Evolution of the Selwyn Basin region, Sheldon Lake and Tay River map areas, central Yukon

Late Precambrian to Cretaceous, weakly metamorphosed strata of the ancestral North American margin comprise four sequences: Upper Precambrian to Middle Devonian (more than 3000 m) turbiditic sandstone, deep-water limestone, shale, and chert (Selwyn Basin), flanked southwesterly in the Siluro-Devonian by shallow-water carbonate and clastic sediments (McEvoy Platform). Early Cambrian pelite hosts deposits of stratiform lead-zinc. Upper Devonian and Mississippian turbiditic quartz-chert sandstone and chert-pebble conglomerate (2000 m) shed from elevated fault blocks of Selwyn Basin strata. Stratiform barite occurs within siliceous shale of mid- to Upper Devonian age. Mississippian to Triassic shale, chert, limestone, minor sandstone, and siltstone (1700 m) deposited on a shallow-marine shelf; and Lower Cretaceous clastic sediments (120+ m) derived from Jura-Cretaceous deformation and uplift. Regional Jura-Cretaceous deformation formed décollement style, northwest-trending folds and large, shallow-dipping thrust faults. Incompetent Cambro-Ordovician to Lower Devonian strata are complexly deformed above a regional flat-lying detachment. Deformation was accompanied by obduction of oceanic ultramafite, basalt, chert, and carbonate (Slide Mountain Terrane) as well as siliceous mylonite and schist (Yukon-Tanana Terrane). Granitic intrusions of the mid-Cretaceous (100 Ma) Selwyn Plutonic Suite crosscut regional structure and are responsible for small skarn and base-metal vein deposits. Coeval pyroclastic rocks of the South Fork volcanics are preserved within huge calderas. Cretaceous-Tertiary dextral slip along Tintina Fault has offset geological elements at least 430 km and formed pull-apart basins along and near the fault. Eocene fill of fluvial clastic and bimodal volcanic rocks host epithermal precious-metal veins.