Development and application of the Re-Os isotope system to sediment-hosted Zn-Pb ores and sedimentary pore waters

• Author / Creator

  Hnatyshin, Danny

• The rhenium-osmium (Re-Os) isotopic system is used to determine the age of, and trace
  the origins of, minerals and fluids found within the Earth's crust. This thesis focuses on
  application of Re-Os geochronology and isotope systematics to sulphide minerals from
  carbonate-hosted Zn-Pb ore deposits, surface waters, and shallow to deep pore waters from the
  Western Canada Sedimentary Basin.
  Re-Os geochronology for the Silvermines deposit in Ireland produced a similar age
  (334.0 ± 6.1 Ma) to a previously published date from the nearby Lisheen deposit (346.6 ± 3.0
  Ma). These ages require that mineralization in the Irish orefield occurred in the shallow
  subsurface, but over a protracted, likely episodic, period in early Carboniferous time. This result
  refutes models of ore formation based on paleomagnetic ages, and may link ore formation to
  periods of volcanism in the orefield.
  Following the success of Re-Os geochronology in the Irish orefield, the Re-Os system
  was applied to a suite of Zn-Pb carbonate-hosted ore deposits from the Canadian Cordillera.
  These include metamorphosed deposits from the southern Canadian Cordillera (Salmo District),
  tectonically complex deposits in northern British Columbia (Robb Lake) and the southern
  Northwest Territories (Prairie Creek) of the northern Canadian Cordillera. Pyrite Re-Os ages of

  300 Ma for all these deposits suggest that mineralization was associated with an extensional
  tectonic regime that developed behind an active subduction zone west of these deposits during
  the Paleozoic. These results agree with previous sphalerite Rb-Sr dating and invalidate the much
  younger paleomagnetic ages for Zn-Pb ores in the Canadian Cordillera. Therefore, other deposits
  that have paleomagnetic age constraints (e.g. Pine Point, Monarch-Kickinghorse) are also now
  considered suspect.
  iii
  This thesis investigated Re at the ppb-level on a micro-scale in sulphide minerals, which
  permits a unique perspective of the Re-Os systematics of minerals widely used for
  geochronology. Laser ablation ICP-MS compositional mapping of the precisely-dated sample
  (8S08FW) from Lisheen, is characterized by a relatively homogenous Re distribution (~1-25
  ppb) and contains negligible alteration or impurity phases. All other samples that were analyzed
  contain Re abundances that could vary by several orders of magnitude. Clean ore-stage pyrite
  typically has the lowest concentration of Re, whereas areas associated with alteration, identified
  by oxidation or Al enrichment, may contain several orders of magnitude higher concentrations of
  Re. The unexpected discovery of putative micron-scale molybdenite crystals that postdate
  mineralization in many samples influences the Re-Os age of some samples. From the Nanisivik
  area of Arctic Canada, unusual Re-Os systematics of one sample from Hawker Creek, are readily
  explained by the findings of two generations of Re-poor and Re-rich pyrite, identified only by
  LA-ICPMS. In light of these results it is recommended that samples are characterized at the
  micron-scale to ensure that only paragenetically simple, unaltered material is selected for Re-Os
  geochronology.
  On a broader scale, the Re-Os systematics of pore fluids were characterized from the
  Williston Basin in southern Saskatchewan to help discern possible sources, sinks, and transport
  mechanisms of Re and Os within sedimentary basins. Pore fluids in near surface aquifers appear to
  mimic surface water Os isotopic compositions (187Os/188Os > 1), although at higher concentrations
  (15-95 ppq). However, deeper confined aquifers typically contain undetectable levels of Re and Os
  (< 300 ppq and < 5 ppq, respectively). This necessitates that removal processes dominate any
  leaching of Re and/or Os from the aquifer skeleton, even in highly saline brines. Interaction between
  water and oil may explain the observed depletion in some cases, however the cause of Re and Os
  iv
  depletion in petroleum-barren aquifers remains enigmatic. It is speculated that Re and/or Os are
  adsorbed into organic matter or clay minerals along the fluid migration pathways.

• Subjects / Keywords

  • Geology
  • Geochemistry
  • Geochronology
  • Re-Os
  • Sulphur Isotopes
  • WCSB
  • Ireland
  • Lisheen
  • Silvermines
  • Robb Lake
  • Prairie Creek
  • Salmo
  • Cordillera
  • Aquifer
  • WCSB
  • Isotopes
  • LA-ICPMS
  • TIMS

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R31G0J990

• License

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