Insight from Detailed Sulfur Isotope Studies

Research Collection Journal Article The role of the Kupferschiefer in the formation of hydrothermal base metal mineralization in the Spessart ore district, Germany Insight from detailed sulfur isotope studies Author(s): Wagner, Thomas; Okrusch, Martin; Weyer, Stefan; Lorenz, Joachim; Lahaye, Yann; Taubald, Heiner; Schmitt, Ralf T. Publication Date: 2010 Permanent Link: https://doi.org/10.3929/ethz-b-000017118 Originally published in: Mineralium Deposita 45(3), http://doi.org/10.1007/s00126-009-0270-2 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Miner Deposita (2010) 45:217–239 DOI 10.1007/s00126-009-0270-2 ARTICLE The role of the Kupferschiefer in the formation of hydrothermal base metal mineralization in the Spessart ore district, Germany: insight from detailed sulfur isotope studies Thomas Wagner & Martin Okrusch & Stefan Weyer & Joachim Lorenz & Yann Lahaye & Heiner Taubald & Ralf T. Schmitt Received: 8 December 2008 /Accepted: 16 November 2009 /Published online: 5 December 2009 # Springer-Verlag 2009 Abstract The Spessart district (SW Germany), located at the styles identified are (1) stratabound Cu-Pb-Zn-(Ag) ores in southwestern margin of the Permian Kupferschiefer basin in Zechstein sedimentary rocks, (2) structurally controlled Central Europe, hosts abundant stratabound and structurally Cu-As-(Ag) ores in Zechstein sedimentary rocks, (3) controlled base metal mineralization. The mineralization crosscutting Co-Ni-(Bi)-As and Cu-Fe-As veins, (4) stratabound metasomatic Fe-Mn carbonate ores in Zechstein dolomite, (5) barren barite veins, and (6) Fe-Mn-As veins in Permian rhyolites. Building on previous work that involved Editorial handling: A. Boyce mineralogical, textural, and chemical characterization of the T. Wagner (*) major mineralization types, we have performed a comprehen- Institute of Isotope Geochemistry and Mineral Resources, sive sulfur isotope study that applied both conventional ETH Zurich, NW F 82.4, Clausiusstrasse 25, and novel laser-ablation multi-collector inductively coupled 8092 Zürich, Switzerland plasma mass spectrometry techniques. The δ34Svaluesof e-mail: [email protected] sulfide minerals from the different ore types are consistently : negative and highly variable, in the range between −44.5‰ M. Okrusch J. Lorenz 34 Lehrstuhl für Geodynamik und Geomaterialforschung, and −3.9‰, whereas the δ S values of barite are all positive Universität Würzburg, in the range between 4.7‰ and 18.9‰.Remarkably, Am Hubland, stratabound and structurally controlled mineralization in 97074 Würzburg, Germany Zechstein sedimentary rocks has the least negative δ34S S. Weyer : Y. Lahaye values, whereas vein-type deposits have consistently more Institut für Petrologie, Geochemie und Lagerstättenkunde, negative δ34S values. The observed pattern of sulfide δ34S Universität Frankfurt am Main, values can be best interpreted in terms of fluid mixing at the Senckenberganlage 28, basement-cover interface. Hydrothermal fluids originating 60325 Frankfurt am Main, Germany from the crystalline basement migrated upward along H. Taubald subvertical fault zones and were periodically injected into Institut für Geowissenschaften, Universität Tübingen, groundwaters that were flowing in the post-Variscan sedi- Wilhelmstr. 56, mentary cover. These groundwaters had interacted with the 72074 Tübingen, Germany Zechstein sedimentary rocks, resulting in fluids characterized R. T. Schmitt by elevated concentrations of reduced sulfur (with negative Museum für Naturkunde, δ34S values) and alkaline pH. Repeated mixing between both Leibniz-Institut für Evolutions- und Biodiversitätsforschung, chemically contrasting fluids caused rapid and efficient Humboldt- Universität, Invalidenstr. 43, precipitation of sulfide ore minerals in hydrothermal veins 10115 Berlin, Germany with highly variable but distinctly negative δ34Svalues. 218 Miner Deposita (2010) 45:217–239 Keywords Kupferschiefer . Germany . Base metals . veins in the Triassic Bunter Sandstone that forms the Sulfur isotopes . Laser-ablation MC-ICP-MS uppermost part of the stratigraphy. Most studies agree that the vein-type mineralization is of hydrothermal origin (Schmid and Weinelt 1978; Wagner and Lorenz 2002; Introduction Okrusch et al. 2007), but their close spatial association with the Kupferschiefer-hosted mineralization points to a possible Unconformity-related ore deposits constitute a widespread genetic relationship. hydrothermal mineralization style that has been recognized The present study reports the results of a comprehensive in many geological terrains worldwide. They comprise sulfur isotope study of both stratabound and vein-type base diverse types of metal associations, with prominent examples metal mineralization in the Spessart district. We have being the U deposits of the Athabasca basin in Canada (e.g., performed detailed in situ analysis of a complete suite of Hoewe and Sibbald 1978; Kotzer and Kyser 1995;Kisteret sulfide minerals, using a novel laser-ablation multi-collector al. 2005) and the Cu-Ag-platinum group elements (PGE) inductively coupled plasma mass spectrometry (ICP-MS) deposits of the Permian Kupferschiefer in Central Europe technique (Bendall et al. 2006). This dataset is combined (e.g., Vaughan et al. 1989;Kucha1990; Speczik 1995; with conventional sulfur isotope data of barite from both Oszczepalski 1999; Piestrzynski et al. 2002). For many of metal-bearing and barren veins that occur in different these deposits, the genetic models are not well established portions of the stratigraphy (crystalline basement, Zechstein, and are subject of an ongoing debate (e.g., Jowett 1986; and Bunter Sandstone). The sulfur isotope data are then Cathles et al. 1993;Blundelletal.2003; Wedepohl and integrated with available geological and geochemical infor- Rentsch 2006). mation to consider (1) the genetic link between stratabound The formation of base metal deposits related to the and vein-type mineralization, (2) the role of sedimentary Permian Kupferschiefer is of particular interest, because sulfur in the different hydrothermal mineralization styles, both sedimentary-diagenetic and hydrothermal processes and (3) the likely mechanisms that have resulted in ore are likely involved in the complex mineralization pattern deposition. that is observed throughout the Kupferschiefer basin (Vaughan et al. 1989; Speczik 1995). The Kupferschiefer hosts three different mineralization styles, which are (1) Geological setting stratabound mineralization of Cu (and Ag) that is present in the reduced part of the stratigraphy (Vaughan et al. 1989; The Spessart district is composed of two major geological Sawlowicz 1989; Speczik 1995); (2) stratabound mineral- units (Fig. 1), which are (1) the basement of the Spessart ization of Au and PGE that is restricted to the oxidized zone crystalline complex (SCC) and (2) the overlying cover (Piestrzynski and Wodzicki 2000; Bechtel et al. 2002; that comprises sedimentary rocks from Lower Permian Piestrzynski et al. 2002); and (3) crosscutting vein-type (Rotliegend) to Triassic (Bunter Sandstone). The SCC mineralization of Cu, Co, Ni, Bi, Ag, and As (Wagner and constitutes a part of the internal zone of the Central Lorenz 2002; Okrusch et al. 2007). Most recent studies European Variscan orogen (Franke 2000). It consists of have focused on the stratabound mineralization styles, NE-trending metamorphosed sedimentary rocks of likely whereas few studies have addressed the role of structurally Neoproterozoic, Cambro-Ordovician, and Silurian age with controlled hydrothermal fluid flow in the formation of intercalated amphibolites and orthogneisses (Okrusch and Kupferschiefer-hosted base metal mineralization (Schmidt- Weber 1996). Deformation and metamorphism took place Mumm and Wolfgramm 2002, 2004; Wedepohl and during the Variscan orogeny under medium-pressure, Rentsch 2006). A comprehensive study that would integrate amphibolite-facies conditions (Okrusch and Weber 1996). observations from spatially associated stratabound and At the end of the metamorphic cycle, the metamorphic rocks crosscutting vein-type mineralization could thus help to were intruded by an igneous complex composed of quartz resolve the potential genetic links between these mineral- diorite, granodiorite, and minor granite. Consistent K-Ar and ization styles. Ar-Ar dates of minerals from various rock types indicate that The Spessart district, which is located in the southwestern uplift and cooling of the SCC took place at 325–315 Ma part of the Kupferschiefer basin, hosts both stratabound (Lippolt 1986; Nasir et al. 1991;Dombrowskietal.1994). mineralization that is present in the Zechstein dolomite and During the Permian, several rhyolite bodies were emplaced the Kupferschiefer, and structurally controlled vein-type in the Spessart for which no geochronological data are yet mineralization (Fig. 1). The veins are hosted by metamorphic available. rocks of the crystalline basement and also extend into the The SCC is unconformably overlain by sedimentary overlying Upper Permian sedimentary strata. The fault zones rocks of Permo-Triassic age (Rotliegend, Zechstein, and that host base metal mineralization continue as barren barite Bunter Sandstone). Lower Permian (Rotliegend) sedimentary Miner Deposita (2010) 45:217–239 219 9°15' 9°30' Germany Gelnhausen Bieber 32 28 31 Altenmitlau 24 Huckelheim 30 29

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