UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre PREDICTIVE PROSPECTIVITY MAPPING OF RARE EARTH ELEMENTS IN BASTNÄS (SKARN)-TYPE ORE DEPOSITS IN WESTERN BERGSLAGEN,SWEDEN INTEGRATION AND ANALYSIS OF GEOSCIENCE DATASETS IN ARCGIS Ejiro Obotuke-Agbonifo ISSN 1400-3821 B961 Master of Science (120 credits) thesis Göteborg 2017 Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN Table of contents 1. INTRODUCTION .................................................................................................................................... 4 1.1 AIM AND APPROACH ...................................................................................................................... 4 1.2 ABOUT RARE EARTH ELEMENTS .................................................................................................. 7 1.3 GENERAL CHARACTERISTICS OF BASTNÄS-TYPE REE MINERALIZATION ............................... 9 1.4 MINING HISTORY OF BERGSLAGEN ............................................................................................ 13 2. BACKGROUND .................................................................................................................................... 15 2.1 REGIONAL GEOLOGY OF BERGSLAGEN....................................................................................... 15 2.2 LOCAL GEOLOGY OF BERGSLAGEN ............................................................................................. 17 2.3 BEDROCK OF STUDY AREA .......................................................................................................... 20 2.4 STRUCTURAL GEOLOGY OF STUDY AREA ................................................................................... 23 2.5 METAMORPHISM OF STUDY AREA.............................................................................................. 25 2.6 ALTERATION IN STUDY AREA ..................................................................................................... 26 3. MATERIALS AND METHODS .............................................................................................................. 29 3.1 PRINCIPLES OF PREDICTIVE MODELING .................................................................................... 29 3.1.1 MECHANISTIC APPROACH .................................................................................................... 30 3.1.2 EMPIRICAL APPROACH ......................................................................................................... 30 3.2 PREDICTIVE PROSPECTIVITY MODELING WITH ARCGIS .......................................................... 31 3.3 PROCEDURE FOR MINERAL EXPLORATION PREDICTIVE MODELING ..................................... 32 3.4 GENERALIZED CRITERIA FOR POTENTIAL EXPLORATION ...................................................... 33 3.4.1 EXPLORATION DATA USED ................................................................................................... 35 3.5 MINERAL DEPOSITS OF REE IN STUDY AREA ............................................................................ 36 4. CRITERIA FOR REE MINERALIZATION EXPLORATION IN BERGSLAGEN ...................................... 39 4.1 GENERAL CLASSIFICATION OF DEPOSITS IN BERGSLAGEN ..................................................... 39 4.2 CONCEPTUAL MODEL FOR BASTNÄS-TYPE DEPOSITS ............................................................. 39 Lithology .......................................................................................................................................... 39 Mineralization ................................................................................................................................. 39 Geophysics ....................................................................................................................................... 39 Geochemistry ................................................................................................................................... 39 Alteration ......................................................................................................................................... 40 Heat source ...................................................................................................................................... 40 5. SPATIAL EXPLORATION FACTORS .................................................................................................... 41 2 5.1 HOST ROCK FACTOR ..................................................................................................................... 41 5.2 HEAT SOURCE FACTOR ................................................................................................................ 43 5.3 GEOCHEMICAL FACTORS ............................................................................................................. 44 5.3.1 Biogeochemistry ..................................................................................................................... 49 5.3.2 Lithogeochemistry ................................................................................................................. 53 5.4 STRUCTURAL FACTOR.................................................................................................................. 56 5.5 GEOPHYSICAL FACTOR................................................................................................................. 57 5.6 ALTERATION FACTOR .................................................................................................................. 59 6. PROSPECTIVITY MODELING .............................................................................................................. 67 6.1. SPATIAL ASSOCIATION ANALYSIS .............................................................................................. 70 6.1.1 SPATIAL ASSOCIATION WITH HOST ROCK .......................................................................... 70 6.1.2 SPATIAL ASSOCIATION WITH HEAT SOURCE ..................................................................... 72 6.1.3 SPATIAL ASSOCIATION WITH GEOCHEMICAL ANOMALIES............................................... 73 6.1.4 SPATIAL ASSOCIATION WITH GEOPHYSICAL FACTOR ....................................................... 78 6.1.5 SPATIAL ASSOCIATION WITH STRUCTURAL FACTOR ........................................................ 80 7. DISCUSSION AND VALIDATION ......................................................................................................... 81 7.1 CONDITIONAL INDEPENCE TEST ................................................................................................ 82 7.2 WEIGHTED OVERLAY MINERAL POTENTIAL MAP .................................................................... 83 7.3 CONCLUSION ................................................................................................................................. 85 Acknowledgements ................................................................................................................................. 89 REFERENCES ........................................................................................................................................... 90 3 1. INTRODUCTION 1.1 AIM AND APPROACH Rare earths minerals are not minerals that have usually attracted attention but recent events have put the spotlight on them as the rare-earth elements (REEs) has, now become a more sought–after natural resource and for that reason, it has earned more attention from several scientists especially mineralogists, geologist and exploration districts around the world (Chakhmouradian & Wall, 2012). Modern societies, are now anxious to obtain this resource needed for many technological developments. The REEs which have grown to become economically significant reserves are known to be constituents in Irons as well as other metals such as flour-apatite, phosphate and REE-silicates (Jonsson et al., 2013). As documented by several researchers, Sweden stands as a major producer of iron in Europe and the apatite-iron- oxide ores of the Grängesberg Mining District (GMD) is one of the largest iron ore accumulations in Bergslagen along-side iron oxide deposits of banded-iron and skarn-iron ores which also occur in the Bergslagen province (Jiao J, 2011). Though Sweden has been known to be the "home of the rare-earth elements", following the fact that several of REEs were first discovered here during the late 18th and early 19th centuries (www.eurare.se; Jansson, 2011, p. 1), it has not ranked as a major producer of this rare metals in most recent times globally (Klinger, 2015). However, seeing that the REE metals are becoming most recently a highly sought-after resource in the global market today, it has become a need to look again into prospects of the REE mineralization here in Sweden. There have been various researches which have shown occurrences of REE mineralization in restricted number of deposits within Sweden as shown in figure 1 and in other to increase the percentage of REE production, there is need to know favourable areas for REE mineralization with consideration of mineral system and available geological, geochemical and geophysical data. This project therefore, seeks to evaluate the prospectivity potential for the REEs in the Bastnäs- type also known as the skarn-iron ores in the Western Bergslagen province of Sweden.