Fractural structure of thick hard roof stratum using long beam theory and numerical modeling

The thick hard rock (THR) roof of the long-wall mining face is prone to the large-sized cantilever roof, and its sudden fracture will cause serious rock dynamic disasters, such as coal and gas outburst and rockburst. In this study, based on the long beam theory, the initial fracture mechanical model for THR was established, and the first weighting characteristics and extreme fracture step distance were calculated. This study introduced a new technology called deep-hole pre-splitting blasting (DPB) which could break the THR by drilling holes with different depths and angles at different levels of roof rock and then blasting it. Field measurement analysis indicated that the immediate roof and lower thick hard strata were fully collapsed to fill the goaf, and the upper thick hard stratum was effectively cut off. The results showed that mechanical model and drilling holes method and DPB technique were so notably that would lead to a foundation for large-scale popularization and application in a Chinese Mine.     

Determination par activation neutronique des rapports Cl/Br des inclusions fluides de divers gypses. Correlation avec les donnees de la microcryoscopie et interpretations genetiques

Gypsum contains liquid inclusions which fill mainly primary cavities. Analysis of inclusions may give some information about the mineral formation process. In places, diagenetic solutions have filled secondary cavities along cleavage planes or replaced initial liquid inclusions in primary cavities; the presence of such secondary inclusions must, therefore, be taken into consideration. This study presents our results on the Cl/Br ratio of liquid inclusions in gypsum. The Cl/Br ratio is practically constant in present sea water, and has been measured in many different types of waters. The Br content of halite has also been extensively studied to trace the compositional changes of a salt-depositing brine. In gypsum Br is present only in microscopic fluid inclusions. For this reason we used the neutron-activation method. We adopted the technique in order to prevent any contamination and obtain directly Cl/Br ratio within 10% accuracy. In order to ascertain that liquid inclusions reside mainly in primary cavities of gypsum, we selected our samples only after microscopic observation. Fifty-eight samples from different types of gypsum were analysed. The salinities of the inclusions, obtained through the data on freezing, and the Cl/Br ratio, obtained through activation-analysis, give us clues as to the nature of the fluids depositing the gypsum. Recent gypsum deposits from French salt-pans of Mediterranean and Atlantic coasts were sampled. The latter has apparently been diagenetically altered by meteoric water; the salinity of many inclusions having been changed while the Cl/Br ratio (315 and 350) in both remains close to the value of present sea water (#300). Liquid inclusions of Recent crystals from New Caledonia, deposited in mangrove swamps are enriched in Br (Cl/Br = 150 and 200). The enrichment might be related to the presence of abundant organic materials. Inclusions in crystals from Sebkha el Melah (Tunisia) also show high Br content (Cl/Br = 194). In this case, the brine was highly concentrated and was saturated with NaCl. The Upper Miocene gypsum from Sicily was studied to test the various models for the genesis of this important evaporite formation of the Mediterranean. Freezing data show some decrease of salinities, probably by groundwater diagenesis, but the Br content is high. The Cl/Br ratio is 175, and this value is similar to that of Sebkha el Melah. Samples from three thick Eocene and Oligocene sequences near Paris and in the South of France were studied. Freezing data and Cl/Br ratio of their inclusions indicate that those gypsum deposits have crystallized in marine environments receiving considerable influx of river-waters.     

Mixed layer depth front and subduction of low potential vorticity water under seasonal forcings in an idealized OGCM

The mixed layer depth (MLD) front and subduction under seasonal variability are investigated using an idealized ocean general circulation model (OGCM) with simple seasonal forcings. A sharp MLD front develops and subduction occurs at the front from late winter to early spring. The position of the MLD front agrees with the curve where \({\rm D}T_{\rm s}/{\rm D}t = \partial T_{\rm s} /\partial t + {\user2{u}}_{\rm g} \cdot \nabla T_{\rm s} = 0\) is satisfied (t is time, \({\user2{u}}_{\rm g}\) is the upper-ocean geostrophic velocity, \(T_{\rm s}\) is the sea surface temperature (SST), and \(\nabla\) is the horizontal gradient operator), indicating that thick mixed-layer water is subducted there parallel to the SST contour. This is a generalization of the past result that the MLD front coincides with the curve \({\user2{u}}_{\rm g} \cdot \nabla T_{\rm s} = 0\) when the forcing is steady. Irreversible subduction at the MLD front is limited to about 1 month, where the beginning of the irreversible subduction period agrees with the first coincidence of the MLD front and \({\rm D}T_{\rm s}/{\rm D}t =0\) in late winter, and the end of the period roughly corresponds to the disappearance of the MLD front in early spring. Subduction volume at the MLD front during this period is similar to that during 1 year in the steady-forcing model. Since the cooling of the deep mixed-layer water occurs only in winter and SST can not fully catch up with the seasonally varying reference temperature of restoring, the cooling rate of SST is reduced and the zonal gradient of the SST in the northwestern subtropical gyre is a little altered in the seasonal-forcing case. These effects result in slightly lower densities of subducted water and the eastward shift of the MLD front.     

Water masses of the northern part of the Iceland Basin in the late Pleistocene

A core of bottom sediments AMK-4438 with a length of 320 cm was taken in the North-Eastern part of the Iceland Basin from the depth of 2240 m. The continuous sampling (every 2 cm) made it possible to study the core using the principle of high-resolving paleoceanology. For the stratigraphic partition of the core, we applied the paleotemperature analysis by planktonic foraminifera and carbonate analysis; the distribution of the iceberg rafted debris (IRD) was studied. As a result, nine isotopic stages were distinguished. The change in the complexes of benthic foraminifera indicates that the present-day deepwater circulation in the North-Eastern part of the Iceland Basin had no analogs in earlier glacial periods, including the MIS 5 age. During almost 300 ka, there were relatively warm, rich in nutrients, and poor in oxygen water masses. The formation of the modern Northern-Eastern deep water in the Iceland Basin began in the Bolling-Allerod 14 ka B.P.     

Placer Deposits of Southern Tamil Nadu Coast,India

Exploration for placer deposits, especially for ilmenites, has been undertaken systematically in the southern coast of Tamil Nadu, India. On the basis of drainage network. Coastal landforms, lithology, and neotectonics, the study area has been grouped into five sectors: Mandapam, Valinokkam, Tuticorin, Manappad, and Kanyakumari. Ilmenites are abundant in Kanyakumari (Max. 53.39 wt%) and Tuticorin (Max. 20.88 wt%) sectors, negligible in Manappad (Max. 0.60 wt%) and Valinokkam (Max. 3.88 wt%) sectors and absent in the Mandapam sector. The abnormal enrichment of ilmenites in the Kanyakumari sector in the absence of any drainage network points to the possibility of a relict source. Literary and scientific evidence corroborates the existence of an Eastern Gondwana land called Lemuria, South of Kanyakumari which was later submerged in the Flandrian transgression. The association of other heavy minerals with ilmenites like overgrown and outgrown zircon supplements the idea of a longer stay of ilmenites in the depositional basin. Ilmenites from these fossil strandlines must have been reworked by the present day coastal processes and deposited in favorable bay-like NE-SW coastal configurations in Kanyakumari-Kuttankuli and Kallar-Vaippar regions under high energy wave conditions. The present study has disclosed the enrichment of ilmenites up to 1 m in depth in the above two zones which can be commercially exploited. The present study also calls for confirming part of the lost continent called Lemuria or Eastern Gondwana by systematic scientific investigations.     

Deciphering the Variscan tectonothermal overprint and deformation partitioning in the Cadomian basement of the Teplá–Barrandian unit, Bohemian Massif

The Teplá–Barrandian unit (TBU) has long been considered as a simply bivergent supracrustal ‘median massif’ above the Saxothuringian subduction zone in the Variscan orogenic belt. This contribution reveals a much more complex style of the Variscan tectonometamorphic overprint and resulting architecture of the Neoproterozoic basement of the TBU. For the first time, we describe the crustal-scale NE–SW-trending dextral transpressional Krakovec shear zone (KSZ) that intersects the TBU and thrusts its higher grade northwestern portion severely reworked by Variscan deformation over a southeastern very low grade portion with well-preserved Cadomian structures and only brittle Variscan deformation. The age of movements along the KSZ is inferred as Late Devonian (~380–370?Ma). On the basis of structural, microstructural, and anisotropy of magnetic susceptibility data from the KSZ, we propose a new synthetic model for the deformation partitioning in the Teplá–Barrandian upper crust in response to the Late Devonian to early Carboniferous subduction and underthrusting of the Saxothuringan lithosphere. We conclude that the Saxothuringian/Teplá–Barrandian convergence was nearly frontal during ~380–346?Ma and was partitioned into pure shear dominated domains that accommodated orogen-perpendicular shortening alternating with orogen-parallel high-strain domains that accommodated dextral transpression or bilateral extrusion. The synconvergent shortening of the TBU was terminated by a rapid gravity-driven collapse of the thickened lithosphere at ~346–337?Ma followed by, or partly simultaneous with, dextral strike-slip along the Baltica margin-parallel zones, driven by the westward movement of Gondwana from approximately 345?Ma onwards.     

Prospects of large-scale noble metal mineralization in the Upper Selemdzha minerogenic zone (by the example of the Malomyr and Sagur-Semertak ore clusters)

The Upper Selemdzha minerogenic zone, which has the potential for noble metal mineralization in the Upper Amur, has been studied. It is confined to the thick strata of Paleozoic terrigeneous-sedimentary rocks (sandstones, siltstones, clay schists, packages of their thin rhythmical interlayering, sedimentary breccias, and conglomerates) in the Tokura subzone of the Selemdzha-Kerbinsk zone in the Amur-Okhotsk area of the Mongol-Okhotsk system, overlain by Early Cretaceous volcanogenic sedimentary rocks and intruded by Early Cretaceous quartz diorites, granodiorites, and dacites. In the Malomyr and Sagur-Semertak ore clusters, there are a few known potential deposits of noble metals and ore occurrences; when studied and prospected, they can exhibit vein-veinlet noble metal mineralization with rich contents of gold and platinoids in ore columns and metasomatic deposits.     

Mining and spoiled land in Zambia: An example of conflicting land use in the third world

Mining of copper and other metals to a lesser extent is the mainstay of the Zambian economy. Copper is mined in the Copperbelt situated in the northern part of the country. It is not only the the most thickly populated part of the country but also the most urbanized. Urban centers developed with the mines as their nuclei and hence pose spatial problems between the needs of a rapidly increasing population on the one hand and the requirements of the mining industry on the other. The provision of raw material for the extractive industries is a geological one. Economic history shows the realization of these potentials and thirdly, lack of planning has permitted exploitation of minerals and dumping of wastes without much regard to reclamation. Spoilation of land by mining activity is mainly caused by the methods of mining as well as by the dumping of the solid and liquid wastes from the ore crushers and concentrators; while air pollution from sulphurdioxide and dust is from the smelters. Legislation has recently being enacted to regulate the dumping of wastes and for the reclamation of waste dumps. However, this has had only a minimal effect on the problem as yet. The soil from a dump which is ready for reclamation is analysed and methods of revegetating such a dump based on ecological principles is attempted. Finally, the conflict for land between the needs of a growing urban population and the requirements of the mining industry is discussed taking Kitwe, the capital of the Copperbelt as an example.     

Spatiotemporal distributions of tsunami sources and discovered periodicities

Both spatial and spatiotemporal distributions of the sources of tsunamigenic earthquakes of tectonic origin over the last 112 years have been analyzed. This analysis has been made using tsunami databases published by the Institute of Computational Mathematics and Mathematical Geophysics (Siberian Branch, Russian Academy of Sciences) and the National Aeronautics and Space Administration (United States), as well as earthquake catalogs published by the National Earthquake Information Center (United States). It has been found that the pronounced activation of seismic processes and an increase in the total energy of tsunamigenic earthquakes were observed at the beginning of both the 20th (1905–1920) and 21st (2004–2011) centuries. Studying the spatiotemporal periodicity of such events on the basis of an analysis of the two-dimensional distributions of the sources of tectonic tsunamis has made it possible to determine localized latitudinal zones with a total lack of such events (90°?75° N, 45°–90° S, and 35°?25° N) and regions with a periodic occurrence of tsunamis mainly within the middle (65°?35° N and 25°–40° S) and subequatorial (15° N–20° S) latitudes of the Northern and Southern hemispheres. The objective of this work is to analyze the spatiotemporal distributions of sources of tsunamigenic earthquakes and the effect of the periodic occurrence of such events on the basis of data taken from global tsunami catalogs.