MASTER'S THESIS Mineralogy and Geochemistry of the Banded Iron-Formation in the Svartliden Gold Deposit, Northern Sweden Marjorie Sciuba Master of Science (120 credits) Exploration and Environmental Geosciences Luleå University of Technology Department of Civil, Environmental and Natural resources engineering Mineralogy and geochemistry of the Banded Iron-Formation in the Svartliden gold deposit, northern Sweden Marjorie Sciuba 2013 The fish doesn’t think, because the fish knows everything. Emir Kusturica, Arizona Dream Front cover: Picture of the Svartliden BIF Acknowledgements Firstly, I indebted Dragon Mining Sweden for the financial support. I warmly thank Roman Hanes for his precious time, because he never has time =) Not only he helped me sampling but appeared to be very patient in teaching and advising me in many ways. Without pushing anything, he showed me the way how a thesis should be. I also thank Kateřina Schlöglová for her help and the time she gave me: from teaching me Corel Draw to her help in mineralogy and in geochemistry. Thank you for your friendship and for being my housemate during a couple of months. I am grateful to Roman and Katia for their several corrections of the thesis. I thank Chris Gordon for giving me that topic the first time we met. Without you, this thesis would have never existed… Thanks for your help in structural geology and for your teaching especially in the field. I gratefully thank Roman and Chris for making me believe that my work would be useful somehow… Sushi Gordon is acknowledged for its support during a couple of weeks. I acknowledge Glenn Bark, my patient supervisor for his help and his advices even we were far away. Thank the whole exploration team of Dragon Mining: Henrik Ask, Leo Hedman, Tobias Lundmark, and of course Niklas Sääv, for their help during six months! I acknowledge also those people who offered me nicely their advices: the passionated David Dolejš who gave me all the keys of the geochemistry of my BIF, Laurent Tissandier from the CRPG in Nancy who allowed me to use the microprobe and Jean Marc Montel my headmaster in France, who first allowed me to come to study in Sweden and then helped with SEM data. Finally, I would like especially to thank un grand professeur, Mr Alain Cheilletz. In just one hour, he gave me the key of this study and made me see the light of the end of this master thesis. iv BADED IRO -FORMATIO I THE SVARTLIDE MIE , GOLD LIE Abstract The Svartliden gold deposit is situated in the Gold Line, South West of the Skellefte District, northern Sweden. It is considered an epigenetic lode style gold deposit dominated by a pyrrhotite- arsenopyrite assemblage. The gold mineralization, dominantly hosted by a volcano-sedimentary sequence, is structurally controlled and occurs along a ENE-trending steeply dipping shear zone. The deposit has been metamorphosed in low- to mid-amphibolite facies and is hydrothermally altered. The mineralization is hosted by a banded iron-formation (BIF) which is present along the host rock sequence. The boudinaged BIF units extend over 1 km and are from a few centimeters to 5 meters thick. The small size of Svartliden BIF is characteristic of Algoma-type BIF. Two scales of layering occur in the BIF: mesobanding, the most prominent structure because of metamorphism and microbanding. At lowest metamorphic grade, quartz-grunerite-magnetite is the dominant assemblage whereas clinopyroxene-fayalite-pyrrhotite are present in addition to those minerals in the highly metamorphosed BIF. Those mineral assemblages are characteristic of low- to mid- amphibolite facies. Gold occurs as inclusions in arsenopyrite, which is dominantly associated with pyrrhotite. The Svartliden BIF is closely associated with volcanic rocks such as amphibolites and ultramafic units. Metamorphism mobilized elements characteristic of hydrothermal input (Cu and Co), whereas Al 2O3, TiO 2, Zr, REE and Y stayed immobile. The (REE+Y)NASC pattern of the BIF shows evidence of both primary hydrothermal solutions and seawater whereas LREE enrichment and the positive Eu anomaly are a signature inherited from hydrothermal solutions. This indicates that the Svartliden BIF was formed by a mixture of seawater and hydrothermal fluids. The tectonic setting of the Gold Line and surrounding areas, interpreted as a volcanic back-arc environment, suggests that the Svartliden BIF is of Algoma-type. Key words : banded iron-formation, Svartliden, Gold Line, amphibolite facies, Algoma-type, Superior-type Corresponding author : email: [email protected] v Table of contents 1. Introduction ..................................................................................................................... 1 1.1. Aim of the study............................................................................................................. 1 1.2. Presentation of the main types of BIF............................................................................ 2 1.2.1. Algoma-type BIF .............................................................................................. 3 1.2.2. Superior-type banded iron-formation................................................................ 6 2. Regional geology............................................................................................................. 11 2.1. Bothnian Basin and Skellefte District............................................................................ 11 2.2. Gold Line mining district............................................................................................... 12 3. Geology of the Svartliden gold deposit........................................................................... 14 3.1. Discovery of the Svartliden gold deposit....................................................................... 14 3.2. Geological settings......................................................................................................... 15 3.2.1. Geology of the deposit...................................................................................... 15 3.2.2. Structural settings.............................................................................................. 16 3.3. Petrography of the Svartliden rock types ....................................................................... 18 3.3.1. Metavolcanic rocks ........................................................................................... 18 3.3.2. Metasedimentary rocks ..................................................................................... 19 3.3.3. Intrusive rocks................................................................................................... 21 3.4. Hydrothermal alteration and ore description.................................................................. 22 3.4.1. Proximal alteration and mineralization............................................................. 22 3.4.2. Distal alteration................................................................................................. 24 4. Methods........................................................................................................................... 25 4.1. Sampling ........................................................................................................................ 25 4.2. Analytical methods......................................................................................................... 26 4.2.1. Optical microscopy ........................................................................................... 26 4.2.2. Mineral chemistry ............................................................................................. 26 4.2.3. Whole rock geochemistry ................................................................................. 26 5. Geological description of the BIF at Svartliden.............................................................. 27 5.1. Localization, thickness and lateral extent of the BIF..................................................... 27 5.2. Relationship between the BIF and the other lithologies ................................................ 27 5.3. Layering and other structures based on metamorphic grade.......................................... 30 5.3.1. Type 1: least altered BIF................................................................................... 30 5.3.2. Type 2: moderatly altered BIF.......................................................................... 31 5.3.3. Type 3: strongly altered BIF............................................................................. 31 5.3.4. Micro-faulting and micro-folding ..................................................................... 33 5.4. Mineralogical and textural description of the BIF ......................................................... 34 5.4.1. Oxides and sulphides ........................................................................................ 34 vi BADED IRO -FORMATIO I THE SVARTLIDE MIE , GOLD LIE 5.4.2. Silicates and other minerals .............................................................................. 37 5.5. Geochemistry of the BIF................................................................................................ 42 5.5.1. Major oxides ..................................................................................................... 42 5.5.2. Trace elements .................................................................................................. 44 5.5.3. Rare earth elements..........................................................................................