Assessing Thallium Elemental Systematics and Isotope Ratio Variations in Porphyry Ore Systems: A Case Study of the Bingham Canyon District

Abstract

The Bingham Canyon porphyry deposit is one of the world’s largest Cu-Mo-Au resources. Elevated concentrations of thallium (Tl) compared to average continental crust have been found in some brecciated and igneous samples in this area, which likely result from mobilization of Tl by relatively low temperature hydrothermal fluids. The Tl-enrichment at Bingham Canyon therefore provides an opportunity to investigate if Tl isotope ratios reflect hydrothermal enrichment and whether there are systematic Tl isotope fractionations that could provide an exploration tool. We present a reconnaissance study of nineteen samples spanning a range of lithologies from the Bingham district which were analysed for their Tl content and Tl isotope ratios, reported as parts per ten thousand (ε205Tl) relative to the NIST SRM997 international standard. The range of ε205Tl reported in this study (−16.4 to +7.2) is the largest observed in a hydrothermal ore deposit to date. Unbrecciated samples collected relatively proximal to the Bingham Canyon porphyry system have ε205Tl of −4.2 to +0.9, similar to observations in a previous study of porphyry deposits. This relatively narrow range suggests that high-temperature (>300 °C) hydrothermal alteration does not result in significant Tl isotope fractionation. However, two samples ~3–4 km away from Bingham Canyon have higher ε205Tl values (+1.3 and +7.2), and samples from more distal (~7 km) disseminated gold deposits at Melco and Barneys Canyon display an even wider range in ε205Tl (−16.4 to +6.0). The observation of large positive and negative excursions in ε205Tl relative to the mantle value (ε205Tl = −2.0 ± 1.0) contrasts with previous investigations of hydrothermal systems. Samples displaying the most extreme positive and negative ε205Tl values also contain elevated concentrations of Tl-Sb-As. Furthermore, with the exception of one sample, all of the Tl isotopic anomalies occur in hydrothermal breccia samples. This suggests that ε205Tl excursions are most extreme during the migration of low-temperature hydrothermal fluids potentially related to sediment-hosted gold mineralization. Future investigation to determine the host phase(s) for Tl in breccias displaying both chalcophile element enrichment and ε205Tl excursions can potentially provide new information about hydrothermal fluid composition and could be used to locate sites for future porphyry exploration.

Thallium and co-genetic trace elements in hydrothermal Fe-Mn deposits of Central Spain

“…For example, the Lengenback Pb-Zn-As-Tl-Ba-mineralization in Triassic dolostones of the Swiss Binn Valley (Hofmann and Knill, 1996) from which a total of 33 thallium mineral species have been identified (Raber and Roth, 2018), the Jas Roux deposit (France) hosted in Triassic calcareous rocks (Johan and Mantienne, 2000), or the Alshar Au-As-Sb-Tl deposit (Macedonia) developed as a mineralized breccia at the contact of volcanic rocks with dolomites and jasper beds (Kochneva et al, 2006). Further information on Tl concentration in igneous rocks can be found in Calderoni et al (1983), Fitzpayne et al (2018), and Rader et al (2018). This frequent Fe and Mn coupling and the presence of redox sensitive elements could be explained by their common hydrothermal origin associated to cap carbonates (Huang et al, 2011).…”

Industrial Particulate Pollution and Historical Land Use Contribute Metals of Concern to Dust Deposited in Neighborhoods Along the Wasatch Front, UT, USA

“…The mine also produces Mo as a secondary product (U.S. Geological Survey, 2021) and processing at the mine includes concentrating Mo. Fitzpayne et al (2018) observed that this Cu-Mo-Au deposit also has high Tl abundances in rock samples compared to continental crust. As a result, this mining, smelting, and concentrating operation releases measureable amounts of Tl, as well as Sb, As, Cd, Cr, Pb, Mn, Hg, Ni, Se, Ag, and V (US Environmental Protection Agency, 2021).…”