The Trace Element Composition of Sedimentary Pyrite: Factors Effecting Uptake and Uses of the Data for Determining Paleo-Ocean Conditions

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The Trace Element Composition of Sedimentary Pyrite: Factors Effecting Uptake and Uses of the Data for Determining Paleo-Ocean Conditions by Daniel

1 The Trace Element Composition of Sedimentary Pyrite: Factors Effecting Uptake and Uses of the Data for Determining Paleo-Ocean Conditions by Daniel D. Gregory (BSc. Honours University of British Columbia) Submitted in fulfillment of the requirements for the degree of Doctor of Philosophy May 2014

2 Declaration This thesis does not contain any material that has been accepted for degree or diploma by the University or any other institution, except where it has been duly acknowledged in the thesis. To the best of the author s knowledge it also contains no previously published material written by another person, except where it is acknowledged in the text of the thesis. Daniel D. Gregory Date: Authority of Access The publishers of the papers comprising Chapters 2 and 3 (Australian Journal of Earth Science and American Mineralogist respectively) hold the copyright for that content, and access to the material should be sought from the respective journals. The remaining non published content of the thesis may be made available for loan and limited copying and communication in accordance with the Copyright Act ii

3 Statement of Co-Authorship The following people and institutions contributed to the publication of work undertaken as part of this thesis: Daniel Gregory, University of Tasmania = Candidate Ross Large,University of Tasmania = Author 1 Sebastien Meffre, University of Tasmania = Author 2 Jacqueline Halpin, University of Tasmania = Author 3 Stuart Bull, University of Tasmania = Author 4 Elena Lounejeva, University of Tasmania = Author 5 Jeffrey Steadman, University, of Tasmania = Author 6 Patrick Sack, Yukon Geological Survey = Author 7 Timothy Lyons, University of California Riverside = Author 8 Anthony Chappaz, Central Michigan University = Author 9 Arthur Hickman, Geological Survey of Western Australia = Author 10 Trevor Ireland, Australian National University = Author 11 Peter Holden, Australian National University = Author 12 Valeriy Maslennikov, Institute of Mineralogy, Russion Academy of Science, Urals Branch = Author 13 John Walshe, CSIRO = Author 14 Adam Bath, CSIRO = Author 15 Author details and their roles: Paper 1, Mineralogy of metal contaminated estuarine sediments, Derwent estuary, Hobart, Australia: Implications for metal mobility: Located in chapter 2 Candidate was the primary author (90%) and with author 2 contributed to the idea, its formalisation and development (8%). Author 1 assisted with refinement and presentation (2%). Paper 2, Comparison of metal enrichment in pyrite framboids from a metal-enriched and metal-poor estuary: iii

4 Located in chapter 3 Candidate was the primary author (90%) and with author 2 contributed to the idea, its formalisation and development (8%). Author 1 assisted with refinement and presentation (2%). Paper 3, Trace Element Content of Unmineralized Sedimentary Pyrite: Located in chapter 4 Candidate was the primary author (54%) and with author 1 (8%) and author 8 (4%) contributed to the idea, its formalisation and development. Author 3 under took some of the analyses and assisted with refinement and presentation (14%). Author 4 assisted with refinement and presentation (1%). Author 5 under took some of the analyses (9%). Author 7 (2%), 9 (2%), 13 (2%) supplied samples and provided background information on the samples. Data acquisition was primarily conducted by the primary author (32%), author 3 (24%) and author 5 (41%). The weighting of 54% for the entire paper is due to the primary authors portion of the data acquisition and the fact that the writing and preparation of the manuscript was completed by the primary author. Paper 4, The Chemical Conditions of the Late Archean Hamersley Basin Inferred from Whole Rock and Pyrite Geochemistry with Δ 33 S and δ 34 S Isotope Analyses: Located in chapter 5 Candidate was the primary author (80%) and with author 1 (5%) contributed to the idea, its formalisation and development. Author 6 (5%) under took some of the analyses. Author 10 (5%) assisted with refinement and presentation. Author 11 (2.5%) and 12 (2.5%) provided access to the SHRIMP-SI and aided in the analysis. Paper 5, Trace element content of pyrite from the Kapai Slate, St. Ives Gold District, Western Australia: Implications for Ocean Chemistry and Ore Deposition: iv

5 Located in chapter 6 Candidate was the primary author (80%) and author 1 (4%) and 14 (3%) contributed to the idea, its formalisation and development. Author 6 (4%) under took some of the analyses. Author 15 (4%) supplied samples and provided background information on the samples and provided early versions of the plan map and cross section using CSIRO s model for the St Ives Gold District. Author 12 (2.5%) and 13 (2.5%) provided access to the SHRIMP-SI and aided in the analysis. We the undersigned agree with the above stated proportion of work undertaken for each of the above published (or submitted) peer-reviewed manuscripts contributing to this thesis: Signed: Ross Large Supervisor CODES, ARC Centre of Jocelyn McPhie Head of School School of Earth Sciences Excellence in Ore Deposits University of Tasmania University of Tasmania Date: v

6 Abstract The trace element content of pyrite has received much research and is important to the fields of environmental geochemistry, ore deposit genesis and paleo-ocean reconstructions. Four aspects of the geochemistry of pyrite are investigated in this thesis: 1) the incorporation of trace elements into pyrite in a modern setting, 2) the variability of trace elements in sedimentary pyrite in ancient marine settings, 3) the use of trace elements in pyrite to interpret palaeo-ocean chemical conditions, and 4) modification of trace elements in sedimentary pyrite associated with later metamorphic and hydrothermal processes. To facilitate these investigations, detailed LA-ICPMS analyses were performed on pyrite from 49 different shale and unconsolidated sediment formations. These include detailed studies of the Derwent and Huon Estuaries that serve as modern high and low metal environments of sedimentary pyrite formation; the Hamersley and Fortescue Basins sediments which provide low metamorphic grade Archean aged examples of sedimentary pyrite; the Kapai Slate which is a high metamorphic grade, hydrothermally overprinted example of Archean aged pyrite and a series of 44 other shale units that are used to create a database of average trace element content of sedimentary pyrite. The examination of trace element contents of sedimentary pyrite in modern settings is an important component of understanding how trace elements are incorporated into pyrite. Recent studies have provided data on the trace element content of pyrite from modern settings with current oceanic trace element contents. However, as the trace element content of the oceans varies throughout geologic time it is important to examine the incorporation of trace metals in pyrite at higher trace element concentrations than present. The Derwent Estuary provides an ideal site to examine the trace element uptake by pyrite in a high metal environment. Detailed mineralogical and geochemical analyses demonstrated the degree to which trace elements were available to be incorporated into pyrite, and LA-ICPMS analyses show the amount of each element incorporated into the pyrite. The data showed that not only is it important to have significant quantities of trace elements available to be incorporated but also, if the concentrations of certain trace elements available for incorporation are high, they can prevent other trace elements from being incorporated into the pyrite. The data have also shown that even though some trace elements can be incorporated into pyrite in contaminated estuaries, the amount of pyrite formed, and the amount of the trace elements within the pyrite, is not sufficient for pyrite to act as a major sink for the contaminants. vi

7 To demonstrate how trace element contents in sedimentary pyrite have varied according to geologic time, depositional setting and pyrite texture, a data base of pyrite chemistry from 45 different shale units was produced using LA-ICPMS. Some trace elements decrease with Earth evolution due to a decrease in Earth degassing and mafic magmatism. However, some elements, such as Mo, increase as a result of enhanced oxygenation that promoted the breakdown of sulfides and contributed additional trace elements to the oceans. Depositional setting of the shales in which the pyrite forms, is also an important control on the trace element content of sedimentary pyrite, with high trace element supply-settings having the highest trace element content. Pyrite texture differs based on diagenetic history and content of Fe and S present at the time of pyrite formation. Generally coarser grained pyrite forms later in digenesis and finer grained pyrite forms earlier (though fine euhedral pyrite is an exception to this). While no systematic differences were noted across the entire dataset with pyrite texture, in individual samples the early formed pyrite had the highest trace element content. The dataset also provides geochemical criteria to characterize sedimentary pyrite and can be used to support inferences made by mineral texture alone. Changes in pyrite from individual basins compared to the averages provided by the dataset can also be used to explain changes in ocean chemistry syn-pyrite deposition, similarly to how traditional analyses of whole rock are compared to average shale chemistry. The variations in pyrite chemistry, as determined by LA-ICPMS, in the shales from the Hamersley and Fortescue basins, Western Australia, were investigated to provide an alternative method for paleo-ocean reconstructions. Pyrite is a sink for several trace elements in the marine environment and the amount of trace elements captured by sedimentary pyrite is essentially a record of the trace element content of the ocean and/or sediments at the time of deposition. Therefore, the content of trace elements in pyrite can be used to determine the chemical conditions of the ocean basin at the time of deposition of the sediments. In the Hamersley and Fortescue basins, trace elements form cycles that generally increase upsection and then decrease abruptly at the end of each cycle. These cycles are interpreted to be reflective of a series of pulses of atmospheric oxygen which result in the decomposition of continental sulfides and thus an increase of metal flux to the ocean. Periodic drops in trace element content reflect influxes of volcanically sourced S and/or Fe (as suggested by positive Δ 33 S shifts) which causes elevated pyrite production and a drawdown of trace elements. Whole rock analyses show similar relationships and support the use of pyrite analyses to determine paleo-oceanic conditions. vii

8 One of the main benefits of using LA-ICPMS to determine trace element content of sedimentary pyrite is that it is a selective, in situ technique, unlike traditional bulk sample or sequential extraction techniques. This allows the determination of sedimentary pyrite trace element content in areas that have undergone significant (greenschist facies) metamorphism and/or hydrothermal overprint. The Kapai Slate from the St Ives gold district is an ideal area to demonstrate this capacity. The sedimentary pyrite from the Kapai Slate fit all the geochemical criteria developed for sedimentary pyrite. These analyses were used to determine that the Kapai Slate was deposited in an anoxic to euxinic basin with relatively low iron content and biological productivity. The analyses of the pyrite from the Kapai Slate also showed that it is not likely to be a major source of gold for the St Ives gold district, though the contained pyrite is elevated in gold. Preliminary investigations suggest that ratios of trace elements in pyrite may be a potential tool in mineral exploration, but further research is required for pyrite chemistry to be used as a robust technique with confidence. By analyzing pyrite from a number of different settings across geologic time this study has greatly increased the understanding of the controls on the trace element contents in pyrite. The analyses of pyrite from the metal enriched Derwent Estuary have demonstrated the effects of high trace element abundance on trace element content in pyrite. The data base of trace element content of pyrite has shown how the trace elements available for incorporation have varied throughout earth s history and how that is reflected in the trace element content of pyrite. A more detailed study of how this element content of pyrite varies within individual basins was provided by the Hamersley and Fortescue basin study which also demonstrated how the pyrite data can be used to determine paleo-oceanic conditions. Finally the Kapai Slate analyses provide an example of how metamorphism and hydrothermal over print effect the trace element content of sedimentary pyrite and how, using LA-ICPMS, the sedimentary pyrite from these basins can still be used to determine paleo-oceanic conditions. viii

9 Acknowledgements This work is part of a larger project under the direction of Ross Large and has been funded by CODES, ARC and CSIRO. Field support and whole rock geochemical analyses for the collection of the St. Ives samples were provided by Goldfields Limited. I would also like to thank the Western Australian core library and Goldfields for access to their core facilities. I would also like to thank the Society of Economic Geologists who provided funding for me to attend three of their international conferences and several field trips, which greatly expanded my understanding of geology and enhanced my scientific network. I am deeply indebted to my supervisors Ross Large, Sebastien Meffre and Stuart Bull who were all always happy to entertain my many questions. Without their expertise and patience this thesis would not have been completed. Thank you John Walshe for helping me gain access to the St. Ives drill core and for helping me understand the extensive geology and genetic models for the formation of the St. Ives deposits. Your time and readiness to show your data to me are very much appreciated. Many thanks to Rick Squire who helped me identify the different lithologies present at St Ives. Thank you also to Matt Crawford, Damien Keys, Mary Jane, Ayesha Ahmed and everyone at the St. Ives core facility for helping me find the right drill intervals and for supplying relevant cross sections, geochemical analyses and other drill core data. I offer my gratitude to Tim Lyons who helped construct an idea of what ultimately became the form in which this thesis would take. Thank you to Bernd Lottermoser and Jacqueline Halpin who provided great critiques of the early versions of some of the chapters. I would also like to thank the reviewers and editors Tony Morrison, Anita Andrew, Martin Reich, Zsolt Berner and Alejandro Fernandez-Martinez of the two chapters that have been accepted for publication. Their comments greatly increased the quality of the chapters in this thesis. Thank you to my co-authors who have contributed comments of the manuscripts, samples for analyses and expertise in the use of the instruments used in my research. I would also like to offer my thanks to Karsten Goemann and Sandrin Feig for their help in the use of the SEM and microprobe and Ashley Townsend, Jay Thompson and Ian Little for conducting the bulk sample analyses used in the study. I must thank Sarah Gilbert, Ian Little, Jay Thompson and Leonid Danyushevsky for their expertise in the use of LA-ICPMS and Stafford McKnight for QXRD analyses in Chapter 2. Thank you to Trevor Ireland and Peter Holden for allowing me to use the SHRIMP-SI and helping me to operate it. ix

10 A special thank you is needed for my family, friends and co-workers at CODES who kept me relaxed throughout the completion of my dissertation. I would especially like to thank my wife whose constant support, encouragement and love have motivated me through the difficult times and has greatly helped me to successfully complete this thesis. x

11 Table of Contents Declaration... ii Authority of Access... ii Statement of Co-Authorship... iii Abstract... vi Acknowledgements... ix Table of Contents... xi List of Tables... xv List of Figures... xvi Appendices... xix Chapter 1: Introduction Preamble Formation of Diagenetic Pyrite Trace metal accumulation of diagenetic pyrite Use of trace metals in determining chemical conditions of paleo-oceans Model of ore deposits sourcing metal from sediments Structure of thesis and objectives of each chapter Statement of authorship Statement of publication References Chapter 2: Mineralogy of metal contaminated estuarine sediments, Derwent estuary, Hobart, Australia: Implications for metal mobility Abstract Introduction Materials and methods of analysis Location and setting Anthropogenic contamination sources Sample collection and preparation Analytical methods Results Geochemical analyses Sequential leach analyses QXRD analyses Electron microprobe analyses SEM analyses Discussion Mineral host of heavy metals Degree of metal enrichment Application of the data acquired from SM1001 to the rest of the estuary Conclusions Acknowledgements References xi

12 Chapter 3: Comparison of metal enrichment in pyrite framboids from a metal-enriched and metal-poor estuary Abstract Introduction Trace element incorporation into diagenetic pyrite Material and Methods Location and setting Sample collection and preparation Analytical methods Results Geochemistry Discussion Conclusions Acknowledgements References Chapter 4: Trace Element Content of Unmineralized Sedimentary Pyrite Abstract Introduction Sedimentary pyrite formation and incorporated trace elements Methods Samples Laser Ablation ICPMS Screening method to ensure only syngenetic and diagenetic pyrite was included Justification for geochemical screening of sedimentary pyrite Results Textural variation of pyrite and effect of metamorphism Distribution of trace elements within sedimentary pyrite Content of trace elements in sedimentary pyrite Discussion Redox conditions and productivity Relationship between sedimentary pyrite texture and composition Relationship between sedimentary pyrite age and composition Conclusions References Chapter 5: The Chemical Conditions of the Late Archean Hamersley Basin Inferred from Whole Rock and Pyrite Geochemistry with Δ 33 S and δ 34 S Isotope Analyses Abstract Introduction Previous work The incorporation of trace elements into pyrite xii

13 5.2.2 Geology of the Hamersley Basin Methods Drill Holes Analytical Methods Whole rock analyses Laser Ablation-ICPMS pyrite analysis S isotope analyses Results Whole Rock Geochemistry Drill Hole DD86WRL Drill Hole ABDP LA-ICPMS pyrite chemistry Drill Hole DD86WRL Drill Hole ABDP Sulfur Isotopes Discussion Iron enrichment and depletion during in the late Archean Source of Sulfur Trace element composition of the late Archean ocean, possible causes and sources Mineral exploration potential Conclusions Reference Chapter 6: Trace element content of pyrite from the Kapai Slate, St. Ives Gold District, Western Australia: Implications for Ocean Chemistry and Ore Deposition Abstract Introduction The use of pyrite chemistry to determine chemical conditions of ancient ocean basins Current gold deposition models St. Ives Gold District Local Geology Metamorphism and Alteration Structural Geology Methods Sample Preparation LA-ICPMS Sulphur isotope analysis by SHRIMP SI Results Pyrite Textures LA-ICPMS analyses Sulphur isotopes Discussion xiii

14 6.5.1 Geochemical evidence supporting textural classification of sedimentary pyrite Sulphur Sources Chemical conditions of the ocean basin at the time of Kapai Slate deposition Possible alternate source of S and Au for Archean Lode Gold Deposits Exploration Implications Conclusions References Chapter 7: Conclusions Key results and contribution to knowledge The Incorporation of trace elements into diagenetic pyrite Environmental Implications of Derwent Estuary Study Data base of average trace element concentration of sedimentary pyrite Correspondence of laser data with whole rock data The use of pyrite geochemistry to determine ocean conditions in shale of high metamorphic grade that have been over printed by hydrothermal processes Gold deposition models for the St Ives gold district Future Research Analyses of pyrite forming in modern sedimentary basins Continued development of the trace element content of diagenetic pyrite data base Continued use of whole rock and pyrite chemistry to determine paleo-ocean condition Continued use of LA-ICPMS to determine chemical conditions of deposition of shales that have been metamorphosed and/or overprinted by hydrothermal fluids References xiv

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