Three-Dimensional Modelling of the Källfallsgruvan Iron Oxide Deposit
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Three-dimensional modelling of the Källfallsgruvan iron oxide deposit, Riddarhyttan ore field, Bergslagen, Sweden: Integrating existing and new data to aid understanding of structural controls and mineral exploration Edna Spahic Natural Resources Engineering, master's 2021 Luleå University of Technology Department of Civil, Environmental and Natural Resources Engineering Acknowledgements The Geological Survey of Sweden (SGU) has provided the financial support to this study (FoU project 36-1341/2019). I therefore extend my greatest gratitude towards SGU for making this project possible. I would like to give a special thanks to my supervisor Tobias Kampmann for the continued assistance, patience, and motivation during this thesis. I could not have asked for a better supervisor. I am also thankful for my external supervisor Stefan Luth (SGU) who has been of great help both during the field work and in the understanding of structural geology. Your input throughout this project has been of great value. I would also like to thank Alexander Lewerentz (SGU) for his aid during the field work as well but also for providing me with valuable information to improve this thesis. In addition, I would like to thank Peter Hedin (SGU) for providing me with a detailed magnetic map over the Riddarhyttan ore field. I would like to thank Jerry Hedström and the whole SGU team at the national drill core archive in Malå for making it possible to conduct the drill core logging and for the support during sampling of drill core sections. I would like to extend my gratitude to Wilfried Tsoblefack working in the support department for helping me with any questions regarding SKUA-GOCAD 19, you always made time to help and supported me from start to finish. I would like to express my sincere gratitude to my family, friends, and boyfriend. They have provided constant encouragement and pushed me all the way during this journey and always believed that I can achieve anything I want if I just believe in myself. I would like to highlight my brother Edin, he has always been my role model and been of great support during my time at LTU. Ti si najbolji brat što se moze poželjeti! Luleå, June 2021 Edna Spahic Abstract The Bergslagen ore province, located in the Fennoscandian shield in the south-central part of Sweden hosts several metallic mineral deposits, one of them being the Källfallsgruvan iron- oxide deposit in the Riddarhyttan ore field, situated in a high-strain shear belt denoted as the West Bergslagen Boundary Zone (WBBZ). An accurate 3D geological model of the Källfallsgruvan iron-oxide deposit has been generated to aid understanding of the ore body geometries and calculating volume and tonnage. The methodology of this study consisted of assessing existing data in the form of legacy mine maps and to integrate new data from field work, drill core logging and 3D geological modelling. The work has resulted in structural interpretations that are put in the context of the regional structural framework in Bergslagen consisting of three deformation events (D 1, D2 and D3) and two metamorphic events (M1 and M2). The field work resulted in six rock units being defined used to construct a geological map, in addition the structural measurements resulted in a hypothetical semi-regional fold and evidence of ductile strike-slip/dip-slip shearing. Logging of drill cores resulted in three rock units being defined, two of them related to the mineralization and one characterizing the host rock (± local variations), correlating to the observed host rock from the field work. The rock units discovered from both the field work and drill core logging are all interpreted to be the metamorphic products of volcanic rocks subjected to alteration of varying degree. Based upon geological field observations with subsurface data and 3D geological modelling it is concluded that, 1) The deposit comprises multiple ore bodies that jointly resemble an S- shaped synform that is steeply inclined-upright, moderately-steeply plunging towards the southwest with an axial plane striking northeast-southwest. The deposit is interpreted to be geometrically controlled by an F2 fold, possibly displaying an interference pattern of type 1, favouring progressive shearing and deformation solely related to D2, 2) Evidence of at least one generation of transpressional tectonic regime exists, interpreted to be D2, 3) The estimated tonnage of 4 938 610 tons of the massive magnetite and semi-massive mineralization revealed that a deposit of such tonnage is presently not economically viable. However, if the Källfallsgruvan iron-oxide deposit or similar is determined to have a significant REE content, such deposit may then be of economic interest and, 4) Possible mineral exploration indicators around Källfalls-like deposits are intensely altered rocks related to magnesium alteration, consisting dominantly of quartz, biotite (increasing towards mineralization), muscovite, chlorite, anthophyllite and cordierite, affected by parasitic folding. Sammanfattning Bergslagen malmprovins, belägen i den Fennoskandiska skölden i sydcentrala delen av Sverige innehåller flera metall mineralfyndigheter, varav en av dem är Källfallsgruvan järnoxidfyndighet i Riddarhyttan malmfält, belägen i en skjuvzon kallat för ”West Bergslagen Boundary Zone (WBBZ)”. En representativ 3D geologisk model av Källfallsgruvan järnoxidfyndighet har genererats för att öka förståelsen av malmkroppens geometrier samt beräkna volym och tonnage. Metodiken bestod av att bedöma existerande data så som gruvkartor och integrera nya data genom fältarbete, borrkärnekartering och 3D geologisk modellering. Arbetet resulterade i strukturella tolkningar som sattes i kontexten av den regionala strukturella bilden i Bergslagen bestående av tre deformations event (D1, D2 och D3) och två metamorfa event (M1 och M2). Fältarbetet resulterade i att sex bergartsenheter definierades som användes för att konstruera en geologisk karta samt så har de strukturella mätningarna resulterat i ett hypotetiskt semi-regionalt veck och bevis för duktil strike-slip-/normal-skjuvning. Borrkärnekarteringen resulterade i att tre bergartsenheter definierades, varav två var relaterade till mineraliseringen och en kännetecknade värdbergarten (± lokala variationer) som korrelerar med den observerade värdbergarten från fältarbetet. Bergartsenheterna som upptäcktes från både fältarbetet och borrkärnekarteringen har tolkats vara metamorfa produkter av vulkaniska bergarter som omvandlats i varierande grad. Baserat på de geologiska fältobservationerna med underjordsdata och 3D geologisk modellering dras följande slutsatser, 1) Fyndigheten består av multipla malmkroppar som gemensamt liknar en S-formad synform som är brant lutande-upprätt, måttligt-brant stupande mot sydväst med ett axialplan som stryker nordost-sydväst. Fyndigheten tolkas vara geometriskt kontrollerat av ett F2 veck, som möjligtvis påvisar ett interferensmönster av typ 1 bildat genom progressiv skjuvning och deformation endast relaterat till D2, 2) Bevis för minst en generation av transpressionstektonisk miljö existerar vilket tolkats vara D2, 3) Det estimerade tonnaget på 4 938 610 ton för den massiva magnetit och semi-massiva mineraliseringen visade att en fyndighet av sådant tonnage är för nuvarande inte ekonomiskt hållbart. Om Källfallsgruvan järnoxidfyndighet eller liknande fyndighet bestäms att ha ett betydande REE innehåll så skulle en sådan fyndighet vara av ekonomiskt intresse och, 4) Möjliga prospekteringsindikatorer runt Källfalls-liknande fyndigheter är intensivt omvandlade bergarter relaterad till magnesiumomvandling främst bestående av kvarts, biotit (ökar mot mineraliseringen), muskovit, klorit, antofyllit och kordierit, påverkad av parasitisk veckning. Table of contents 1. Introduction ...................................................................................................................1 2. Geological background ....................................................................................................3 2.1 Regional geology of the Bergslagen ore province ..........................................................3 2.2 Semi-regional geology of the Riddarhyttan ore field ......................................................7 2.3 Källfallsgruvan iron-oxide deposit ..............................................................................8 3. Method........................................................................................................................ 10 3.1 Existing data.......................................................................................................... 10 3.2 New data............................................................................................................... 12 3.2.1 Field Work ..................................................................................................... 12 3.2.2 Drill core logging ............................................................................................ 12 3.2.3 Modelling process ........................................................................................... 13 3.2.3.1 Preparation required before 3D modelling........................................................ 13 3.2.3.2 Geological 3D modelling .............................................................................. 14 3.2.3.3 Adjustments of the 3D model......................................................................... 16 3.2.4 Tonnage estimation of the Källfallsgruvan iron-oxide deposit ...............................