Conceptual models in exploration geochemistry: Norden 1975

This compilation and summary of geochemical exploration conditions in Norden is the second in a series of special issues on exploration geochemistry. The first issue dealt with the Canadian Cordillera and Canadian Shield. The conceptual models from the Canadian Shield form an integral part of the present volume. These studies are an attempt to pull together very extensive exploration geochemical information and define it in terms of a limited number of conceptual models.A total of 45 case histories are presented in this volume which cover various aspects of collection, analysis and interpretation of data from glacial till, stratified drift, organic deposits, stream sediments and water. These data are described in a relationship to the conceptual models outlined by Bradshaw (1975). An overall summary is given with respect to these models and also a summary is given of the relative importance of frost heave, transport by glaciation, transport by water and wind, multiple glacial transport, ion and molecular dispersion, groundwater transport, transport by capillary water, electrochemical transport and mixed dispersion.The final section contains 13 short articles dealing with methods of geochemical exploration which are presently used in the different countries of Norden.     

Geochemical prospecting for baryte and celestite using a portable radioisotope fluorescence analyser

A method is described for determining the Ba and Sr content of soils in the field laboratory using a portable, isotope source, X-ray fluorescence analyser. The application of these techniques to the exploration for vein-type barytes and stratiform celestite deposits in the west of England is described. Satisfactory accuracy is achieved in comparison with other methods, along with considerable economies in time and effort. Detection limits (2 × standard deviation) are 200–300 ppm for Ba and about 500 ppm for Sr.     

Multiplicity of numerical solutions for slope stability problems

Existence of more than one numerical solution to the slope stability equations derived on the basis of force and moment equilibrium requirements of statistics is indicated. These solutions satisfy the boundary conditions at both ends of a potential slide mass. In the particular case considered, the details of the calculated response for the slices for each solution set assist the designer in selecting the more reasonable solution to the problem.     

Orthopyroxene–sillimanite–sapphirine granulites from the Bamble granulite terrane, southern Norway

Silica-deficient sapphirine-bearing rocks occur as an enclave within granulite facies Proterozoic gneisses and migmatites near Grimstad in the Bamble sector of south-east Norway (Hasleholmen locality). The rocks contain peraluminous sapphirine, orthopyroxene, gedrite, anthophyllite, sillimanite, sapphirine, corundum, cordierite, spinel, quartz and biotite in a variety of assemblages. Feldspar is absent.
Fe²⁺/(Fe²⁺+ Mg) in the analysed minerals varies in the order: spinel > gedrite ≥ anthophyllite ≥ biotite > sapphirine>orthopyroxene > cordierite.
Characteristic pseudomorph textures indicate coexistence of orthopyroxene and sillimanite during early stages of the reaction history. Assemblages containing orthopyroxene-sillimanite-sapphirine-cordierite-corundum developed during a high-pressure phase of metamorphism and are consistent with equilibration pressures of about 9 kbar at temperatures of 750–800°C. Decompression towards medium-pressure granulite facies generated various sapphirine-bearing assemblages. The diagnostic assemblage of this stage is sapphirine-cordierite. Sapphirine occurs in characteristic symplectite textures. The major mineralogical changes can be described by the discontinuous FMAS reaction: orthopyroxene + sillimanite → sapphirine + cordierite + corundum.
The disequilibrium textures found in the Hasleholmen rocks are characteristic for reactions which have been in progress but then ceased before they run to completion. Textures such as reaction rims, symplectites, partial replacement, corrosion and dissolution of earlier minerals are characteristic of granulite facies rocks. They indicate that, despite relatively high temperatures (700–800° C), equilibrium domains were small and chemical communication and transport was hampered as a result of dry or H₂O-poor conditions.