V. M. Novikov

Structural-morphological features of kaolinite from clayey rocks subjected to different stages of lithogenesis: Evidence from the Voronezh anteclise

This paper reports the results of precision structural-morphological study of kaolinite from clayey rocks taken in various areas of the Voronezh anteclise subjected to different stages of lithogenesis: primary kaolins of the weathering crust, proluvial-talus and lacustrine secondary kaolins, as well as lacustrine-swampy fireproof and deltaic-lagoonal refractory clays. The clayey material was transported over more than 300 km. The formation of the fireproof and refractory kaolin deposits in the Voronezh anteclise was related to the Devonian and Early Cretaceous stages of the geological evolution of the region. In terms of spatiotemporal and facies features, the studied genetic series of the kaolin clay deposits is unique. It was established that the sequential structural-morphological evolution o kaolinite in the considered deposits was caused by its mechanical disintegration during transport and redeposition. Interrelation between organic and mineral matters in the fireproof clays was revealed for the first time. Experimental studies of the behavior of kaolinite during sequential grinding and heating confirmed the main reasons for its natural degradation. The formation of virtually monomineral kaolin clays was provoked by the “flow-through” diagenesis, which is similar to weathering in trend. Evolution of mineral matter of the considered genetic series in kaolinite clay deposits was accompanied by the increase of δ18O values and their dispersion. Peculiarities identified in the behavior of kaolinite and related oxygen isotope characteristics of different-aged denudation and redeposition products of the Devonian weathering crust can play an indicator role in studying different stages of the lithogenesis of clayey rocks.

Kaolinite history in the weathering crust and associated clay deposits: EPR data

During the Aptian, these deposits containing sec� ondary kaolin composed an elevated erosion–denu� dation plain with quite rugged relief and a series of river valleys stretching from the south to the north. Erosion of the Mamon Series resulted in the removal of rough material to the alluvial, lagoon–deltaic, and shallow sea plains. The maximal length of transfer exceeded 300 km. According to the SEM investiga� tions, the presence of relict minerals of the Mamon series rocks as fragments of vermicular kaolinite crys� tals, rounded grains of quartz, feldspar, rutile, garnet, and zircon is a direct sign for a genetic link between the considered accumulative formations and the removal source. Argillaceous–aleurite–sand deposits of the alluvial plain were formed as a result of confluence of river val� leys. The Latnen deposit of kaolin fireproof clays is located in this facial geomorphological environment. They form lenses in sand series. The composition of clays is variable along the section. This results from various concentrations of admixtures of quartz, mont� morillonite, gibbsite, iron sulfides, and carbonaceous material. The mentioned peculiarities of Latnen clays result from the processes of “flowing” diagenesis occurring under reducing acid conditions of flotants enriched in organic material [2].

The first find of biogenic nanosiderite in oxidized ferrous quartzite of the Lebedinsk deposit, Kursk Magnetic Anomaly

The first data on biogenic nanosiderite originally discovered in oxidized Fe-quartzites from the Lebedinsk deposit of the Kursk Magnetic Anomaly (KMA) are reported. Two generations of siderite with radically different morphology and crystal-chemical and physical properties were identified. The biogenic origin is substantiated for the late generation (nanosized siderite particles). We suggest that the early ores were transformed as a result of the evolution of the atmosphere and biosphere in the area of the KMA in the Phanerozoic. Such significant differences in the properties of biogenic nanosiderite and early rhombohedral siderite may provide evidence for their different origins. The early generation of siderite was most likely formed during an abiogenic process.

Biogenic nanogoethite in the weathering crust of the basalts of Vietnam: Crystal morphology and thermal and magnetic properties

Studies of the mineral substance in the weathering crust (CW) of the basalts of Vietnam have shown that these basalts might be considered as a natural laboratory for the formation of mineral bionanostructures of specific crystal morphology and thermal and magnetic properties. It is suggested that the crystallization of goethite in the cuirass and underlying bauxites of the CW of Vietnam resulted from the coagulation of colloidal particles and of hydrated iron oxide under the impact of bacterial colonies, which determined the specific features.

The role of organic matter in the formation of fireproof clay of the Latnenskoe deposit

634 Organic matter of vegetal and (or) bacterial origin in the Earths crust under the conditions of hypergen� esis carries two functions: destructive, providing decomposition and dissolution of primary minerals, and creative, which controls incorporation of mineral� ized organic remnants in the composition of new hypergene formations. Biomineral interactions and their role in mineral formation are related to one of the most important problems of the twentyfirst century in mineralogy (1, 2). It has become much more evident that bacteria occur in all environments and on all sur� faces and that they actively participate in rock weath� ering, material transportation, sedimentation, and diagenesis. Biofilms and cyan bacterial mats play an important role in the processes of mineral formation as well (3). Additional support for these facts was obtained during study by a scanning (SEM) and trans� mitting (TEM) electron microscopy, thermal analysis, and IRspectroscopy of fireproof clay from the Latn� enskoe deposit; as a result, the interaction between organic and inorganic materials during their forma� tion was originally discovered. The deposit is located in 15 km to the west of Vor� onezh in the Don-Veduga-Devitsa interfluves. Clay composes oval lenses with a width of several hundred meters and a length of a few kilometers; it occurs in the middle part of the section of sand-gravel alluvial deposits of Aptian age. The thickness of productive horizon ranges from n to 40 m; the average thickness of proper fireproof clay is 3-4 m. Clay is mainly com� posed of kaolinite, the concentration of which is 70- 90%. Terrigenous hydromica and quartz, as well as authigenous montmorillonite and gibbsite, usually

The Latnenskoe refractory clay deposit (Central Russia)

This paper reports the results of our recent studies and generalizes previously known data on the geology, mineralogy, geochemistry, and genesis of the Russia’s largest Latnenskoe refractory clay deposit. It is shown that conditions of its localization were defined by regional and local factors. The regional factors controlled the distribution of the clay raw material in the region, while the local factors were responsible for the genesis and composition of refractory clays of the Latnenskoe deposit. Our studies showed that the formation of refractory clays is not only related to terrigenous but also to authigenic processes of sedimentation. The terrigenous component of clays was formed by the erosion of kaolin weathering crusts of the Voronezh anteclise crystalline basement and Paleozoic sedimentary hydromica–kaolinite rocks. Authigenic processes were significantly contributed by organic matter, which determined the environmental pH and Eh parameters. It is established that the mineral matter of clays of the deposit is represented by three morphological modifications (crystalline, amorphous, and biomorphic), which were formed subsequently and (or) simultaneously and could be transformed into each other. Application of a complex of modern precision methods allowed us to reveal a previously unknown biomorphic modification of kaolinite, the major rock-forming mineral, as well as mixed-layer kaolinite-smectite in the clays. It is shown that the distribution of major and trace elements and the sulfur isotope composition in different technological types of clay depend mainly on the facies conditions of their formation. Technological properties of clay raw material are considered.

An unusual association of mixed-layer minerals in Paleogene bentonite shale of the Voronezh anteclise

77 Bentonite shale is widely applied in different areas of industry and agriculture. Its quality mostly depends on the mineral composition, which is controlled by sedimentation and diagenetic processes with partici pation of organic matter [1]. In this paper, we consider new data on the mineral composition and genesis of bentonite shale and its deposits formed in marine environments from the example of Paleogene deposits of the Voronezh anteclise (VA). By application of modern precise methods, for the first time for these clays, mixed layered kaolinite–montmorillonite was detected, and indicator function of silica and carbon ate of fossilized benthos was recovered. According to the distinguished mineral associations, the stadial analysis of the conditions of the bentonite shale for mation on the VA was suggested and performed for the first time. Shale layers quite thick for industrial development and occurring at a shallow depth are known in the Upper Paleocene (Sumskaya Formation) and Upper Eocene (Kievskaya Formation) deposits [2] (Fig. 1a, 1b). The mineral composition of shale was studied on an ARL X’TRA X ray diffractometer (TFS SARL, Switzerland), CamScan 4 (Cambridge) and TESCAN VEGA IIXMU (Tescan) scanning electron micro scopes, a JEM 2100 transmitting electron microscope (JEOL, Japan), and using a synchronous thermal analysis on a STA 449F1 Jupiter apparatus (Netzscht, Germany) at a heating rate of 10°C/min and X ray fluorescent analysis on an Axios mAX Advanced appa ratus (PANalytical, Netherlands). Deposits of the Sumskaya Formation with a total thickness of 7.5–12.5 m are abundant in the south eastern part of the considered territory and transgres sively overlie Upper Jurassic chalk and marl [3]. The Nikol’skoe deposit, in which bentonite shale com poses a horizontal layer (2.0–5.5 m) in sand–shale rocks, is located there [4]. According to the granulom etric composition, the material is classified as medium or fine dispersed.

Iron in the kaolinites from kaolin and bauxite weathering crusts after granites: EPR data

Kaolinite is an economically important clay mineral. It is proposed to use electron paramagnetic resonance (EPR) in order to estimate the quality of kaolin concentrate while studying deposits [1]. This is related to the fact that most EPR signals of kaolinite are ascribed to Fe 3+ ions. Some of them occur as an isomorphic impurity in the mineral structure, while others are incorporated in various micro- and nanoinclusions. The iron admixture significantly affects the physical, chemical, and, of particular importance, technological properties of kaolins. One of the main kaolin sources is weathering crusts, whose formation is accompanied by structural, morphological, and chemical transformations of kaolinite [2, 3]. However, the reasons for its transformation in the weathering profiles of different mineralogical-genetic types and ages remain insufficiently studied. In this work, we present the results of EPR study of kaolinites from the Zhuravlinyi Log (South Urals) and Chaimat (South Vietnam) deposits, which are confined to the weathering crusts after compositionally similar leucocratic granites. The weathering crust of the Zhuravlinyi Log deposit is made up of one kaolin zone up to 40 m thick with a subzone of 10 m and more of alkali kaolins in its lower part. The eluvial kaolin is overlain by the Miocene clays of the Svetloe Formation. The weathering crust at the Chaimat deposit consists of two zones: the lower 10- to 16-m-thick kaolin zone and laterite bauxites in the upper 1‐4 m. The ages of the weathering crusts are respectively, Cretaceous and Middle Miocene. Samples for study were taken from the lower, middle, and upper horizons of the kaolin zones of the considered objects, as well as from laterite bauxites of the Chaimat deposit. Samples were collected through intervals along borehole 2005 at the Zhuravlinyi Log deposit and the section of the Chaimat deposit (Fig. 1). EPR spectra of clay fractions (<63 µ m) of the studied kaolinite samples were recorded on a compact PS-100 radiospectrometer in the X-range at room temperature.