MASTER'S THESIS Mineral Chemistry of Gangue Minerals in the Kiirunavaara Iron Ore Joakim Nordstrand Master of Science (120 credits) Exploration and Environmental Geosciences Luleå University of Technology Department of Civil, Environmental and Natural resources engineering Fall 08 Till T. Abstract The iron-ore of Kiirunavaara is one of the largest magnetite-apatite mineralisation in the world. It is well known for its purity and size and its origin has been the subject of an intense debate for over a century. The composition of the most important minerals from an economic point of view, magnetite and apatite, has been well studied but little is known about the composition and role of the silicate minerals. Nowadays, even the silicates have been targeted for investigations, both in Kiirunavaara and in similar deposits elsewhere, e.g., Sierra la Banderra, Chile. The growing interest derives mainly from the importance of the gangue minerals in ore processing but also because they might hold the key to the origin of the ores. In this study, a large scale microprobe investigation of over 250 analyses has been carried out mainly focussing on silicates within the ore body but also to some extent on sulphates, phosphates and carbonates. Most of the analysed grains belonged to either the amphibole group or the mica group. Amphiboles and micas are by far the most abundant silicates within the ore body. Through (EMPA) analysis of 198 separate mineral grains, this investigation led to the broadest and most updated characterisation of silicates within the Kiirunavaara ore body. It also briefly looks at setting and chemistry of sulphates, phosphates, and carbonates. This study indicates that silicates may have been formed during shifting periods of crystallization and chemical environments, and that the mineral assemblage and composition do not oppose a magmatic origin. Aknowledgements I would like to thank the mine planning department at LKAB and my manager, Carlos Quinteiro for providing the resources needed to carry out this study. I would also like to thank Lassi Pakkanen and Bo Johansson for their help and hospitality during my visit at GTK, Espoo. I also want to send a special thanks to Nils Jansson and Therese Bejgarn at LTU for guiding me through some difficult hours of petrography. Thanks also to my supervisor at LTU, Olof Martinsson for planning and aiding during petrographic sessions, as well as my opponent, Ivar van der Stijl for his thorough work when inspecting this thesis. Sincere thanks also goes to Fredrik Johansson for a professional help regarding lay-out of pictures and diagrams. And to Jaqueline Nason for an indispensable help in language correction. I would also like to extend my sincere appreciation to my family, especially Lucile, for coping with my late nights at the office and my extra days of work during our vacations. Last but not least, my deepest gratitude to my supervisor at LKAB, Ulf B. Andersson, for hours of reading, editing, calculating and guiding me in the right direction. It has been tough at times but a learning experience. Contents Chapter 1: Introduction ............................................................................................... 1 Regional geology .................................................................................................... 2 Local Geology ......................................................................................................... 4 Ore body description ............................................................................................... 4 Kiruna type ore ........................................................................................................ 5 Methodology ............................................................................................................... 7 Sampling ................................................................................................................. 7 Analysis ................................................................................................................... 7 Data processing ...................................................................................................... 8 Results ........................................................................................................................ 9 Silicates ................................................................................................................... 9 Amphibole ........................................................................................................... 9 Mica ................................................................................................................... 12 Chlorite .............................................................................................................. 15 Talc and clay-minerals ....................................................................................... 17 Titanite ............................................................................................................... 19 Allanite ............................................................................................................... 19 Epidote .............................................................................................................. 21 Zircon and thorite............................................................................................... 21 Feldspar and quartz ........................................................................................... 21 Carbonates ........................................................................................................... 22 Sulphates and phosphates .................................................................................... 23 Oxides ................................................................................................................... 24 Discussion ................................................................................................................ 25 Silicates ................................................................................................................. 25 Amphibole ......................................................................................................... 25 Mica and chlorite ............................................................................................... 27 Talc and clay-minerals ....................................................................................... 29 Titanite ............................................................................................................... 30 Allanite ............................................................................................................... 32 Zircon and thorite............................................................................................... 32 Carbonates ........................................................................................................... 33 Conclusions .............................................................................................................. 35 Amphibole ............................................................................................................. 35 Mica ...................................................................................................................... 35 Chlorite .................................................................................................................. 36 Talc ....................................................................................................................... 36 Titanite .................................................................................................................. 36 Zircon and thorite .................................................................................................. 36 Carbonates ........................................................................................................... 36 Sulphates and phospates ...................................................................................... 37 In general .............................................................................................................. 37 Recommendations .................................................................................................... 38 Bibliography .............................................................................................................. 40 Chapter 1: Introduction The Kiirunavaara ore body is one of the world’s largest magnetite-apatite mineralisation. It is famous worldwide for its size, quality and mining method. For more than a hundred years, the town of Kiruna has depended on its iron ores. More than a billion tonnes has already been mined out of Kiirunavaara alone. Despite its importance, there are still questions regarding its specific composition and the discussion regarding its origin is still one of the most intense debates in the science of economic geology. The importance of understanding this ore body, from mineralogical, structural and ore-genetical points of view is increasing as the production is advancing deeper and the demand for iron ore is increasing. Few previous studies have been carried out over the years to characterize the silicate mineralogy of the Kiirunavaara iron ore, where the most recent studies mainly focused on the characterisation of REE- bearing minerals (Parak, 1973; Harlov et al., 2002; Edfelt, 2007; Smith et al., 2009). The silicate composition is important both for ore extraction purposes