Palaeomagnetism of the Howards Pass Zn-Pb deposits, Yukon, Canada

The Howards Pass district is located in the Selwyn Basin, Yukon. The district consists of >15 laminated clastic-dominated (CD) sphaleritegalena (ZnPb) deposits in the zinc corridor that trends northwestsoutheast and extends for similar to 35 km. The stratiform mineralized zone, the Active Member, is hosted in carbonaceous cherts and black shales of the Early Silurian Road River Group. Using mostly thermal and then alternating field step demagnetization isolated a stable characteristic remanent magnetization (ChRM) by the core-magnetization-angle method from 18 sites (339 specimens) in 18 variably oriented exploration drill hole cores from 6 ZnPb mineralized panels. Rock magnetic analyses show that the main remanence carriers are single- or pseudosingle-domain pyrrhotite and titanomagnetite. The deposits mean ChRM direction yields a pole position of either similar to 170 Ma on the North American apparent polar wander path or similar to 162 Ma on a corrected path for the Intermontane Belt (IMB) terranes. A negative palaeomagnetic fold test indicates that the mineralization's ChRM is post-folding, setting a minimum age for regional metamorphic deformation of similar to 170 +/- 20 Ma and supporting an Early Jurassic arrival for the IMB's collision and accretion to North America. An autochthonous or para-autochthonous North American tectonic model is favoured for the ChRM of the metamorphosed Selwyn Basin strata rather than an allochthonous IMB model. Further, the palaeomagnetic age indicates that the coarse-grained ZnPb mineralization in fine fractures that cut the laminated fine-grained ZnPb mineralization at Howards Pass at least was formed by remobilization during Middle Jurassic metamorphism.