2018 Geological Work in the Caribou Pass area, NTS 105PWednesday, November 21, 2018 - 12:20 to 15:59 Lobby - Capitol Theatre
The western border of the Northwest Territories (NWT), within NTS map sheet 105P, both north and south of the Canol Heritage Trail, was mapped at 1:250,000 scale in the 1970’s. Parts of northwestern 105P were re-visited as a part of the Northwest Territories Geological Survey (NTGS) Sekwi Project in 2006-2008. However, the geology of the region remains poorly understood, in part due to the predominance of shaley units with no marker horizons and the presence of extensive covered areas. Maps created by the Yukon Geological Survey west of the border provide a level of detail that is not matched on the NWT side. The Caribou Pass region has the potential to host intrusion-related mineral deposits including skarn (W, Au, Mo, and Cu) and Carlin-type gold, sedimentary-related phosphate and barite, and shale-dominated base metals deposits. Stream silt collected during geochemical reconnaissance in the early 2000s included 23 samples containing 13 to 93 ppb gold.
Rocks in the region were deposited as sediments in the Selwyn Basin on the western margin of Laurentia beginning in the Proterozoic. Paleozoic rocks record the development of: (1) the Misty Creek Embayment, an extensional sub-basin that developed along the eastern edge of the Selwyn Basin from the Cambrian until the Middle Devonian; (2) adjacent parts of the Mackenzie carbonate platform that encroached on the embayment beginning in the late Silurian; and (3) a widespread, unnamed basin in which mainly clastic strata were deposited from the Middle Devonian until the Mississippian. These three stratigraphic packages were folded, thrust eastward, and intruded by felsic plutons during a Cretaceous orogeny. Existing maps do not subdivide large areas of Cambrian to Devonian basinal strata.
Field mapping by the NTGS in 2018 was partially successful in subdividing the Cambrian to Devonian package of strata. A previously unidentified sandstone unit, probably volcanogenic, is exposed at the base of the Middle Cambrian Hess River Formation in two places. If this unit is in stratigraphic position, it may refine our understanding of magmatism within the Embayment. The Ordovician Rabbitkettle Formation is thin and poorly developed, in many places providing no clear demarcation between the shaley strata of Hess River Formation below and Duo Lake Formation above. The Early Devonian Hailstone Formation was identified above Duo Lake Formation in the heart of the Caribou syncline, whereas the platformal Silurian Cloudy and Devonian Tsetso formations were tentatively identified above Duo Lake Formation on the east limb of the syncline. A succession of dolostone reefs on the west limb of the syncline, including a thrombolite reef, are similar to Silurian reefs in Mount Kindle Formation to the north. The recent work also hints at structural complexities not shown on existing maps. A focus of future work will be determining which aspects of the stratigraphy and structure are related to prospectivity for Carlin-type gold. This will be addressed by mapping at 1:50,000 scale and detailed stratigraphic work.