FACULTY OF SCIENCE AND TECHNOLOGY DEPARTMENT OF GEOLOGY Petrography, geochemistry and genesis of the Skiftesmyr Cu-Zn VMS- deposit, Grong, Norway Kristoffer Jøtne Walsh GEO-3900 Master’s Thesis in Geology November 2013 GEO-3900 Master’s Thesis in Geology PETROGRAPHY, GEOCHEMISTRY AND GENESIS OF THE SKIFTESMYR CU-ZN VMS-DEPOSIT, GRONG, NORWAY Kristoffer Jøtne Walsh Department of Geology, UiT – The Arctic University of Norway, November, 2013 2 3 Acknowledgements I wish to thank my supervisors, Professor Kåre V. Kullerud and Perry O. Kaspersen, former CEO and Country Manager of MetPro AS, for all their help and comments, and MetPro AS for making this thesis possible. I would also like to thank Professor Erling Krogh Ravna for assistance with the XRF analyses, and express my gratitude to former MetPro AS geologist Stefan Winterhoff for assistance with field work, and Per Samskog, MetPro AS exploration geologist, for MapInfo tutoring. Last, but not least, I would like to thank my family, friends and fellow students for their support and encouragement. Kristoffer Jøtne Walsh Tromsø, Nov. 2013 4 5 Abstract The Skiftesmyr Cu-Zn VMS-deposit is located in the Grong municipality of Northern Trøndelag, Norway. The mineralization has been known since at least 1903, when mention of small workings in the area were first published, and has later been the subject of several exploration projects by different companies, of which MetPro AS is the latest. The Skiftesmyr deposit is a part of the Gjersvik Nappe, which is a part of the Köli Nappe Complex, which in turn is a part of the Upper Allochthon of the Scandinavian Caledonides, and is likely of Mid- Ordovician age. Petrographic and geochemical studies were carried out on samples from trenches cutting across the mineralized horizons. Geochemical analyses performed on the igneous rocks suggest that the deposit formed in a back-arc environment in relation to a relatively mature (compared to e.g. the Skorovas and Gjersvik deposits) island arc. In terms of lithological associations Skiftesmyr can be classified as bimodal-mafic and/or mafic- dominated, depending on the interpretation of the available geochemical data, and has several traits in common with both the Noranda deposits, Quebec, and the deposits of the Troodos Massif, Cyprus. The dominant ore minerals are chalcopyrite and sphalerite, with only minor amounts of Cu-enriched sulphides associated with supergene enrichment processes present. 6 7 Table of contents: 1. Introduction .......................................................................................................................... 10 1.1. Context of the study: ...................................................................................................... 10 1.2. Purpose of the study ...................................................................................................... 11 1.3. The Skiftesmyr deposit .................................................................................................. 12 1.4. Previous work ................................................................................................................ 13 1.5. Geology of the Skiftesmyr area ..................................................................................... 15 1.5.1. Regional geology .................................................................................................... 15 1.5.2. Rocks, structures and tectonostratigraphy of the Gjersvik Nappe .......................... 17 1.6. VMS-type deposits ........................................................................................................ 20 1.6.1. Introduction ............................................................................................................. 20 1.6.2. VMS deposits of the world ..................................................................................... 20 1.6.3. The formation of volcanogenic massive sulphide deposits .................................... 21 1.6.4. Classifications of VMS deposits ............................................................................. 22 1.6.5. VMS deposits of the Norwegian Caledonides ........................................................ 29 2. Methods ................................................................................................................................ 30 2.1. Sample collection and trenching .................................................................................... 30 2.2. Geochemistry ................................................................................................................. 30 2.2.1. ME-ICP61 ............................................................................................................... 30 2.2.2. XRF ......................................................................................................................... 32 2.3. Production of thin sections ............................................................................................ 32 2.4. Microscopy .................................................................................................................... 32 3. Observations ......................................................................................................................... 34 3.1. Observations in thin section .......................................................................................... 34 3.1.1. Different lithologies present in the samples ............................................................ 34 3.2. Observations in reflected light ....................................................................................... 44 3.2.1. Samples from the mineralized zones ...................................................................... 44 3.2.2. Disseminated opaque grains in host rocks .............................................................. 52 3.3. Geochemistry ................................................................................................................. 53 3.3.1. Volcanic and volcanogenic rocks ........................................................................... 53 3.4. Field relationships and trench mapping ......................................................................... 66 4. Discussion ............................................................................................................................ 68 8 4.1. Genesis of the deposit .................................................................................................... 68 4.1.1. Metallogeny ............................................................................................................ 68 4.1.2. Volcanostratigraphy ................................................................................................ 68 4.1.3. Igneous rock classification and determination of magmatic affinity and tectonic setting using trace element geochemistry ......................................................................... 69 4.1.4. Quartz keratophyres and felsic samples .................................................................. 70 4.1.5. Deposit genesis ....................................................................................................... 73 4.2. Ores and ore minerals .................................................................................................... 78 4.2.1. Ores and ore minerals ............................................................................................. 78 4.2.2. Precious metals ....................................................................................................... 79 4.2.3. Alternate uses for waste rocks and tailings ............................................................. 80 4.3. Alteration ....................................................................................................................... 80 4.4. Surface weathering ........................................................................................................ 86 4.4.1. Features of surface weathering and supergene enrichment .................................... 86 4.4.2. Surface weathering and acid mine drainage (AMD) .............................................. 89 4.5. Deformation structures in sulphides .............................................................................. 91 5. Conclusion ............................................................................................................................ 94 References: ............................................................................................................................... 96 Appendices: ............................................................................................................................ 102 1. Abbreviated mineral names and other commonly used abbreviations ........................... 102 1.1 Abbreviated mineral names (from Kretz, 1983) ....................................................... 102 1.2 Commonly used abbreviations and terms ................................................................. 103 2. Trench collar locations ................................................................................................... 104 3. Geochemical data ........................................................................................................... 105 3.1. ALS geochemical data (ME-ICP61 & AuAA23 ..................................................... 105 3.2. XRF geochemical data ............................................................................................