Zircon Macrocrysts from the Drybones Bay Kimberlite Pipe (Northwest Territories, Canada): A High-Resolution Trace Element and Geochronological Study

Abstract

Zircon macrocrysts in (sub)volcanic silica-undersaturated rocks are an important source of information about mantle processes and their relative timing with respect to magmatism. The present work describes variations in trace element (Sc, Ti, Y, Nb, lanthanides, Hf, Ta, Pb, Th, and U) and isotopic (U-Pb) composition of zircon from the Drybones Bay kimberlite, Northwest Territories, Canada. These data were acquired at a spatial resolution of ≤100 µm and correlated to the internal characteristics of macrocrysts (imaged using cathodoluminescence, CL). Six types of zircon were distinguished on the basis of its luminescence characteristics, with the majority of grains exhibiting more than one type of CL response. The oscillatory-zoned core and growth sectors of Drybones Bay zircon show consistent variations in rare-earth elements (REE), Hf, Th, and U. Their chondrite-normalized REE patterns are typical of macrocrystic zircon and exhibit extreme enrichment in heavy lanthanides and a positive Ce anomaly. Their Ti content decreases slightly from the core into growth sectors, but the Ti-in-zircon thermometry gives overlapping average crystallization temperatures (820 ± 26 • C to 781 ± 19 • C, respectively). There is no trace element or CL evidence for Pb loss or other forms of chemical re-equilibration. All distinct zircon types are concordant and give a U-Pb age of 445.6 ± 0.8 Ma. We interpret the examined macrocrysts as products of interaction between a shallow (<100 km) mantle source and transient kimberlitic melt.

Lamprophyre as the Source of Zircon in the Veneto Region, Italy

“…In Figure 13g, we reported a distinction for zircons coming from various igneous lithologies based on ZrO 2 /HfO 2 and ZrO 2 [38,50]. The data were compared with the EMPA data of other occurrences in lamprophyres, from the area of Abu Ruscheid (Egypt), from the kimberlites of the Great Slave Lake (Canada) and finally from granitic pegmatites of Laoshan (China) [21,50,51]. The zircons from pegmatites that represent an extreme granite differentiate have higher HfO 2 and lower ZrO 2 /HfO 2 .…”

Editorial for Special Issue “Arctic Mineral Resources: Science and Technology”

“…On the basis of detailed mineralogical studies (including crystal-structure analysis) of forsterite [11], sulfides [12] and pyrochlore-supergroup minerals [13], the authors construct a 3-D model of the deposit and try to decipher major features of its genesis and evolution. Zircon macrocrysts from the Drybones Bay kimberlite pipe (Northwest Territories, Canada) are the subject of a detailed study of Reguir et al [14], who, on the basis of a high-resolution trace element and geochronological study, provide strong evidence that the macrocrysts are the products of interaction between a shallow (<100 km) mantle source and transient kimberlitic melt.…”