Talk
Critical Minerals Geology and Exploration

U-Pb and Lu-Hf Characterization of Zircon from Granites Associated with Tungsten Mineralization, Mackenzie Mountains, Canada

Online pre-recorded

Author(s)

K.L. Rasmussen (Presenting)
University of Alberta
P. Lecumberri-Sanchez
University of Alberta
H. Falck
Government of the Northwest Territories, GNWT

The Mackenzie Mountains in southeastern Yukon and southwestern NWT host significant tungsten mineralization, including 10.796 Mt at 1.2% WO3 at Cantung (combined historic and current estimates), 44.9 Mt at 0.851% WO3 at Mactung, and 0.75 Mt at 1.17% WO3 at Lened (Green et al., 2020). Mineralization is associated with a narrow belt of crustally derived mid-Cretaceous granite plutons belonging to the Tungsten plutonic suite. Melt source is one of the major controls proposed for tungsten metallogeny; however, the source of fertile magmas spatially associated with tungsten mineralization in the Mackenzie Mountains remains largely unknown due to a lack of exhumation. A second critical aspect for the formation of tungsten mineralization is thought to be the presence of a long-lived fractionating magmatic system capable of concentrating tungsten in the melt and magmatic fluid phases. This study uses magmatic and inherited cores in zircon from plutons belonging to the Tungsten plutonic suite to characterize the U-Pb age and Lu-Hf composition of the evolving magmas and their basement source(s).

Magmatic and inherited cores were identified by SEM-CL mapping of zircon grains then analyzed in a split-stream LA-ICPMS system such that the Lu-Hf and U-Pb isotopic compositions of the cores are determined in-situ simultaneously. The first phase of analyses targeted magmatic cores for several plutons near Cantung, including the Mine Stock pluton underlying the Cantung orebody. Preliminary results are consistent with the hypothesis that the magmatic systems were active for several million years prior to final crystallization. Inherited cores analyzed in the first phase of the study returned Paleoproterozoic to Neoarchean ages, although more work is needed to provide inferences on melt and metal source(s). Future analyses will focus on older inherited cores in the Cantung area, as well as magmatic and inherited cores in the Mactung and Lened areas north of Cantung. In addition to documenting the extended crystallization history of the plutons associated with significant tungsten mineralization, this study endeavours to determine the most likely lithological source(s) for the melt and metals in the Cordilleran basement. The results of this work will contribute to our understanding of the framework for the generation of world-class tungsten provinces globally.