Paleomagnetic dating of magmatic phases at the Cantung tungsten deposit, Northwest Territories, Canada

Abstract

The Cantung tungsten–copper (W–Cu) skarn orebodies are hosted by Proterozoic and Lower Cambrian metasedimentary rocks next to the Cretaceous “Mine Stock” monzogranite. Paleomagnetic analyses of 283 specimens from the Open Pit scheelite–chalcopyrite orebody (17 sites) and from adjacent host rocks including the aplite dikes (11 sites) isolated a stable characteristic remanent magnetization (ChRM), mostly by alternating field and then thermal step demagnetization. The step demagnetization results along with rock magnetic analyses of the W concentrate show that the main remanence carriers are single- or pseudosingle-domain pyrrhotite, titanomagnetite, and (or) magnetite. There is no statistically significant difference at 95% confidence between the site mean ChRM directions for the W–Cu ore, the host rock, or the aplite dikes populations. This result indicates that the intrusion of the Mine Stock is coeval with the genesis of the scheelite skarn ore and with dike emplacement to give an overall mean ChRM direction of declination 342.9°, inclination 82.0° (N = 22 sites, radius of cone of 95% confidence α95 = 4.2°, precision parameter k = 54.7) that defines a paleopole at 76.2°N latitude, 212.2°E longitude (radius of cone of 95% confidence A95 = 8.1°). This paleopole is concordant with the coeval 98 Ma North American paleopole at 92% confidence, which provides strong evidence that the eastern Selwyn Basin has been an autochthonous part of North America since the mid-Cretaceous.