GEOTECHNICAL REPORT 6 FinlandsTHE FINNISH Stenindustri-NATURAL STONE förbundASSOCIATION rf Natural stones of the Kuru granite batholith in south-central Finland Olavi Selonen, Paavo Härmä and Carl Ehlers 2017 THE FINNISH NATURAL STONE ASSOCIATION Geotechnical report 6 Natural stones of the Kuru granite batholith in south-central Finland YHTEENVETO: Kurun graniittialueen rakennuskivet Olavi Selonen Åbo Akademi University Department of natural sciences Geology and Mineralogy FI-20500 Turku, Finland E-mail: [email protected] Paavo Härmä Geological Survey of Finland FI-02151 Espoo, Finland E-mail: [email protected] Carl Ehlers Åbo Akademi University Department of natural sciences Geology and Mineralogy FI-20500 Turku, Finland E-mail: [email protected] ISSN 2489-3161 Layout: Sonck-Koota Publisher: The Finnish Natural Stone Association P.O.Box 381, FIN-00131 HELSINKI www.suomalainenkivi.fi Front cover. The Satakunta bridge across the Tammerkoski rapids in Tampere, Finland. The bridge is built in grey granite from Kuru. Photo: Olavi Selonen. Small photo: www.suomalainenkivi.fi Kansikuva. Tampereen Satakunnansilta on rakennettu Kurun harmaasta graniitista. Kuva: Olavi Selonen. Pikkukuva: www.suomalainenkivi.fi HELSINKI 2017 GEOTECHNICAL REPORT 6 CONTENTS 1 Introduction ....................................................................................................................... 2 2 Geological outline ............................................................................................................. 2 3 Rock types of the Kuru batholith ..................................................................................... 4 3.1 Grey granite .........................................................................................................4 3.2 Red granite ..........................................................................................................5 3.3 Mafic rocks ..........................................................................................................6 4 The geological structure of the Kuru batholith .............................................................. 6 4.1 Geological control of natural stone deposits in the Kuru batholith ..................7 5 Natural stone production in the Kuru batholith ............................................................. 8 5.1 Kuru Grey ........................................................................................................................8 5.2 Kuru Redbrown ...............................................................................................................9 5.3 Kuru Black ................................................................................................................... 10 6 Geotechnical features of the Kuru Grey granite ........................................................... 10 6.1 Rock stress in the Kuru Grey granite .......................................................................... 12 7 Assessment of suitability of the rock types of the Kuru batholith as natural stone .. 13 7.1 Grey granite .................................................................................................................. 13 7.2 Red granite and mafic rocks ....................................................................................... 14 7.3 Further investigations .................................................................................................. 14 8 Concluding comments ................................................................................................... 14 Acknowledgements .............................................................................................................. 15 References ............................................................................................................................ 15 YHTEENVETO: Kurun graniittialueen rakennuskivet.......................................................... 18 APPENDICES ........................................................................................................................ 24 1 The Finnish Natural Stone Association 1 INTRODUCTION Aurola (1967), no recent compilation of data on the natural stones of the batholith has been The Kuru granite batholith1 in south-central published. Our aim is to provide the reader with Finland, is one of the areas where natural stone the basic information on the area combined has been produced for more than a century. with a comprehensive list of literature for further Extraction of grey granite started in the mid- reading. The batholith area was revisited by the 19th century for constructions in the city of authors in 2016‒17. Tampere, approx. 50 km south of Kuru (Aurola 1967, Kylkilahti 1989). 2 GEOLOGICAL OUTLINE From being a local site of stone production, the extraction industry in the area has developed The Kuru granite batholith is located in south- into an essential production centre for Finnish central Finland around the Lake Vankavesi (an natural stone. Today, the classical Kuru Grey is a open lake area in the northern part of the Lake regular choice in the selection of Finnish granites Näsijärvi) mainly in the areas of Kuru and Kapee on the global natural stone market (Selonen & in the municipality of Ylöjärvi and in the city of Härmä 2003, Selonen et al. 2012). The Kuru Tampere, respectively (Fig.1). A small strip of batholith belongs to the best-known granite the eastern part of the batholith is situated in the production areas in Finland together with the municipality of Ruovesi. The batholith covers an Wiborg batholith in southeastern Finland and area of approx. 100 km2 shown on the Finnish the Vehmaa batholith in southwestern Finland Geological Survey map-sheets 2213 and 2214 (Selonen et al. 2016) (App. 1). (Simonen 1952, Matisto 1961, Nironen 2003). Geological maps with explanations by Simonen The Kuru batholith consists of intrusions of 1. (1952), Matisto (1961), and Nironen (2003) grey granite, 2. red granite, and 3. mafic rocks cover the Kuru batholith. Geological features varying from gabbro and diorite to quartz and natural stones of the batholith have been gabbro, quartz diorite, and hornblende gabbro studied by Aurola (1967), Härmä et al. (2006), (“black granites”), the grey granite being the Nyman (2007), and Selonen et al. (2012). main rock type (Selonen et al. 2012) (Fig. 2). The usability of the leftover material from the Kuru Grey quarries was investigated by In a regional geological context, the Kuru Vasenius (1998). The history of the natural batholith is situated in the southern part of the stone production is described by Aurola (1967) Central Finland Granitoid Complex (CFGC) and Kylkilahti (1989), and the history of the (Fig. 2). The CFGC comprises different production of rollers for paper machines by synkinematic intrusions, from gabbros to Peltola et al. (2012, 2014, 2015). Geotechnical granites (1890‒1880 Ma), consisting mainly of and material properties of the Kuru grey granite foliated coarse-grained granites and granodiorites have been studied, e.g. by Aurola (1967), (Nironen 2005, Nikkilä 2016, Mikkola et al. Ahtiainen (1974), Mononen (2005, 2006), 2016, Nironen 2017). Undeformed or weakly Pérez (2009), Saksala et al. (2013), Formeau et foliated postkinematic intrusions (1880‒1870 al. (2014), Saksala et al. (2014), and Hokka et Ma) are found around the margins of the CFGC al. (2016). (Selonen & Ehlers 1996, Nironen et al. 2000, Nironen 2005). The age of the grey granite in For this geotechnical report, we have compiled the Kuru batholith is 1875±5 Ma (Nironen the currently available knowledge on the 2003), indicating an age of emplacement after geological features and the natural stones of the culmination of the 1890‒1880 Ma old the Kuru granite batholith. Since the report by Svecofennian orogeny. 1 A batholith is a large, generally discordant plutonic Tectonically, important features around the (granitic) body, having an aerial extent of 100 km2 or Kuru batholith are prominent NW‒SE and more and no known floor (Jackson 1997). 2 GEOTECHNICAL REPORT 6 Siikalahti Jäminkipohja ± Hulipas Kekkonen Kuru Hyytiälä Hainari Niemikylä Murole Muhujärvi Vekara Vankavesi Kapee JUUPAJOKI Hankala Parkkuu 66 Korkeakoski Heinälammi Kaanaa Lauttakulma 58 Velaatta Viteli Kokkila Länsi-Teisko Ukaa Enokunta Hirsilä 338 Terälahti Aakkola NÄSIJÄRVI 65 Savonkylä Kulju Teisko Asuntila Kutema Viitapohja ORIVESI Hanhilahti Kyöstilä Kämmenniemi Koppala Yliskylä Paavola Vahanta Pulesjärvi Värmälä 9 Säynäjärvi Eräjärvi Aitoniemi YLÖJÄRVI Suinula Kivisalmi Aitolahti 58 3 Ruutana Längelmävesi 65 TAMPERE E12 12 11 E63 0 10 km KANGASALA Figure 1. Geographical location of the Kuru granite batholith in the northern part of the Lake Näsijärvi (indicated by a rectangle) in south-central Finland. Kuva 1. Kurun graniittialueen maantieteellinen sijainti Näsijärven pohjoisosassa Pirkanmaalla. NE‒SW trending fracture zones, shear zones, They show en echelon patterns and bayonet- and lineaments, extending towards north of the structures. The diabases are fine and even- batholith (Selonen & Ehlers 1996, Nironen et grained, comprising small non-oriented needle- al. 2000, Nironen 2003). like plagioclase laths. The matrix is composed chiefly of amphibole with some biotite, and The host rocks to the Kuru batholith include opaque minerals. 1890‒1880 Ma old intrusions of Svecofennian granodiorites (Fig. 2). The granodiorites are even-grained or carrying feldspar phenocrysts (Aurola 1967, Nyman 2007). Greenish-black, younger (ca 1645 Ma) diabase dykes