River bank erosion control by soil nailing

A study has been done for analysing soil nailed cuts with circular type wedge failure by friction circle method. Various parameters such as nail length, nail diameter, nail inclination, wall inclination and angle of internal friction of soil have been considered to determine the factor of safety of nailed open cuts. The study shows that for cohesionless soil nailed cut, factor of safety increase with increase of parameters like angle of internal friction of soil, length of nail (L) versus height of cut (H) ratio, cohesion of soil and nail inclination (upto 15°) with horizontal. The study revealed that nails grouted with cement perform better than driven nails. A case study further confirms the analytical findings. Received 7 October     

Evolution of stress fields in the Por’ya Guba dike field (Kandalaksha Gulf, White Sea)

The tectonic evolution of the Por’ya Guba segment of the White Sea Rift System began in the late Paleoproterozoic, i.e., soon after completion of the Svecofennian collision. The fracture system that controlled localization of the lamproite dike complex was formed under conditions of horizontal compression combined with shear. Subsequently, this system predetermined the location of a rift-graben segment that formed as a result of simple shear. The reactivation of the rift system in the Middle Paleozoic proceeded in two stages. The first stage, when strike-slip movements along previously formed faults predominated, resulted in formation of quartz-carbonate veins bearing base-metal mineralization. The veins that filled the shear fractures opened owing to local reorientation of the stress field. The second stage fitted the transtension conditions, and the Late Devonian alkaline ultramafic dikes of this stage introded into the already existing fracture system, which was oriented at a roughly right angle to the predominant stress orientation.     

Manganoan garnet rocks associated with the Broken Hill Pb–Zn–Ag orebody, Australia

Summary The Palaeoproterozoic Broken Hill Pb–Zn–Ag stratiform orebody is intimately associated with manganoan garnet-bearing rocks. On stratigraphic and chemical grounds it is argued that garnet-rich metasediments below, equivalent to and above massive sulphide were hydrothermal precipitates. Other manganoan garnet rocks formed during pre-metamorphic hydrothermal alteration, syn-metamorphic dehydration and reaction of manganese with prograde pelitic rocks, reaction between cataclastic manganese-bearing sulphide rocks injected along axial planes, shears and faults and pelitic wall rocks and reaction between dolerite dykes and sulphide rocks.     

New data on hydrocarbons in auriferous conglomerates of the Witwatersrand ore region, Republic of South Africa

Genesis of deposits in the world’s largest Witwatersrand auriferous region (South Africa) remains a debatable issue over several decades. Based on geological and mineralogical-geochemical investigations, we previously proposed a sedimentary-exhalative hypothesis for its origin. In the present communication, we have attempted to develop and scrutinize this concept based on the study of organic matter in ore and nonore conglomerates, quartz in conglomerate pebbles, and fluid inclusions in quartz from pebbles and cement of ore and nonore conglomerates.