Late Devonian paleomagnetic age for the Polaris Mississippi Valley-type Zn–Pb deposit, Canadian Arctic Archipelago

Abstract

The Polaris Mississippi Valley-type (MVT) zinc–lead deposit is located in the Middle to Upper Ordovician Thumb Mountain Formation of the Cornwallis Fold Belt in the Canadian Arctic Archipelago. Paleomagnetic analysis was done on samples from 29 sites in the sphalerite–galena ore, the surrounding dolomitic envelope, and the adjacent host-rock limestones, using alternating-field and thermal step demagnetization, scanning electron microscopy with energy-dispersive analysis, and saturation isothermal remanente analyses. Excluding the modern viscous remanence component, the ore, dolomite alteration, and host limestones carry only a prefolding A remanent magnetization component that resides in single- and pseudosingle-domain magnetite, both as discrete grains and as inclusions in the MVT ore minerals. All evidence indicates that the mineralization and magnetization events were coeval. The mean magnetization direction of D = 145.8°, I = −31.1° (α95 = 5.9°, k = 26.2, N = 24) after tilt and a minor plunge correction gives a Late Devonian pole position of 28.6°N, 121.2°E (dp = 3.7°, dm = 6.6°, N = 24). The results indicate that the ore deposit was formed during the onset of the Ellesmerian Orogeny and tilted later in the orogeny.