Ancient roots of tungsten in western North America

Abstract

The highly irregular and localized distribution of tungsten deposits worldwide constitutes a supply challenge for basic industries such as steel and carbides. Over Earth’s history, tungsten has preferentially accumulated at paleocontinental margins formed during the breakup of supercontinents. Later crustal thickening of these paleogeographic regions and the magmas they produce are associated with large tungsten districts. However, all of the largest tungsten deposits in the modern North American Cordillera, which preserves over 3 b.y. of geologic record in a paleocontinental margin with abundant crustal magmatism, are limited to the narrow Canadian Tungsten Belt in northwestern Canada. We use neodymium isotopic compositions of scheelite (CaWO4) from the Canadian Tungsten Belt and the paleogeographic distribution of tungsten deposits in the North American Cordillera to constrain the factors that control tungsten distribution. We document that tungsten is specifically associated with materials that, on average, were derived from the mantle during the Mesoarchean to Paleoproterozoic. Weathering and erosion of the supercontinents Columbia and Rodinia favored pre-enrichment of tungsten in sediments. The orogenic heating of pre-enriched sediments produced reduced melts that were capable of efficiently scavenging tungsten and formed the largest deposits in North America.