Ore Textures: Recognition and Interpretation

282 Pages·2009·119.591 MB·English

by  Roger Taylor

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
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(cid:2)c Springer-VerlagBerlinHeidelberg2009
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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