E. A. Zhegallo

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.

Modes of iron-manganese mineralization on the bottom of Lake Baikal

The investigation of the bottom of Lake Baikal carried out during the 2008 summer season by means of Mir manned deep-submergence vehicles resulted in the recovery of a series of sediments, ferruginous crusts, and peculiar mineralized tubes several centimeters high and up to 2–6 cm in diameter. According to the scanning electron investigation, these formations consist mainly of the enclosing sediment particles and biogcnie silica cemented by iron and minor manganese hydroxides. The chemical composition of the tubes is similar to both that of the enclosing sediments and slightly ferruginous crusts and nodules, but the tubes and crusts are somewhat richer relative to the sediments in some microelements, namely, arsenic, cadmium, and uranium. In general, the structure and composition of these tubes reminds one of the worm tubes common in the sediments of a number of seas. The investigation of the rare earth elements in some samples or ferruginous formations and sediments revealed a positive europium anomaly, which might be related to either the composition of the surrounding continental magmatic rocks or to the influence of hypothetical hydrothermal solutions.

Evolution of manganese ore genesis in the earth’s geological history and the role of the biosphere

The formation of manganese rocks and ores occurred during the whole geological history of the Earth. Five metallogenic epochs (Early to Middle Proterozoic, Late Proterozoic, Early to Middle Paleozoic, Late Paleozoic, and Meso-Cenozoic) and 7 very important phases (Early, Middle, and Late Proterozoic, Early to Middle Paleozoic, Late Paleozoic, Late Mesozoic, and Meso-Cenozoic) can be distinguished. The phases of manganese ore genesis at many stratigraphic levels are closely related to the global climatic and tectonic reconstructions (the breakup of the continent of Gondwana and periods of glaciations and aridization) and biotic events (mass extinction of organisms). Based on carbon isotopic composition in manganese carbonates, participation of oxidized organic carbon is established.

Formation particularities of hypergene ferromanganese nodules: Far East Russia and Vietnam

Ferromanganese nodules (pisolites) form accumulations in basal layers of Pliocene-Quaternary clayey sections of Far East Russia and Vietnam. They are composed of minerals that are in common for both these regions (authigenic vernadite, feroxyhyte, goethite, halloysite, and terrigenous quartz) and minerals that are characteristic of either the northern (authigenic hollandite, lithiophorite, and bernessite) or southern (authigenic alumophorite, lepidocrocite, ferrihydrite, gibbsite, and terrigenous ilmenite) regions. Pisolites are considered to be microbial colonies with Mn and Fe oxides frequently forming biomorphs. The growth of the colonies was accompanied by dying off and mineralization of microorganisms successively from the central toward the peripheral parts of the nodules. The formation of metalliferous pisolites was linked to the oxidizing geochemical barrier developed at the interface between compact sedimentary clays and the underlying porous readily permeable weathered products of basalts.

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

Phosphorites of the Chiatura manganese deposit and specific features of their formation

The paper presents results of the detailed study of phosphorites from manganiferous beds of the Chiatura deposit. The relatively high-grade (P2O5 20–28%) phosphorites are represented by various rocks ranging from the variety dominated by massive phosphates with a rare aleuritic admixture of quartz and feldspar grains to rocks mainly composed of terrigenous material with phosphates in the matrix. Phosphates make up the matrix of various organic remains: differently preserved diatom algae and microbial species. Some relatively large organic remains (in particular, sponge spicules) are typically composed of iron minerals (with manganese admixture) rather than phosphates. Manganese ores comprise phosphorite fragments composed of phosphatized cyanobacterial mat. Phosphorites of the Chiatura deposit were likely formed in a shallow-water zone away from the continental land.

Phosphogenesis on selected low atolls in the near-equatorial part of the Western Indian Ocean

The compositions, structures, and microstructures of different types of phosphorites and poorly phosphatized rocks from low atolls in the near-equatorial part of the Western Indian Ocean are described. The rocks were examined under optical and scanning microscopes using microprobing techniques and etching of selected samples with weak solvents as well as with the help of chemical analyses. It is proved that phosphorites have been formed owing to the uneven phosphatization of the primary carbonate rocks; the degree of their phosphatization ranges from traces to 40% P2O5. In the phosphorites, numerous organic remains were encountered; they included fragments of plankton, debris of tortoise shells, and coccoidal and filamentous bacteria-like formations. It is suggested that the phosphorites were formed due to the high local biological productivity over the outer edges of coral reefs and are not related to guano accumulation or to endoupwelling.

Quaternary phosphatized limestones with initial Fe-Mn mineralization from the Kammu Seamount (Milwaukee Seamounts, northern Pacific)

Phosphatized biogenic limestones and phosphorites with initial Fe-Mn mineralization dredged from the summit surface of the Kammu Seamount (Milwaukee Seamounts, northwestern Pacific) are studied. The rocks are largely composed of nannofossils and planktonic foraminifers with an admixture of benthic foraminifers, bryozoans, and other organic remains, presumably including bacterial ones. The nannofosssil and foraminiferal assemblages indicate the Quaternary age of the sediments, and their phosphatization is consistent with the phosphatization age determined previously based on nonequilibrium uranium (within the limits of 1 My). The age of phosphatization and the Fe-Mn mineralization in the sediments from Pacific seamounts that young implies the dependence of these ore-forming processes on oceanic environments favorable for ore accumulation rather than on their age.