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There are four main types of boninites in ophiolite suites, which either spatially coexist with ophiolites, though belong to other tectonic units (1), or are present as later constituents of ophiolite sequences (crosscutting dikes or lavas on top) (2), or build ophiolite sequences together with island-arc tholeiites and basaltic andesites, followed by younger volcanics of MORB or BABB affinites (3), or occupy the whole mafic portion of ophiolite sequences, together with island-arc tholeiites and basaltic andesites (4). The latter type, considered in more detail for the case of ophiolites from the southeastern Sayan Mountains (Siberia, Russia), presents an example of inconsistency between the model of ophiolite formation in mid-ocean ridge settings and subduction-related island-arc fingerprints in ophiolitic mafic rocks. The patterns of boninites record several evolution models of oceanic systems, with melting and intrusion of boninites in forearc, arc, and back-arc settings. The existing models are controversial, possibly, because there is no single mechanism to account for all types of boninites.

We present new data on geochemistry, isotopic geochemistry, and geochronology of the Early Cambrian igneous rocks of the northeastern Siberian Craton (Kharaulakh anticlinorium, contact between the Siberian Platform and the West Verkhoyansk sector of the Verkhoyansk fold-and-thrust belt) united into an Early Cambrian bimodal complex. This complex comprises trachyrhyolites forming pebbles in conglomerates near the base of the Cambrian sugcession, overlying trachybasalts, and mafic sills and dikes cutting Neoproterozoic strata. According to chemical composition, the felsic rocks are high-alkali rhyolites and correspond to A-type granites. The high contents of Ta, Nb, Hf, Tb, and Zr in these rocks suggest the presence of enriched mantle material in their magmatic sources. The mafic volcanics are high-Ti trachybasalts and trachydolerites with similar geochemical characteristics corresponding to alkali basalts or OIB. The high (Tb/Yb)PM ratios in these volcanics evidence that their magmatic source was the garnet peridotite mantle located at depths more than 90 km and characterized by a low degree of melting. However, the rhyolites, trachybasalts, and trachydolerites show high positive εNd(T) values (4.2-4.7, 7.5-8.9, and 7.2-8.2, respectively) indicating a depleted mantle source and no crustal contamination. The high (Nb/Yb)PM ratio points to the mixing of magmas from enriched and depleted mantle sources. Mafic magmas might have been generated from a heterogeneous source or interacted with depleted mantle before intrusion. Both the felsic and the mafic rocks formed in within-plate environments. U-Pb zircon dating yielded concordant ages of 525.6 ± 3.9 and 537.0 ± 4.2 Ma, corresponding to the Early Cambrian age of the rhyolites. The date of 546.0 ± 7.7 Ma obtained for one sample points (with regard to the error) to the Late Vendian-Early Cambrian age. Thus, at the Vendian-Early Cambrian boundary, the northeastern Siberian Platform was subjected to continental rifting accompanied by bimodal magmatism. According to paleotectonic reconstructions, this part of the Siberian Craton might have been connected with the eastern margin of Laurentia in the Late Neoproterozoic (Late Riphean-Late Vendian), and continental rifting that started at the Vendian-Cambrian boundary led to their separation. The obtained isotope-geochronological data suggest that the studied bimodal complex began to form at the Vendian-Cambrian boundary and this process terminated no earlier than the end of the Terreneuvian (Tommotian), i.e., the complex formed during rifting for about 20 Myr.

The authors report the numerical modeling data on stress state of rock mass in the vicinity of hydraulic fracturing when two closely-spaced intervals of the well are subjected to shearing and normal load. The article shows applicability of such coupled loading in creation of fracture across an uncased well.

The authors study numerically a problem on vortex flows in bounded domain in granular material using discrete element method. The granular material is composed of spherical particles with the assigned distribution of radii. Dry friction and rolling resistance at particle interfaces are taken into account. The kinematic patterns of granular material specimen deformation are described, and the trajectories of some particles are shown. The article gives values of normal and shear stresses acting at the study domain boundaries from the side of the material.

The authors use physical and DEM modeling to analyze stresses and strains in broken ore discharged from accumulating bins using plate feeder. It is substantiated that the determinant of the peak load on the feeder and the discharge unit is dilatancy. It is shown that the absolute value of the peak load is conditioned by physico-mechanical characteristics of discharged ore, structural design of discharge unit and deformation constraint. The article demonstrates possibility of upgrading one of conventional schemes of discharge unit and shows prospects for new designs.

Variations in strength and stress state of rocks fail to explain the difference observed in efficiency of seismic radiation from separate sources within the limits of the same mine field. The laboratory and numerical experiments show that insignificant variation in ultimate strength of a fracture and, thus, different shear fracture stiffness results in radical change in the seismic event efficiency. The experimentally obtained relations between the key parameters should be taken into account in geomechanical modeling of full-scale objects.

Based on the integrated analysis of micro-strains obtained using speckle-photography method in Brazilian Test of rock specimens and analytically calculated elastic fields of stresses and strains, the authors show that there exist significant correlation dependences between the damage in a certain domain of a rock specimen and the level of the external load. Given a verified geomechanical model describing properly evolution of stresses in a rock specimen, this fact offers pre-requisites for estimation of damage in different areas of a rock specimen by monitoring condition only in one of such areas.

The authors have undertaken experimental and theoretical modeling of fracture growth under the penetration of rigid wedge in brittle rock. The test specimens were made of organic glass to facilitate measurement of size and shape of a fracture. The wedge loading was executed quasi-statically on a testing machine and dynamically by a drop wedge. The scheme developed in the framework of the theory of elasticity for the theoretical description of the fracture growth process accounts for the finite size of the wedge cutting point and the influence of free surface. The theoretical and experimental shapes of fractures are compared.

The authors have determined the causes of drop in performance of induced block caving using fans of blastholes 105 mm in diameter and single blastholes 250 mm in diameter, as well as the sources of increased drilling cost and expansion of start-up time of production blocks in Abakan underground mine. Alternatives of improvement in drilling efficiency under current conditions are discussed.

The article substantiates the need of designing a rotary-percussion drilling tool to drill holes 40-60 mm in diameter and to 50 m long. The drilling rig with a downhole air hammer has been designed and manufactured. The authors have carried out analytical and experimental research to determine drilling velocity in different rocks of varying hardness.