Polymetallic mineralisation at Hornkullen, Western Bergslagen: a metamorphosed Svecofennian formation?

• Autorzy: Andersson S.
• Języki publikacji: EN

Abstrakty

EN

Although the Fe-Pb-Cu-(As-Ag) mineralization at Hornkullen in the classic Bergslagen ore province has been a subject of economical assessments earlier in addition of being mined intermittently during the last 100s of years, the metallogenesis of the deposit is poorly constrained. The region enclosing the deposit has experienced a rather complex geological and tectonic evolution; consequently several conceivable processes that could have influenced the mineralization need to be considered. The mineralization, which is situated in the western part of the Bergslagen province in Sweden, is hosted in ca 1.90-1.88 Ga Svecofennian metavolcanic and metasedimentary rocks. These were deposited in association with an extensional back-arc system inboard an active continental magmatic region (Allen et al. 1996). This succession subsequent underwent deformation and metamorphism during the Svecokarelian orogeny in regional greenschist to amphibolite facies (e.g. Stephens et al. 2008). At the western margin, the area was later intruded by younger granitoid rocks, (referred to as the GSDG intrusive rocks suite (Stephens et al. 2009) or the Trans-scandinavian Igneous Belt (e.g. Hogdahl et al. 2004), locally the so-called Filipstad granite, dated at 1783 ± 10 Ma (Jarl & Johansson, 1988). The metasupracrustal rocks in the Hornkullen area are enclosed as an inlier in this intrusive suite. The region has also locally been affected by the ca 1.0-0.9 Ga Sveconorwegian orogeny (e.g. Stephens et al. 2009), probably in a brittle regime. The present hypothesis is that the mineralization is syngenetic, i.e. formed in conjunction with the Svecofennian volcanic activity. However, as stressed so far, the mineralization has been affected by several thermal and deformational processes following its formation. The aim of this project is therefore to assess whether the deposit comprises of metamorphically overprinted, syn-volcanic assemblages or not. To assess this, comprehensive studies of phase and textural relations on ore minerals were conducted. Additionally, fluid inclusion analysis is planned that would give further constrain on the ore-forming fluid. Tentative results so far suggest overprinting of brittle structures to some extent in the ore mineralogy.

Słowa kluczowe

EN

mineralisation; Hornkullen; Svecofennian formation

• Wydawca: Wydawnictwa AGH
• Czasopismo: Geology, Geophysics and Environment
• Rocznik: 2012
• Tom: Vol. 38, no. 4
• Strony: 454--455
• Opis fizyczny: Bibliogr. 4 poz.

Twórcy

autor

Andersson S.

• Uppsala University, CEMPEG, Department of Earth Sciences, Villavdgen 16, 752 36 Uppsala, Sweden

Bibliografia

• 1. Allen R.L., Lundstrom I., Ripa M., Simeonov A. & Christofferson H., 1996. Facies Analysis of a 1.9 Ga, Continental Margin, Back-Arc, Felsic Caldera Province with Diverse Zn-Pb-Ag-(Cu-Au) Sulfide and Fe Oxide Deposits, Bergslagen Region, Sweden. Economic Geology, 91, 979-1008
• 2. Hogdahl K., Andersson U.B. & Ekelund O. (eds), 2004. The Transscandinavian Igneous Belt (TIB) in Sweden: a review of it character and evolution. Geological Survey of Finland Special Paper, 37, 125.
• 3. Jarl L.-G. & Johansson L., 1988. U-Pb zircon ages of granitoids from the Smlland-Varmland granite-porphyry belt, southern and central Sweden. Geologiska Fóreningens i Stockholms Forhandlingar, 110, 21-28.
• 4. Stephens M.B., Ripa M., Lundstrom I., Persson L., Bergman T, Ahl M., Wahlgren C.-H., Persson P.-O. & Wickstrom L., 2009. Synthesis of the bedrock geology in the Bergslagen region, Fennoscandian Shield, south-central Sweden. Sveriges Geologiska Undersokning, Ba 58, 259.