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Seminar Series – Sarah Gleeson, GFZ Helmholtz Centre
September 12, 2019 @ 12:00 pm - 1:00 pm
Earth Sciences Seminar Series Thursday Sept.12, 2019 at 12 pm
Sarah Gleeson, GFZ Helmholtz Centre Potsdam
“Diagenesis, Sulfur, and Giant Zn Deposits”
The North American Cordillera contains a number of large Zn deposits hosted in Palaeozoic biosiliceous, carbonaceous, radiolarian-rich mudstones. Stratabound barite units are associated with the ore deposits, but are also found regionally in barren, correlative sequences. Recent studies have shown that stratabound barite, pyrite and authigenic carbonate formed in the sediment at the sulphate methane transition zone (SMTZ), and are therefore a product of pre-ore diagenesis. In situ δ34S values from pre-ore pyrite preserve evidence of the anaerobic oxidation of methane coupled with sulphate reduction (AOM-SR), which was an important source of reduced sulphur during diagenesis. The hydrothermal systems are superimposed on this diagenetic environment, do not exhale onto the seafloor and developed in non-euxinic conditions. The δ34S values in ore-stage pyrites suggest reduced S is derived from a number of sources, including recycling of sulphate from diagenetic barite.
The radiolarian-rich host rocks, likely dominated by Opal A in the top 100s of metres of the sediment, had high porosities and permabilities that allowed the ore deposits to form in the sub-surface and precluded significant exhalation of the hydrothermal system into the water column. Therefore, the biosiliceous nature of host rock, together with the ability of the hydrothermal fluids to dissolve authigenic barite and carbonate, are major controls on the genesis and size of these important deposits.
Bio: Sarah received a B.A. (mod.) in geology from Trinity College Dublin and a Ph.D. in geochemistry from the Royal School of Mines, Imperial College (University of London). Subsequently, she held postdoctoral positions at the Natural History Museum, London, and the University of Leeds before moving to the University of Alberta to take up a position as an assistant professor in 2001. Since 2016, she has been the W3 professor in mineral resources at the Freie Universität Berlin and leads the Inorganic and Isotope Geochemistry section at GFZ Helmholtz Centre Potsdam.
She was the recipient of the Waldemar Lindgren Award from the Society of Economic Geologists in 2007, as well as the William Harvey Gross Medal (2010) and the H.S. Robinson Lecturer Award (2011–2012) from the Mineral Deposits Division of the Geological Association of Canada. She also received the Young Scientist Award from the Mineralogical Association of Canada in 2010. Sarah has broad research interests in mineral deposit genesis, hydrothermal fluid flow, and water-rock interaction. Recently, her research has been focused on Cu, Zn, and Au deposits in sedimentary basins, sedimentary geochemistry, diagenesis, and ore-forming processes.