The Niblack project is a precious metal-enriched polymetallic volcanogenic massive sulphide (VMS) deposit hosting at least six known VMS occurrences, including the historic Niblack mine, the Dama zone, Lindsy zone, Mammoth zone as well as the Lookout and Trio deposits.
The deposit is hosted within strata of the Craig subterrane of the Neoproterozoic Alexander terrane. The Alexander terrane, which underlies the southern portion of Prince of Wales Island, formed along a convergent plate margin in the late Precambrian to Early Devonian time.
Figure 2: Niblack Anchorage schematic stratigraphic section highlighting stratigraphic locations of major massive sulphide zones and uranium-lead geochronology stratigraphic location and summary. Adapted from McNulty et. al., 2014.
Wales Group strata at the Niblack Property consists of a bimodal sequence of mafic and felsic volcanic flows, domes, and volcaniclastics overlain by interlayered mafic volcanosedimentary wackes and pillow basalts. This package is overlain by Moira Sound Unit younger volcanosedimentary cover (see Figure 1).
Within the Wales Group sequence, a stratigraphic framework has been defined for the Niblack property which breaks the stratigraphy into three distinctive units: the Niblack Stratigraphic Footwall Succession, the Niblack Felsic Succession and the Niblack Stratigraphic Hanging Wall Succession (see Figure 2). The Footwall Succession is consistent of dacitic to basaltic volcanics and volcaniclastics and the Hanging Wall Succession is constituted of mafic volcanosediments and basaltic pillow lavas.
Most notably, the 100-200m Niblack Felsic Succession hosts all known VMS mineralization on the property. This thick sequence of prospective folded rhyolitic volcanic rocks extends for at least six miles across the property and hosts six known massive sulphide zones: the historic Niblack mine, the Dama zone, Lindsy zone, and Mammoth zone, as well as the Lookout and Trio deposits.
The Niblack stratigraphic package has been subject to multiple phases of later deformation and greenschist facies metamorphism which occurred during the Middle Cambrian to Early Ordovician and the Middle Silurian to early Devonian. Renewed deformation occurred during the accretion of the Alexander terrane to the Cordillera in the mid-Jurassic to Cretaceous. Folding on the property is north-vergent, moderate to tight, and overturned. The six known VMS zones sit on a property-scale synformal anticline-antiformal syncline pair (see Figure 3 and Figure 4).
Figure 4: Schematic cross section of the Niblack property, highlighting the location of major massive sulphide zones, the portal, underground workings, and the location of the historic Niblack mine site. Adapted from Roberts et. al., 2013.
Exploration Potential and Reinterpretation:
Earlier operators interpreted the aforementioned folds to be a simple property-scale anticlinal-synclinal pair. However, in most recent stages of exploration and research, U-Pb age dating and analysis of way-up indicators in sedimentary and volcanosedimentary beds led to the discovery that the stratigraphy is overturned. This breakthrough led to a reinterpretation of these folds as an overturned synformal anticline-antiformal syncline pair. This reinterpretation was not tested in previous exploration and opens a large new prospective area across the property based on the new projection of the permissive Niblack Felsic Succession. This reinterpreted model is driving current exploration, which is targeting and testing these newly defined prospective zones (see Figure 5).
All of the known six zones at Niblack remain open and are candidates for further resource expansion.
Figure 5: Old (yellow) and new (purple) interpreted projection of prospective Niblack Felsic Succession rhyolite horizon to surface on aerial photograph of the Niblack Anchorage, highlighting the location of the six massive sulphide zones.
Six VMS zone - including the historic Niblack mine, the Dama zone, Lindsy zone, Mammoth zone as well as the Lookout and Trio deposits – have been identified on the property so far.
A total of 246 surface drillholes and 164 underground drillholes were drilled between 1975 and late 2012. Mineral resource estimates have been completed for the Lookout and Trio deposits.
A total of 10 surface drillholes totalling 1,775 were drilled in late 2020 at the historic Niblack mine site, with results pending in early 2021.