Abstract
Abstract The detrital zircons in tills overlying the Guichon Creek batholith, British Columbia, Canada, have trace element concentrations and ages similar to those of zircons from the bedrock samples from which they are interpreted to have been sourced. Rocks from the core of the batholith that host porphyry copper mineralization have distinct zircon compositions relative to the distal, barren margin. We analyzed 296 zircons separated from 12 subglacial till samples to obtain U-Pb ages and trace element compositions. Laser ablation U-Pb ages of the detrital zircons overlap within error with chemical abrasion-thermal ionization mass spectrometry U-Pb ages of the Late Triassic Guichon Creek batholith and confirm that the detrital zircons are likely derived from the batholith. The youngest intrusions of the batholith produced the Highland Valley Copper porphyry deposits and contain distinctive zircons with elevated Eu/EuN* >0.4 attributed to high magmatic water contents and oxidation states, indicating higher porphyry copper potential. Zircon from till samples adjacent to and 9 km down-ice from the mineralized centers have mean Eu/EuN* >0.4, which are indicative of potential porphyry copper mineralization. Detrital zircon grains from more distal up- and down-ice locations (10–15 km) have zircon Eu/EuN* mean values of 0.26 to 0.37, reflecting background values. We conclude that detrital zircon compositions in glacial sediments transported several kilometers can be used to establish the regional potential for porphyry copper mineralization.
Highlights
The demand for copper is expected to increase in the few decades as a result of the growth of developing economies, the electric car revolution, and the requirements for conductors in green technologies (Elshkaki et al, 2016; Ali et al, 2017; Sverdrup et al, 2019)
Uranium-Th-Pb ages and trace element concentrations were determined from 564 spot analyses on 296 till zircons grains
Hafnium concentrations in the detrital zircon range from 8,000 to 14,500 ppm (Fig. 4), and trace element concentrations vary in the following ranges: Y (149–1,814 ppm), Nb (0.09– 1.25 ppm), Ta (0.046–1.148 ppm), SREE (138–1,329 ppm), Th (3.9–305 ppm), and U (22–774 ppm)
Summary
The demand for copper is expected to increase in the few decades as a result of the growth of developing economies, the electric car revolution, and the requirements for conductors in green technologies (Elshkaki et al, 2016; Ali et al, 2017; Sverdrup et al, 2019). Exploration for buried deposits is more challenging and expensive and often less successful (Schodde, 2017); new tools are required to increase exploration success. Porphyry copper deposits are a major global source of copper and are formed in magmatic-hydrothermal systems that contain resistate igneous accessory and hydrothermal alteration minerals. The chemistry of accessory minerals such as zircon, apatite, and titanite in magmatic rocks has been used to assess the propensity of an intrusion to generate porphyry copper deposits—a property commonly referred to as porphyry fertility (Ballard et al, 2002; Dilles et al, 2015; Bouzari et al, 2016; Lu et al, 2016, 2019; Lee et al, 2017; Shu et al, 2019). The Ce and Eu—two rare earth elements with dual
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