Ore Textures Roger Taylor Ore Textures Recognition and Interpretation 123 RogerTaylor Townsville Queensland 4810 Australia ISBN978-3-642-01782-7 e-ISBN978-3-642-01783-4 DOI10.1007/978-3-642-01783-4 SpringerDordrechtHeidelbergLondonNewYork LibraryofCongressControlNumber:2009926869 (cid:2)c Springer-VerlagBerlinHeidelberg2009 Thisworkissubjecttocopyright.Allrightsarereserved,whetherthewholeorpartofthematerial isconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation,broad- casting,reproductiononmicrofilmorinanyotherway,andstorageindatabanks.Duplicationofthis publicationorpartsthereofispermittedonlyundertheprovisionsoftheGermanCopyrightLawof September9,1965,initscurrentversion,andpermissionforusemustalwaysbeobtainedfromSpringer. ViolationsareliabletoprosecutionundertheGermanCopyrightLaw. Theuseofgeneraldescriptivenames,registerednames,trademarks,etc.inthispublicationdoesnotim- ply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevantprotective lawsandregulationsandthereforefreeforgeneraluse. Coverdesign:Bauer,Thomas Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Acknowledgments Given the eleven years required to produce the original five volumes, the list of contributors is considerable. They constitute numerous individuals and financial sponsor companies who deserve special acknowledgement. It is impractical to give lengthy written credit to all concerned, and the list below only outlines some of their contributions. Thank you everybody. Special thanks are extended to Dr Peter Pollard and Dr Gavin Clarke who contributed continuously via encour- agement, editing, rock preparation, and their own extensive knowledge of ore textures. The outstanding plates are the work of Roger Yeldham and Brian Pump from the James Cook University photographic division. Although not obvious here, David Lloyd contributed the initial graphic design which made the individual volumes so attractive. The difficult and delicate task of combining five volumes into a single offering has been con- ducted by Elisabeth Sillmann of blatterwald Design. Her high quality graphic design skills are gratefully acknowl- eged, and will be evident to all readers. Some anonymous frogs who gracefully permitted use of their photographic images in the original volumes are also acknowledged (unfortunately only two could be included here). INDIVIDUAL CONTRIBUTORS Dr A. Allibone Specimen loan and stuctural expertise Mr D. Andrews Specimen loan and photography Dr E. M. Baker Photography Professor T. H. Bell Structural advice Dr N. Adshead-Bell Structural advice Dr S. Beams Specimen loan Ms E. Caragianides Sundowners Ms D. Casey Word processing and fund raising Dr G. W. Clarke Specimen loan, specimen preparation, photography and textural expertise Dr G. Dong Specimen loan Ms M. Drögemuller Word processing and fund raising Dr K. Hickey Structural advice Mrs K. Hotschilt Photography Dr W. P. Laing Specimen loan Mrs L. Laivens Word processing Ms H. Lawrie Editing Mr D. Lloyd Graphic design Ms F. McKinstry Frog photograph Ms M. Meyers Editing Dr R. Meyers Editing and general advice Dr G. W. Morrison Specimen loan, photography and textural expertise Dr B. New Structural advice Professor G. N. Phillips Specimen loan and general advice Dr P. J. Pollard Specimen loan, editing, photography, textural expertise and general advice Mr B. Pump Photography Mr S. Richards Frog photograph Ms E. Sillmann Graphic design, typesetting Dr P. J. Williams Specimen loan and general advice Associate Professor S. E. Williams Frog photograph Dr P. J. Wormald Specimen loan Dr M. Worsley Specimen loan Mr R. Yeldham Photography V COMMERCIAL SPONSORS Aberfoyle Resources Limited Homestake Australia Ltd ABX Exploranciones Ivanhoe Mines Ltd Acacia Resources Limited James Cook University Anglo American Exploration (Australia) Pty Ltd Metana Minerals NL ARIMCO Mining Pty Ltd MIM Exploration Pty Ltd Aurora Gold Pty Ltd Mount Isa Mines Ltd Australasian Institute of Mining and Metallurgy Mount Leyshon Gold Mines Ltd (North Queensland Branch) Newcrest Mining Ltd Aztec Mining Company Ltd Newmont Gold Company Battle Mountain (Australia) Inc Normandy Exploration Ltd Barrick Gold Corporation (Australia) North Ltd BHP Pty Ltd North Flinders Exploration BHP Billiton (Cannington) Nuigini Mining (Australia) Pty Ltd Billiton Australia Pac Min Mining Company Ltd CRA Exploration Pty Ltd Pancontinental Mining Ltd Companhia Vale Do Rio Doce (CVRD) Pasminco Exploration Cyprus Gold Australia Corp. Placer Exploration Ltd Delta Gold NL Plutonic Mining Department of Minerals & Energy (Queensland) Phelps Dodge Australia Inc Department of Minerals & Energy, PNG P. T. Freeport Indonesia Department of Resource Industries Reynolds Australia Metals Ltd Dominion Mining Ltd RGC Ltd Economic Geology Research Unit (EGRU) James Rio Tinto Cook University Ross Mining NL Freeport McMoran Copper and Gold Co RTZ (South America) Giants Reef Mining Sons of Gwalia Ltd Geopeko Teck Cominco Ltd Goldfields Exploration The Key Centre for Economic Geology, James Cook Gold Mines Of Australia University Great Central Mines and Centaur Mining and Western Mining Corporation Exploration Ltd VII Preface This text has resulted from some forty years of experience during which the author has puzzled over the meaning of ore textures. The learning process has been slow and is still incomplete. The bemusement began directly upon leaving the academic confines, which in retrospect left one keen young geologist very ill-equipped to interpret the mineralising process via field or hand lens style observation of the rocks. Enlightenment has proceeded via a series of events:- 1. The slow process of field observation as an industry-based mine and exploration geologist. 2. The opportunity to visit numerous different styles of ore deposit both as an academic and consultant. 3. The need to answer questions from several generations of enquiring students. 4. The privilege of being able to conduct research. 5. The good fortune to be associated with a few top class economic geologists who actually knew what they were doing! Professor Willard C. Lacy deserves the most credit for quietly demonstrating the value of first principles concerning fluid channelways, combined with an ability to look properly at the tex- tures. Despite rapid technological advances this skill remains fundamental both to the practic- ing exploration geologist and to the academic researcher who is interested in understanding ore forming processes. The five volumes comprising this presentation were originally compiled individually over a period of eleven years, and aimed to progressively guide the observer though the principles of recogni- tion concerning infill, alteration, overprinting, and finally to ore-related breccias. Most observers have no significant problems with infill and alteration concepts in relation to narrow veins, but frequently flounder when the same components are repackaged as breccias. The plates have been carefully chosen to illustrate recognition procedure whilst giving a visual guide to a wide range of examples. The plate captions have been specifically written in a lengthy simplistic form to assist the genuine beginner. They contain a wealth of detail which is intended to lay a foundation for good textural observational methodology. A few more complex plates have been sporadically included to add appeal for those at connoisseur level. The book is not intended as a rigorous academic text. However, it is noted that the subject of textural interpretation still remains absent from most institutional training courses, and it is thus hoped that this contribution will be of direct assistance to many enquiring readers. Townsville, March 2009 Roger G. Taylor IX Contents Ore Textures – Recognition and Interpretation Volume 1 • Infill Textures 1 List of Plates 3 1 Introduction 5 2 Recognition Criteria 5 2.1 Incomplete Infill 5 2.1.1 Remaining Void Space 5 2.1.2 Crystals Projecting Into a Cavity 5 2.2 Complete Infill 6 2.2.1 Euhedral or Partially Euhedral Crystal Outlines 6 2.2.2 Zoned Crystals 8 2.2.3 Banded or Layered Textures 10 2.2.4 Large-Scale Triangular Textures 12 2.2.5 Small-Scale Triangular or Partially Triangular Textures 16 3 Problems and Working Techniques 21 3.1 Common Misconceptions 21 3.2 Problems with the Well-Formed Crystal Criterion 21 3.3 The Edge Problem 21 3.4 The Working Backwards Technique 22 4 How and Where to Look for Infill Textures – Channelway Recognition 25 4.1 General Approach 25 4.2 Vein Styles 25 4.3 Breccia Styles 25 4.4 Other Styles 26 4.4.1 Miarolitic 26 4.4.2 Igneous Interstitial Mineralisation 30 4.4.3 Dissolution within Granite Systems 30 Volume 2 • Alteration Textures 35 List of Plates 37 1 Introduction 39 2 Basic Principles 40 3 Approach to Alteration 43 3.1 Alteration Recognition 43 3.2 The Movement Principle – Observational Positioning 43 3.3 Mineral Identification – Nomenclature 43 3.4 Changeover Observations – Transitional Zones 44 3.5 Textural Observation 44 3.5 Channelway Identification 44 XI 3.7 Chemical Awareness 45 3.8 Examples of Alteration Types and Structural Style 45 Types Structural Style Sericite Vein 47 Greisen, Silica-Sericite Pipe 49 Phyllic, Silica -Sericite Stockwork-Vein 51 Chlorite Miarolitic 53 Chlorite Fault Breccia-Vein 55 Silica Fault Breccia-Vein 57 Propylitic, Chlorite-Epidote Vein 59 Propylitic, Chlorite-Epidote, Silica, Sulphide Intrusive Breccia 61 Potassic (K-Feldspar, Potassium Feldspar) Stockwork 63 Adularia (Potassium Feldspar) Breccia 65 Potassic (Biotite) Intrusive Breccia 67 Albite Vein 69 Argillic Clay-Carbonate, Sulphide Pervasive-Vein-Breccia 71 Advanced Argillic, Pyrophyllite, Silica-Alunite Vein (Ductile Style) 73 Hematite – Red Rock Layer Controlled, Vein 75 Magnetite-Albite, Chlorite-Epidote Vein 77 Silica-Pyrite-Carbonate Vein 79 Silica-Pyrite-Carbonate Vein 81 Sulphide-Silica-Pyrite, Silica-Magnetite Breccia 83 Sulphide-Pyrrhotite Layer Controlled, Vein 85 Topaz Fault Breccia-Vein 87 Albite, Chlorite (Granite) Background, Selective Semi-Pervasive 89 4 Alteration minerals – Some General Observations 90 5 Assessment Sheet 95 6 References 97 Volume 3 • Overprinting Textures 99 List of Plates 101 1 Introduction 103 2 Overprinting criteria 105 2.1 General 105 2.2 First Order Criteria – Confidence Building 105 2.2.1 Mineral Superimposition – Sequential Infill 105 2.2.2 Structural Superimposition – Crosscutting Veins, Breccia 105 2.3 Second Order Criteria – Suspicion Arousing 105 2.3.1 Mismatches Between Alteration and Infill Components 105 2.3.2 Inconsistent Alteration Configurations 106 2.3.3 Alteration of Alteration 106 2.4 Third Order Criteria – Indirect Overprinting – Mineral Assemblages 106 2.5 Fourth Order Criteria – Indirect Overprinting – Temperature Indicators 106 3 Overprinting Textures – Broader-Scale Perspectives 107 3.1 Broad-Scale Perspectives 107 3.2 Recording Observations 107 XII Ore Textures • Recognition and Interpretation • Contents 4 First Order Criteria – Mineral Superimposition 109 4.1 Sequential Infill 109 4.2 Textures and Problems 109 5 First Order Criteria – Structural Superimposition 117 5.1 Crosscutting Veins – Stockwork Styles 117 5.2 Textures and Problems 117 6 First Order Criteria – Structural Superimposition 135 6.1 Breccia – Fragments of Early Stage Mineralisation Contained within Later Stages 6.2 Textures and Problems 135 7 Second Order Criteria 145 7.1 Suspicion Arousing, Parallel Overprinting Veins 145 7.2 Alteration Mismatching – Inconsistent Alteration and/or Infill Sequences, Alteration of Alteration 145 8 References 161 Volume 4 • Broken Rocks – Breccias I 163 List of Plates 165 1 Introduction 169 2 Observation of Broken Rock Patterns 171 3 Approach to Understanding Broken Rock Patterns 173 4 Arrangement of Plates – Design Philosophy 175 4.1 General Patterns of Broken Rocks and Problems Involved with Recognition, Scale Perception, and Overprinting 176 4.2 Systems/Rocks with Pronounced Shear (Brittle – Ductile, Ductile Components) 198 4.3 Systems/Rocks with Pronounced Brittle Components 204 4.4 Textures of Related/Miscellaneous Interest 218 5 References 222 Volume 5 • Broken Rocks – Breccias II 223 List of Plates 225 Introduction, Scope and Arrangement of Volume 229 1 Initial Recognition 231 2 General Features – Range in Styles and Scale of Intrusive Breccia 244 3 Multistage Structural and Hydrothermal Overprinting 256 4 Special Features Associated with Selected Intrusive Breccias 264 5 Intrusive Breccia Associated with Maar-Volcanoes and Associated Structures 274 6 Intrusive Breccia in Other Epithermal Systems 280 7 References 282 Index 283 Ore Textures • Recognition and Interpretation • Contents XIII