SOCIETY OF ECONOMIC GEOLOGISTS, INC.

STRUcTURAL cONTROLS ON ORE GENESIS

EditorsJ.P. Richards and R.M. Tosdal

REvIEwS IN EcONOMIc GEOLOGY

volume 14

Society of Economic Geologists, Inc.

Reviews in Economic Geology, Vol. 14

Structural Controls on Ore GenesisJ.P. Richards and R.M. Tosdal, Editors

Additional copies of this publication can be obtained from

Society of Economic Geologists, Inc.7811 Shaffer ParkwayLittleton, CO 80127

www.segweb.org

ISBN: 978-1-629495-72-9

Byron BergerU.S. Geological SurveyMS 964, Federal CenterDenver, CO 80225-0046USATel. +303.236-5533Fax: +303.236-3200E-mail: bberger@usgs.gov

Jean BraunResearch School of Earth SciencesThe Australian National UniversityCanberra, ACT 0200AustraliaTel. +61.2.6125.5512Fax: +61.2.6125.5443E-mail: Jean.Braun@anu.edu.au

Stephen F. CoxDepartment of Geology and

Research School of Earth SciencesThe Australian National UniversityCanberra, ACT 0200AustraliaTel. +61.2.6125.0045Fax: +61.2.6125.5544E-mail: sfcox@geology.anu.edu.au

Thomas G. HildenbrandU.S. Geological SurveyMS 989, 345 Middlefield Rd.Menlo Park, CA 94025USATel. +650.329.5303Fax: +650.329.5313E-mail: tom@usgs.gov

Robert C. JachensU.S. Geological SurveyMS 989, 345 Middlefield Rd.Menlo Park, CA 94025USATel. +650.329.5300Fax: +650.329.5313E-mail: jachens@usgs.gov

Mark A. KnackstedtResearch School of

Physical Sciences and EngineeringThe Australian National UniversityCanberra, ACT 0200AustraliaTel. +61.2.6125.2495Fax: +61.2.6125.1884E-mail: mak110@rsphy1.anu.edu.au

Steve LudingtonU.S. Geological SurveyMS 989, 345 Middlefield Rd.Menlo Park, CA 94025USATel. +650.329.5371Fax: +650.329.5374E-mail: slud@usgs.gov

Nick OliverEconomic Geology Research UnitSchool of Earth SciencesJames Cook UniversityTownsville, QLD 4811 AustraliaTel. +61.7.07.4781.5049Fax: +61.7.07.4725.1501E-mail: Nick.Oliver@jcu.edu.au

Alison OrdCSIRO Division of

Exploration and Mining PO Box 437Nedlands, WA 6009AustraliaTel. +61.8.9389.8421 Fax: +61.8.9389.1906E-mail: a.ord@dem.csiro.au

K. Howard Poulsen34 Walford WayNepean, ON K2E 6B6Canada Tel. +613.723.1766Fax: +613.723.7192E-mail: hpoulsen@attcanada.ca

Jeremy P. Richards Department of Earth

and Atmospheric SciencesUniversity of AlbertaEdmonton, AB T6G 2E3Canada Tel. +780.492.3430Fax: +780.492.2030E-mail: Jeremy.Richards@ualberta.ca

François RobertBarrick Gold Corporation7257 DunverVerdun, QC H4H 2H6CanadaTel. +514.732.0021Fax: +514.732.0021E-mail: frobert@barrick.com

Richard H. SibsonUniversity of OtagoDepartment of GeologyPO Box 56DunedinNew ZealandTel. +64.3.479.7506Fax: +64.3.479.7527E-mail:rick.sibson@stonebow.otago.ac.nz

Richard M. TosdalMineral Deposit Research Unit University of British ColumbiaVancouver, BC V6T 1Z4CanadaTel. +604.822.5149Fax: +604.822.6088E-mail: rtosdal@eos.ub.ca

Phaedra UptonDepartment of GeologyUniversity of OtagoPO Box 56DunedinNew ZealandTelephone: +64.3.479.7519Fax: +64.3.479.7527E-mail:

phaedra.upton@stonebow.otago.ac.nz

Richard K. ValentaMIM ExplorationGPO Box 1042 Brisbane, QLD 4001 AustraliaTel. +61-7-3214.9245Fax: +61-7-3214.9133E-mail: rkvalent@mim.com.au

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The Authors:

BYRON R. BERGER graduated from Occidental College,Los Angeles, with a B.A. degree in economics, and from theUniversity of California at Los Angeles with an M.S. degree ingeology. From 1971 to 1977, he worked in the MineralsExploration Department and Minerals Exploration ResearchDivision, Research and Development Department, of theContinental Oil Company. In 1977 he joined the U.S. Geo-logical Survey, where he has been a research geologist andhas served as Chief, Branch of Geochemistry (1983–1988)and Deputy Chief, Office of Mineral Resources (1988–1992).He is presently a member of the Crustal Imaging and Char-acterization Team and conducts research on (1) thermal,mechanical, and hydraulic coupling in ore formation, (2)the environmental geology and geochemistry of mineralizedareas, and (3) the development of tectonic and structuralmodels of epizonal hydrothermal mineral deposits for min-eral resource assessment applications.

JEAN BRAUN is a fellow in the Geodynamics Group at theResearch School of Earth Sciences at the Australian NationalUniversity. His research specializes in computational model-ing of geodynamic processes, including fluid transport inpermeable media. He holds a B.Sc. degree in physics fromthe University of Liège, and a Ph.D. degree in oceanographyfrom Dalhousie University.

STEPHEN COX is professor of structural and economicgeology, jointly in the Department of Geology and theResearch School of Earth Sciences at the Australian NationalUniversity. His research interests are primarily in the cou-pling between deformation processes and fluid flow incrustal regimes, with applications to ore genesis and crustalmechanics. His research is pursued via field-based studies,microstructural and microchemical analyses, and high-pres-sure/high-temperature experimental studies. He holds aB.Sc. (Hons) degree from the University of Tasmania and aPh.D. degree from Monash University.

THOMAS G. HILDENBRAND is a geophysicist with the U.S.Geological Survey in Menlo Park, California. He received hisB.S. degree in engineering physics and his M.S. and Ph.D.degrees in engineering geoscience from the University ofCalifornia at Berkeley. He began his career at the U.S. Geo-logical Survey as a postdoctoral fellow from 1975 to 1977.From 1984 to 1990, he served as Section Chief and then asChief of the Branch of Geophysics, an interdisciplinary teamdevoted to the theoretical development and application ofpotential-field, electrical, and remote sensing techniques. Asa research scientist, Hildenbrand is interested in interpretingpotential-field data by developing geologic models address-ing the origin and evolution of crust in various tectonic set-tings. Recent research activities have been directed towardextracting geologic information from potential-field data inthe (1) assessment of mineral resources on local andregional scales in western United States, (2) investigation oflocal structures affecting groundwater flow at the Nevada

Test Site, with the purpose of examining environmentalrestoration issues, (3) study of crustal structure and funda-mental geologic processes related to earthquake and vol-canic hazards in the central and western United States (pri-marily the New Madrid seismic zone and rift systems onvolcanic islands such as Hawaii), and (4) determination ofthe location, attitude, and displacement history of potentiallydangerous, often concealed faults in the San Francisco andLos Angeles areas.

ROBERT JACHENS received his B.S. degree in geologyfrom San Jose State University and his M.S. and Ph.D.degrees in geophysics from Columbia University. He was aresearch associate, Lamont-Doherty Geological Observa-tory, from 1972 to1976, and has been a geophysicist with theU.S. Geological Survey from 1976 to the present. Jachen’sprimary interest is in the application of gravity and magnetictechniques to the solution of geologic problems. Work hasincluded studies of tidal gravity, temporal gravity changesassociated with tectonic and volcanic deformation, earth fis-suring due to groundwater extraction, regional geophysicsin mineral resource assessments, plate tectonics of westernNorth America, continent-scale relationships between grav-ity and upper-crustal geology, and the tectonic evolution ofthe California coast ranges. His most recent work hasfocused on the use of regional gravity and magnetic anom-alies to understand the structure of and offsets on faults ofthe San Andreas system, applications of geology and geo-physics to defining the hydrogeologic framework of aquifersystems, and the creation and visualization of 3-D geologicmaps.

MARK KNACKSTEDT is an Australian Research CouncilQueen Elizabeth II Fellow in the Department of AppliedMathematics at the Research School of Physical Sciencesand Engineering at the Australian National University. Hisresearch interests include multiphase flow in porous media,application of percolation theory to the geological sciences,and characterization of disordered materials. He holds abachelor’s degree from Columbia University and a Ph.D.degree from Rice University, both in chemical engineering.

STEVE LUDINGTON received his B.S. degree in geologyfrom Stanford University in 1967, and a Ph.D. degree in geol-ogy from the University of Colorado in 1974. He worked forthe mineral industry from 1969 to 1974, doing explorationin the central and southern Rocky Mountains. In 1974, hejoined the U.S. Geological Survey. He has worked for theSurvey in Denver, Colorado, and Reston, Virginia, and since1987, he has been in Menlo Park, California. Until the mid-1980s, Ludington was a specialist, interested in Climax-typemolybdenite deposits and other mineral deposits associatedwith evolved granites. More recently, he has participated inregional mineral resource studies in Costa Rica, Venezuela,and Bolivia, and in Nevada. He coordinated the NationalMineral Resource Assessment of the U.S. Geological Survey

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BIOGRAPHIES

for precious and base metals. At present, he is engaged inusing regional geochemistry to elucidate the tectonic frame-work of the northern Great Basin.

NICK OLIVER is professor of economic geology and Direc-tor of the Economic Geology Research Unit at James CookUniversity, a position he has held for four years. Previously heheld academic positions at Curtin University, Monash Uni-versity, and research positions at CSIRO and the CarnegieInstitute Geophysical Laboratory, where his researchinvolved analysis of large hydrothermal systems throughcombinations of petrology, geochemistry, and structuralgeology. He has a B.Sc. (Hons) degree from the University ofQueensland and a Ph.D. degree from Monash University.His research experience covers a broad range of deposittypes and geological settings, from banded iron formationsthrough various epigenetic base metal and gold deposits,regional alteration patterns in the Mt. Isa block, Yukon gran-ite-related gold, and greenstones and metamorphosed mas-sive sulfides in Finland. With collaborators in CSIRO and theminerals industry, he has applied numerical modeling toassist with interpretation of field and mine patterns for mostof these districts. He is a fellow of the Society of EconomicGeologists and was awarded the 1999 Mineralium DepositaReviewer of the Year.

ALISON ORD received a B.Sc. (Honours) degree from theUniversity of Edinburgh in 1977, and a Ph.D. degree fromthe University of California at Los Angeles in 1981. From1981 to 1984, she held a postdoctoral research fellowship atMonash University, studying the effect of defect chemistry onthe strength of quartz at high pressures and temperatures.She joined the Commonwealth Scientific and IndustrialResearch Organisation of Australia (CSIRO) in 1984 as aresearch scientist in the division of Geomechanics. She isnow a chief research scientist in the division of Explorationand Mining, leading the research group, Structural Controlson Mineralisation. Her principal areas of research are explo-ration of the fundamental controls of mechanics, solid andfluid, on the formation of giant ore deposits, includingnumerical modeling of deformation-fluid flow-thermal trans-port-chemical reaction feedback systems. She has interestsalso in 3-D vision systems for the mining and mineral pro-cessing industries, particularly remote and automatic systemsfor determining joint structures in pit walls and fragmentsize distributions on muck piles and conveyor belts. She is onthe editorial board of the Australian Journal of Earth Sciencesand is a member of the Geological Society of Australia.

HOWARD POULSEN was born and raised at Thunder Bay,Ontario, and attended the University of Waterloo (HonorsB.Sc. degree, physics, 1970), Lakehead University (M.Sc.degree, structural geology, 1980) and Queen’s University(Ph.D. degree, economic geology, 1984). With more than 25years of cumulative research experience at Lakehead Unver-sity, the Ontario Geological Survey, and the Geological Sur-

vey of Canada, he is currently a consulting economic geolo-gist who specializes in structural geology of ore deposits. Hisresearch has focused mainly on problems of significance tothe global mineral exploration and he has authored or co-authored 55 journal papers and reports. He served as anassociate editor for Economic Geology from 1993 to 1998 and isa fellow of the Society of Economic Geologists as well as amember of the Association of Geoscientists of Ontario. Hecurrently teaches a graduate-level course in structural geol-ogy and ore deposits for the mineral exploration program atQueen’s University.

JEREMY P. RICHARDS received his B.A. degree (1983) ingeology from the University of Cambridge, UK, his M.Sc.degree (1986) in economic geology from the University ofToronto, Canada, and a Ph.D. (1990) in economic geologyfrom the Australian National University. After holding a two-year postdoctoral position at the University of Saskatchewan,Canada (1990–1992), he joined the faculty at the Universityof Leicester, UK, and was Course Director of the MineralExploration M.Sc. program from 1994 to 1997. He joinedthe University of Alberta in 1997, and is currently associateprofessor of economic geology. Research interests havespanned a wide range in both pure and economic geology,and include investigations of Keweenawan and centralAfrican copperbelt geology, alkalic-type epithermal Audeposits in Papua New Guinea and British Columbia, por-phyry Cu-Mo deposits in Ontario, and in Chile, Argentina,and Ecuador, and volcanology and structural geology of theCentral Andes. In the face of the current downturn in metalprices, his most recent foray is into sand and gravel resourcesin Alberta. Actually, there is a lot of gold in those gravels!

FRANÇOIS ROBERT is a graduate of Ecole Polytechniquein Montreal, where he received his B.Sc. (1978), M.Sc.(1980) and Ph.D. (1983) degrees. His doctoral work focusedon the geology, structure, and hydrothermal characteristicsof the Sigma gold deposit in Abitibi. Following one-year post-doctoral studies at the University of Michigan, where he stud-ied fluid inclusions of the Sigma deposit, he joined the Geo-logical Survey of Canada, in 1985, as a research scientist withthe mineral deposits group. His research focused largely onthe geology and structure of gold deposits and districts inmetamorphic terranes, in Canada and abroad. He workedclosely with industry and participated in a number of mis-sions for international agencies and governments. Hereceived the Society of Economic Geologists Waldemar Lind-gren Award in 1990 for his work on gold deposits. In 1997,he joined Barrick Gold Corporation as Senior ResearchGeologist. In addition to his other duties, he serves as in-house technical consultant on different projects worldwide.

RICHARD (RICK) SIBSON graduated with a B.Sc. (Hons)degree in geology from the University of Auckland, and M.Sc.and Ph.D. degrees from Imperial College, London. Hetaught at Imperial College (1973–1982) and at the University

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BIOGRAPHIES (continued)

of California at Santa Barbara (1982–1990) before returningto New Zealand as professor of geology at the University ofOtago (1990–2001). His research focuses on the structure ofcrustal fault zones and the mechanics of shallow crustal earth-quakes. Increasing recognition of fluid involvement in fault-ing has led to an interest in mechanisms for fluid redistribu-tion around seismically active faults, and structural controlson the development of fault-hosted hydrothermal mineral-ization. He is author or co-author of more than 60 researchpapers and is an elected fellow of the Geological Society ofLondon, the Geological Society of America, the AmericanGeophysical Union, and the Royal Society of New Zealand.

RICHARD TOSDAL received a B.A. degree from the Uni-versity of California at Santa Barbara, an M.Sc. degree fromQueen’s University in Kingston, Ontario, and a Ph.D. degreefrom the University of California at Santa Barbara. Tosdalhas worked for the U.S. Geological Survey and as an inde-pendent geologist for the mining industry. He currently isthe Director of the Mineral Deposit Research Unit at theUniversity of British Columbia in Vancouver, where he super-vises research groups investigating intrusion-related Audeposits, Carlin-type sedimentary rock-hosted deposits,epithermal systems, and pericratonal VMS deposits, and isdeveloping projects in the diamond-related fields and in car-bonate terranes. He has worked on geologic, tectonic, andmetallogenic problems in the cordilleras and cratons ofNorth and South America. His personal research interestsinclude the role of structure and tectonics in ore genesis andmagmatism, the role of climate in ore genesis, and thesource of metals in ore deposits.

PHAEDRA UPTON received a B.Sc. (Hons) degree inchemistry from Canterbury University in 1989, and a Ph.D.degree in geology from the University of Otago in1995. Shewas a postdoctoral fellow with CSIRO from 1996 to 1998.Since 1998 she has been a Foundation of Research, Scienceand Technology postdoctoral fellow at the University ofOtago. Her research is focused on the geodynamics of, andthe fluid flow systems associated with, convergent plateboundary settings. The majority of her work has been basedaround the Southern Alps of New Zealand. She uses geody-namic modeling, fieldwork, and stable isotope geochemistryin her studies of coupled deformation and fluid flow. She isa member of the Geological and Geophysical Societies ofNew Zealand and of the American Geophysical Union.

RICK VALENTA is Chief Geologist of Mount Isa MinesExploration and has been with MIM for over six years. Priorto that he lectured in geophysics, image interpretation, andstructural geology at Monash University and also consultedfor MIM, World Geoscience, and Aerodata. He has a B.Sc.(Hons) degree from the University of New Brunswick and aPh.D. degree from Monash University (specializing in defor-mation and ore genesis at the Hilton Pb-Zn mine near Mt.Isa). Rick has been instrumental in regional and local areaselection and geological synthesis of MIM projects in Aus-tralia, Africa, and South America. He is well known acrossAustralia as an expert in integrated geological and geophysi-cal approaches to project generation and terrain interpreta-tion. He is involved with several collaborative research pro-jects, including one on geophysical interpretation, structure,and ore genesis in the Ernest Henry Cu-Au district.

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BIOGRAPHIES (continued)

vi

The spark for this volume arose amid the euphoria ofcompleting Techniques in Hydrothermal Ore Deposits Geology(Reviews in Economic Geology, v. 10), and the accompany-ing Society of Economic Geologists-sponsored short courseat the 1998 Geological Society of America Annual Meeting inToronto. Dick Tosdal noted the lack of any structural geol-ogy in the Techniques volume, and I glibly replied that thiscould be the subject of a whole Reviews volume on its own.Several espressos later we shook hands on a new project, thisone also to be presented in Toronto, but as part of theProspectors and Developers Association of Canada Conven-tion in March 2001.

The reason that Dick’s comment triggered such precipi-tate action was that we recognized, both in ourselves and inthe wider economic geology community, a lack of clearunderstanding about this fundamental aspect of our disci-pline. The mantra of hydrogeologists and hydrothermalore deposits geologists alike is “permeability, permeability,permeability,” and one of the best ways to enhance perme-ability is by fracturing rock. This we all know, but for manyof us, formal training in structural geology ceased in ourundergraduate years. What this volume aims to do is to pro-vide a refresher on basic aspects of structural geology andits control on fluid flow, and also to review some of themore sophisticated models that can be used to predictpaleo fluid flow paths—and therefore, zones of potentialmineral deposition—from structural and rheological data.The closing chapter attempts to place deposit-scale struc-tural controls on ore deposition in the context of regionalcrustal stress fields and plate tectonic models, using por-phyry deposits as an example.

The volume is intended for economic geologists whosespecialization is not structural geology, and should appealto a wide audience from academia and industry, includingstudents. It is not intended to supplant formal instructionin this field, but instead aims to renew interest in structuralapproaches to ore deposits geology, and to showcase someof the developments that allow the formulation of predic-tive models for deposit localization.

Perhaps surprisingly—and this may be a relief to somepeople—only one chapter alludes to multiple deformationevents, the staple of many classic structural geology courses.

For those readers who seek more discussion of this aspectof the discipline, we provide below a Table of Events for theconstruction of a Reviews in Economic Geology volume:

Event Reality

Protolith formation Volume editors dream up concept; invite authors to submit chapter outlines

D1 Editors tell authors what they actually wanted

Unconformity Time passes...S1, M1 Manuscripts prepared by authors

regardless, and sent out for reviewUnconformity Time passes...D2 Reviews receivedS2 Reviews consideredUnconformity Time passes...M2 Some changes made and revised

versions submittedMineralization Revised manuscripts accepted by

editorsD3, M3 Copyediting and productionUplift Publication of volumeErosion No! Volume withstands the test of

time…

No volume such as this can be prepared without the ded-icated efforts of the various authors, and Dick and I thankthe 14 contributors who stayed the course. We also thankDavid John, who guest-edited our own contribution, and allthe reviewers who provided timely and incisive critiquesthat have, we hope, kept us honest—their names are listedbelow. Production of this volume would not have been pos-sible without the untiring efforts of Lisa Laird and AliceBouley at SEG, and Lee Ewert, who expertly handled thecopyediting.

Jeremy P. RichardsRichard M. Tosdal

PREFACE

ReviewersJennifer AdamsAnne-Marie BoullierRon BruhnMark DuffettDavid HillJay HodgsonCarol Finn

Michel JébrakDavid JohnRobert KerrichJohn RidleyTom SchroeterStephen TemperleyTed Theodore

Chapter 1—Principles of Structural Control on Permeability and Fluid Flow in Hydrothermal Systems

S. F. Cox, M. A. Knackstedt, and J. BraunAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Principles of Fluid Flow in Porous and

Fractured Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . .2Principles of Macroscopic Fracture Formation . . . . .10Evolution of Flow Pathways

during Deformation . . . . . . . . . . . . . . . . . . . . . . . .19Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . .22References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Chapter 2—Seismogenic Framework for Hydrothermal Transport and Ore Deposition

Richard H. SibsonAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26Seismogenic Crust . . . . . . . . . . . . . . . . . . . . . . . . . . .26Tectonic Stress and Fluid Pressure Regimes . . . . . . .31Faults, Fractures, and Fluid Pressure Levels . . . . . . .35Dynamic Structural Permeability . . . . . . . . . . . . . . .38Fluid Redistribution Mechanisms

Linked to the Earthquake Stress Cycle . . . . . . . . . .41Summary Discussion . . . . . . . . . . . . . . . . . . . . . . . . .47Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . .47References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

Chapter 3—Deformation, Fluid Flow, and Ore Genesis in Heterogeneous Rocks, with Examples and Numerical Models from the Mount Isa District, Australia

Nicholas H. S. Oliver, Alison Ord, Richard K. Valenta, and Phaedra Upton

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Principles of Fluid Flow . . . . . . . . . . . . . . . . . . . . . .52Deformation and Fluid Flow . . . . . . . . . . . . . . . . . . .54Heterogeneous Deformation and Fluid Flow . . . . . .54Numerical Models . . . . . . . . . . . . . . . . . . . . . . . . . . .56Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . .72References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72

Chapter 4—Utility of Magnetic and Gravity Data in Evaluating Regional Controls on Mineralization: Examples from the Western United States

T. G. Hildenbrand, Byron Berger,R. C. Jachens, and Steve Ludington

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75Potential-Field Data and Methods . . . . . . . . . . . . . . .76Mineralized Areas in the Western United States . . .85Relationships of Geophysical Structures

and Deposit Patterns . . . . . . . . . . . . . . . . . . . . . . . .90Conclusions and Summary . . . . . . . . . . . . . . . . . .104Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . .106References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

Chapter 5—Vein Formation and Deformation in Greenstone Gold Deposits

François Robert and K. Howard PoulsenAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111Introduction and Scope . . . . . . . . . . . . . . . . . . . . .111Structure of Greenstone Gold Districts . . . . . . . . .112Veins and Their Analysis . . . . . . . . . . . . . . . . . . . . .118Classification of Veins . . . . . . . . . . . . . . . . . . . . . . .124Vein Deformation and Superimposed Strain . . . . .138Structural Timing of Veins . . . . . . . . . . . . . . . . . . .146Discussion of Concluding Remarks . . . . . . . . . . . . .150Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . .152References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152

Chapter 6—Magmatic and Structural Controls on the Development of Porphyry Cu ± Mo ± Au Deposits

R. M. Tosdal and J. P. RichardsAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157General Porphyry Model . . . . . . . . . . . . . . . . . . . .158Convergent Plate Margin Magmatism . . . . . . . . . . .165Volcanoes and Shallow-Level

Intrusive Complexes: The Environment of Porphyry Cu Deposits . . . . . . . . .166

Structural Sequence in Porphyry Systems . . . . . . .171Origin of Breccia Pipes in Porphyry Cu Deposits . .173Tectonic Setting of Porphyry Cu Deposits . . . . . . .174Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . .175Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . .177References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177

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CONTENTS