Sulphur isotope geochemistry of black shale-hosted antimony mineralization, Arnsberg, northern Rhenish Massif, Germany: implications for late-stage fluid flow during the Variscan orogeny

Abstract

Vein-type and bedding-concordant mesothermal (180-410 8C) stibnite-sulphosalt mineralization at Arnsberg, NE Rhenish Massif, Germany, is hosted by Carboniferous pyrite-rich black shales and siliceous limestones. A detailed sulphur isotope study of the stibnite-sulphosalt mineralization and pyrite from a variety of regional host-rock lithologies has been carried out using an in situ laser combustion technique. The ä 34 S values of stibnite of various textural types are distinctly negative and lie in a narrow range between À23.9‰ and À17.1‰ (mean À20.1‰). In contrast, regional sedimentary-diagenetic pyrites display a large variation of their ä 34 S values between À45.4‰ and þ9.3‰. There is little evidence for significant modification of the hydrothermal fluid during deposition and the S isotope signatures suggest that the sulphur of the stibnite mineralization was not locally derived. The ä 34 S values of pyrite in Givetian shales display a significantly narrower range of À28.2‰ to À7.5‰ and their mean composition (À17.1‰) is close to the ä 34 S values of the Arnsberg stibnite deposits. Considering the temperature-dependent isotopic fractionation between stibnite and reduced sulfur species, the ä 34 S values of the mineralizing fluid (À16.8‰; 200 8C) and the Givetian rock source are essentially identical. Therefore, we propose a model of leaching and isotopic homogenization of sulphur from the Middle Devonian shales and a subsequent northward migration of these fluids. The fluids were trapped in permeability-controlled positions within anticlinal zones, where fluid cooling induced deposition of stibnite and sulphosalts.

Tellurium, selenium and cobalt enrichment in Neoproterozoic black shales, Gwna Group, UK: Deep marine trace element enrichment during the Second Great Oxygenation Event

“…The enrichments of Te, Co and Se within the Gwna Group shale suggest that other black shales in the Proterozoic and lower Palaeozoic deserve further study for their content of critical elements, specifically those deposited during periods of significant atmospheric fluctuations (Johnson et al., ; Large et al., ; Tomkins, ). This suggests the potential for other types of mineral‐bearing deposit based on black shale protoliths deposited during key time periods (Coveney & Nansheng, ; Giordano, ; Large, Bull, & Maslennikov, ; Pedersen, Nielsen, Boyce, & Fallick, ; Wagner & Boyce, ), particularly where supergene processes may have resulted in small‐scale ore deposits near surface.…”

Orogenic paleofluid flow recorded by discordant detrital zircons in the Caledonian foreland basin of northern Greenland

“…Proposed fluid sources include a combination of orogenic uplift (gravity)-driven meteoric groundwater, tectonic-driven dewatering, and mineral dehydration metamorphic sources (e.g., Garven, 1985;Oliver, 1986;Nesbitt and Muehlenbachs, 1994;Craw et al, 2002;Mark et al, 2007). Sulfur isotopes indicate latestage fluid flow during the Variscan orogeny in the northern Rhenish Massif, Germany, at 200 °C (Wagner and Boyce, 2003), dropping to 100 °C in regional dolomitization events in SE Ireland, 170 km in advance of the orogenic front (Hitzman et al, 1998). Similar events are reported in foreland regions of many fold-andthrust belts, including the Rocky and MacKenzie Mountains of Canada (e.g., Morris and Nesbitt, 1998) and northern Victoria Land, Antarctica (Rossetti et al, 2006), indicating the ubiquity of major fluid events moving far in advance of orogenic fronts.…”

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“…The enrichments of Te, Co and Se within the Gwna Group shale suggest that other black shales in the Proterozoic and lower Palaeozoic deserve further study for their content of critical elements, specifically those deposited during periods of significant atmospheric fluctuations (Johnson et al, 2017;Large et al, 2014;Tomkins, 2013). This suggests the potential for other types of mineral-bearing deposit based on black shale protoliths deposited during key time periods (Coveney & Nansheng, 1989;Giordano, 1989;Large, Bull, & Maslennikov, 2011;Pedersen, Nielsen, Boyce, & Fallick, 2003;Wagner & Boyce, 2003), particularly where supergene processes may have resulted in small-scale ore deposits near surface.…”