Geology of the Mayo Map Area, Yukon Territory (NTS 105M)

Late Proterozoic to Triassic, moderately to highly strained sedimentary rocks are exposed in two overlapping thrust sheets in the Mayo map area. The more southerly Robert Service Thrust sheet contains Hyland Group (Late Proterozoic to Cambrian) sandstone and grit with rare limestone and minor maroon argillite, overlain by a Cambrian to Middle Devonian succession of dark coloured siltstone, limestone and chert in the southern quarter of the map area. These strata, a component of the regional Selwyn Basin, are unconformably overlain by Upper Devonian Earn Group argillite, chert and chert pebble conglomerate. The latter succession contains widespread indications of stratiform Pb-Zn-barite mineralization. To the north the Tombstone Thrust sheet consists of highly strained Earn Group (formerly ?Lower Schist?) carbonaceous phyllite, felsic meta-tuff and metaclastic rocks, succeeded by Carboniferous Keno Hill quartzite, that is thickened by internal recumbent folds or thrusts in the north central part of the map area. These units host the Ag-Pb-Zn veins of the Elsa-Keno Hill camp, and contemporaneous meta-tuff that contains a volcanogenic massive sulphide deposit immediately northeast of the map area. Jurassic (?) and Cretaceous contraction produced regionally developed penetrative fabrics and folds of various scales as well as thrust faulting. A domain of intensely developed foliation and lineation underlies the northern half of the map area, imparted during two or more phases of movement on the Tombstone Thrust. Granitic intrusions of the 91-94 Ma Tombstone Suite crosscut regional structure. The McArther batholith parallels the Tintina Trench and is associated with copper skarns. Other stocks throughout the map area are notable for vein-tungsten and tin, and were the probable heat source for epi- and meso-thermal veins of the Elsa-Keno Hill mining camp. In neighbouring regions, Tombstone intrusions are the focus of exploration for disseminated vein-gold similar to deposits north of Fairbanks, Alaska and east of Dawson, Yukon.