INTRODUCTION TO PRACTICAL ORE MICROSCOPY LONGMAN EARTH SCIENCE SERIES Edited by Professor J. Zussman and Professor W. S. MacKenzie, University of Manchester B. C. M. Butler and J. D. Bell: Interpretation of Geological Maps P. R. Ineson: Introduction to Practical Ore Microscopy P. F. Worthington: An Introduction to Petrophysics B. W. D. Yardley: An Introduction to Metamorphic Petrology INTRODUCTION TO PRACTICAL ORE MICROSCOPY P. R. Ineson D Routledge Taylor &. Francis Group LONDON AND NEW YORK First published 1989 by Longman Group Limited Published 2013 by Routledge 2 Park Square, Milton Park, Abingdon, Oxon 0X14 4RN 711 Third Avenue, New York, NY 10017, USA Routledge is an imprint of the Taylor & Francis Group, an informa business Copyright © 1989, Taylor & Francis. All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereaf­ ter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, profes­ sional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowl­ edge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN 13: 978-0-582-30140-5 (pbk) British Library Cataloguing in Publication Data Ineson, P. R. Introduction to practical ore microscopy. - (Longman earth science series) 1. Ores 2. Microscope and microscopy I. Title 553 TN265 Library of Congress Cataloging in Publication Data Ineson, P. (Peter) Introduction to practical ore microscopy. (Longman earth science series) Bibliography: p. Includes index. 1. Ores - Optical properties. 2. Optical mineralogy. 3. Microscope and microscopy. I. Title. II. Series. QE390.I53 1989 552\06 88-3015 ISBN 0-470-21072-9 (USA only) CONTENTS Preface and Acknowledgements ix CHAPTER 1 INTRODUCTION 1 CHAPTER 2 THE ORE MICROSCOPE 2 2.1 General comments 2 2.2 The rotatable stage 3 2.3 The objective lens(es) 4 2.4 The ocular (eyepiece) lens(es) 6 2.4.1 Care and cleaning of lenses 6 2.5 The polariser and analyser 6 2.6 The reflector 7 2.7 The light source (illumination, illuminator) 7 2.8 Sample holder 8 2.9 Mechanical stage 8 2.10 Eyepiece and stage micrometers 9 2.11 Photometer 9 2.12 Monochromators and filters 9 CHAPTER 3 SAMPLE PREPARATION 10 3.1 General comments 10 3.2 Preparation 10 3.3 Grinding and polishing 11 3.3.1 Vibropolishing 13 3.3.2 Electrolyte polishing 13 3.4 Polished thin sections 13 3.5 Etching 14 3.6 Grain mounts 14 3.7 Sample storage 14 CHAPTER 4 MINERAL IDENTIFICATION 16 4.1 Simple optical techniques 16 4.1.1 Introduction 16 4.1.2 Colour 17 vi Contents 4.1.3 Bireflectance and reflection pleochroism 18 4.1.4 Crossed polars anisotropy 19 4.1.5 Internal reflections 22 4.2 Reflectance 23 4.2.1 General comments 23 4.2.2 Qualitative methods 23 4.2.3 Quantitative methods 24 4.3 Simple physical techniques 30 4.3.1 Introduction 30 4.3.2 Crystal morphology (forms and habits) 31 4.3.3 Zoning 32 4.3.4 Cleavage and parting 32 4.3.5 Twinning 33 4.3.6 Inclusions and intergrowths 34 4.3.7 Tenacity 34 4.3.8 Streak 34 4.4 Hardness 34 4.4.1 Polishing hardness 35 4.4.2 Scratch hardness 35 4.4.3 Microindentation hardness 35 CHAPTER 5 TEXTURES OF THE ORE MINERALS 38 5.1 Introduction 38 5.2 Descriptive textures 38 5.2.1 Single grains 38 5.2.2 Aggregates 49 5.3 Genetic textures due to primary deposition 52 5.3.1 Growth fabric textures 52 5.3.2 Colloidal textures 57 5.3.3 Sedimentary textures 59 5.4 Genetic textures resulting from transformation 60 5.4.1 Paramorphic replacement texture 60 5.4.2 Exsolution - simple and complex 61 5.4.3 Replacement textures 66 5.4.4 Relic(t) textures 73 5.4.5 Decomposition textures 73 5.4.6 Oxidation (weathering) textures 73 5.4.7 Cementation textures 75 5.5 Deformation textures 75 5.5.1 Curvature of linear features 75 5.5.2 Schlieren 76 5.5.3 Brecciation or cataclasis 76 5.6 Annealing textures 76 5.6.1 Recrystallisation textures 76 5.6.2 Re-equilibration textures 77 5.7 Metamorphic textures 77 5.7.1 Dynamic metamorphic effects 77 5.7.2 Thermal metamorphic effects 78 5.7.3 Skarns 79 5.8 Miscellaneous or special textures 80 5.8.1 Framboids or framboidal texture 80 Contents vii CHAPTER 6 PARAGENESIS 81 6.1 Introduction 81 6.2 Aids in erecting a paragenetic sequence 83 6.2.1 Crystal shape 83 6.2.2 Relict (pseudomorphic) complexities 83 6.2.3 Mutual grain boundary problems 84 6.2.4 Colloform banding 84 6.2.5 Growth zoning 84 6.2.6 Cross-cutting relationships 84 6.2.7 Twinning 84 6.2.8 Exsolution 85 6.2.9 Replacement 85 6.2.10 Fluorescence 85 6.2.11 Additional reading 86 CHAPTER 7 STRUCTURAL ETCHING 87 7.1 General comments 87 7.2 The method 87 7.3 The reagents 88 CHAPTER 8 MINERAL TABLES 89 8.1 Introduction and explanation of the tables 89 Argentite 91 Arsenopyrite 93 Bismuthinite 94 Bomite 96 Boulangerite 97 Cassiterite 99 Chalcocite 100 Chalcopyrite 102 Chromite 103 Cinnabar 104 Cobaltite 105 Copper 106 Covellite 107 Cubanite 108 Cuprite 110 Enargite 111 Galena 112 Goethite 114 Gold 115 Graphite 116 Hematite 117 Ilmenite 119 Lollingite 120 Magnetite 121 Manganite 122 viii Contents Marcasite 123 Millerite 125 Molybdenite 126 Niccolite 127 Pentlandite 128 Platinum 129 Proustite 130 Psilomelane 131 Pyrargyrite 132 Pyrite 133 Pyrolusite 134 Pyrrhotite 135 Rutile 136 Scheelite 138 Silver 139 Sphalerite 140 Stannite 141 Stibnite 142 Sylvanite 144 Tennantite 145 Tetrahedrite 146 Uraninite 147 Wolframite 148 APPENDIX 1 COMMON MINERAL ASSEMBLAGES OR ASSOCIATIONS 149 APPENDIX 2 DIAGRAM OF OPTICAL DETERMINATIONS OF THE ORE MINERALS ON THE BASIS OF REFLECTANCE VALUES (FOR 589 nm) AND MICROHARDNESS (VHN) 167 APPENDIX 3 REFLECTED LIGHT OPTICS 168 APPENDIX 4 LIST OF ABBREVIATIONS 171 References 173 Index 177 PREFACE AND ACKNOWLEDGEMENTS The study of the ore minerals, by whatever means, relies especially on the experience and help of a teacher. This book could not have been produced in its present form without the help and advice of colleagues around the world for which I am most grateful; the following are particularly thanked: A. M. Evans, P. Garrard, C. Halls, J. McMahon Moore, AH. Rankin, F.J. Sawkins and S. G. Walters, as well as the instrument manufacturers who kindly provided text illustrations and technical information. I have also gained immensely over the years from teaching students in the UK and the USA and from the feedback they have provided. Professor J. Zussman provided continual and invaluable assistance in reading the manuscript and suggesting major and minor modifications. However, any errors and imperfections which remain in the text are the author’s responsibility. I would be pleased to receive communications with respect to these in the hope that a future edition can thereby be improved. p. R. INESON June, 1988 We are indebted to these copyright holders for permission to reproduce the following tables: Elsevier Science Publishers B. V. for table 4.5 (Picot Sc Johan 1982) from pp. 28-34; Geological Survey of Canada for tables 4.6 Sc 4.9 (McLeod Sc Cham­ berlain 1968); Pergamon Press for table 5.2 (Ramdohr 1980) from Vol. 1, pp. 185-93; John Wiley Sc Sons Inc. for table 7.1 (Craig Sc Vaughan 1981) from pp. 31-2.