OXYGEN ISOTOPE ZONATION ABOUT THE IZOK AG-ZN-CU VMS DEPOSIT, SLAVE PROVINCE, NUNAVUT, CANADA:HANGING WALL VECTOR TO MINERALIZATION

Oxygen isotope compositions were determined for 99 whole-rock samples of rhyolitic host rocks collected in the vicinity of the Ag-bearing Izok Zn-Cu volcanogenic massive sulfide deposit in order to map and define the responsible paleo-hydrothermal system. The results reveal a distinct pattern of oxygen isotope zonation spatially centered over the massive sulfide lenses produced by water/rock reaction in a hydrothermal system. The zonation indicates that this paleo-hydrothermal system is relatively ‘up right’, centered over the massive sulfide lenses. Analyzed samples are primarily from the hanging wall, and have δ¹⁸O_V-SMOW values as high as 14.7 ‰. In contrast to isotopic studies describing ¹⁸O-depleted footwall reaction and upflow zones, the ¹⁸O-enriched zoning pattern in the Izok Lake area, developed in a waning system, serves as a clear hanging wall ‘vector’ to the buried sulfide lenses. This isotopic ‘fingerprint’ of an Archean hydrothermal system has been retained in the rocks, despite subsequent amphibolite facies metamorphism and mild deformation. The isotopically-mapped hydrothermal alteration about the Izok deposit is wholly consistent with isotopic models developed from other studies. Moreover, the isotopic zonation broadly corresponds to an isopleth indicating loss of Na₂O from the rocks, and, to some extent, with a mapped distribution of the Ishikawa alteration index. Short-wave infrared spectral mapping of white-mica and biotite+chlorite-related absorption features reflectance spectra of outcrops measured in the field yields absorption intensity maps that also correspond generally with the oxygen isotope zoning patterns. However, the pattern of oxygen isotope zonation provides a more focused ‘target’ above the buried massive sulfide lenses, in addition to the identification of the ‘polarity’ of the hydrothermal system.