Diagenetic Controls on Hydrothermal Fluid Flow in the Osiris, Isis, and Isis East Carlin-Type Gold Showings, Nadaleen Trend, Yukon

  • Author / Creator
    Beaton, Neil I.
  • Following ATAC Resources Ltd.’s 2010 discovery of the gold prospects in the Nadaleen Trend (Central Yukon), company geologists and consultants determined that Precambrian carbonate rocks within the trend contain large endowments of gold located in the hinges of anticlines and fault zones. Subsequent studies revealed that additional gold mineralization is found away from these structures, spatially associated with “dolomitization fronts”, i.e. lithological contacts between dolomite and other units. Geochemical studies reveal that the carbonate host rocks of the Nadaleen Trend precipitated in anoxic, ferruginous seawater during the Ediacaran Period. Large volumes of dolomite and pyrite were generated during near-surface diagenesis, and the pyrite became enriched in trace metals. During further burial, calcite veining and stylolitization occurred. This preceded a base metal mineralization event in which a second generation of dolomite formed; this process created significant new porosity and permeability in the host rocks. Further calcite veining and a second generation of stylolitization subsequently occurred. This was post-dated by the ore stage which consisted of the precipitation of gold-bearing arsenian pyrite and a third generation of dolomite. Ore fluids travelled vertically along faults and laterally into Permeable zones associated with saddle dolomite and stylolites. Gold-bearing fluids travelled through these conduits until they encountered pyrite grains, at which point a sulfidation reaction occurred. This reaction resulted in deposition of gold-bearing arsenian pyrite on the pre-existing grains of pyrite. Since the first two generations of pyrite occur most commonly in dolomite rather than limestone, gold mineralization occurred preferentially in dolomite. A post-ore stage occurred consisting of calcite, realgar, and orpiment. Electron microprobe analysis and laser ablation inductively coupled plasma mass spectrometry reveals that the hydrothermal fluids were reducing and acidic, and thus were capable of dissolving carbonates to create porosity. Carbon, oxygen, and strontium isotopic data on calcite and dolomite indicate that the hydrothermal fluids isotopically equilibrated with the host rocks. The mineralization present in the Nadaleen Trend has geological features similar to those of world-class Carlin-type gold deposits, a class of gold deposits modelled after the Carlin Trend in Nevada.

  • Subjects / Keywords
  • Graduation date
    Fall 2015
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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