Anisotropic and foliated rock masses, the behaviour of which are dominated by closely spaced planes of weakness, present particular difficulties in the assessment of pit slope stability. Various numerical modelling techniques are available that explicitly simulate the joints and discontinuities within an anisotropic rock mass. However, due to the computational intensity of these numerical techniques, it is not practical to explicitly simulate the joint fabric of an entire three-dimensional pit slope for routine stability assessment. In order to simulate the effects of anisotropic rock mass strength and deformation behaviour on pit slope stability, a modelling methodology has been developed to account for rock mass anisotropy and scale effects using a continuum based ubiquitous joint constitutive model. This paper outlines the anisotropic modelling methodology and presents a series of demonstration models that have been used to validate the technique.  <...>

The Puutsaari intrusion is a potassium-rich magmatic complex in the eastern part of the Svecofennian domain close to the Archaean border. The intrusion is generally undeformed in contrast to 1880-1875 Ma-old country rock tonalitic migmatites and diatectites. The main rock types are: (1) mafic rocks of a gabbro-norite-diorite-quartz monzodiorite series; (2) quartz diorite-tonalite-granodiorite; and (3) coarse-grained microcline granite. The three rock-types intruded coevally forming a peculiar three-component mingling system. The mafic rocks, enriched in K, P, Ba, Sr and LREE, have marked shoshonitic affinities (K2O = 1.97-5.40, K2O/Na2O = 0.6-2.37). On a regional scale they demonstrate transitional geochemistry between less enriched syn-orogenic 1880 Ma-old gabbro-tonalite complexes and strongly enriched 1800 Ma post-collisional shoshonitic intrusions. The microcline granite as well as the tonalite-granodiorite rocks are geochemically similar to crustal anatectic granitoids of the NW Ladoga Lake area. The three rock groups do not form a single trend on Harker-type diagrams and are unlikely to be related by fractional crystallisation or mixing. Zircons from the Puutsaari microcline granite and from the mafic rock series have been dated by ion-microprobe (NORDSIM) at 1868.2 9/ 5.9 and 18699/7.7 Ma, respectively. Most zircons recovered from a granite sample had zoned or homogeneous cores and unzoned fractured rims. No statistically significant variation of zircon core and rim ages from the granite was established in the course of this study. Zircons from the mafic rock are unzoned. It is suggested that the mafic rocks at Puutsaari were derived from an enriched mantle shortly after the main Svecofennian collisional event and the roughly 1.88 Ga regional metamorphic culmination. The emplacement of the mafic melt caused anatectic melting of various crustal protoliths and produced coeval granitic and tonalitic compositions.

Growing evidence suggests that the mechanism of Palaeozoic continental growth in Central Asia was by subduction– accretion with punctuated collisions that produced ophiolitic sutures between accreted blocks. The Bayankhongor ophiolite is the largest ophiolite in Mongolia and possibly all of Central Asia, and is interpreted to mark the collisional suture between the Baidrag and Hangai continental blocks. New 207Pb/206Pb zircon evaporation ages for granite plutons and dykes that intrude the ophiolite and its neighbouring lithotectonic units suggest that the ophiolite was obducted at c. 540 Ma at the beginning of a collisional event that lasted until c. 450 Ma. The new data, combined with that of previous studies, indicate regional correlation of isotopic ages north-westward from Bayankhongor to southern Tuva. These data record oceanic crust formation at c. 570 Ma, followed by approximately 30 million years of subduction–accretion that culminated in obduction of ophiolites, collision related metamorphism, and magmatism in the period c. 540–450 Ma. Correlation of isotopic-age data for the ophiolites of western Mongolia and southern Tuva suggests that the ophiolites define a major collisional suture in the Central Asian Orogenic Belt (CAOB) that defines the southern and western margins of the Hangai continental block.

Pregold mineralization at the Getchell Carlin-type gold deposit includes quartz and base metal vein mineralization associated with intrusion of a Cretaceous granodiorite stock. The veins contain minor pyrite and trace chalcopyrite, arsenopyrite, galena, and sphalerite. The pyrite is moderately coarse and, in thin section, has high relief, is well polished, and is fractured and locally cemented by the gold ore assemblage. White micas are associated with veins near the granodiorite intrusion. Gold was not observed or detected by fire assay analyses of samples or electron microprobe analyses of pyrites. Microprobe analyses show that pregold pyrites have near-stoichiometric compositions. Variable, low arsenic is present in pyrite in samples overprinted by gold mineralization. Secondary ion mass spectrometry (SIMS) analyses detected trace gold in the coarse, near-stoichiomet-ric pyrite in overprinted samples. The pregold vein assemblage was fractured and cemented by gold ore-stage mineralization