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Formation of hydrothermal REE- phosphate deposits
STEFAN S. ANDERSSON
ACADEMIC DISSERTATION To be presented, with the permission of the Faculty of Science of the University of Helsinki, for public examination in auditorium D101, Physicum, Kumpula Campus, on May 29 2019, at 12 noon.
DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A76 / HELSINKI 2019 © Stefan S. Andersson (synopsis and Paper III) © Reprinted with permission of Mineralogical Society of America (Paper I) © Reprinted with CC BY license, Elsevier (Paper II) Cover photo: Highly birefringent and fractured xenotime in Djupedal (© Stefan S. Andersson, field of view is 5 mm)
Author´s address: Stefan S. Andersson Department of Geosciences and Geography P.O. Box 64 00014 University of Helsinki, Finland [email protected] ([email protected])
Supervised by: Professor Thomas Wagner Institute of Applied Mineralogy and Economic Geology RWTH Aachen University & Department of Geosciences and Geography University of Helsinki
Dr. Erik Jonsson Department of Mineral Resources Geological Survey of Sweden & Department of Earth Sciences Uppsala University
Reviewed by: Professor Martin Smith School of Environment and Technology University of Brighton
Priv.-Doz. Dr. Michael Marks Department of Geosciences University of Tübingen
Opponent: Professor emeritus Ulf Hålenius Swedish Museum of Natural History ISSN-L 1798-7911 ISSN 1798-7911 (print) ISBN 978-951-51-4915-2 (paperback) ISBN 978-951-51-4916-9 (PDF) http://ethesis.helsinki.fi
Unigrafia Helsinki 2019
The Faculty of Science uses the Urkund system (plagiarism recognition) to examine all doctoral dissertations. DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
Andersson S.S., 2019. The formation of hydrothermal REE-phosphate deposits. Unigrafia. Helsinki. 53 pages, 4 tables and 7 figures.
Abstract
Rare earth elements (REE) are important CaCl2-HF-H2O fluids at high temperatures of metals used in green and low-carbon energy and ~600 °C at c. 1.8 Ga. Subsequently, the ore as- information technologies and are widely used semblages were variably modified during cool- for geological petrogenetic studies. It is becom- ing by CaCl2-NaCl to NaCl-CaCl2 brines, and ing increasingly evident that the REE can be partly, CO2-rich fluids down to temperatures of mobile in certain hydrothermal fluids and even ~300 °C and to at least 1.75 Ga. form hydrothermal REE deposits. This study fo- Hydrothermal REE deposits rich in REE- cuses on the formation of hydrothermal REE phosphates are commonly associated with deposits rich in the REE-phosphates (monazite alkaline magmatism, particularly in silicate-
[(LREE,Y)PO4] and xenotime [(Y,HREE)PO4]). carbonatitic systems. This is because REE The main objective of the study was to char- and P both exhibit strong chemical affinities acterise the Olserum-Djupedal REE-phosphate with carbonatitic systems and the potential mineralisation in SE Sweden. Based on this, the for mobilisation of REE and P are high. This study evaluates different sources of REE and P study shows that REE deposits can also form in hydrothermal deposits and assesses how REE by hydrothermal activity related to subalkaline and P are transported in hydrothermal fluids. To magmatic rocks. Peraluminous granites exhibit characterise the Olserum-Djupedal REE miner- the greatest potential to exsolve fluids carrying alisation, this study combines fieldwork, petro- REE and P, which can lead to the formation graphical and textural analysis, major and trace of hydrothermal REE deposits rich in REE- element mineral chemistry of REE-bearing min- phosphates. erals and the main gangue phases, stable Cl iso- The general understanding on how hydro- topic and halogen analysis of fluorapatite, and thermal REE-phosphate deposits form is that fluid inclusion microthermometry and LA-ICP- REE and P are transported in separate fluids MS analysis. and that the REE-phosphates form when these The primary Olserum-Djupedal REE miner- two fluids mix, or the REE-phosphates form alisation comprises co-existing monazite-(Ce), when REE-bearing fluids interact with P-rich xenotime-(Y) and fluorapatite. These occur main- rocks. The lack of rocks pre-enriched in P in ly within veins dominated by biotite, magnetite, the Olserum-Djupedal district and the gedrite and quartz forming within metasedimen- co-crystallisation of fluorapatite, monazite-(Ce) tary rocks in or close to the contact aureole of a and xenotime-(Y), however, suggest that such peraluminous alkali feldspar granite. The veins scenarios not necessarily account for all occur- are also hosted by the granite within the outer- rences of hydrothermal REE-phosphate depos- most part of this granite. Primary REE-miner- its. As an alternative, REE and P can have been als formed by granitic-derived NaCl-FeCl2-KCl- transported by the same fluid. This study dem-
4 onstrates that the most probable conditions for temperature hydrothermal systems, the interac- co-transport of REE and P are at temperatures tion of REE-bearing fluids with P-rich rocks or exceeding 400 °C and with increasing salinity fluids is probably the most efficient mechanism of the fluids, conditions that agree well with that for precipitating REE-phosphates. In high-tem- of the Olserum-Djupedal system. The most perature magmatic-hydrothermal systems, REE effective co-transport of REE and P would and P probably share a common origin and were occur at acidic conditions by REE-Cl, REE- transported by the same fluid. In such systems,
F or REE-SO4 complexes. Yet, co-transport of pH changes, cooling and the destabilisation of the REE and P may also be feasible at neutral to alka- chief REE transporting complexes jointly con- line conditions by REE-OH complexes. In low- tribute to the precipitation of REE-phosphates.
5 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
Svensk sammanfattning
De sällsynta jordartsmetallerna (på engelska för- Hydrotermala mineraliseringar med REE- kortat REE; Rare Earth Elements) är en grupp fosfater förknippas vanligtvis med alkalina grundämnen som idag har en nyckelroll i mån- magmatiska bergarter och karbonatiter eftersom ga högteknologiska applikationer inklusive s.k. både REE och P i regel uppvisar en stark kemisk grön och fossilfri energiteknik. Över tid har flera affinitet till sådana magmor. Den här studien REE-mineraliseringar konstaterats ha bildats helt visar att REE-fosfatförekomster även kan bildas eller delvis av hydrotermala fluider (högtemper- av hydrotermal aktivitet relaterad till magmatiska erade vattenlösningar). Hur sådana förekomster bergarter av betydligt mindre alkalin karaktär. Av kan bildas är ett idag högaktuellt forskningsom- dessa system så har graniter med peraluminös råde. Den här studien är fokuserad på bildan- karaktär störst potential att avge fluider anrikade det av hydrotermala REE-förekomster inne- på både REE and P. hållande REE-fosfaterna monazit [(LREE,Y) Den generella uppfattningen om hur hydro-
PO4] och xenotim [(Y,HREE)PO4], två viktiga termala REE-fosfatmineraliseringar har bildats värdmineral för REE i jordskorpan. Studien in- är att REE och P transporterats i separata flu- riktar sig främst på att karakterisera de nyup- ider och att REE-fosfater fällts ut som en kon- ptäckta REE-mineraliseringarna i området kring sekvens av att dessa fluider blandats, eller att Olserum-Djupedal utanför Västervik i sydöstra REE-fosfater bildats som ett resultat av att Sverige. Fortsättningsvis undersöks ursprunget REE-förande fluider reagerat med fosforrika av REE och P i dessa förekomster, hur REE och bergarter. Avsaknaden av fosforrika bergarter i P transporteras i de hydrotermala lösningarna och området kring Olserum-Djupedal och förekom- vilka processer som lett fram till bildandet av sten av samexisterande fluorapatit, monazit-(Ce) monazit och xenotim från dem. och xenotim-(Y) visar dock att sådana scenarier Den primära mineraliseringen i Olserum- inte nödvändigtvis förklarar alla förekomster av Djupedal domineras av samexisterande monazit- hydrotermala REE-fosfatmineraliseringar. Som (Ce), xenotim-(Y) och REE-förande fluorapatit i ett alternativ kan REE och P ha transporterats gångar huvudsakligen bestående av biotit, mag- i samma fluid. De mest troliga förhållanden för netit, gedrit och kvarts. Gångarna förekommer samtransport av REE och P är i fluider med tem- i metasedimentära bergarter kring och i kontak- peraturer som överstiger 400°C och som har höga tgården till en peraluminös alkalifältspatgranit. salthalter. Vidare så gynnar låga pH samtrans- Gångarna uppträder även i utkanten av samma port av REE och P då olika metallkomplex med granit. Sammantaget visar resultaten att den REE, exempelvis REE-Cl, REE-F eller REE- primära REE-mineraliseringen har ett hydroter- SO4, är väldigt stabila under dessa förhållanden. malt ursprung och bildades för omkring 1,8 mil- Samtransport av REE och P är också möjlig vid jarder år sedan av högtempererade (ca. 600°C) ett mer neutralt eller basiskt pH. I ett scenario fluider från den närliggande graniten. De primära som innefattar samtransport av REE och P så associationerna omvandlades därefter under kan pH-förändringar, sänkta temperaturer och avtagande temperatur till ca. 300°C för åtmin- destabilisering av viktiga REE-metallkomplex i stone 1,75 miljarder år sedan. kombination bidra till utfällning av REE-fosfater.
6 Sammanfattningsvis kan man säga att i låg- fosforrika bergarter. I många högtempererade tempererade hydrotermala system har REE- magmatisk-hydrotermala system (> 400°C) fosfaterna sannolikt inte bildats av fluider så har förmodligen REE och P i REE-fosfaterna omfattande samtransport av REE och P, utan däremot haft ett gemensamt ursprung och trans- genom blandning av två olika fluider eller ge- porterats i samma fluid. nom samverkan mellan REE-förande fluider och
7 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
Acknowledgements
Despite all the hard work in the last couple of Gabriel, thanks for being my office mate at the years, this PhD journey has been very rewarding beginning of my studies. To Johan, thank you and enjoyable. However, my journey would not for enabling me to speak some Swedish while have been possible without all the support and at work. encouragements I have received during the years. I would like to give my gratitude to Tasman I would like to express my sincere gratitude to Metals/Leading Edge Materials and especially all who have helped me in any way. Johan Berg and Magnus Leijd for your support First, I would like to give a special thanks to during fieldwork and for allowing me access my supervisor Thomas Wagner for your support to proprietary information. The staff at the and contribution to this project. Your knowledge NORDSIM facility (Martin Whitehouse, Lev in the field, your ability to give swift and helpful Ilyinsky and Kerstin Lindén) are heartily thanked feedback and your positive attitude towards my for the assistance during the SIMS analysis. I work have helped me in my pursuit to produce further would like to thank the SGU staff at high-quality science. the national drillcore archives in Malå for your I am grateful that my second supervisor, valuable help during logging and sampling. Erik Jonsson, has been part of the journey. Thank you Pasi Heikkilä for your assistance After supervising my M.Sc. thesis, you were with the microprobe and Helena Korkka for the the one recommending me and giving me the preparation of thin and thick sections used in this opportunity to work on this project. Your inputs project. Dan Harlov donated reference material throughout the years have been vital for my for this project, which is greatly acknowledged. scientific progress and for the outcome of this The GeoDoc graduate Programme is thanked project. for providing the additional financial support I wish to thank Tapani Rämö for all your for international conferences and research help during the finalising stage of this project. visits. My sincere gratitude goes out to all my I would further like to express my gratitude to current and former friends and colleagues at the every one part of our former research group at Department of Geosciences and Geography, who the department (Tobias Fusswinkel, Radoslaw have assisted me in any way and provided me Michallik, Henrik Kalliomäki, Anselm Loges, company; thank you! Dina Schultze, Gabriel Berni and Johan To my friends and teammates in my table Fredriksson) for your company, support and help. tennis club MBF, thanks for helping me think To Tobias, thank you for your friendship and for of something else than work. I am very pleased your willingness to share your knowledge and that I took up this hobby again. Thanks to my expertise. To Radek, thanks for your friendship family for supporting me and being there for and all your help with the microprobe. To Henrik, me. Importantly, I would like to end with giving thanks for being my office mate for all these my endless and heartfelt gratitude to my dearest years and all our scientific and non-scientific Julia for your ever-lasting support, love and discussions. To Anselm and Dina, thanks for encouragement. I dedicate this thesis to you. your company and help with various things. To
8 Contents
Abstract...... 4 Svensk sammanfattning...... 6 Acknowledgements...... 8 List of original publications...... 10 Abbreviations...... 11 List of tables and figures...... 11
1 Introduction...... 12 1.1 The REE; what are they?...... 12 1.2 Hydrothermal REE deposits...... 15 1.3 Hydrothermal transport of REE and P...... 16 1.4 Objectives of the study...... 19
2 Geological background...... 19 2.1 Regional Geology...... 19 2.2 Geology of the Olserum-Djupedal district...... 21
3 Analytical methods...... 22 3.1 Sampling and field work...... 22 3.2 Petrographical and textural analysis...... 22 3.3 Major and trace element mineral chemistry...... 22 3.4 Stable Cl isotope and halogen analysis of fluorapatite...... 23 3.5 Fluid inclusion microthermometry and LA-ICP-MS analysis...... 24
4 Summary of original papers...... 25 4.1 Paper I...... 25 4.2 Paper II...... 26 4.3 Paper III...... 27
5 Discussion...... 28 5.1 Textural, mineralogical and fluid-chemical evolution of the hydrothermal Olserum-Djupedal REE-phosphate mineralisation...... 28 5.2 Source of REE and P in REE-phosphate deposits...... 32 5.3 Hydrothermal transport of REE and P and precipitation of REE- phosphate minerals...... 36 5.4 Outlook and remaining research topics...... 41
6 Conclusions...... 41
References...... 42
Appendix...... 50
9 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
List of original publications
This thesis is based on the following publications:
I Andersson, S.S., Wagner, T., Jonsson, E., Michallik, R.M., 2018. Mineralogy, para- genesis, and mineral chemistry of REEs in the Olserum-Djupedal REE-phosphate mineralization, SE Sweden. Am. Mineral. 103, 125-142. https://doi.org/10.2138/am- 2018-6202
II Andersson, S.S., Wagner, T., Jonsson, E., Fusswinkel, T., Leijd, M., Berg, J.T., 2018. Origin of the high-temperature Olserum-Djupedal REE-phosphate mineralisation, SE Sweden: A unique contact metamorphic-hydrothermal system. Ore Geol. Rev. 101, 740-764. https://doi.org/10.1016/j.oregeorev.2018.08.018
III Andersson, S.S., Wagner, T., Jonsson, E., Fusswinkel, T., Whitehouse, M.J., 2019. Apatite as a tracer of the source, chemistry, and evolution of ore-forming fluids: the case of the Olserum-Djupedal REE-phosphate mineralisation, SE Sweden. Accepted for publication in Geochimica et Cosmochimica Acta. https://doi.org/10.1016/j. gca.2019.04.014
The publications are referred to in the text by their Roman numerals.
Author’s contribution to the publications
I This study was initially planned by T. Wagner and E. Jonsson but revised by T. Wagner, E. Jonsson, and S.S. Andersson. Sampling was mainly conducted by S.S. Andersson with assistance from T. Wagner and E. Jonsson. Petrographical/textural analysis and EPMA and LA-ICP-MS analyses were performed by S.S. Andersson. Analytical EPMA protocols were co-developed by S.S. Andersson and R.M. Michal- lik. Results were interpreted jointly by S.S. Andersson, T. Wagner, and E. Jonsson. S.S. Andersson prepared the manuscript with contributions from the co-authors.
II This study was initially planned by T. Wagner and E. Jonsson but revised by T. Wagner, E. Jonsson, and S.S. Andersson. Fieldwork and sampling were mainly conducted by S.S. Andersson with assistance from T. Wagner, E. Jonsson, M. Leijd and J. Berg. Petrographical/textural analysis, EPMA and LA-ICP-MS were performed by S.S. Andersson. T. Fusswinkel assisted with LA-ICP-MS analysis. The results were interpreted jointly by S.S. Andersson, T. Wagner, and E. Jonsson. The manuscript was prepared by S.S. Andersson with contributions from the co-authors.
10 III This study was designed by T. Wagner, E. Jonsson, and S.S. Andersson. Selection of samples and analyses by EPMA, SIMS, and LA-ICP-MS were performed by S.S. Andersson. Analytical protocols for EPMA and LA-ICP-MS were developed by S.S. Andersson. M. Whitehouse assisted with SIMS analysis and T. Fusswinkel with LA- ICP-MS analysis. Results were interpreted jointly by S.S. Andersson, T. Wagner, E. Jonsson, and T. Fusswinkel. S.S. Andersson prepared the manuscript with contribu- tions from the co-authors.
Abbreviations
BSE Back-scattered electrons EPMA Electron-probe micro-analysis FIA Fluid inclusion assemblage HFSE High-field strength elements LA-ICP-MS Laser-ablation inductively coupled plasma mass spectrometry REE Rare earth elements SIMS Secondary ion mass spectrometry TIB Transscandinavian igneous belt
List of tables and figures
Table 1 List of REE and their properties, page 13 Table 2 Compilation of REE concentrations in crustal fluids, page 39 Fig 1 REE abundance in the crust, page 15 Fig 2 Geological setting, page 20 Fig 3 Geological map of the Olserum-Djupedal district, page 21 Fig 4 Modified paragenetic illustration, page 29 Fig 5 Halogen ratios, page 31 Fig 6 Sources of REE, page 33 Fig 7 Acid dissociation constants, page 37 Table A1 Fluid inclusion microthermometric data, page 50 Table A2 Fluid inclusion LA-ICP-MS data, page 52
11 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
1 Introduction the stable nature of the REE as oxides (termed “earths”) rather than metals (Wall, 2014). The challenge in separating the elements is reflected The scientific interest in the rare earth elements in the extended period it took to isolate them. The (REE) has always been strong. With the increas- first REE to be isolated, or more accurately, the ing recognition that the REE can be mobile in first “earth”, was “yttria” by the Finnish chemist certain hydrothermal fluids, recent geochemi- J. Gadolin in 1794 from the mineral gadolinite 2+ cal modelling has highlighted how the REE be- [(REE,Y)2Fe Be2O2(SiO4)2] from the Ytterby have in hydrothermal systems, i.e., how REE pegmatite in Sweden (Gupta and Krishnamurthy, are transported in aqueous solutions and what 2005). From the Bastnäs mines in Sweden, it was controls the precipitation of REE (e.g., Migdisov realised in the same time period that another and Williams-Jones, 2014; Migdisov et al., 2016; mineral (cerite; [Ce9(Mg,Fe)(SiO4)6(SiO3OH)
2018; Perry and Gysi, 2018). These models are (OH)3]) was found to contain the REE, and in based on experimental data, and it is thus im- 1804, “ceria” was separated. However, it was portant to test and compare them to how REE soon realised that “yttria” and “ceria” were mix- behave in natural hydrothermal systems. This tures of several REE. From “yttria” and “ceria”, study explores the key processes and system all REE were finally discovered by 1907 (Gupta parameters that are important for the formation and Krishnamurthy, 2005; Wall, 2014). Prome- of hydrothermal REE deposits rich in the REE- thium was not verified until 1945 (Gupta and phosphates monazite [(LREE,Y)PO4] and xe- Krishnamurthy, 2005), because of its very short 145 notime [(Y,HREE)PO4]. This is done by study- half-life; the most stable isotope Pm has a half- ing the Olserum-Djupedal REE mineralisation life of 17.7 years (Audi et al., 2003). in south-eastern Sweden. This is an exceptional The difficulties in separating the REE stem example of a hydrothermal REE system domi- from the very similar physical and chemical nated by monazite-(Ce), xenotime-(Y) and flu- properties exhibited by the individual REE orapatite, thus providing a unique opportunity (excluding Sc). This mainly originates from to study how REE and P behave in hydrother- the similar electronic configuration of the REE mal systems. (Table 1). The lanthanides are part of the f-block of elements together with the actinides. Starting 1.1 The REE; what are they? from Ce, the inner transition 4f electron shells The REE include the 15 lanthanides (Z = 57 to 71, in the atoms are subsequently filled towards La to Lu) and Y (Z = 39; Table 1). Scandium (Z Lu. Lanthanum is technically not a lanthanide = 21) is officially also included in this definition (the term means lanthanum-like) due to the by the International Union of Pure and Applied lack of 4f electrons (Gupta and Krishnamurthy, Chemistry (IUPAC; e.g., Gupta and Krishnamur- 2005). Because of the shape of the seven inner thy, 2005; Wall, 2014), although commonly ex- 4f-orbitals, they exert only a weak shielding cluded from the REE when discussing geologi- effect on the valence electrons from the cal processes. Contrary to what the term “rare positive nucleus charge. Thus, with increasing earth” may imply, the REE are not particularly atomic number, the effective nuclear charge rare in nature. This term was given because of increases, and the valence electrons are more the extreme difficulties in chemically separating strongly pulled towards the nucleus. This result the elements from one and other and to signify in a steady reduction in the atomic and ionic
12 Applications/uses Beta source for thickness gases, lasers submarines, nuclear-pow- ered battery Aerospace materials, consumer electronics, lasers, magnets, lightning, sporting goods Ceramics, communication systems, LED, lightning, frequency meters, fuels additive, jet engine turbines, televisions, microwave communica- tions, satellites, vehicle oxygen sensors energy storage, fuel cells, night vision instruments, rechargeable batter- storage, fuel cells, night vision instruments, rechargeable energy ies Colour glass, fibre optic data transmission, lasers Microwave equipment, colour glass X-ray phosphors Catalysts, positron emission tomography (PET) detectors Anti-lock brakes, air bags, anti-glare glass, cell phones, computers, electric vehicles, lasers, MRI machines, magnets, wind turbines Electric vehicles, home electronics, lasers, permanent magnets, wind turbines Aircraft engine alloy, airport signal lenses, catalyst, ceramics, colour- Aircraft engine alloy, ing pigment, electric vehicles, fibre optic cables, lighter flint, magnets, wind turbines, photographic filters, welder's glasses electric vehicles, flight control surfaces, missile and radar systems, optical glass, permanent magnets, precision guided munitions, stealth wind turbines technology, LCD, Plasma), tag complex for the medical field microwave applications, MRI machines, power plant radiation leaks detector optic data recording, permanent magnets, wind turbines additive, polishing agent, pollution-control systems 5.92 1.57 0.16 0.237 Compact fluorescent lamps, catalyst in petroleum refining, television, 0.161 Improving stainless steel properties, stress gages 0.457 0.246 0.148 Aircraft electric systems, electronic counter measure equipment, 0.199 magneto-topic recording technology, Computer data technology, 0.613 Catalytic converters, catalyst in petroleum refining, glass, diesel fuel 0.0546 0.0247 0.0246 0.0928 0.0563 Compact fluorescent lamps, lasers, LED, television screens (CRT, 0.0361 Compact fluorescent lamps, electric vehicles, fuel cells, televisions, (ppm) abundance C1 Chondrite 1 4 14 63 7.1 4.7 0.7 1.96 (ppm) abundance Upper crust Upper Effec- 1.12 (3+) 0.97 (4+) tive ionic 1.300 (2+), 1.196 (3+), radius (Å) radius (3+) 1.072 (3+) (3+) 0.83 (3+) 1.052 (3+) (3+) 1.042 (3+) 0.3 1.032 (3+) 0.31 (3+) 1.062 (3+) 2.3 (3+) 1.216 (3+) 31 (3+), 0 1 11 10 12 13 14 (ionic) [Ar] (3+) 0.87 (3+) [Kr] (3+) 1.075 (3+) 21 Electron Electron [Xe] 4f [Xe] 4f 2 (3+) 1.179 (3+) [Xe] 4f 3 (3+) 1.163 (3+)[Xe] 4f 4 (3+) [Xe] 4f 5 (3+) 27 1.132 (3+) [Xe] 4f 6 (3+) [Xe] 4f 7 (3+) 1.107 (3+) [Xe] 4f 9 (3+) 1.083 (3+) 3.9 [Xe] 4f 8 (3+) 1.095 (3+) [Xe] 4f 0 (4+) [Xe] 4f [Xe] 4f 7 (2+), [Xe] 4f [Xe] 4f [Xe] 4f [Xe] 4f [Xe] 4f configuration 1 1 1 1 3 4 5 6 7 11 10 13 12 14 5d1 5d 1 14 5d 4f 3d 4d 4f 4f 2 2 2 2 2 2 4f 4f 2 2 (atomic) Electron Electron [Xe] 6s 2 4f [Xe] 6s 2 4f [Xe] 6s 2 4f [Xe] 6s 2 4f 9 [Kr] 5s [Xe] 6s [Xe] 6s [Xe] 6s [Xe] 6s 2 4f [Xe] 6s [Xe] 6s 2 4f [Xe] 6s [Xe] 6s 2 4f 7 5d1 configuration 88.91 44.96 [Ar] 4s 162.5 168.93 173.04 164.93 144.24 157.25 167.26 140.91 [Xe] 6s 2 4f weight Atomic 39 57 138.91 21 58 140.12 62 150.36 63 151.96 65 158.93 59 Y Er 68 Ce Tb List of the REE, some properties and their applications. Table compiled from Shannon (1976), McDonough and Sun (1995), Rudnick and Gao (2003), Gupta and Krishnamurthyand Gupta (2003), Gao and Rudnick (1995), Sun and McDonough (1976), Shannon from compiled Table applications. their and properties some REE, the of List Element Symbol Z Samarium Sm Yttrium Lanthanum La Scandium Sc Cerium Thulium Tm 69 Erbium Ytterbium Yb 70 Lutetium Lu 71 174.97 [Xe] 6s Promethium Pm 61 144.91 [Xe] 6s 2 4f Holmium Ho 67 Neodymium Nd 60 EuropiumGadolinium Eu GdTerbium 64 Dysprosium Dy 66 Praseodymium Pr (2005), and Navarro and Zhao (2014). Zhao and Navarro and (2005), Table 1. Table
13 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A size, which is termed the lanthanide contraction tion (Table 1). The trivalent ions, excluding Ce3+ (Gupta and Krishnamurthy, 2005; Wall, 2014). and Yb3+, display very sharp absorption-emission The magnitude of this effect becomes stronger bands in the ultraviolet and visible light spectrum for the heavy rare earth elements (HREE), thus resulting from f-f-electron transitions (Gupta and approaching similar atomic and ionic sizes as Y. Krishnamurthy, 2005). This has been utilised in This readily explains the common association several applications, for example, in colouring of Y with the HREE, and why Y usually is or decolouring glass or ceramics. More technical placed between Dy and Ho in normalised REE applications include the REE as doping agents distribution patterns. or activators in crystals (for example Nd-doped The 4f-electrons also govern the magnetic Yl-Al-garnet, Nd:YAG) so they can be used as behaviour of the REE. Excluding REE lacking solid-state lasers. These are widely used for cut- these electrons (Sc, Y, and La) and those that ting procedures in medical applications, or cut- have filled 4f-shells (Yb and Lu), the REE are ting, welding and marking metals, or as the laser strongly paramagnetic and becomes antiferro- source in laser-ablation techniques. The REE are magnetic or ferromagnetic at lower temperatures. also commonly used as phosphors, i.e., materi- Gadolinium(III) exhibits the highest magnetic als that exhibit luminescence, for video display moment because it can have 7 unpaired electrons screens (CRT, plasma, LCD), fluorescent lights in the f-shell, and is therefore used in magnetic and LED, amongst others. resonance imaging (MRI) techniques. Samari- The REE are classified as critical metals um in alloys with cobalt (SmCo5) create strong (particularly Nd, Eu, Dy, Tb, and Y) for mod- magnets with high coercivity (a measure of a ern-day industrial and green-energy applications material’s resistance to becoming demagnetised). (Goodenough et al., 2016; Paulick and Mach-
However, Nd in alloy with Fe and B (Nd2Fe14B) acek, 2017, and references therein). The global create even stronger magnets. Because of Nd production of REE doubled from 1994 (65000 being the 3rd most abundant REE and Fe being t) to 2010 (130000 t), while today’s numbers are readily available (compared to Co), these strong around 120000 t (Weng et al., 2015; Paulick and Nd-magnets are now widely used in a variety of Machacek, 2017). China has been the dominat- applications, such as in electric motors for the ing supplier following the loss of other actors electric car industry and in generators in wind from the market in the late 1990s (e.g., USA turbines, or in applications requiring small but and Australia amongst others), and today, at least strong magnets such as in hard drives and smart- 85% of the REE are supplied by China, mainly phone speakers (Table 1; Gupta and Krishnamur- from the giant Bayan Obo deposit. Following thy, 2005). Dysprosium is also used as a key dop- the global REE price peak in 2011 as a result ant in the Nd magnets to increase the coercivity of export restrictions from China and domestic and the high-temperature performance. ambitions, the price of REE has dropped back The REE mostly occur in nature in a trivalent to levels prior to the boom, and other producers state but can also occur as divalent or tetravalent than China have again entered the market, like ions because of the strive to attain empty, half- USA (Mountain Pass), Australia (Mt. Weld) and filled or filled f-shell configurations. For instance, Russia (Lovozero). From the exploration boom, Ce may occur as (IV) because it can obtain an the defined REE mineral resources outside of empty f-shell, whereas Eu commonly occurs as China more than doubled from 40 Mt (2011) to (II) as it can attain a half-filled f-shell configura- 98 Mt (2016; Paulick and Machacek, 2017). The
14 global total rare earth oxide (TREO) resources 2012; Massari and Ruberti, 2013), because of are estimated to about 165 Mt, which would the expanding use of REE in current and future be enough to cover hundreds of years of the de- technologies (Wall, 2014). There are also few mand of REE at present yearly consumption rates substitutes for some of the REE (Wall, 2014). (120000 t; Paulick and Machacek, 2017). How- The vulnerability of China being the major actor ever, the demand for the most critical REE is in the market is a strong incentive to study how estimated to increase at a rate of approximately the REE behave in geological systems. 5-10% per year, albeit with some caveats (Hatch,
R O S A
S H N C F M T C P F M S S Rare earth elements C N C R Ce C G N Nd Gd P Sc C N Y S La Er H T A Sm Dy G C Pr Yb T M S Eu T C TbHo Ag I Tm Lu S I H Ru T Pd Au Rh R Pt Os R Ir A A Fig. 1. Crustal abundance of chemical elements as a function of atomic number. Modified from Haxel et al. (2002).
1.2 Hydrothermal REE deposits than those with odd atomic numbers because of The REE are lithophile elements, i.e., they are the Oddo Harkins effect (North, 2008). enriched in the crust (Castor and Hendrick, The REE are typically disseminated in the 2006). The REE have a similar crustal abundance Earth’s crust and rarely enriched in high concen- as Cu and Zn down to that of Bi and are more trations. When they do occur in higher concentra- abundant than the precious metals Au and Pt (Fig. tions, they make up a REE mineralisation. If the 1; Table 1). Light rare earth elements (LREE; REE concentrations are high enough so that REE from La to Sm) are more abundant than the heavy extraction is economically feasible, they consti- rare earth elements (HREE; from Eu to Lu). REE tute a REE deposit. The enrichment of REE to with even atomic numbers are more abundant form REE deposits can occur through primary
15 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A processes such as from magmatism or hydrother- thermal deposits (Kutessey II, Kyrgyzstan; Djen- mal (re-)mobilisation, or by secondary processes churaeva et al., 2008), in IOCG deposits (e.g., such as weathering and by gravity separation dur- Lala, China; Chen and Zhou, 2015), and in vein- ing sedimentary processes. Hydrothermal REE type REE-Th deposits in USA (Diamond Creek deposits are those that have formed dominantly and Lemhi Pass; Long et al., 2010). In many of by hydrothermal processes; i.e., REE-minerals these deposits, monazite-(Ce) or monazite-(Nd) precipitated from hot aqueous solutions (hydro- is the dominating REE-phosphate. Importantly, thermal fluids). Most of the hydrothermal REE a rather newly recognised group with xenotime- deposits form in association with magmatism (Y) as the principal mineral is unconformity- of different chemical affinity, from alkaline to related REE deposits, which show a similar peralkaline granites and syenites (e.g., Strange geological environment and formation condi- Lake, Canada; Gysi and Williams-Jones, 2013; tions as unconformity-related uranium deposits Vasyukova et al.; 2016), to carbonatites (e.g., (e.g., Maw Zone in the Athabasca Basin, Can- Lofdal, Namibia; Wall et al., 2008; Bodeving ada; Rabiei et al., 2017; Wolverine, Killi Killi et al., 2017), to peralkaline agpaitic rocks (e.g., Hills and John Gault deposits, Australia; Vallini Nechalacho, Canada; Möller and Williams- et al., 2007; Richter et al., 2018; Nazari-Deh- Jones, 2016, 2017), and seldom with subalkaline kordi et al., 2018). granitic or granitoid rocks (e.g., Kutessay II, Kyr- gyzstan, Djenchuraeva et al., 2008). Iron-oxide 1.3 Hydrothermal transport copper-gold (IOCG) deposits, although likely of REE and P associated with magmatism as well, are mostly Prerequisites for the formation of hydrothermal mined for Cu or Au but can sometimes contain REE deposits rich in the REE-phosphates are: 1) high concentrations of REE (e.g., Olympic Dam, significant transport of REE and P in hydrother- Australia; Schmandt et al., 2017). mal fluids, either together or in separate fluids and Excluding REE deposits associated with 2) efficient precipitation mechanisms to remove peralkaline systems, in which REE mostly are the REE, and in part, P, from the fluid(s). Trans- hosted in REE silicates or oxides (e.g., gado- port of REE in a fluid requires the formation of linite, fergusonite [(REE,Y)(Nb,Ti)O4] and alla- stable metal complexes with available ligands nite [(Ca,REE,Y)2(Al,Fe)3(SiO4)Si2O7)O(OH)]) (anion species) in the fluid at the specific con- and primary magmatic zircon- and titanosili- ditions of the hydrothermal system to keep the cates (e.g., eudialyte [Na15Ca6Fe3Zr3Si(Si25O73) REE in solution. A variety of ligands occur in - - 2- - 2- (O,OH,H2O)3(Cl,OH)2]), common REE-bear- natural systems, such as Cl , F , SO4 , OH , CO3 , 3- ing minerals in most hydrothermal systems are and PO4 . As a first approximation, based on the the REE-phosphates monazite [(LREE,Y)PO4] HSAB (Pearson’s hard/soft acid/base) principle, and xenotime [(Y,HREE)PO4], and the REE- REE are hard cations (high charge and small fluorocarbonates, chiefly bastnäsite [(REE,Y) ionic radius) and should form stable complexes - - 2- 2- CO3F]. The REE-phosphates can be the princi- with hard ligands such OH , F , CO3 , and SO4 pal REE-bearing minerals in deposits associated , and less stable complexes with the borderline with carbonatites (e.g., Ashram, Canada, Mitch- ligand Cl- (Williams-Jones and Migdisov, 2014). ell and Smith, 2017; Fen, Norway, Andersen, Indeed, experimental studies have demonstrated 1986; Marien et al., 2018; Lofdal, Namibia, that the dominant REE-F complexes are two to Williams-Jones et al., 2015), in granitic-hydro- three orders more stable than the dominant REE-
16 Cl complexes (Migdisov et al., 2009). However, trostatic attraction between charged ions). This the ability to form stable complexes is not the also means that Cl- forms stable ion-pars with only important factor in controlling the transport Na+ and K+, cations common in hydrothermal of REE. This depends strongly on the activity fluids, at elevated temperatures, thus decreasing or the concentration of the specific ligand in the the availability of Cl- ions. However, NaCl° and system, and if the specific ligand is bounded or KCl° complexes are relatively weak compared not to other aqueous species present in the fluid. to the REE complexes at higher temperatures, This is in turn strongly dependent on the solu- thus compensating for the reduced Cl activity bility of the REE mineral containing this spe- and promoting REE complexing with increasing cific ligand because the mineral will act as a temperature (Williams-Jones and Migdisov, 2014). buffer of the REE concentrations in the fluid. A The most common ligand in hydrothermal more insoluble REE-mineral can buffer the REE fluids is Cl-. Experimental studies have shown to rather low concentrations. The availabilities that the mono- and dichloride species, REECl2+ + of ligands also depend on pH and temperature. and REECl2 , are the dominating REE-Cl species Hydrochloric acid (HCl) is a strong acid and at up to 300 °C. The overall stabilities of the REE- temperatures up to 300-400 °C, HCl is largely Cl complexes increase with temperature and the dissociated and occurs as the free ions H+ and complexes with LREE are more stable than with Cl- at a pH higher than 2. At even higher tem- HREE, an effect that is accentuated at higher peratures, HCl can even be largely associated temperatures (Migdisov et al., 2009; 2016). at acidic conditions. However, hydrofluoric acid REE complexes involving F- were early be- (HF) is a weaker acid and depending on temper- lieved to be the major REE-transporting agent ature, only at near-neutral and alkaline pH does in hydrothermal fluids because REE form very HF occur as the free dissociated ions H+ and F- stable complexes with F compared to Cl. This (Migdisov and Williams-Jones, 2014). Thus, at was mainly based on early theoretical predic- near-neutral to alkaline conditions, more F ions tions, which showed an increased mobility of the are available to bind with the REE, but this also REE along the lanthanide series (increasing sta- coincides with a reduction of the solubility of the bilities of REE-F complexes; Wood, 1990; Haas REE-fluoride mineral and the REE concentration et al., 1995). This increase in stabilities of REE-F in the fluid drops. However, the involvement of complexes follows the HSAB principle because stable REE-OH complexes at higher pH may the data were extrapolated from ambient condi- oppose the buffering effect the REE-fluorides tions. Because F- is a hard ligand, and the REE have on the REE concentrations, and the fluid become increasingly harder along the lanthanide may retain high concentrations of REE even at series (ionic radius decreases), the stabilities of higher pH conditions. REE-F complexes should increase with increas-
The solvent, H2O, is also important because, ing atomic number, which is the case at ambi- with increasing temperature and decreasing pres- ent temperatures (Williams-Jones et al., 2012). sure, the degree of hydrogen bonding decreases However, at elevated temperatures, the decreased
(dielectrical constant decreases). This explains hydrogen-bonding ability of H2O enables elec- why metals occur dominantly as simple cations tron transfer and “softening” of ions. Thus, F- in solutions at ambient conditions whereas, at is much softer at elevated temperatures than at elevated temperatures, metals form complexes ambient conditions, which will result in that the because of strong ion-pairing (stronger elec- increase in REE-F complex stabilities along the
17 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A series should be weaker or even reversed. This rograde up to 300 °C (solubility decreases with also explains why HREE-Cl relative to LREE- increasing temperature; Poitrasson et al., 2004; Cl complexes are much weaker at elevated tem- Cetiner et al., 2005; Gysi et al., 2015; 2018). peratures than at ambient conditions (because However, another recent study suggests a pro- Cl- is much softer; Williams-Jones et al., 2012). grade solubility (increases with temperature) of Experimental studies show that the stabilities monazite from 300 °C up to 800 °C (Pourtier of the REE-F complexes mostly decrease along et al., 2010), which may indicate that REE-P the series at elevated temperatures (> 150 °C) complexing may be important at higher temper- and that they are overall less stable than predicted atures, or that phosphate is co-transported with theoretically, which conforms to the above theo- REE in the fluid and the REE are complexed ry of “softening” of ions (Migdisov et al., 2009; with other ligands. 2016). At ambient temperatures and up to 100 Other potential ligands in hydrothermal 2+ + 2- - 2- - °C, REEF and REEF2 are the dominant spe- fluids include SO4 , OH , CO3 , and HCO3 . The cies. Above 100 °C, REEF2+ is the only dominant REE-sulphate complexes are more stable than species, and its stability increases with tempera- REE-Cl complexes, but not as stable as REE-F ture (Migdisov et al., 2009). Experimental work complexes. The dominating species are REE- + 2- on Y shows that at low temperature (100 °C), SO4 and REE(SO4) , and experimental studies + 3+ 2+ YF2 dominates, whereas Y and YF are the show that they become increasingly stable at in- dominant species at low and high F activity at creasing temperatures (Migdisov and Williams- temperatures up to 250 °C (Loges et al., 2013). Jones, 2008). The hydroxyl group (OH-) forms Phosphorous in aqueous solutions mostly stable complexes with the REE at high pH con- ° ° occurs as phosphoric acid (H3PO4 ) and the ditions. The principal species are REE(OH)3 , - 2- 3- 2+ + dissociated acids H2PO4 , HPO4 or PO4 , or as REE(OH) , and REE(OH)2 . At elevated tem- polyphosphoric acids and their dissociated ions peratures (290 °C), all three species are impor- ° - 3+ (e.g., H4P2O7 and H3P2O7 ) depending on tem- tant, in addition to the simple hydrated REE perature, pH and activity of P (Pourtier et al., ion, which dominates at low pH. There is also 2010). The stabilities of phosphate complexes an increase in stability with temperature (Wood 2- with the REE have not been studied at hydro- et al., 2002). The carbonate (CO3 ) or bicarbon- - 2 - thermal conditions. Because H2PO4 , HPO4 - and ate (HCO3 ) ligands form stable complexes with 3- + 2+ PO4 are hard ligands, REE form stable com- the REE (REECO3 and REEHCO3 ) consistent 2+ + plexes (REEH2PO4 , REEHPO4 , REEPO4) with the HSAB principle. No experimental stud- with them at ambient temperatures (Haas et al., ies have been conducted up to this point, and the 1995; Williams-Jones and Migdisov, 2014). In data at hydrothermal conditions originates from - contrast to REE complexation with H2PO4 , com- the theoretical predictions (Wood, 1990; Haas et 2- 3- plexation of REE with HPO4 and PO4 should al., 1995). These show that the stabilities increase + also only occur at high pH conditions because with temperature and that the REECO3 species
H3PO4 is a weak acid. Thus, at low pH, only is overall the stronger complex. In organic-rich - strongly protonated forms of the ligands occur fluids, carboxylates such as acetate (CH3COO ) ° - - (H3PO4 and H2PO4 ). A limiting factor for sig- and propanoate (CH3CH2COO ) may be impor- nificant REE transport by phosphate complexing tant REE transporting ligands (Lecumberri-San- is the low solubilities of monazite and xenotime. chez et al., 2018). The solubilities of monazite and xenotime are ret-
18 formed by an accretionary-type orogeny at 1.92- 1.4 Objectives of the study 1.77 Ga. This unit is bordered in the west and The main objectives of this study were: south by the large, NNW-SSE trending plutonic 1) By using a multi-analytical approach, and subvolcanic TIB complex, which formed comprehensively characterise the hydrothermal along an active continental margin between 1.85 REE mineralisation in the Olserum-Djupedal and 1.65 Ga (Gorbatchev, 2004). district. This included detailed studies on the The Västervik Formation consists of meta- mineralogy, paragenetic evolution and mineral- supracrustal rocks, mainly quartzites, and meta- chemistry of the REE-bearing minerals and the arenites and minor meta-argillites and metavol- gangue minerals (Papers I, II, and III), charac- canic rocks, deposited between c. 1.88 and 1.85 terisation of the style of mineralisation and field Ga within an extensional tectonic regime (Gav- relationships (Paper II), and identification of the elin, 1984; Beunk and Page, 2001; Bergström source and evolution of the hydrothermal fluids et al., 2002; Sultan et al., 2005). Subsequently, (Papers II and III). magmatic rocks of various geochemical and tec- 2) Based on the findings from the papers, tonic affinity intruded the metasupracrustal unit. evaluate different sources of REE and P in These have traditionally been referred to as con- hydrothermal REE-phosphate deposits and sisting of an older, c. 1.85 Ga deformed augen discuss how REE and P are transported in gneiss and younger, c. 1.81-1.77 Ga granitoids fluids, and compare this to models of hydro- of the TIB-1 suite (Gavelin 1984; Kresten, 1986; thermal transport of REE (and P) based on Åhäll and Larsson, 2000; Andersson and Wik- experimental studies. Ultimately, the aim is to ström 2004). Nolte et al., (2011) and Kleinhanns define conditions that are imperative for the for- et al. (2015) recently proposed a new tectono- mation of hydrothermal deposits rich in REE- magmatic model for the Västervik region based phosphates. on new zircon U-Pb age data, and new petro- graphical and geochemical classification of the granitoids. According to this model, deposition of 2 Geological background the Västervik sediments first occurred in a back- arc environment between 1.88-1.85 Ga followed by ferroan magmatism at around 1.85 Ga. Dur- 2.1 Regional Geology ing 1.85-1.81 Ga, a compressional regime was The studied Olserum-Djupedal REE-phosphate prevalent featuring the intrusion of Cordilleran- mineralisation is located in the Olserum-Djupedal type (or magnesian) granitoids. These comprise district, which comprises three main mineralised most of the magmatic rocks in the region. This areas; Olserum, Bersummen, and Djupedal. stage was followed by an extensional or trans- The Olserum-Djupedal district is situated NW tensional regime with the intrusion of moderately of the city of Gamleby in the Västervik region, shallow, mostly peraluminous ferroan anatectic close to the border between the Palaeoprotero- granites at or slightly after 1.8 Ga. A series of zoic Västervik metasedimentary Formation and syn- and anticlines trending NW and SE com- the Transscandinavian Igneous Belt (TIB) and prise the main structural fabrics in the Västervik just south of the Svecofennian domain (Fig. Formation (Gavelin, 1984), and are presumably 2; Gavelin, 1984; Gaál and Gorbatchev, 1987, pre- to syn-kinematic with the emplacement of Gorbatchev, 2004). The Svecofennian domain the youngest anatectic granites (Westra et al.,
19 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
1969; Elbers, 1971). (palaeoplacers) containing uraninite and thucho- The Västervik region hosts a variety of Fe ± lite, 2) magnetite ore with U ± REE minerals; and U ± REE mineralisations (Uytenbogaardt, 1960; 3) U ± REE minerals in pegmatites and aplites. Welin, 1966a, 1966b; Hoeve, 1974, 1978), but is Previous interpretations of the three types of U ± mostly known for the occurrence of various types REE mineralisations include: 1) magmatic origin of Cu ± Mo ± Co ± Fe mineralisations, e.g., the (Uytenbogaardt, 1960); 2) palaeoplacer origin Gladhammar deposit (Tegengren, 1924; Uyten- remobilised during the intrusion of the younger bogaardt, 1960; Sundblad, 2003; Billström et al., anatectic granites (Welin, 1966a, 1966b); or 3) 2004). Three types of U ± REE mineralisations hydrothermal origin linked with Na ± Ca altera- have been recognised (Uytenbogaardt, 1960): 1) tion and formation of distinct quartz-plagioclase quartzite-hosted heavy mineral-rich palaeobeds rocks (Hoeve, 1974, 1978). 16°20’E 16°40’E
Djupedal
Olserum Bersummen LLDZ
Fig.2 57 °55’N
Loftahammar Gamleby 57 °50’N
Lake Vänern
Svecofennian Berg domain Lake Vättern
Sveconorwegian domain TIB
OJB Klockartorpet
TIB 57 °45’N Västervik
Phanerozoic cover rocks N Gränsö Malmö 100 km 0 2 4 km
TIB granitoids/syenitoids Metabasites Brittle faults Västervik Formation Na±Ca metasomatism Ductile shear zones
Fig. 2. Geological map of the Västervik region with black stars indicating the location of the exposed REE mineralised areas. Open stars represent locations of supplementary samples. The lower-left inset map portrays the regional geology of southern Sweden, redrawn from Andersen et al. (2009). LLDZ: Loftahammar-Linköping Deformation Zone (Beunk and Page, 2001); TIB: Transscandinavian Igneous Belt (Gorbatschev, 2004); OJB: Oskarshamn-Jönköping Belt (Mansfeld et al., 2005).
20 the rocks of the Västervik Formation. Similar 2.2 Geology of the Olserum- metasedimentary REE-bearing rocks are also ex- Djupedal district posed in the Bersummen area and as larger mig- Detailed geological mapping in the Olserum- matisised REE-bearing metasedimentary bodies Djupedal district prior to this study is lacking. farther NW in the Djupedal area. The metasedi- This section is thus based on field mapping con- mentary rocks are non-foliated to gneissic whose ducted during this study (Paper II). The domi- fabric is trending roughly NW to SE. Feldspar- nant rock type in the district is a ferroan, per- porphyritic TIB intrusions occupy the area to aluminous, calc-alkalic to alkali-calcic, alkali- the north of the Olserum-Djupedal REE min- feldspar TIB granite with an age about 1.8 Ga eralisation (Fig. 3). Characteristic white quartz- (Fig. 3). Metasedimentary REE-bearing rocks plagioclase rocks formed by Na ± Ca metasoma- (Olserum-Djupedal metasediments) are exposed tism, similar to those described by Hoeve (1974, in an ESE-WNW trending zone in the contact 1978), are widespread in an area north of the zone between the alkali-feldspar granite and Djupedal area (Fig. 3).
16°20’E 16°22’E 16°24’E 57 °59’N TIB intrusives, unspecified Lake Ryven TIB, porphyritic intrusives TIB, quartz monzonite Olserum-Djupedal granite Västervik Formation Olserum-Djupedal metasediments Metabasites Brittle faults Ductile shear zones Main localities with exposed REE mineralisation
Area affected by strong Old iron mines 57
Ca-Na metasomatism °58’N
Djupedal
Olserum Bersummen 57
Lake °57’N Bersummen
N 0 0.5 km Lake Storsjön
Fig. 3. A simplified geological map of the Olserum-Djupedal district. Modified after Paper II.
21 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
3 Analytical methods 3.3 Major and trace element mineral chemistry Major and trace element analysis on REE- 3.1 Sampling and field work bearing minerals and gangue minerals were Samples for the study (papers I, II and III) were performed by electron-probe micro-analysis all collected during 2015 and 2016. Samples (EPMA) and laser-ablation inductively cou- were both obtained from drill cores drilled by pled plasma spectrometry (LA-ICP-MS) anal- Tasman Metals Ltd. and stored at the archives ysis at the University of Helsinki. EPMA was of the Geological Survey of Sweden in Malå conducted on monazite-(Ce), xenotime-(Y), al- and from surface sampling during field mapping lanite-(Ce)–ferriallanite-(Ce), bastnäsite-(Ce) in 2015 and 2016. Sampling was targeted to and synchysite-(Ce) (Paper I), on biotite, mag- obtain a representative suite of samples of the netite, amphibole (gedrite and anthophyllite), REE mineralisations and the host rocks. Field tourmaline (schorl-dravite and uvite), musco- mapping was conducted to get an understanding vite and chlorite (Paper II), and on fluorapatite of the style and timing of the REE mineralisa- (Paper III). All measurements were performed tion in the Olserum-Djupedal district. Additional by wavelength-dispersive spectrometry on a sampling and field mapping from other occur- JEOL JXA-8600 Superprobe integrated with rences in the Västervik region (Klockartorpet, the SAMx hardware and XMAs/IDFix/Diss5 Gränsö, and Berg; Fig. 2) were conducted for analytical and imaging software package on regional comparison. carbon-coated thin or thick sections. For the REE-bearing minerals, X-Ray lines 3.2 Petrographical and were selected to minimise the interference textural analysis between the different REE following the Petrographical and textural analysis were con- guidelines of Pyle et al. (2002). Beam current ducted using a standard petrographical micro- and accelerating voltage used were optimised scope. More detailed textural analysis and pre- and set to 25 nA and 20 kV, respectively. Anal- liminary identification of minerals were- per yses were performed with a defocused beam of formed during the electron microprobe sessions ~7 μm diameter for monazite-(Ce) and xenotime- using back-scattered electron (BSE) imaging and (Y), and a focused beam for allanite-(Ce)–fer- energy-dispersive spectrometry analysis. This riallanite-(Ce), bastnäsite-(Ce) and synchysite- was performed on a JEOL JXA-8600 Super- (Ce). For biotite, magnetite, amphibole, tourma- probe at the University of Helsinki. line, muscovite and chlorite, all analyses were A CITL CL8200 Mk5-2 cold-cathode cath- performed using a beam current of 15 nA, odoluminescence system coupled to a Leica an accelerating voltage of 15 kV and a fo- DM2700 polarisation microscope and equipped cused beam. For fluorapatite, the settings were with a Peltier-cooled Leica DFC450C high- optimised to minimise the F and Cl diffusion in resolution digital camera at the University apatite due to electron beam exposure (Stormer of Helsinki was used for cathodoluminescence et al., 1993; Stock et al., 2015). Final conditions (CL) imaging of feldspars (Paper II) and apatite used were a defocused beam of ~15 μm, a beam (Paper III). The beam current and voltage used current of 15 nA, and an accelerating voltage of were 0.25 mA and 7.0 kV, respectively. 15 kV. Complete analytical details (X-Ray lines,
22 standards, counting times, and analyser crystals) can be found in Papers (I), (II) and (III), and their 3.4 Stable Cl isotope and halogen respective supplementary information. analysis of fluorapatite LA-ICP-MS trace element analysis was per- The in situ stable Cl isotopic and halogen (F, formed with a Coherent GeoLas MV 193 nm Cl, Br, and I) compositions of fluorapatite from laser-ablation system coupled to an Agilent the Olserum-Djupedal REE mineralisation were 7900s ICP mass spectrometer. Trace element acquired by secondary ion mass spectroscopy concentrations were measured in monazite- (SIMS). These analyses were performed at the (Ce), xenotime-(Y), allanite-(Ce)–ferriallanite- NORDSIM facility in Stockholm using a Cam- (Ce) and bastnäsite-(Ce) (Paper I), in biotite and eca IMS1280 large geometry SIMS instrument. magnetite (Paper II), and in fluorapatite (Paper To avoid beam exposure to fluorapatite prior to III). Flow rates were set to 15 L/min for Ar plas- analysis, the SIMS analyses were conducted on ma gas, 1.0 L/min for He carrier gas, and 0.85 L/ new epoxy mounts prepared from the same sam- min for Ar auxiliary gas for during all sessions. ple cut-offs as those used for the thin or thick Replicate measurements of the reference mate- sections, which were used during initial BSE im- rials NIST SRM 610 and USGS GSE-1G were aging. These mounts were then gold-coated and conducted to bracket the sample analyses and to pre-selected spots were measured with SIMS, correct for instrumental drift. NIST SRM 610 one spot for the halogens and one for the Cl iso- was selected as an external standard for mon- topes as close to each other as possible. EPMA azite-(Ce), xenotime-(Y), bastnäsite-(Ce) and and LA-ICP-MS analysis were subsequently fluorapatite, whereas the GSE-1G standard was performed on a spot adjacent to the SIMS spots. selected for biotite, magnetite, and allanite-(Ce)– The halogen and the Cl isotopic composi- ferriallanite-(Ce). For quantification of element tions were measured with a critically focused concentrations, 27Al (biotite and allanite-(Ce)– 133Cs+ beam yielding a current of 1.2-1.6 nA for ferriallanite-(Ce)), 43Ca (fluorapatite),57 Fe (mag- the halogen routine and 1.25-1.55 nA for the Cl netite), 89Y (xenotime-(Y)) and 140Ce (monazite- isotopic routine. The mass resolving power was (Ce) and bastnäsite-(Ce)) were selected as in- set to ~4000 M/ΔM for the halogens and ~2500 ternal standards. Data treatment and quantifica- M/ΔM for the Cl isotopic routine. A field aper- tion of LA-ICP-MS signals were done with the ture of 3000 μm was used for both analytical SILLS software package (Guillong et al., 2008). routines to minimise surface contamination. The Energy density, repetition rate and the spots were also pre-sputtered for 90 s prior to number of pulses of the laser were optimised analysis in a 20 by 20 μm area to reduce surface for the individual minerals. The accuracy of contamination. For the halogens, secondary ion the LA-ICP-MS system has been verified and intensities were collected over five scans with a monitored by daily measurements of the refer- total integration time of 120 s on Faraday cup ence material NIST SRM 612 as an unknown. (for species with counts > 106 cps) or electron The long-term accuracy for most elements is multiplier (for species with counts < 106 cps). within 5% of the reference material (Spandler Because of the interference of CaCl species et al., 2011). Complete analytical details (laser on 79Br and 81Br, Br was measured on the com- settings, spot sizes, isotopes measured, dwell bined [81Br + 44Ca37Cl + 46Ca35Cl]- mass peak. times) can be found in Papers (I), (II) and (III). The peaks were normalised to the 40Ca31P matrix signal and the standard Durango apatite was used
23 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A to determine absolute concentrations. Measure- ing runs is c. 5 °C. ments of the Durango standard (n = 25) yielded For L-V inclusion, salinity was calculated a relative standard deviation of 1% for F, 1.2% from the final ice melting temperature assum- for Cl, 11.4% for Br, and 1.5% for I. For the Cl ing NaCl-H2O compositions using the equation isotopic analysis, 35Cl and 37Cl were collected of Bodnar (1993). For L-V-S inclusions, three simultaneously using multicollection mode on different types were recognised based on appear- Faraday cup with an overall counting time of ance at room temperature, behaviour during 160 s, conducted over four blocks of ten integra- microthermometry and compositions determined tions. Measurements of the Durango apatite stan- by LA-ICP-MS. Different approaches were used dard with a known isotopic composition (δ37Cl to estimate the salinities of these fluid inclusions = +0.5‰) were regularly interspersed between depending on the type. For L-V-S inclusions the unknowns to correct for instrumental drift approximated by the NaCl-FeCl2-KCl-CaCl2- and matrix-dependent instrumental fractionation. H2O system (Na-Fe-K-Ca brines; Table A1), an The Cl isotopic compositions are expressed us- estimated total salinity of 45 wt% for all fluid in- ing the δ-notation defined as: clusions assemblages (FIA) was used based on an average temperature of halite melting of 300 °C. δ37Cl (‰) = {[(37Cl/35Cl) - (37Cl/35Cl) ] / sample SMOC L-V-S inclusions in the CaCl2-NaCl-H2O system (37Cl/35Cl) } ∙ 1000 SMOC (Ca-Na brines) did not freeze during cooling, and melting of ice, hydrohalite or antarcticite could where SMOC is the Standard Mean Ocean Chlo- not be observed. Salinity and bulk composition ride with a defined value of 0.0‰ (Kaufmann et were thus estimated by combining the measured al., 1984). The reproducibility of δ37Cl was 0.09 mass Na/(Na+Ca) ratio by fluid inclusion LA- to 0.20‰ based on multiple measurements (n = ICP-MS analysis and the temperature of halite 50) of the Durango apatite standard during three melting (final melting temperature; Steele-Ma- analytical sessions. cInnis et al., 2011). Halite melting temperatures were initially measured for many of the FIA’s 3.5 Fluid inclusion microthermo- after LA-ICP-MS analysis to avoid the risk of metry and LA-ICP-MS analysis decrepitation of fluid inclusions during heating Fluid inclusions were studied on double-polished prior to LA-ICP-MS analysis (marked with * in thick sections of quartz (200 to 500 μm thick- Table A1). However, because of the low halite ness). Microthermometry was performed on a melting temperatures of these inclusions (< 200 Linkam THMSG-600 heating-freezing stage °C), halite melting temperatures could be mea- mounted on a Leica DM2500P petrographic sured prior to LA-ICP-MS analysis for the FIA’s microscope. Daily calibration was made using targeted during the second session of LA-ICP- synthetic H2O, H2O-NaCl and H2O-CO2 fluid in- MS analysis. An average Na/(Na+Ca) ratio (of clusion standards (SynFlinc™). Calibration was 0.125) was used for the FIA’s not analysed by performed against the H2O-CO2 Q3 quadruple LA-ICP-MS. For one FIA (sample EJ-14-2B, point (–56.6 °C), the H2O-NaCl eutectic (–21.2 FIA17), melting of antarcticite was observed. °C), and the melting of ice (0.0 °C). Heating runs The salinity and bulk composition could thus were calibrated against the critical temperature be calculated using melting temperatures of ant- of H2O (374.1 °C). Estimated reproducibility for arcticite and halite, which yield a similar Na/ freezing experiments is 0.3 °C and that for heat- (Na+Ca) ratio and salinity as those calculated
24 using this ratio determined by LA-ICP-MS anal- with the major element signals. Host correction ysis and halite melting temperatures. For L-V-S was made assuming 100% SiO2 and by closely inclusions in the NaCl-CaCl2-(KCl)-H2O system bracketing the fluid inclusions signals. Fluid in- (Na-Ca brines), salinity and bulk composition clusion LA-ICP-MS data are presented as FIA were calculated using the ice and halite melting averages (Table A2). temperature employing the graphical method of Vanko et al. (1988). Fluid inclusion LA-ICP-MS was performed 4 Summary of original papers using an Agilent 7900s quadrupole ICPMS cou- pled to a Coherent Geolas Pro MV 193 nm excimer laser-ablation system at the University 4.1 Paper I. Mineralogy, para- of Helsinki. A 1 cm3 ablation cell was used for genesis, and mineral chemistry fast washout to ensure high element sensitivities of REEs in the Olserum- Djupedal REE-phosphate and low limits of detections. The analytical proto- mineralization, SE Sweden col and settings used followed that of Fusswinkel et al. (2017, 2018). Elements measured were 7Li, This study established the mineralogical, tex- 11B, 23Na, 24Mg, 27Al, 39K, 44Ca, 49Ti, 55Mn, 56Fe tural and mineral-chemical framework for a or 57Fe, 66Zn, 85Rb, 88Sr, 133Cs, 137Ba, 208Pb, 89Y, relatively unusual hydrothermal REE miner- 140Ce, 146Nd, 35Cl, 81Br, and 127I. Data treatment alisation in the Olserum-Djupedal district in was performed with the SILLS software package SE Sweden. By combining mineralogical and (Guillong et al., 2008). Elements were quantified petrological studies with mineral chemistry of using the reference material NIST SRM 611 as the REE mineral phases, we could show that an external standard, except for Cl, Br, and I. The abundant xenotime-(Y) and monazite-(Ce) co- halogens were standardised to the natural scapo- crystallised with fluorapatite and subordinate lite standard Sca-17 (Seo et al., 2011; Fusswinkel (Y,REE,U,Fe)-(Nb,Ta)-oxides during an initial et al., 2018). Concentrations were calculated us- high-temperature stage (~600-650 °C). These ing Na concentrations (as NaCl equivalent) de- mainly formed within veins dominated by biotite, termined from microthermometry as an internal magnetite, amphibole, and quartz. Further, fol- standard. A mass balance routine implemented in lowing the evolution of the hydrothermal fluid, the SILLS software using cation/chlorine ratios allanite-(Ce) formed locally. Subsequent cool- from the LA-ICP-MS signals was used to deter- ing of the hydrothermal system induced altera- mine the bulk fluid composition. Cations used for tion and replacement of primary xenotime-(Y), mass balancing were Na, Ca, K, or Fe depend- monazite-(Ce), fluorapatite and (Y,REE,U,Fe)- ing on the fluid inclusion type. The intervals for (Nb,Ta)-oxides, which resulted in the remobili- the fluid inclusions were selected based on the sation of REE, Th, U and Nb-Ta, and the forma- peaks of the major components in the fluid in- tion of secondary monazite-(Ce), xenotime-(Y), clusions (Ca, Na, and Cl) and the return of these fluorapatite and allanite-(Ce)–ferriallanite-(Ce) signals to the background level. The signals of and subordinate uraninite, thorite, columbite- all remaining elements were carefully checked (Fe) and (Th,U,Y,Ca)-silicates. Monazite- for each of the fluid inclusions. Calculated ele- xenotime thermometry showed that these ment concentrations for the remaining elements alteration processes occurred down to temper- were rejected if the signals were not synchronous atures of about ~400 °C. Bastnäsite-(Ce) and
25 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A minor synchysite-(Ce) formed from lower-tem- present in the outermost parts of the pluton. The perature (<400 °C) alteration of allanite-(Ce) and veins and vein zones are frequently transected by allanite-(Ce)–ferriallanite-(Ce) and represented abundant pegmatitic to granitic dykes in Olserum the latest stage of REE mineral formation. The and Bersummen areas. In the Djupedal area, mineralogy and alteration processes between the extensive post-mineralisation migmatisation two main mineralisation areas, i.e., Olserum and formed within the REE-mineralised metasedi- Djupedal areas, were found to differ from each mentary rocks. Collectively, the field evidence other slightly. This was interpreted to result from led us to suggest a close association of the REE the increase in the Ca concentration of the fluid mineralisation with the granite. in the Djupedal area. This caused the forma- The major and trace element chemistry of tion of allanite-(Ce) and extensive replacement co-existing biotite and magnetite revealed that of primary monazite-(Ce). This contrasts with the all the mineralised areas belong to the same REE assemblages in the Olserum area, where no REE-mineralising system. High concentrations allanite-(Ce) formed and monazite-(Ce) only of Na in biotite and amphibole and the abun- exhibited moderate replacement to secondary dance of biotite indicated a Na-K-rich character fluorapatite. The primary hydrothermal REE- of the original REE-mineralising fluid forming bearing assemblages and alteration processes the REE-phosphates. As shown by the presence in the Olserum-Djupedal mineralisation dem- of Ca-rich minerals such as allanite-(Ce) and cal- onstrate the joint mobility of REE, Th, U, and cic tourmaline (uvite) in the Djupedal area, the Nb-Ta in F-bearing high-temperature fluids. fluid evolved to more Na-Ca-rich compositions during cooling of the hydrothermal system. At 4.2 Paper II. Origin of the high- this stage, alteration of the granite and the wall temperature Olserum-Djupedal rocks induced by the Ca-Na nature of the flu- REE-phosphate mineralisation, ids produced distinct white quartz-plagioclase SE Sweden: A unique contact metamorphic-hydrothermal system rocks. Halogen fugacities as calculated from bio- tite compositions showed that the primary REE- This study combined field and petrographic mineralising fluid was Cl-dominant, but with a relationships with major and trace element chem- high F component. The calculated log(fHF/fHCl) istry of the main gangue minerals to constrain values decrease in a sequence from granite- and the timing and origin of the Olserum-Djupedal metasediment-hosted biotite in the Olserum area
REE mineralisation. Field relationships revealed (log(fHF/fHCl) of –1.0 to –1.2) to metasediment- that REE mineralisation is exposed at three main hosted biotite in the Bersummen (log(fHF/fHCl) of areas; Olserum, Bersummen and Djupedal, and –1.5 to –1.8) and Djupedal areas (log(fHF/fHCl) of dominantly occurs as ESE-WNW to SE-NW –1.6 to –2.0). trending veins and vein zones in metasedimen- The combined evidence led us to propose tary rocks in or close to the contact aureole of a hydrothermal origin of the REE mineralisa- a ferroan, peraluminous alkali-feldspar granitic tion, formed by granitic-derived REE-P-Cl-F- pluton. The veins and vein zones host abundant enriched fluids expelled at an early stage of the monazite-(Ce), xenotime-(Y) and fluorapatite, magmatic evolution. Following this, an older which are variably fractured and recrystallised. model involving the assimilation and remobili- REE-bearing veins were also found to be sation of former heavy mineral-rich beds was hosted within a granite to granitic gneiss discarded. The primary REE mineralisation and
26 alteration processes in the Olserum-Djupedal try of the evolving ore-forming fluid. Later low- district were probably coeval with regional-scale temperature remobilisation was found to only K-Na and Na-Ca metasomatism closely associ- cause marginal changes in halogen and trace el- ated with granitic magmatism at around 1.8 Ga ement concentrations in specific domains of the in the Västervik region. fluorapatite crystals (rims, recrystallised grains, and domains adjacent to fractures), whereas δ37Cl 4.3. Paper III. Apatite as a tracer values remained unchanged. This suggests that of the source, chemistry, and apatite can retain its initial composition inherit- evolution of ore-forming fluids: ed by the original ore-forming fluid despite later the case of the Olserum-Djupedal REE mineralisation, SE Sweden. overprinting fluid events. As apatite was found to be sensitive to This study explored the suitability of using changing fluid compositions, apatite showing apatite as a tracer of the source, chemistry, the chemically least evolved character needed and evolution of ore-forming fluids using the to be recognised in order to trace the origin of halogen (F, Cl, Br, and I), stable Cl isotopic and the primary ore-forming fluid. In the Olserum- trace element compositions of fluorapatite from Djupedal REE mineralisation, this corresponds the Olserum-Djupedal REE mineralisation in to the granite-hosted primary fluorapatite. This SE Sweden. Based on the textural relations and fluorapatite has δ37Cl values (–0.4 to +1.6 ‰) mineral-chemical compositions, four main fluid and molar halogen ratios (Br/Cl of 0.45 to 0.80 events were recognised; 1) deposit-scale zoning · 10-3 and I/Cl of 190 to 310 · 10-6) comparable of primary fluorapatite representing the prima- to fluids associated with S-type granites in SE ry hydrothermal fluid flow, 2) high-temperature England (δ37Cl of +1.7 to +2.0 ‰, Br/Cl of 0.45 dissolution-reprecipitation processes following to 0.9 · 10-3 and I/Cl of 50 to 110 · 10-6), which primary fluorapatite formation, 3) internal zon- have a similar petrogenesis as the Olserum- ing of primary fluorapatite caused by lower- Djupedal granite. The small fractionation of temperature remobilisation, and 4) secondary flu- Br from I observed between altered fluorapatite orapatite replacing primary monazite-(Ce). The and Na-Ca and Ca-Na fluid inclusions analysed primary hydrothermal fluid flow was recognised by LA-ICP-MS suggested that Br and I do not as a down-temperature flow and was recorded in necessarily fractionate to the degree proposed a sequence from granite-hosted fluorapatite, via earlier and that Br and I may even have com- Br metasediment-hosted fluorapatite in the Olserum parable partition coefficients (D apatite-fluid and I area to metasediment-hosted fluorapatite in the D apatite-fluid). This led us to interpret the halogen Bersummen and Djupedal areas. This sequence signatures and the stable Cl isotopic composition recorded a gradual increase in Cl (~800 to 5000 of the granite-hosted fluorapatite to represent an ppm) and Br (~1 to 20 ppm) concentrations, and original magmatic fluid. a decrease of F (~3.75 to 2.9 wt%) and I (~0.75 No trace element in primary fluorapatite to 0.45 ppm) concentrations and in δ37Cl values adhered to the trend defined by the deposit-
(+1.0 to –0.5 ‰). Calculated log(fHF/fHCl) values scale zoning. This suggested that trace element of primary fluorapatite followed those of co- compositions of apatite are mostly influenced existing biotite for the defined sequence, indi- by host rock environment and co-crystallisation cating that the incorporation of the halogens into with other minerals. However, the characteris- apatite are dominantly governed by the chemis- tically elevated Fe concentrations of primary
27 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
fluorapatite may suggest elevated FeCl2 of the forming stage have been identified. In paper II ore-forming fluid. Moreover, the REE and par- and III, biotite and fluorapatite have been used ticularly normalised ratios (La/Sm, La/Yb, Gd/ as proxies for the ore-forming fluid. Halogen Yb, and Y/Ho) were found to trace the evolution compositions of biotite and fluorapatite indi- of the primary ore-forming fluid and can also cate that the REE-mineralising fluid was at first discriminate between apatite forming by min- dominantly Cl-bearing but with a relatively high eral replacement from apatite forming from the F concentration. Subsequent crystallising of primary ore-forming fluid. In conclusion, apatite fluorapatite and biotite depleted the fluid in was found to be suitable in tracing the source, F, passively enriching the fluid in Cl. The chemistry, and evolution of ore-forming fluids. relatively high F concentration in the fluid aided with the transport of high field strength elements (HFSE) such as Nb-Ta and Th that accompanied 5 Discussion the REE in the primary REE-mineralising fluid (e.g., Keppler and Wyllie, 1990, 1991; Jiang et al., 2005; Timofeev et al., 2015, 2017). 5.1 Textural, mineralogical and The mineral paragenesis and major and trace fluid-chemical evolution of the element chemistry of the main gangue miner- hydrothermal Olserum-Djupedal als suggest a Na-K-Fe-Ca dominated composi- REE-phosphate mineralisation tion of the primary ore-forming fluid. Initially, This section aims to bring together the early four- the fluid probably possessed a high K/Na ratio stage paragenesis model (Paper I) with new find- because of the abundance of biotite precipitated ings from subsequent papers and from fluid in- from this fluid. The Ca concentration must have clusion data into a new integrated model (Fig. 4). been relatively high too to precipitate fluorapa- During stage A, primary mineralisation started tite but low enough to promote the formation at high temperatures (550-650 °C) with the for- of REE-phosphates from the available P in the mation of coeval fluorapatite, monazite-(Ce) and fluid instead of only fluorapatite. In addition, the xenotime-(Y) with subordinate (Y,REE,U,Fe)- Ca and F concentrations were sufficiently low (Nb,Ta)-oxides. These formed in veins and vein to inhibit fluorite saturation. L-V-S fluid inclu- zones dominated by biotite-magnetite from fluids sions identified in quartz from pegmatitic dykes exsolved from the Olserum-Djupedal granite cross-cutting the REE ore in the Olserum area early during crystallisation and fractionation. exhibit Na-Fe-K-Ca compositions (Table A2). The veins and vein systems developed primarily Although these inclusions likely represent a more in metasedimentary rocks in the contact aureole evolved and trapped fluid, as indicated by low of the granite and within the outermost zone of homogenisation temperatures and by the occur- the granite. Primary mineralisation took place rence in cross-cutting pegmatite dykes, they are at c. 1.8 Ga, coeval with the crystallisation of likely close in composition to the original REE- Olserum-Djupedal granite. Fluid flow was pre- mineralising fluid. sumably from the granite towards the metased- Incipient dissolution and re-precipitation of imentary rocks, with the mineralisations in the fluorapatite forming monazite-(Ce) and xeno- Bersummen and Djupedal areas forming in a time-(Y) inclusions took place when the hydro- more distal position. thermal system was still at high temperatures, No fluid inclusions from the primary ore- comparable to those forming the primary min-
28 Stage A: Primary phosphate F A stage, T 550-650 °C, 1.8 Ga Y M C G O Y REE F N T
N C C F C C C A C O F REE P H O C C
M D Stage : First modification stage, T ≤ 600 °C M C H D C C N C A
I C D Stage C: Alteration Y stage, T 400 500 °C D F C C N C P C H O O
S P C
A
D T D N C C C H O T S Stage D: REE-fluoro- carbonate stage T N T C T 300 °C, ≤ 1.75 Ga? A C Y C C F
C C N C C M C H O R C C S CO H O
Fig. 4. A modified schematic illustration showing the textural evolution of the REE-mineralising system in the Olserum- Djupedal REE mineralisation. Modified after Paper I. eralisation. The fracturing of primary minerals by extensive alteration, which caused remobili- during stage B aided in the modification of the sation of REE, Th, U, and Nb-Ta. Highly cal- primary ore assemblages by initiating remobili- cic fluids in the Djupedal area triggered the per- sation of REE and other elements. In the vasive and partial alteration of monazite-(Ce) Djupedal area, the fluid evolved to more forming secondary fluorapatite and allanite- calcic compositions, promoting the formation (Ce)–ferriallanite-(Ce). The calcic fluids also of allanite-(Ce) and calcic tourmaline (uvite). promoted the formation of accessory fluorite During subsequent cooling, the ore assem- and scheelite. In the Olserum and Bersummen blages were further modified during stage C areas, monazite-(Ce) only exhibits moderate re-
29 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A placement to secondary fluorapatite indicating clusions also contain a carbonate solid phase and a lower calcic component of the metasomatic rarely hematite. Halogen (Cl, Br, and I) measure- fluid. Monazite-(Ce) and xenotime-(Y) from all ments of the brine inclusions show that they are mineralised areas were heavily altered, resulting very rich in Br and I relative to seawater (Fig. 5). in the formation of uraninite, thorite and other The very high salinity and the high Br/Cl and I/ (Th,U,Y,Ca)-silicates. Local alteration of prima- Cl ratios are proposed to result from fluid desic- ry (Y,REE,U,Fe)-(Nb,Ta)-oxides led to the for- cation during the chloritisation of biotite, allanite- mation of columbite-(Fe), uraninite, xenotime- (Ce) or allanite-(Ce)–ferriallanite-(Ce) and, in
(Y) ± monazite-(Ce). Monazite-xenotime ther- part, magnetite, where chlorite sequestered H2O mometry showed that these alteration processes from the fluid. This also resulted in halite pre- occurred down to temperatures of about ~400 °C. cipitation, which can explain the increasing Br The clear difference in alteration assem- and I in the fluid as they are both incompatible blages between the Olserum and Bersummen in halite (Holser, 1979; Campbell et al., 1995; areas to that of the Djupedal area were caused Fusswinkel et al., 2018). Because bastnäsite-(Ce) by chemically distinct fluids. High-density L-V-S formed during the chloritisation of allanite-(Ce) fluid inclusions have been found in quartz from or allanite-(Ce)–ferriallanite-(Ce), it is likely that the Djupedal area (Ca-Na brines; Table A1 and the Ca-Na brine was related to this and trapped A2) and in quartz from the Olserum area (Na- in quartz after bastnäsite-(Ce) had formed. Low Ca brines). Although they were trapped at lower trapping temperatures of the Ca brine inclusions temperatures (probably below 300 °C) than the (< 300 °C) indicate that bastnäsite-(Ce) formed at inferred lower-temperature limit for this altera- around 300 °C. Alteration of the primary miner- tion stage, they show distinct chemical compo- alisation stage likely occurred to at least 1.75 Ga. sitions that likely depict the differences in fluid Some primary fluorapatites in the Olserum compositions between the areas during the alter- area have distinctly different Br/Cl and I/Cl ation stage. High-density fluid inclusions in the signatures following the fluid desiccation trend Djupedal are very calcic, whereas similar high- (Fig. 5). Hematite trapped in the Ca-Na brine in- density fluid inclusions in the Olserum area are clusions demonstrates that hematite was stable more sodic but still relatively rich in Ca (Table during the entrapment of the Ca-Na and Na-Ca A2). Such a difference in composition is con- brines. Hematite is extensively replacing magne- sistent with the alteration features recognised in tite in the surrounding mineral matrix of this type the different mineralised areas. of fluorapatite. It is thus likely that the halogen The formation of bastnäsite-(Ce) marks the chemistry of this fluorapatite was inherited by latest stage of REE-mineral formation. Bast- alteration fluids similar to the Na-Ca and Ca-Na näsite-(Ce) formed locally in the Djupedal area brines when extensive martitisation took place. during chloritisation of allanite-(Ce) or allanite- I have also observed a more intense martitisa-
(Ce)–ferriallanite-(Ce). This required CO2-rich tion of magnetite in the Djupedal area where fluids. Quartz from the Djupedal area frequently quartz contain abundant Na-Ca fluid inclusions. contains secondary fluid inclusion arrays with The good agreement between this fluorapatite almost pure low-density CO2 inclusions (Table and the measured fluid inclusions indicates a A1). The Ca-Na brine inclusions from the smaller fractionation of Br from I during apa- Djupedal area also frequently co-exist with tite precipitation. similar CO2 inclusions. The Ca-Na brine in- By using the halogen compositions of the
30 JUDQLWHKRVWHGÀXRUDSDWLWHWKHSULPDU\K\GUR- PDOÀXLGIRUDUHDVRQDEOHVDOLQLW\RIZW WKHUPDOÀXLGFRPSRVLWLRQFDQEHFDOFXODWHG7KLV NaCl eq., equals to molar Br/Cl and I/Cl ratios FDOFXODWLRQLVEDVHGRQWKHSDUWLWLRQFRHI¿FLHQWV of ~1.1 · 10DQGā-6, respectively (Fig. Br IRU%UDQG,EHWZHHQDSDWLWHDQGÀXLG ' apatite- 6XFKDÀXLGFRPSRVLWLRQLVSODXVLEOHIRUD I ÀXLGa DQG' DSDWLWHÀXLGa PDJPDWLFK\GURWKHUPDOÀXLGUHODWHGWR6W\SH derived from the halogen compositions of the PDJPDWLVP7KHHOHYDWHG,&OUDWLRFRXOGUHÀHFW DOWHUHGÀXRUDSDWLWHDQGWKHÀXLGLQFOXVLRQVDQG a source of the granitic melts in the Olserum- DQHVWLPDWLRQRIWKHÀXLGVDOLQLW\7KHUHVXOWLQJ Djupedal district enriched in I relative to the halogen composition of the primary hydrother- JUDQLWHVGH¿QLQJWKH6W\SH¿HOG Br/I [molar] 104 103 102 101 100
Fluid desiccation and halite preci- pitation trend 1 with Br/I = 2.5 10 Seawater mixed
with Br/I = 0.5 -3 SET Seawater mixed Porphyry-style (I-type) mag- matic fluids Sea- water Upper continental crust
Bulk continental crust 0 10 Mantle Calculated primary fluid composition S-type magmatic (10 wt% NaCl eq.) Br/Cl [molar] x 10 Sylvite fluids
Halite 10-1 100 101 102 103 104 I/Cl [molar] x 10-6 Primary fluorapatite, Olserum Secondary fluorapatite, Olserum Primary fluorapatite, Djupedal FI assemblages, Ca-Na brine Primary fluorapatite, Granite-hosted FI assemblages, Na-Ca brine Primary fluorapatite, Altered FI assemblages, Na-Fe-K-Ca brine Secondary fluorapatite, Djupedal
Fig. 5. 'LDJUDP RI WKH PRODU %U&O UDWLR YHUVXV WKH ,&O UDWLR IRU GDWD RI WKH 2OVHUXP'MXSHGDO 5((SKRVSKDWH PLQHUDOLVDWLRQ7KHSRUSK\U\W\SHPDJPDWLF¿HOGLVGH¿QHGE\GDWDIURP,UZLQDQG5RHGGHU .HQGULFNHWDO DQG6HRHWDO DQGWKH6W\SHPDJPDWLFÀXLG¿HOGE\GDWDIURP%|KONHDQG,UZLQ ,UZLQDQG 5RHGGHU %DQNVHWDO DE DQG6HRHWDO 7KHPDQWOH¿HOGLVGH¿QHGE\GDWDIURP.HQGULFN et al. (2013, 2017). The average values for the bulk continental crust and upper continental crust are adopted from 5XGQLFNDQG*DR 6(7LVWKHVHDZDWHUHYDSRUDWLRQWUHQG'LDJUDPPRGL¿HGDIWHU)XVVZLQNHOHWDO
31 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
In summary, primary REE mineralisation concentration in the melt. In carbonatite-silicate formed from granitic-derived fluids at high systems, however, specific rocks with very high temperatures (~600 °C) at c. 1.8 Ga. The P2O5 contents, usually termed phoscorite occur fluids were relatively reducing and dominated (Chakhmouradian et al., 2017, and references by Na-K-(Fe-Ca)-Cl-F, which locally evolved therein). Other parameters than apatite solubil- to more Cl- and Ca-bearing fluids. During sub- ity, such as the activity of F and P, and possible sequent cooling of the hydrothermal system, the fluid exsolution, thus dictate whether apatite will ore assemblages were variably altered by Ca-Na crystallise as a cumulate phase or if P will to Na-Ca-dominated fluids down to temperatures be enriched in a residual carbonatite melt. of around 300 °C to at least 1.75 Ga. Because the REE are compatible in apa- tite, REE will be depleted in carbonatite-silicate 5.2 Source of REE and P in systems where significant apatite fractionation REE-phosphate deposits occurs, although fractionation of other miner- Because many hydrothermal REE-phosphate als and magma replenishment also affects the deposits are associated with alkaline magmatic REE budget in such systems (Chakhmouradian rocks, particularly carbonatites, it is warranted et al., 2017). Yet, carbonatites or carbonatite- to discuss first what type of processes enrich the alkaline silicate systems exhibit strong affinities REE and, in part P, in carbonatites. Because car- for REE, especially LREE (Fig. 6), and for P. bonatites commonly co-exist with coeval ultra- The observation that monazite, which typically mafic and alkaline rocks, their origin have main- forms by late hydrothermal-carbothermal pro- ly been assigned to fractional crystallisation or cesses (e.g., Zaitsev et al., 2015; Chakhmoura- liquid immiscibility of alkali-rich carbonatite- dian et al., 2017, and references therein; Marien silicate magmas derived from the lithospheric et al., 2018), is the principal REE-mineral in or asthenospheric mantle, whereas only a few many hydrothermal REE deposits associated may originate directly from low-degree mantle with carbonatites is thus not surprising consider- melts (Mitchell, 2005; Chakhmouradian and ing the high probability for mobilisation of REE Zaitsev, 2012). and P in such systems. The endowment of REE in carbonatites can In peralkaline quartz-saturated rocks that be explained either by fractional crystallisation exhibit a strong affinity for the REE (Fig. 6), of REE-poor oxides and silicate minerals and the P content is usually low (e.g., Boily and subsequent extraction of a carbonatite fraction- Williams-Jones, 1994; Dostal et al., 2014, ated melt, or by carbonatite-silicate liquid Möller and Williams-Jones, 2016), presum- immiscibility because the REE (and P) mostly ably due to early fractionation of apatite as prefer the carbonatite melt over the silicate melt result of the low solubility of apatite in peral- (Chakhmouradian and Zaitsev, 2012; Veksler et kaline silicate magmas (Watson and Capobian- al., 2012; Martin et al., 2013). Because apatite co, 1981). In quartz-undersaturated peralkaline solubility is high in carbonatite melts compared systems, which also are strongly affiliated with to silicate melts (Watson and Capobianco; 1981; high REE concentrations (Fig. 6), the P concen- Harrison and Watson, 1984; Wolf and London, tration can be high too, especially in cumulate 1994; Hammouda et al., 2010; Chakhmouradian units related to alkaline-carbonatite magmatism et al., 2017), fractional crystallisation in a pure (e.g., rocks in the Kola Province; Zaitsev et al., carbonatite system will lead to an enriched P 2015, and references therein). However, mona-
32 105 High-grade agpaitic Grade comfort zone ore at Nechalacho, Canada High-grade carbo- natite ore at Bear Lodge, USA High-grade ore 104 at Olserum- High-grade per- Djupedal alkaline ore at Strange Lake, Canada 103
2 Peralkaline 10 granites
1 10 Bulk continental crust Agpaitic rocks Ferroan granites Phonalite
Whole-rock/primitive mantle 0 Olserum-Djupedal 10 Nephelinite to Carbonatites granite nepheline syenite
10-1 La Ce Pr NdSmEu Gd Tb Dy YHoErTmYbLu Fig. 6. Whole-rock REE distribution diagrams normalised to primitive mantle for the most relevant magmatic sources RI5((0RGL¿HGDIWHU&KDNPRXUDGLDQDQG=DLWVHY 1RUPDOLVDWLRQDIWHU0F'RQRXJKDQG6XQ 1RWH WKDWWKH¿HOGRIQHSKHOLQLWHWRQHSKHOLQHV\HQLWHFRQWLQXHVXQGHUWKH¿HOGVRIWKHDJSDLWLFDQGSHUDONDOLQHURFNVRQ WKH/5((VLGHRIWKHGLDJUDPDQGWKDWWKHDJSDLWLF¿HOGRYHUODSVZLWKWKHSHUDONDOLQHJUDQLWHV LQGLFDWHGE\GDVKHG green lines). Sources: peralkaline granites (Boily and Williams-Jones, 1994; Kovalenko et al., 1995; Kynicky et al., 'RVWDOHWDO 0|OOHUDQG:LOOLDPV-RQHV DJSDLWLFURFNV 6¡UHQVHQHWDO 6M|TYLVWHWDO Möller and Williams-Jones, 2016); carbonatites (Lottermoser, 1990; Xu et al., 2008; Moore et al., 2015; Trofanenko et al., 2016; Bodeving et al., 2017; Marien et al., 2018); bulk continental crust (Rudnick and Gao, 2003); ferroan granites (Collins et al., 1982); the others are from Chakmouradian and Zaitsev (2012). zite or xenotime are uncommon hydrothermal HWDO WKHF 0D+DOSDQHQFDUERQ- minerals associated with such rocks. DWLWH 5XNKORYDQG%HOO DQGWKHF For the REE-phosphate rich Olserum- Ma Naantali carbonatite (Woodard and Heth- Djupedal REE deposits, no alkaline source of HULQJWRQ 7KH$OPXQJHV\HQLWHFRPSOH[ REE is plausible because of the complete lack in Bergslagen is the closest alkaline rocks with of rocks with such compositions with the same a similar age in Sweden (c. 1.88 Ga; Delin and age (1.8 Ga) in the Västervik region. Alkaline %DVWDQL 3HUDONDOLQH DJSDLWLF URFNV DW rocks of Palaeoproterzoic age in the Fennoscan- the Norra Kärr alkaline complex are geo- dian Shield mainly occur in Finland, including graphically close but are much younger (1.49 Ga; WKHF0D.RUVQlVFDUERQDWLWH 6DUDSll 6M|TYLVWHWDO 7KH1DDQWDOLFDUERQDWLWH
33 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A dykes intruded at a similar age as that inferred members as a result of decreasing temperature for the Olserum-Djupedal REE mineralisation, and solubility of apatite (Watson, 1979, 1980; suggesting that carbonatites may have formed at Watson and Capiobianco, 1981; Harrison and depth during the tectonic regime that was preva- Watson, 1984; Piccoli and Candela, 2002). In lent at that time (cf., Rutanen et al., 2011; Wood- peraluminous silicate melts, the solubility of apa- ard and Hetherington, 2014). However, several tite increases with peraluminousity, and peralu- lines of evidence strongly suggest a granitic minous granites can have significantly higher source of the REE for the Olserum-Djupedal P2O5 contents than metaluminous granites with REE mineralisation: 1) field relationships indi- similar silica contents (Bea et al., 1992, 1994; cate a strong spatial and temporal relationship Pichavant et al., 1992; Wolf and London, 1994). of the mineralisation with the dominant TIB The solubilities of monazite and xenotime are Olserum-Djupedal granite in the district (Fig. 3), low and decrease with increasing peraluminos- 2) the halogen compositions of fluorapatite indi- ity, and are highest for peralkaline silicate melts cate a hydrothermal fluid flow from this granite (Montel, 1986, 1993; Rapp et al., 1987; Wolf and towards the metasedimentary host rocks and, 3) London, 1995). Thus, for peraluminous melts, the halogen and Cl isotopic compositions of flu- melting at the source will generate a melt un- orapatite is consistent with a granitic source of the dersaturated in apatite and crystallisation of feld- ore-forming fluids. In addition, the composition spar will increase the P/Ca ratio so that excess of the Naantali carbonatite is LREE-dominated P can be incorporated into P-minerals with low (Woodard and Hetherington, 2014), whereas the solubilities such as monazite or xenotime and ore at Olserum-Djupedal REE mineralisation is into K-feldspars with increasing fractionation more HREE-rich (Fig. 6). The mineral-chemical and peraluminosity (London et al., 1999; Pic- compositions of fluorapatite and monazite-(Ce) coli and Candela, 2002). This is consistent from the Olserum-Djupedal REE mineralisa- with the Olserum-Djupedal granite, which tion are also distinct from those of the Naantali contains xenotime-(Y) and monazite-(Ce) but carbonatite (Woodard and Hetherington, 2014). rarely primary fluorapatite. Xenotime-(Y) and Findings from this study suggest that REE monazite-(Ce) are predominantly enriched in bi- and P can be derived from other sources than otite-magnetite schlieren in the granite and rarely alkaline magmatic sources. The clear associa- as disseminated grains within the groundmass. tion of the Olserum-Djupedal REE mineralisa- London (1992) noted that P exhibits highly noni- tion with the peraluminous Olserum-Djupedal deal mixing in felsic melts, which can cause local granite suggests that REE and P were derived heterogeneities due to unmixing of P-enriched from this magmatic system. But how can the domains. Local high P solubility can proba- high-grade REE-phosphate ore (Fig. 6) be recon- bly also stem from local heat fluxes. Notably, ciled with the generally low REE (∑REE ~300 London (1992) further suggested that these ppm) and P (0.04-0.07 wt% P2O5) contents of P-enriched domains would accumulate with the granite? REE and other HFSE in basic and Fe-rich The solubility of apatite in silicate rocks melts domain. This could explain the common is highest for hot mafic melts compared to and local occurrence of monazite-(Ce) and xeno- colder felsic melts. In metaluminous silicate time-(Y), and zircon within the biotite-magnetite melts, the P2O5 concentration decreases with schlieren. Thus, the low REE and P whole-rock increasing fractionation towards high silica contents may not necessarily imply low REE and
34 P concentrations of the original melt. In addi- perature and peraluminosity of the melt, while tion, P can be lost to pegmatites formed from it decreases with increasing F concentration of more evolved P-enriched residual melts via the melt (Webster and Holloway, 1988). At 650 filter-pressing or be lost due to extensive sericitic °C, REE partitioning into the fluid is about 50% and argillic alteration of alkali feldspars (Lon- stronger than at 775 °C in peraluminous melts don, 1992; London et al., 1993). (London et al., 1988). Phosphorous favours the Although the Olserum-Djupedal granitic sys- melt over the fluid, but the partitioning of P to tem yet is poorly understood, abundant pegma- the fluid is one magnitude higher in peralu- titic and granitic dykes and veins crosscut both minous compared to metaluminous systems, the main granitic body and the surrounding ore- and P usually has a higher or a similar parti- bearing metasedimentary rocks. These dykes tion coefficient as the REE (London et al., 1988; and veins contain sillimanite, which indicates a 1993). The most suitable conditions for partition- strongly peraluminous character, and the dykes ing of REE and P into the fluids should thus be and veins probably represent the most evolved in peraluminous systems exsolving high-salinity melt. Primary fluorapatite is rare in these dykes fluids, possibly at temperatures of about 650 °C. and veins too, but fine-grained secondary fluor- These conditions coincide well with that of the apatite is abundant close to or in altered feld- Olserum-Djupedal REE-mineralising system. spar domains. This could imply that feldspar in The detailed exposition about the P and REE these evolved rocks initially contained high P concentrations of felsic melts and fluid-melt par- concentrations, which were released and formed titioning of REE and P serves to illustrate that a fluorapatite during feldspar alteration. It is thus fractionating peraluminous granitic system has quite plausible that P to some extent was a great potential to exsolve fluids relatively extracted from the initial melt and enriched in enriched in REE and P. Fluid exsolution at an P-rich pegmatites. early stage for the Olserum-Djupedal REE min- Fluid exsolution could also sequester REE eralisation, as proposed in Paper II, is also advan- and P from the melt. The REE almost invariably tageous because the ore-forming fluid will have partition in favour of the melt over the fluid/ more time to interact and scavenge REE and vapour (London et al., 1988; Webster et al., P from minerals (potentially early-crystallised 1989; Reed et al., 2000; Zajacz et al., 2008; monazite-(Ce) and xenotime-(Y)) and from the Borchert et al., 2010). However, partition melt. In addition, if fluid saturation occurs early, coefficients (Dfluid-melt) for REE are higher for per- the F concentration of the melt will be relatively Cl aluminous melts compared to metaluminous and low because of limited fractionation, and D fluid- peralkaline melts and increase with peraluminos- melt remains high (Audétat et al., 2000). Thus, low ity (London et al., 1988; Borchert et al., 2010). REE and P2O5 concentrations of the granite do They also increase with a pressure drop (Flynn not imply low REE and P concentrations of the and Burnham, 1978; Webster et al., 1989; Bai peraluminous melt at the time of primary REE and Van Groos, 1999) and strongly increase with mineralisation, but rather resulted from a com- increasing Cl concentrations of the fluids (Web- bination of fluid exsolution, melt heterogeneities ster et al., 1989; Reed et al., 2000; Borchert et and late pegmatite extraction. In other silicate al., 2010). Chlorine always partitions into the systems, low solubility of apatite will lead to ear- fluid over the melt, and the partition coefficient ly crystallisation of apatite during fractionation, Cl for Cl (D fluid-melt) increases with increasing tem- removing most of the P in the system. Lower
35 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
REE and P fluid-melt partition coefficients in of the increased dissociation of HF at increasing such systems also indicate a lower potential for pH (Fig. 7), which results in more F ions being the exsolution of REE-P-rich fluids. able to bind with the REE until the fluid reaches
In hydrothermal REE deposits not related to REEF3(s) saturation (Williams-Jones et al., 2012; any known igneous activity such as xenotime- Migdisov et al., 2016). However, REEF3 miner- (Y)-rich unconformity-related REE deposits als are rare in nature, but the point is rather that (Vallini et al., 2007; Rabiei et al., 2017; Nazari- insoluble REE-F-bearing minerals, for example, Dehkordi et al., 2018; Richter et al., 2018), REE bastnäsite-(Ce), may govern the availability of and P are probably transported in separate fluids. REE in hydrothermal fluids at increasing pH. The source of P is likely from P-enriched sedi- However, it is also possible that high stabilities mentary beds such as phosphorites, which also of REE-OH-F complexes at high pH can inhibit can contain high concentrations of REE (Ems- saturation of REEF3(s) or other REE-F-bearing bo et al., 2015), while REE originate from the minerals and retain the REE in solution (Vasyu- alteration of basement rocks (Nazari-Dehkordi kova and Williams-Jones, 2018). To precipitate et al., 2018). the REE as REE-bearing minerals, a process or processes are required to drive the system into 5.3 Hydrothermal transport of conditions that promote REE mineral formation REE and P and precipitation instead of favouring REE complexation. Based of REE-phosphate minerals on geochemical modelling (Migdisov and Wil- Transport of REE in a fluid requires the formation liams-Jones, 2014; Migdisov et al., 2016), pos- of stable metal complexes with available ligands sible mechanisms to induce REE precipitation in the fluid at the specific conditions of the hydro- are 1) pH-changes, 2) introduction of binding thermal system to keep the REE in solution. Re- ligands, 3) destabilisation of REE-transporting cent experimental studies on the stabilities of dif- complexes, or 4) cooling. ferent REE complexes at elevated temperatures Phosphorous, as phosphate, is considered a (up to 250 °C) and geochemical modelling show strong binding ligand in REE-mineralising sys- that significant REE transport primarily occurs tems and probably contribute nothing to the 2+ + by REE-Cl complexes (REECl and REECl2 ) transport of REE. This has been inferred based only at acidic conditions in Cl-F-bearing fluids on the low and retrograde solubilities of mona- (e.g., Migdisov et al., 2009, 2014, 2016). Addi- zite and xenotime at temperatures up to 300 °C 2- tion of the SO4 ligand expands the pH range in acidic solutions (pH ≤ 2; cf., Poitrasson et in which the REE can be transported, especially al., 2004; Cetiner et al., 2005; Gysi et al., 2015; at higher temperatures (300-400 °C) due to the 2018; Migdisov et al., 2016). Modelling shows 2- formation of stable REE(SO4) (Migdisov et al., that when phosphate is introduced into the 2016). In F-free fluids, the REE can be trans- hydrothermal system, either by fluid-rock inter- ported at neutral conditions to slightly alkaline action with P-enriched rocks or by mixing with 2- conditions with the addition of SO4 (Migdisov P-enriched fluids, the REE in the solution will et al., 2016), or even at alkaline conditions by immediately react with phosphate and precipitate REE-OH complexes (Wood et al., 2002; Pourt- monazite or xenotime. This is probably a very ier et al., 2010; Perry and Gysi, 2018). The re- efficient precipitation mechanism when REE and duced solubilities for the REE at higher pH in P are not transported by the same fluid. Pourtier F-bearing fluids are thought to originate because et al. (2010) suggested that monazite solubility
36 MP H PO HPO H HPO PO H
H F HF H
PO H H H PO H P O H P O H H H PO PO H HC C H A T C
Fig. 7. A diagram showing the acid dissociation constant (pKa) for the reactions involving the common phosphate ° - 2- ° ° species (H3PO4 , H2PO4 , and HPO4 ), HCl , and HF as an effect of temperature at 200 MPa. The blue line shows how the neutral pH changes with temperature. Calculated using data from the SUPCRT92 database (Johnson et al.,
1992) and complementary data from Shock et al. (1997) and Tagirov et al. (1997). At pKa, the activities of dissociated ° - (e.g., H3PO4 ) and associated (e.g., H2PO4 ) species are equal. When pH > pKa, the dissociated species predominate. is prograde at least from 300 to 800 °C at more ments and at conditions approximating those of neutral pH, which indicates that REE may be the Olserum-Djupedal REE-mineralising system complexed with phosphate at higher tempera- (Xing et al., 2019) showed that: tures, or that phosphate is co-transported with 1) The solubility of La was higher in F- REE in the fluid and the REE are complexed bearing fluids compared to F-free fluids because with other ligands (e.g., OH-). This supports the of the stability of LaF2+. study of Ague (2017), who demonstrated a strong 2) The pH of F-bearing fluids decreases with correlation between REE and P mobility during increased temperature and salinity. For a salinity regional metamorphism in crustal and subduc- exceeding 2 m (~10 wt% NaCl) and a tempera- tion zone environments. ture over 400 °C, the pH of the F-bearing fluids A recent attempt to model the mobility of is lower than that of F-free fluids. This directly REE (along with Fe and U) by F-bearing fluids affects the solubilities of REE as the REE are in rock-buffered granitic-hydrothermal environ- more soluble at lower pH.
37 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
3) The soluble P concentration is in general acidic conditions but depending on the stabili- higher for F-free fluids compared to F-bearing ties of REE-OH-F complexes at these temper- fluids. However, at temperatures above ~400 °C atures, co-transport of REE and P may be fea- and salinities exceeding 10 wt% NaCl, the con- sible even at neutral to alkaline conditions (cf., centration of P is higher for F-bearing fluids than Vasyukova and Williams-Jones, 2018). The low for F-free fluids. It also seems that the differ- solubilities of monazite and xenotime in acidic ence between the soluble P concentration in F- fluids at temperatures below 300 °C (Poitrasson bearing fluids relative to F-free fluids increases et al., 2004; Cetiner et al., 2005; Gysi et al., 2015; with increasing temperature, even beyond the 2018; Migdisov et al., 2016) likely preclude co- maximum temperature of 450 °C for the model. transport of REE and P at those conditions. In These results suggest that co-transport of F-free fluids, co-transport of REE and P are REE (as F- and Cl-complexes) and P can occur also probable to more neutral or alkaline con- in acidic fluids with a salinity greater than 10 wt% ditions, particularly with increasing temperatures NaCl at temperatures above 400 °C. These con- up to 800 °C. An evaluation of different mecha- ditions also coincided with the highest solubility nisms that can precipitate REE-phosphates can of Fe in F-bearing fluids. The rock-buffered thus be made: concentration of La in the fluid is ~1 ppm. 1) pH change; changes in pH of the solution If compared to various magmatic-hydrothermal would be achieved by for instance fluid-rock REE-bearing fluids (Table 2), this concentration interaction with a suitable rock or mixing with is similar to some low to intermediate salinity a fluid of different pH (Migdisov and Williams- fluids from the Strange Lake REE deposit and Jones, 2014; Migdisov et al., 2016). At acidic pH, ° other magmatic-hydrothermal systems. However, P mostly occurs as associated H3PO4 or possi- ° it is one magnitude lower than compared with bly as H4P2O7 at high P concentration (P ~ 0.1 many brine inclusions, especially the extremely molal or 0.3 wt% P; Pourtier et al., 2010). When ° ° high-salinity “fluids” at Capitan Mountain and pH increases, H3PO4 (and H4P2O7 ) become in- - associated REE mineralisation (Table 2; Banks creasingly dissociated and more H2PO4 ions (and - et al., 1994; Campbell et al., 1995; Audétat et H3P2O7 ions) will dominate. For instance, at 500 ° al., 2008). Soluble P concentration in the model °C and 200 MPa, pKa is 4.7 for H3PO4 (and 3.7 -3 -4 ° by Xing et al. (2019) is low, 10 to 10 ppm. for H4P2O7 ; neutral pH is at 5.1 at these condi- However, in vapour/melt experiments for per- tions; Fig. 7). Thus, if the REE- and P-bearing aluminous granitic systems, concentrations of fluids initially were rather acidic, the fluid will P and of individual REE in the co-existing get increasingly richer in dissociated ions upon vapour phase were ~400 ppm and ~0.2 ppm, neutralisation until it eventually reaches satura- respectively (London et al., 1988). This indi- tion with respect to REEPO4(s). When this occurs cates that exsolved magmatic fluids from per- is strongly controlled by the solubility product aluminous granitic systems can contain elevated of REEPO4(s), which also will depend on the P concentrations. initial concentrations of REE3+ and P in the flu-
In summary, high capability for co-transport id. REEPO4(s) saturation is also controlled by of REE and P in F-bearing fluids seems most the stabilities of REE complexes at higher pH probable with increasing salinity of the fluids (e.g., REE-OH complexes), which may retain and at temperatures above 400 °C. Moreover, the REE in solution. Additional components in co-transport of REE and P primarily occurs at the fluid such as F (or CO2) will determine if
38 Zajacz et al. (2008) Audétat et al. (2008) Zajacz et al. (2008) Audétat and Pettke (2003); Audétat et al. (2008); Zajacz et al. (2008) Audétat et al. (2008) and Williams- Vasyukova Jones (2018) Audétat et al. (2008) Zajacz et al. (2008) Audétat and Pettke (2003) Banks et al. (1994); Campbell et al. (1995); Audétat et al. (2008) Audétat et al. (2008) Norman et al. (1989) Zajacz et al. (2008) Ulrich et al. (2002) References Bühn et al. (2002) Bühn and Rankin (1999) A2) This study (Table 2
2 2 2 , brine) 1 , brine) 1 Ce: 2.1 (low-salinity) La: 2.1-3.7 (low-salinity), 1.2-4.2 (brine) (low-salinity), 1.3-5 (brine) Ce: 3.2-11 La: 1.3-2.9 (low-salinity) Ce: 1.1-5 (low-salinity; 1-5 (brine) Ce: <24 (low-salinity), 6-16 (brine) La: 1-7.4 (low- to intermediate salinity) Ce: 3.1-15 (low- to intermediate salinity) Ce: 0.5-3 (low-salinity), <8 (brine) Ce: 3800-12800 (normalised), 20.5 Ce: 2.4 (low-salinity), 100 (brine) La: 70-330 (brine) Ce: 13 (low-salinity), 80-580 (brine) Ce: <12 (low-salinity), 4-180 (brine) La: 2.8-71 (intermediate salinity) Ce: 2.8-89 (intermediate salinity) Ce: 21.4 (brine) Ce: 9 (low-salinity) La: 4-150 (430 Ce: 1-30 (210 La: 9200-13300 (normalised), 10.5 (normalised), 13.5 Ce: 11400-17200 La: 3360-18900 (normalised), 25.3 Ce: 0.85-1.25 (brines) 2 2 Na, K, Al, Fe, Cu Na, K, Na, K, Fe, (Mn)Na, K, Fe Ce: 0.1-48 (low-salinity), 1-17 (brine) Na, K, Fe, Mn Na, K, Fe, (Mn, Cu) Na, Ca, (K) Na, K, Fe Na, K, Ca, Fe, CO Na, K, (Fe, Al) Na, K, (Fe, Na, K, Fe, Mn, Ca Na, K, Fe Na, K, Fe Na, K, Fe, Mn La: 9.4 (brine) Na, K, Al, FeNa, K, La: 1.7 (low-salinity) Major elementsMajor REE concentrations (ppm) Na, Fe, K, Mn Na, K, Ca, Fe, CO Na, Fe, K, Ca fluids.
> 400 °C 150-420 °C 410 °C 189-390 450-570 °C 380 °C 300-750 °C Homogenisation temperature ~300 °C 7-8.5 3.1-6.3, 28.1-52 400-620 °C 6.5-15, 31.5-35 350-550 °C 3.7-7.5, 26-29.6 420-480 °C 10-21.7, 31.9-33.1 650-720 °C 4-23 1-6.2, 26.3-31.6 400-510 °C Salinity (wt% NaCl eq.) 2.7-6.2, 38-2-49.7 450-600 °C 4-5 2.2, 62.7-80.4 590-650 °C 16.7-21.9 53-69 5.9 37-70 ~45 magmatic-hydrothermal different of concentrations
, and Li-mica granites 5 O 2 S-type granite with Sn-W-(Cu-Ag- mineralisations W-(Bi) Pb-Zn) and with REE and HFSE minerals Metaluminous granite (A/CNK = 0.98-1.02), miarolitic cavities REE mineralisation Alkalic granite, Zn-Pb-Cu mineralisation Metaluminous granite (A/CNK = 0.98-1.02), miarolitic cavities (Alkali)-granite with Th-U-REE mineralisation Peraluminous granites (A/CNK = 1.06-1.17), miarolitic cavities Strongly peraluminous, high F and P Peraluminous granites (A/CNK = 1.06-1.17), miarolitic cavities Porphyry Cu-Au deposit Type Peraluminous granite (A/CNK = 1.05-1.11) REE Porphyry Mo-Nb-(Cu-W) of
Compilation Mole, Australia Mt. Malosa, Malawi Alkali pegmatite, miarolitic cavities Rito del Medio, Mexico Santa Rita, USAStrange Lake, Canada Peralkaline granite associated with Porphyry Cu-(Mo-Au) Stronghold, USA Okorusu, Namibia Carbonatite Canada Pinabete, Mexico Capitan Mt., USA Cave Peak, USA Copper Flat, USACuasso al Monte, Italy Porphyry Cu-Mo deposit Ehrenfriedersdorf, Germany Baveno, Italy Locality Alumbrera, Bajo de la Argentina Kalkfeld, Namibia Carbonatite Olserum-Djupedal, Sweden Represents one outier concentratioons of quartz and leachate Aveage 1 2 Table 2. Table
39 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A
the fluid will become saturated with REEF3(s) the stabilities of their respective REE-complexes. (or possible REE-fluorocarbonates) instead of 3) Cooling generally reduces the solubility of
REEPO4(s) with increasing pH. As the solubil- REE in fluids by the lowering the stabilities of ity of REEPO4(s) thus is dependent on tempera- transporting REE complexes (e.g., Migdisov et ture, pH, stabilities of REE complexes, and the al., 2016). Cooling also decreases the solubility concentrations of different elements in the fluid of monazite in neutral-pH fluids at temperatures (e.g., Cl, F, P, and S), all these parameters need to between 300 and 800 °C (Pourtier et al., 2010). 0 be considered for a specific hydrothermal REE- Cooling also increases the dissociation of H3PO4 mineralising system if precipitation by changes at constant pH. Cooling, however, also increases in the pH is a feasible precipitation mechanism the availability of the important REE complexing or not. ligands Cl- and F- due to the increased dissocia- 2) The destabilisation of REE-transporting tion of HCl° and HF° species. These competing 2+ + complexes; because REECl and REECl2 , factors thus dictate whether saturation of the flu- 2+ + and in some fluids, REEF , or REESO4 and id with REEPO4(s) will occur during cooling. 2- ° + REE(SO4) , or REE(OH)3 and REE(OH)2 , are 4) Introduction of phosphate ligand; very the chief REE transporting agents, destabilising efficient precipitation mechanism if REE and these will decrease the solubility of REE and P are not co-transported or if a REE-bearing fluid saturate the solution in REEPO4(s). To destabi- interacts with P-enriched lithologies. Yet, even lise REE-Cl complexes, mixing with fluids of if REE and P are co-transported, with additional lower salinity such as metamorphic or meteoric P added to the solution, it would probably reach fluids will dilute the REE-transporting fluid and saturation of REEPO4(s) earlier. One potential thus the ability to dissolve the REE (Migdisov limitation with this mechanism is identifying the et al., 2016). If the REE-transporting fluid con- rock type or fluid that are sufficiently enriched tains high S concentration, transport of REE by in P to facilitate this process. In carbonatite-
REE-SO4 complexes are very likely. The desta- silicate systems, such a rock could potentially bilisation of these complexes could be effec- be early apatite cumulates or apatite-rich carbon- tively achieved by precipitation of insoluble atites (Zaitsev et al., 2015; Chakhmouradian et barite, or by the reduction of SO4 to sulphide or al., 2017, and references therein). In such sys- other reduced species (Migdisov et al., 2016). A tems, fluid-interaction with early formed apa- decrease of F in the fluid by precipitating miner- tite is likely the most important precipitation als exhibiting a strong preference for F such as mechanism. In other hydrothermal systems, fluorapatite (Zhu and Sverjensky, 1991; Spear however, it could be challenging to recognise and Pyle, 2002; Harlov, 2015; Kusebauch et al., pre-existing P-enriched rocks. A joint source of 2015a, 2015b) will effectively destabilise REE-F REE and P may thus be more common than complexes and Th-F and (Nb,Ta)-F complexes. not in many magmatic-hydrothermal systems. In This could be responsible for the formation of low-temperature systems such as unconformity- REE-(Nb,Ta) oxides in the Olserum-Djupedal related REE deposits, co-transport of REE and P REE mineralisation. The destabilisation REE- is unlikely, and they are probably transported in OH complexes may be achieved by fluid mixing separate fluids. Some specific basinal fluids can with a lower pH-fluid. However, if REEPO4(s) be P-enriched, and xenotime precipitates when saturation occurs will be highly dependent on the the REE-bearing fluid mixes with the basinal concentrations of other elements in the fluid, and P-enriched fluid (Nazari-Dehkordi et al., 2018).
40 studies on the stabilities of different REE com-
5.4 Outlook and remaining plexes (including PO4-complexes) at magmatic- research topics hydrothermal conditions would be extremely Although the approach of this research project desirable. Constraints on the concentration of has shifted slightly from the original idea, the P in magmatic-hydrothermal fluids of differ- purpose has stayed the same; to contribute to ent affinity would be vital in order to model the the understanding of how hydrothermal REE formation of hydrothermal REE-phosphate deposits form. The main goal was to identify the deposits. Likewise, reliable concentrations main REE-transporting agents in hydrothermal of individual REE in magmatic-hydrothermal REE systems by determining the compositions of fluids, and of other potential ore-forming flu- REE-bearing fluids and to use geochemical mod- ids, would also be highly desirable. At that point elling to identify key depositional mechanisms. would it be possible to make better predictions While this goal has partially been reached, this on how REE are transported in crustal fluids study has primarily contributed to the under- and how REE deposits form in various hydro- standing and recognition of a new and potentially thermal settings. regional-scale hydrothermal REE system, and the implications this have had on the gen- eral understanding of hydrothermal REE- mineralising systems. 6 Conclusions Modelling of hydrothermal REE-mineral- ising systems has aptly been made in several This study has foremost focused on understand- studies in recent years (Migdisov and Williams- ing the origin and evolution of the Olserum- Jones, 2014; Migdisov et al., 2016; 2018; Perry Djupedal REE mineralisation in SE Sweden. and Gysi, 2018; Xing et al., 2019). These studies The mineralisation is unique in many aspects, have laid the foundation for the understanding of like in the paragenesis and style, and hosts abun- REE transport and precipitation of REE-bearing dant monazite-(Ce), xenotime-(Y) and variably minerals. However, the models have not consid- REE-bearing fluorapatite. The main findings and ered co-transport of REE and P. This is mainly implications of the study can be summarised as because of the general lower temperatures used follows: for these models. This is, however, a direct conse- I. Primary REE mineralisation in the Olserum- quence of the lack of experimental studies at the Djupedal district formed at magmatic-hydrother- relevant conditions where co-transport of REE mal conditions (~600 °C) by magmatic NaCl- and P is likely to occur. FeCl2-KCl-CaCl2-HF-H2O fluids at c. 1.8 Ga. Additional experimental data are thus During subsequent cooling, the ore assemblages required before new geochemical modelling can were variably altered by CaCl2-NaCl to NaCl- be conducted. Such new models should also CaCl2 brines and partly by CO2-bearing fluids consider high-temperature conditions, which down to temperatures of around 300 °C and to would be applicable to the Olserum-Djupedal at least 1.75 Ga. REE-mineralising system. For instance, studies II. Co-crystallisation of fluorapatite, mona- on the solubilities of monazite, xenotime and zite-(Ce) and xenotime-(Y) in the Olserum- the apatite end-members as well as other REE- Djupedal REE mineralisation and lack of bearing minerals (e.g., bastnäsite) in addition to rocks pre-enriched in terms of P suggest a
41 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A joint source of REE and P. There is no need to References invoke a scenario where REE and P are trans- ported by separate fluids. Ague, J.J., 2017. Element mobility during regional III. High capability for co-transport of metamorphism in crustal and subduction zone en- vironments with a focus on the rare earth elements REE and P is most probable at increasing (REE). Am. Mineral. 102, 1796–1821. salinity of the hydrothermal fluids and at Åhäll, K.I., Larson, S.Å., 2000. Growth-related 1.85- 1.55 Ga magmatism in the Baltic Shield; a re- increasing temperatures above 400 °C. Acid- view addressing the tectonic characteristics of ic conditions would make the co-transport of Svecofennian, TIB 1-related, and Gothian events. REE and P more effective. Yet, depending on GFF 122, 193–206. Andersen, T., 1986. Compositional variation of some the stabilities of REE-OH complexes at these rare earth minerals from the Fen complex (Tele- temperatures, co-transport of REE and P may mark, SE Norway): implications for the mobility of rare earths in a carbonatite system. Mineral. be feasible even at neutral to alkaline conditions. Mag. 50, 503–9. Additional constituents in the fluid such as F, S Andersen, T., Andersson, U.B., Graham, S., Aberg, and, CO will also influence the co-transporting G., Simonsen, S.L., 2009. Granitic magmatism 2 by melting of juvenile continental crust: new con- ability of the fluid. straints on the source of Palaeoproterozoic granit- IV. While hydrothermal REE mineralisations oids in Fennoscandia from Hf isotopes in zircon. J. Geol. Soc. London. 166, 233–247. are typically related to alkaline magmatism, par- Andersson, U.B., Wikström, A., 2001. Growth-related ticularly to alkaline silicate-carbonatitic systems, 1.85-1.55 Ga magmatism in the Baltic shield; a this study shows that high-grade hydrothermal review addressing the tectonic characteristics of Svecofennian, TIB 1-related, and Gothian events. REE-mineralising systems can also develop in GFF 123, 55–58. association with subalkaline magmatism. Out Audétat, A., Pettke, T., 2003. The magmatic-hydro- thermal evolution of two barren granites: a melt of the subalkaline granitic systems, fraction- and fluid inclusion study of the Rito del Medio and ating peraluminous granites show the greatest Canada Pinabete plutons in northern New Mexico potential to exsolve fluids carrying REE and P, (USA). Geochim. Cosmochim. Acta 67, 97–121. Audétat, A., Günther, D., Heinrich, C.A., 2000. Mag- which can lead to the formation of hydrothermal matic-hydrothermal evolution in a fractionating REE deposits rich in REE-bearing phosphates. granite: a microchemical study of the Sn-W-F- mineralized mole granite (Australia). Geochim. V. REE-phosphate precipitation by the Cosmochim. Acta 64, 3373–3393. interaction of a REE-bearing fluid with a P-rich Audétat, A., Pettke, T., Heinrich, C.A., Bodnar, R.J., rock or fluid is a very efficient mechanism at 2008. Special paper: The composition of magmat- ic-hydrothermal fluids in barren and mineralized conditions where co-transport of REE and P are intrusions. Econ. Geol. 103, 877–908. improbable. In fluids co-transporting REE and P, Audi, G., Bersillon, O., Blachot, J., Wapstra, A.H., 2003. The NUBASE evaluation of nuclear and cooling, pH changes or the destabilisation of the decay properties. Nucl. Phys. A 729, 3–128. main REE transporting agents, or more viably, a Bai, T.B., Koster Van Groos, A.F., 1999. The distri- combination of these are likely the most promi- bution of Na, K, Rb, Sr, Al, Ge, Cu, W, Mo, La, and Ce between granitic melts and coexisting nent mechanisms precipitating REE-phosphates. aqueous fluids. Geochim. Cosmochim. Acta 63, 1117–1131. Ballerat-Busserolles, K., Sedlbauer, J., Majer, V., 2007.
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Appendix Salinity (wt%) 45.0 45.0 45.0 45.0 45.0 31.3 30.6 47.9 (0.13) # 46.6 (0.08) # 46.1 47.9 52.0 (0.13) # 44.7 (0.12) # 49.6 (0.17) # 55.5 (0.12) # 52.0 9.0 7.1 13.4 19.6 0.4 0.5 0.4 mode 2 Th CO 2 Th CO 2 CO L-V-S → L-S L-V-S L-V-S → L-S L-V-S L-V-S → L-S L-V-S L-V-S → L-S L-V-S L-V-S → L-S L-V-S L-V-S → L-S L-V-S L-V-S → L-S L-V-S L-V → L L-V Th Th mode Tm 170 190 165 → L-S L-V-S 98 104 104 100 306 → L L-V 101 95 → L L-V Th (Max) 227 162 → L-S L-V-S 234 206 → L-S L-V-S 137 105 → L-S L-V-S 176* 307* 283 → L-S L-V-S 128 117 159* 143* 131 → L-S L-V-S 119 408 105 104 Th (Min) 120 280* 207 279* 219 → L-S L-V-S 115 130 304* 186 130 155 138 → L-S L-V-S 90 145 144 84 104 89 60 91 84 108 105 162 145 → L-S L-V-S 70 n.m.237 n.m. n.m. 94 95 239 374 331 → L L-V 251 399 333 → L L-V 279 375 356 → L L-V 1 Tm Ant 290 Tm Halite 309 304 304 310 150 119 137 148 173 126 177 187 171 inclusions. fluid
27.8 143 26.6 130 5.9 4.5 9.5 16.2 0.2 0.3 0.3 Tm Ice – – – measured of data
Type L-V-S, Na-Fe-K-Ca brine L-V-S, L-V-S, Na-Fe-K-Ca brine L-V-S, L-V-S, Na-Ca brineL-V-S, – L-V-S, Na-Ca brineL-V-S, – L-V-S, Ca-Na brine L-V-S, L-V-S, Ca-Na brine L-V-S, L-V-S, Ca-Na brine L-V-S, L-V-S, Ca-Na brine L-V-S, L-V-S, Ca-Na brine L-V-S, L-V-S, Ca-Na brine L-V-S, L-V, medium salinityL-V, – L-V, medium salinityL-V, – L-V, low salinity, hetero- low salinity, L-V, geneously trapped geneously trapped L-V, low salinity, hetero- low salinity, L-V, geneously trapped microthermometric of FI Assem - blage FIA1 Na-Fe-K-Ca brine L-V-S, FIA11 Na-Fe-K-Ca brine L-V-S, FIA9 Na-Fe-K-Ca brine L-V-S, FIA2 FIA23 FIA29 FIA8 Ca-Na brine L-V-S, FIA12 FIA23 FIA9 Ca-Na brine L-V-S, FIA22 FIA9 Ca-Na brine L-V-S, FIA4FIA24 medium salinity L-V, – FIA11 medium salinity L-V, – FIA20 FIA10 hetero- low salinity, L-V, FIA15
Summary Sample OLR12001-26.5 OLR12001-26.5 OLR12001-26.5 FIA21 OLR12001-26.5 FIA5 OLR12001-26.5 OLR12001-26.5 #2 FIA24 OLR12001-26.5 #2 FIA25 DJU18 DJU18 DJU18 DJU18 EJ-14-2A EJ-14-2A EJ-14-2A EJ-14-2B EJ-14-2B DJU18 EJ-14-2A OLR12001-26.5 #2 OLR12001-26.5 #2 FIA12 DJU09 DJU18 DJU26 Table A1. Table
50 Salinity (wt%) 40.0 53.7 19.3 23.6 49.3 0.7 0.9 ) ) ) ) ) ) ) ) ) ) ) ) ) ) H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O -(L -(L -(L -(L -(L -(L -(L mode 2 -(L -(L -(L -(L -(L -(L -(L CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 -V -V -V -V -V -V -V CO2 CO2 CO2 CO2 CO2 CO2 CO2 L L L L → L → L → L → L → L → L → L Th CO L L L 2 Th CO n.m. 2 56.9 12.1 56.7 27 56 30.4 55.9 30.6 56.9 27.3 57 27 56.8 56.1 29.6 – – – – – CO – – – L-V-S → L-S L-V-S Th Th mode Tm Th (Max) Th (Min) 315 367 357 → L L-V n.m. n.m.n.m. n.m. n.m. n.m. 120 295*107 245 107 → L-S L-V-S 107 236 327 248 → L L-V 1 Tm Ant 290 180 175 24.8 120 130 120 → L-S L-V-S Tm Halite 15.9 21.9 –0.4 – – Tm Ice 2 and L-V and L-V and L-V 2 2 2 2 2 2 2 2 O) verified by Raman spectroscopy. geneously trapped brine and CO brine and CO CO with varying salinity with varying salinity CO Co-existing CO Type L-V, low salinityL-V, –0.6 Fe-K-Ca brine and CO 2 ∙6H 2 FI Assem - blage FIA17 hetero- low salinity, L-V, FIA18FIA17 Ca-Na Co-existing L-V-S Ca-Na Co-existing L-V-S FIA19 Co-existing CO FIA29 FIA16FIA19 CO CO FIA25 FIA15 FIA30 FIA10 Na- Co-existing L-V-S Sample DJU26 DJU09 EJ-14-2B EJ-14-2B EJ-14-2A OLR12001-26.5 #2 OLR12001-26.5 #2 EJ-14-2A EJ-14-2A EJ-14-2A OLR12001-26.5 Melting of antarcticite (CaCl Table A1 continuation Table Data for the assemblages are reported as the median of several inclusions except for the minimum and maximum Th values; n.m. = not measured. 1 * Th and Tm (halite) measured after LA-ICP-MS analysis; high homogenisation temperatures may indicate stretching of fluid inclusions during ablation. in # the Value bracket is the measured Na/(Na+Ca) mass ratio from LA-ICP-MS analysis.
51 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A 6.5 3.2 269 271 34.8 40.5 55.3 L-V, L-V, 2545 11460 38650 FIA12 salinity 26.5 #2 medium OLR12001- <1 1.7 n.a. n.a. n.a. n.a. 116 14.9 98.8 L-V, L-V, 1370 4508 46400 salinity 26.5 #2 medium 8.7 4.7 7.8 11.8 9.8 109 n.p. 157 255 32.0 56.6 175 42.2 24.6 <0.5 brine FIA9 FIA11 Ca-Na L-V-S, L-V-S, 10 1.3 115 336 192 253 705 922 1223 11.6 17.2 <0.2 <1.2 183 40.0 18.1 1034 2473 8950 34100 2865 5840 brine Ca-Na L-V-S, L-V-S, EJ-14-2A EJ-14-2A OLR12001- 11 1.2 3.7 3.5 5.0 118 25.5 12.8 45.1 70.7 <0.2 brine Ca-Na L-V-S, L-V-S, DJU18 155143 144625 152500 2470 6.0 n.a. <8 n.a. <0.4 174 132 412 960 <0.04 <14 418 98 18.1 22.8 13.9 55.5 46.5 45.0 50.0 13.5 19.5 1768 1141 brine Ca-Na L-V-S, L-V-S, 178800 EJ-14-2B 494 668 467 198 724 391 19.9 87.8 48.0 brine 14430 Ca-Na L-V-S, L-V-S, DJU18 assemblages.
58 6.2 5.9 214 688 919 37.7 45.8 42.1 49.5 43.0 brine 10232 4703 Ca-Na L-V-S, L-V-S, EJ-14-2A inclusions
9.4 611 197 18.6 3490 brine fluid 15088 102 Na-Ca L-V-S, L-V-S,
26.5 #2 of OLR12001- averages n.a. 889 6867 9764 brine
11113 Na-Ca FIA24 FIA25 FIA12 FIA2 FIA22 FIA23 FIA23 L-V-S, L-V-S, 26.5 #2 as OLR12001- reported
5.8 2.5 2.5 7.5 11.3 209 102 276 50.4 554 1386 3631 brine FIA6 93325 67583 73075 24402 23352 23450 13814 19543 30718 26.5 #2 Fe-K-Ca L-V-S, Na- L-V-S, OLR12001- Data data.
7.0 4.4 946 76.8 85.4 38.4 33.1 51.4 24.5 63.5 32.8 1810 brine L-V-S, L-V-S, 26.5 #2 OLR12001- Na-Fe-K-Ca LA-ICP-MS
67 6.3 5.7 116 10.4 9.0 8.0 brine 45736 39700 35250 33109 36660 30238 13183 13351 3278 2270 FIA13 FIA20 26.5 #2 Fe-K-Ca L-V-S, Na- L-V-S, OLR12001- inclusion fluid of 9.0 7.0 n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. 185 95.9 145 135 240 133 9.2 1.2 465 295 405 425 254 183 261
29.0 22.6 24.6 23.7 17.2 45.0 45.0 45.0 45.0 31.0 30.5 52.0 42.9 26.5 <0.1 n.a. n.a. n.a. n.a. n.a. n.a. <0.6 n.a. 1437 1072 77.2 1515 3498 3359 92.3 31.8 2130 1675 89.3 2046 4073 3396 7263 5716 3680 5465 brine FIA1 25433 20709 15920 27181 40850 33863 165462 151857 47067 114000 88818 96640 Fe-K-Ca L-V-S, Na- L-V-S, OLR12001- Summary 2 2 Ba Cs Sr Rb Zn CaCl Fe Mn NaCl Ti Salinity (wt%) Ca K Mg Al FeCl Na KCl B Li (ppm) Type Sample FI Assemblage FI Table A2.. Table
52 25 <8 0.2 938 L-V, L-V, <0.03 <0.03 FIA12 salinity 26.5 #2 medium OLR12001- <5 n.p. <0.8 n.p. L-V, L-V, <0.07 salinity 26.5 #2 medium 98 5.9 brine FIA9 FIA11 Ca-Na L-V-S, L-V-S, 15 1.7 n.a. n.a. <0.04 <0.1 n.a. n.a. <0.01 n.a. n.a. <0.01 brine Ca-Na L-V-S, L-V-S, EJ-14-2A EJ-14-2A OLR12001- 71 8.82 2053 972 3047 brine Ca-Na L-V-S, L-V-S, DJU18 339 1.74 1.03 1.42 brine 11182 Ca-Na L-V-S, L-V-S, EJ-14-2B <19 <70 <4 n.a. n.a. 95.7 332 54.3 13.2 80.5 16.5 1.49 10.3 18.2 4.2 brine 33.95 8.54 10.3 Ca-Na L-V-S, L-V-S, DJU18 91 100 7.7 68.4 0.17 3183 6195 brine Ca-Na L-V-S, L-V-S, EJ-14-2A 73 <0.3 brine <0.02 Na-Ca L-V-S, L-V-S, 26.5 #2 OLR12001- 67 45.6 50 1974 4486 brine <0.07 <0.01 <0.02 <0.03 3.59 Na-Ca FIA24 FIA25 FIA12 FIA2 FIA22 FIA23 FIA23 L-V-S, L-V-S, 26.5 #2 OLR12001- 16 14.8 0.87 1056 brine FIA6 26.5 #2 Fe-K-Ca L-V-S, Na- L-V-S, OLR12001- 23 1.9 1.8 4.6 10.4 6.7 <1.2 <0.3 brine L-V-S, L-V-S, 26.5 #2 OLR12001- Na-Fe-K-Ca 11 <3 <59 <30 <9.5 <13 <3 10.5 16.5 <0.1 brine <0.03 <0.2 FIA13 FIA20 26.5 #2 Fe-K-Ca L-V-S, Na- L-V-S, OLR12001- 14 2.4 1.2 n.a. 18.4 0.85 1.24 <0.3 0.95 26.5 1910 744 880 2233 1595 376 1732 5105 6336 605 20.2 1827 92.3 15.3 443 brine FIA1 <0.02 <0.01 356333 265000 201000 257188 191333 190875 209923 266619 273000 214714 250250 230000 81950 68875 Fe-K-Ca L-V-S, Na- L-V-S, OLR12001- Al, (for Fe, and Ti) are uncertain and erratic; high concentrations may have resulted from analysed trapped solid inclusions in the fluid inclusions.
-3
-6 Br/Cl · 10 I Br Cl Nd Ce Y P Pb (ppm) I/Cl · 10 (molar) Sample (molar) Type FI Assemblage FI Table A2 continuation Table n.a. = not analysed during LA-ICP-MS analytical session. n.p. = not present in fluid inclusion, the element was removed during data processing. in italic Values
53