Part 1. An absolute method tor the measurement of reflectivity. Part 2. The distribution of heavy metals in granites

Abstract

Part 1. An Absolute Method for the Measurement of Reflectivity. Because of the difficulty in establishing reflectivity standards for use in the measurement of reflectivity by comparison, the present method was developed to allow the measurement of absolute reflectivity at perfectly normal incidence. A glass cube with a semi-metallised surface was mounted in the centre of a horizontal circle goniometer, a photomultiplier clamped over the viewing telescope and the specimen supported in front of the glass cube. Monochromatic plane polarised light was passed through a system of lenses which cause the now parallel light beam, after passing through the cube, to fall on the specimen surface with perfectly normal incidence. Facility is provided for measurements in both air and oil. A mathematical treatment of the intensity relationships of the various direct and reflected light rays is given, from which the reflectivity of the specimen (and also the glass cube) can be calculated. The reflectivity of several standard samples in both air and oil is recorded. Part 2. The Distribution of Heavy Metals in Granites. The present survey was conducted in order to extend the possible application of primary cycle geechemical prospecting. Nine different areas of Hercynian and Caledonian granites in Great Britain were studied and both trace and major element analyses recorded. Care was taken to include only unweathered samples for analyses, and three mineral fractions, namely, biotite, raiuscovite and feldspar plus quartz were separated and analysed independently. A method for calculating the plagioclase, orthoclase and quartz percentages in the feldspar plus quartz fraction by the use of x-ray diffraction is given. Analyses are included to show the variation of trace elements away from a mineral vein, the variation of element concentration within a given granite, and the number of samples required to detect a significant difference between two trace element populations. As well as discussing geochemical prospecting, details of the degree of fractionation and order of intrusion of different phases of the same granite, and comparisons between different granites, are given.