performance of the near-field of a long-term nuclear waste disposal facility. Thermally induced mass transport might prevent the release of the radioelements from the very-near field environment and thus be involved in the confinement properties of the disposal system. Lastly, the presence of an aluminium-rich environment increases the efficiency of the retention by favouring the crystallization of oxides that trap the heaviest elements.
In spite of the great success of using clays and clay minerals in a large diversity of applications, an obstacle of users often is the limited knowledge in clay science. The successful future applications of clays and clay minerals strongly require a deeper understanding of the clay mineral structures and properties, that is, the structure–property relations. This chapter provides a survey of clay teaching in different countries. Nevertheless, clay teaching generally does not reach a level of knowledge required for future developments. Thus, this chapter is a strong challenge to intensify clay science teaching.
Zn-clays are associated with several supergene nonsulfide ore deposits worldwide, where they are either the prevailing economic
minerals, or minor components of the weathering-derived mineral assemblage. A TEM-HRTEM study on Zn-clays from nonsulfide
ore deposits of Accha and Yanque (Peru) was carried out, to properly determine the chemistry and complex texture of these
clays, not fully defined in other previous works on these (but also on other similar) deposits. The Zn-clays occurring at
Accha and Yanque are constituted by a mixture of sauconite and Zn-bearing beidellite. The chemical composition of sauconite
varies in a range of values, without any chemical gap, around the average composition:
Beidellites present an average composition close to stoichiometry with the addition of Zn:
The chemical composition of both sauconite and beidellite is consistent through the samples, with sauconite affected by a
wider variation in composition than beidellite. The textures of Zn-bearing smectites clearly indicate that a part of these
clays grew on precursory mica-like phyllosilicates, whereas another part was derived from a direct precipitation from solutions.
The occurrence of a paragenesis with trioctahedral and dioctahedral smectites demonstrates that, as observed in other environments,
also in a Zn-bearing system both smectite types are stable. As proved for other analogous trioctahedral-dioctahedral smectite
systems (e.g., saponite-beidellite), also in the sauconite-beidellite system a chemical compositional gap exists within the
series. The texture indicating a direct precipitation from solutions does not exclude that a smectite amount could be genetically
related to hydrothermal fluids, even if several other characteristics (e.g., the paragenetical association with Fe-hydroxides
typical of gossans) confirm the supergene origin for the bulk of the deposit.
In the words of Ross and Hendricks (1945), “Clay minerals . . . are the dominant materials of shales and surficial rocks and so are among the most important structural materials of the earth’s surface.” Clay minerals play a significant role in many aspects of life, ranging from their domination of the properties of the soils and sediments beneath us to their ubiquitous commercial use in many products and industries (Newman, 1984; Odom, 1984; Jepson, 1984, 1987). Iron in the crystal structures of these layer silicates significantly affects their physical and chemical properties, and thus is of great importance in the world around us.
A new procedure has been developed for fast preparation of saponite clays under non-hydrothermal synthesis conditions of 90
°C and 1 atmosphere. Saponites were synthesized from a stoichiometric mixture containing Si/Al3+ gel, M2+-nitrate (M2+ = Mg, Zn, Ni, Co, or Cu), urea, and water within a few hours. The synthesis products were characterized with XRD, IR, TEM,
XRF, N2-physisorption, Al-EXAFS, and 27Al- and 29Si-MAS-NMR. Incorporation of Mg, Zn, Co, Ni, or a combination of these cations in the octahedral sheet, as well as controlling
the Si/Al ratio in the tetrahedral sheet in the range between 5.67 and 39.0, could easily be established. Pure Cu-saponite
could not be synthesized due to the preferred formation of chrysocolla, but a combination of Mg2+ and Cu2+ resulted in saponite formation. The chemical composition strongly influences the textural properties of the saponites. It
is possible to prepare saponite samples of a specific surface area and pore volume of 100 to 750 m2/g and 0.15 to 1.05 mL/g, respectively. The lateral size and the amount of stacking of the saponite platelets could be influenced
by the composition, synthesis duration, and amount of urea. The new synthesis procedure provides an easy way to prepare large
quantities of saponites with far-reaching control on the texture as well as the composition.
This chapter presents history of clay science. Clays were known and used since antiquity but yet remain essential to the synthesis and development of modern materials, such as clay-polymer nanocomposites. However, clay science is a relatively young discipline, having begun only about a century ago. Many factors contribute to the rapid development of clay science over the past 100 years. Among these development of analytical and instrumental techniques, enhanced clay production, and increased industrial applications. Until the middle of the 19th century, the only tools available for the study of clays were the optical microscopy and chemical analysis. Clays are considered to be “colloidal complexes” of amorphous materials with properties that were typical of colloidal substances.
Two varieties of Zn-smectite were synthesized hydrothermally: sauconite, with an ideal composition of Na0.4Zn3(Si3.6Al0.4)O10(OH)2·n H2O; and a Zn equivalent of hectorite, with an ideal composition of Na0.4 (Li0.4Zn2.6)Si4O10(OH)2·n H2O (referred to here as Zn-hectorite). For comparison, hydrothermal synthesis of the related trioctahedral smectites of hectorite, Na0.4(Li0.4Mg2.6)Si4Ol0(OH)2·n H2O and hectorites containing Cu, Co or Ni in the octahedral sheets instead of Mg were also attempted. The results showed that sauconite, Zn-hectorite and hectorite could be synthesized in the temperature range 100-125°C but hectorites containing Cu, Co or Ni in the octahedral sheet, under the same conditions or even at a temperature of 150°C, could not.
The formation of sauconite and hemimorphite from glasses and oxide precursors in aqueous solution at 150–200°C is described. A tentative schematic stability diagram for a portion of the system Na2O-ZnO-SiO2-H2O at 150°C is presented. The relevance of this work to the use of a sodium zinc borosilicate glass as a matrix for the immobilization of nuclear fuel reprocessing wastes is discussed briefly.
Between Late Cretaceous and Miocene time the central part of Tunisia emerged. During this period a karstic system developed in Senonian limestones of the Ain Khamouda area. It is known that three facies occur in the resulting caves: (1) red mineralised crust containing goethite, hemimorphite and smithsonite; (2) white clay containing 0.1–8.5% ZnO; (3) Miocene sand and sandstone. The white clay has been studied using STEM (scanning transmission electron microscopy) in order to determine with which minerals Zn is associated. Two zinciferous phases were found, the first being a swelling clay of sauconite type, the second a nearly amorphous Zn-hydroxide gel. Halloysite which is the main component of the white clay seems totally devoid of Zn. The difference between Zn minerals contained in the crust and in the clay can be related to pH gradients. Minute particles (3–10 nm) of pure Ag, were found in the clay, indicating that the present mineralisation is probably related to the alteration of sulphides.
Thin spessartine-quartzite layers (coticules) are interstratified with Ordovician (Salmian) shales of the Venn-Stavelot Massif, Ardennes. These coticules indicate sudden interruptions in the sedimentation process of the shales. The lower contact of the coticules represents an abrupt change in the chemical composition from the underlying shales. In contrast, the upper limit of the coticules is chemically more diffuse. Phase relations of the phengitebearing spessartine-quartzites including paragonite, chlorite, and chloritoid or kaolinite as subordinate phases give evidence for a manganese-montmorillonitic source material of the coticules. This is in good agreement with the internal structures observed in the coticule layers (swelling and sliding effects, Liesegang structures). Since there is a positive correlation between the oxidation ratio of the enclosing shales and the chemical composition of the coticules, it is proposed that the source material of the coticules developed in situ by halmyrolysis out of tuffs. High oxidation ratios of the shales with iron fixed in the trivalent state but with divalent and thus mobile manganese led to the formation of coticule starting material, dominantly a manganese-montmorillonite. Halmyrolysis products formed under low oxidation ratio conditions of the enclosing shales are characterized by hydrosilicates rich in iron. The Obrochishte manganese deposit, Bulgaria, is discussed as a nonmetamorphic equivalent of the coticules of the Ardennes.
The crystal structure of hendricksite, a trioctahedral mica of biotite type, characterized by high Zn2+ and Mn2+ contents has been refined by least square methods. The structural formula is: (K0.89Na0.10Ba0.04)(Mg1.57Zn0.54Mn
0.402+Fe
0.252+Al0.07Ti0.07Cr0.01)(Si2.92Al1.08)O10 (OH)2. The space group isC2/m and the cell parameters are:a=5.340(2) Å,b=9.524(2) Å,c=10.235(3) Å, β=100.07(2)o, the cell volume isV=497.98 Å3. The final unweightedR=0.072. Average cation-anion distances in polyhedra are: T−O=1.659 Å, M(1)−O=2.093 Å, M(2)−O=2.088 Å, A−Olong=3.316 Å and A−Oshort=3.004 Å; A is the alkaline cation. The rotation angle of tetrahedra is α=6.7°. The analysis of electron densities, of the dimensions and distorsions of polyhedra shows that Zn2+ is exclusively in octahedral sites; there is no order between six-fold coordinated cations. A comparison between the structural features of hendricksite and those of the two main end-members of biotites, phlogopite and annite, is presented.
The effect of the strong covalence of Zn−O bonds is particularly visible on the dimensions and orientations of the thermal ellipsoids of octahedral sites M(1) and M(2) which contain zinc. In all the published structures of trioctahedral micas, the ellipsoids of cationic sites are uniaxial positive, elongated parallel toc
*. In hendricksite, this is observed only for the two zinc-free sites (T and A; in the octahedra M(1) and M(2), which contain zinc, the ellipsoids are approximately uniaxial negative, flattened parallel toa, which is a unique situation.
Zinc which habitually favours the tetrahedral coordinations with oxygen, enters the octahedra only, i.e. the chemically anisotropic sites, in hendricksite. The strong polarizability of Zn2+ is proposed to explain this behaviour.
An examination of the behaviour of Zn2+ in other compounds shows that this situation is general, zinc favours chemically anisotropic sites and specially those adjacent to OH or H2O.
Extensive solid-state characterization (AEM/SEM/HRTEM) was completed on six SON68 (inactive R7T7) waste glasses which were altered in the presence of saturated water vapor (200°C) for 22, 91, 241, 908, 1000, 1013, and 1021 days. The samples were examined by AEM in cross-section (lattice-fringe imaging, micro-diffraction, and quantitative thin-film EDS analysis). The glass monoliths were invariably covered by a thin altered rind, and the surface layer thickness increased with increasing time of reaction, ranging from 0.5 to 30 μm in thickness. Six distinctive zones, based on phase chemistry and microstructure, were distinguished within the well-developed surface layers. Numerous crystalline phases such as analcime, gyrolite, tobermorite, apatite, and weeksite were identified on the surfaces of the reacted glasses as precipitates. The majority of the surface layer volume was composed of two basic structures that are morphologically and chemically distinct: The A-domain consisted of well-crystallized fibrous smectite aggregates; and the B-domain consisted of poorly-crystallized regions containing smectite, possibly montmorillonite, crystallites and a ZrO2-rich amorphous silica matrix. The retention of the rare-earth elements, Mo, and Zr mostly occurred within the B-domain; while transition metal elements, such as Zn, Cr, Ni, Mn, and Fe, were retained in the A-domain. The element partitioning among A-domains and B-domains and recrystallization of the earlier-formed B-domains into the A-domain smectites were the basic processes which have controlled the chemical and structural evolution of the surface layer. The mechanism of surface layer formation during vapor hydration are discussed based on these cross-sectional AEM results.
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